Wednesday, August 31, 2022
Sunday, February 19, 2017
Monday, February 22, 2016
Posted here are three servo amplifier circuits popular in the 60's. Microtrol of England used the top circuit using low parts count among the circuits. It was for a power system with a center tap.(4 wire connectors). Heathkit (U.S.) also used a centr tap in the battery but is unique in using the AM radio tuner capacitor as the feedback adjuster to adjust the pulse width. The third circuit of O.S.(Japan) used a center tap as well but is the circuit that used the tap only in the final stage. As such, this circuit can be converted to a 3 wire system without a center tap in the battery system. The final stage can be converted into an H bridge circuit to run a motor rated at the supply voltage.
They all employ the same principle of producing a local pulse of the opposite polarity to the incoming pulse. Also, the local pulse is initiated when an incoming pulse appears. Two transistors wired as flip flop produces the local pulse. A POT or the tuning CAP in Heathkit's circuit controls the pulse width. When an incoming signal appears, the local pulse is initiated. since they are of opposite polarities, they cancel one another if the widths are the same. It is the differential pulse that is detected by either the PNP or the NPN transistor, depending on the polarity of the net pulse, which sends signals to the driver and final transistors to run the motor CW or CCW. The motor suns a set of gears to produce torque. The final shaft is connected to the feedback POT/CAP to adjust the local pulse to match the incoming pulse at which point no differential pulse is produced.
The author successfully duplicated all these circuits and the O.S. circuit modified to run an H bridge, eliminating the center tap.
Tke note that any of these circuits can be used as a switch to turn on a relay (horns, lights, water pump etc.) Instead of running a motor, a relay is substituted.
They all employ the same principle of producing a local pulse of the opposite polarity to the incoming pulse. Also, the local pulse is initiated when an incoming pulse appears. Two transistors wired as flip flop produces the local pulse. A POT or the tuning CAP in Heathkit's circuit controls the pulse width. When an incoming signal appears, the local pulse is initiated. since they are of opposite polarities, they cancel one another if the widths are the same. It is the differential pulse that is detected by either the PNP or the NPN transistor, depending on the polarity of the net pulse, which sends signals to the driver and final transistors to run the motor CW or CCW. The motor suns a set of gears to produce torque. The final shaft is connected to the feedback POT/CAP to adjust the local pulse to match the incoming pulse at which point no differential pulse is produced.
The author successfully duplicated all these circuits and the O.S. circuit modified to run an H bridge, eliminating the center tap.
Tke note that any of these circuits can be used as a switch to turn on a relay (horns, lights, water pump etc.) Instead of running a motor, a relay is substituted.
Wednesday, October 12, 2011
Friday, July 8, 2011
Update on RC Propo System
This update is meant for those with background in digital ICs like the shift register. itis just another perspective in explaining the RC system.
UPDATE....
THE RC SYSTEM
Early airplane modellers had one wish: to control their model aircraft remotely. Early attempts used as many as 4 strings. Then the advent of vacuum tubes promised the development of wireless control. The only thing available then in the thirties was a crystal control frequency generator which they called the transmitter and a no crystal receiver with only a relay as the output. It was soon discovered that modulating the carrier wave with a tone produced better results. The ingenious device invented was the ESCAPEMENT, the predecessor of the servo. The escapement had a rubber band providing torque to an output shaft which had a vane locked into a bellcrank . The relay pulled bellcrank which released the vane. An off center shaft then took three positions, left,center, and right. The transmitter had only one button. When pressed, it closes the relay in the receiver which unlatches the vane and allow the shaft to take a position at a time. The commands left, center, right were sequential. It was enough for the modeller at that time. In the early sixties someone had one of these in my hometown and that was the latest. The model plane was stubby, had big wings, big dihedral, and had the famous .049 COX glow engine. The plane was tossed into the air with engine at full speed. There was no throttle control. The rudder was the only control. First click veers the model left, second click center,3rd click right. 4th click center again. The next big news was the development of multi channels. Different tones were generated in the transmitter and a xylophone like reed bank sat on top of the main relay. The reeds responded to different tones. The reeds in turn activated a secondary relay which activated escapements. Later on, attempts were made to use electric motors. A crank shaft was attached to the motor shaft where a spring held the postion to center. The concept of mark space ratio was adopted to bring the motor shaft to a position by turning it on and off. The model wiggled while turning. Then geared motors were used in the fifties when PNP transistors became available. They were discovered at Bell Labs in the U.S. in 1949. To bring the final output of a motor in position, a transistor was turned on which run the motor. Then a POT adjusted the bias of the transistor till it cancels the incoming signals effect on the transistor.. This was the precursor of the modern day servo which suffered from delayed reaction to overshoot. Two Americans working in companies studying cutting edge technology used the concept of adding a locally generated opposite polarity pulse to the incoming pulse. The result was the differential pulse which could be go bothe ways by way of polarities. The pulses were repeated continously. The differential pulse was amplified which turned the motor one way or the other. A POT attached to the final output shaft of the serv and Q3o adjusted the local pulse until it matches the incoming pulse to cancel the differential pulse and thus stops the motor and maintain a new position. The system was big news and was was called PROPORTIONAL since the servo movement simulates that of a lever attached to the transmitter POT.
The standard pulse width adopted was 1MS to 2MS. The neutral position required a 1.5MS pulse. PULSE WIDTH defined the servo position. It later on became known as PULSE WIDTH MODULATION , a misnomer actually. RC radios today have 2 channels, meaning it can operate 2 servos. The pulse commands are sent to the servos sequentially. In the receiver, Flip Flop ICs are used to generate the variable width pulses sequentially to the servos similar to running lights. In running lights, the ON time for each bulb is uniform. A series of flip flops encapsulated in a package is called a shift register IC. A continous clock runs the register to light the bulbs in sequence and is usually generated by the timer IC LM555. In an RC system, after an initial clock which is cyclically generated, it is followed by subsequent clocks whose delays from the previous one can be varied. In the case of a 2 channel system, a Free Running Multivibrator called FRM cyclically generates the first clock which turns the first channel port ON. A second clock produced by a single transistor turns it OFF and the 2nd channel port ON. The third clock turns the 2nd channel port OFF. A PAUSE is introduced before the next cycle begins. Each initial pulse, and the 2 more pulses and the pause is called a FRAME. In the case of a 2 channel system, the max delays between the initial clock and the 2nd clock and on to the 3rd clock is 2MS x 2 or 4MS. If a 6MS pause is introduced, the duty cycle of the FRM is set at 10MS. When both clock delays is at 1MS, the PAUSE time becomes 8MS. The pause detected at the receiver "resets" the shift register to start with channel 1 on the next initial clock. The clock generator is called an ENCODER and the shift register is called a DECODER. The circuit below shows an ENCODER using discrete components. Q1 and Q2 form the FRM. Q2 comes on every 10MS and the small capacitor .0015 mfd discharges into diode D1 which is the initial clock. When the collector of Q2 turn negative, the timing capacitor to the base of Q3 is discharged and turns Q3 off. However, resistor to the base of Q3 recharges the timing capacitor until Q3 turns on producing the 2nd clock via D2. Same thing for Q4. However, the delays in recharging the timing capacitors can be controlled by the POTS in the collectors of Q2 and Q3. These minute clocks are amplified and made uniform to abolut .25MS by a pair of transistors in a monostable mode. The second transistor Q6, is actually a switch which shuts off evrytime there is a clock from a diode. Q6 switches off the RF section in a wireless radio system. In the receiver, the break in the carrier wave is detected and reconverted back into a clock. THUS, THE TRANSMITTER SENDS CLOCKS TO THE SHIFT REGISTER DECODER IN THE RECEIVER. The encoder and decoder can be connected by 2 wires to make a wired remote controller. The encoder can generate more clocks by adding transsistors in its chain. An 8 channel shift register is available. Therefore an 8 channel system can be constructred.
The RF sections in an existing radio can be bypassed if we desire the ENCODER to drive the DECODER via wires. That is actualy done when we use a transmitter in a flight simulator in a com puter. The crystal is unplugged and only the ENCODER is used. We may disable the RF in a receiver as well by removing the crystal. ENCODER is connected to the DECODER via a pair of wires. This is called "wired remote" which can be used for underwater craft such as a model submarine or an underwater camera.
The transmitter and receiver as well as the servo amplifier can all be made using discrete components. All parts are locally available. Even the decoder can be made using transistors. It is however practical to use a shift register IC for a decoder. ICs can also be used to construct encoders in subsequent projects.
July 6, 2011
BK 0922810680
UPDATE....
THE RC SYSTEM
Early airplane modellers had one wish: to control their model aircraft remotely. Early attempts used as many as 4 strings. Then the advent of vacuum tubes promised the development of wireless control. The only thing available then in the thirties was a crystal control frequency generator which they called the transmitter and a no crystal receiver with only a relay as the output. It was soon discovered that modulating the carrier wave with a tone produced better results. The ingenious device invented was the ESCAPEMENT, the predecessor of the servo. The escapement had a rubber band providing torque to an output shaft which had a vane locked into a bellcrank . The relay pulled bellcrank which released the vane. An off center shaft then took three positions, left,center, and right. The transmitter had only one button. When pressed, it closes the relay in the receiver which unlatches the vane and allow the shaft to take a position at a time. The commands left, center, right were sequential. It was enough for the modeller at that time. In the early sixties someone had one of these in my hometown and that was the latest. The model plane was stubby, had big wings, big dihedral, and had the famous .049 COX glow engine. The plane was tossed into the air with engine at full speed. There was no throttle control. The rudder was the only control. First click veers the model left, second click center,3rd click right. 4th click center again. The next big news was the development of multi channels. Different tones were generated in the transmitter and a xylophone like reed bank sat on top of the main relay. The reeds responded to different tones. The reeds in turn activated a secondary relay which activated escapements. Later on, attempts were made to use electric motors. A crank shaft was attached to the motor shaft where a spring held the postion to center. The concept of mark space ratio was adopted to bring the motor shaft to a position by turning it on and off. The model wiggled while turning. Then geared motors were used in the fifties when PNP transistors became available. They were discovered at Bell Labs in the U.S. in 1949. To bring the final output of a motor in position, a transistor was turned on which run the motor. Then a POT adjusted the bias of the transistor till it cancels the incoming signals effect on the transistor.. This was the precursor of the modern day servo which suffered from delayed reaction to overshoot. Two Americans working in companies studying cutting edge technology used the concept of adding a locally generated opposite polarity pulse to the incoming pulse. The result was the differential pulse which could be go bothe ways by way of polarities. The pulses were repeated continously. The differential pulse was amplified which turned the motor one way or the other. A POT attached to the final output shaft of the serv and Q3o adjusted the local pulse until it matches the incoming pulse to cancel the differential pulse and thus stops the motor and maintain a new position. The system was big news and was was called PROPORTIONAL since the servo movement simulates that of a lever attached to the transmitter POT.
The standard pulse width adopted was 1MS to 2MS. The neutral position required a 1.5MS pulse. PULSE WIDTH defined the servo position. It later on became known as PULSE WIDTH MODULATION , a misnomer actually. RC radios today have 2 channels, meaning it can operate 2 servos. The pulse commands are sent to the servos sequentially. In the receiver, Flip Flop ICs are used to generate the variable width pulses sequentially to the servos similar to running lights. In running lights, the ON time for each bulb is uniform. A series of flip flops encapsulated in a package is called a shift register IC. A continous clock runs the register to light the bulbs in sequence and is usually generated by the timer IC LM555. In an RC system, after an initial clock which is cyclically generated, it is followed by subsequent clocks whose delays from the previous one can be varied. In the case of a 2 channel system, a Free Running Multivibrator called FRM cyclically generates the first clock which turns the first channel port ON. A second clock produced by a single transistor turns it OFF and the 2nd channel port ON. The third clock turns the 2nd channel port OFF. A PAUSE is introduced before the next cycle begins. Each initial pulse, and the 2 more pulses and the pause is called a FRAME. In the case of a 2 channel system, the max delays between the initial clock and the 2nd clock and on to the 3rd clock is 2MS x 2 or 4MS. If a 6MS pause is introduced, the duty cycle of the FRM is set at 10MS. When both clock delays is at 1MS, the PAUSE time becomes 8MS. The pause detected at the receiver "resets" the shift register to start with channel 1 on the next initial clock. The clock generator is called an ENCODER and the shift register is called a DECODER. The circuit below shows an ENCODER using discrete components. Q1 and Q2 form the FRM. Q2 comes on every 10MS and the small capacitor .0015 mfd discharges into diode D1 which is the initial clock. When the collector of Q2 turn negative, the timing capacitor to the base of Q3 is discharged and turns Q3 off. However, resistor to the base of Q3 recharges the timing capacitor until Q3 turns on producing the 2nd clock via D2. Same thing for Q4. However, the delays in recharging the timing capacitors can be controlled by the POTS in the collectors of Q2 and Q3. These minute clocks are amplified and made uniform to abolut .25MS by a pair of transistors in a monostable mode. The second transistor Q6, is actually a switch which shuts off evrytime there is a clock from a diode. Q6 switches off the RF section in a wireless radio system. In the receiver, the break in the carrier wave is detected and reconverted back into a clock. THUS, THE TRANSMITTER SENDS CLOCKS TO THE SHIFT REGISTER DECODER IN THE RECEIVER. The encoder and decoder can be connected by 2 wires to make a wired remote controller. The encoder can generate more clocks by adding transsistors in its chain. An 8 channel shift register is available. Therefore an 8 channel system can be constructred.
The RF sections in an existing radio can be bypassed if we desire the ENCODER to drive the DECODER via wires. That is actualy done when we use a transmitter in a flight simulator in a com puter. The crystal is unplugged and only the ENCODER is used. We may disable the RF in a receiver as well by removing the crystal. ENCODER is connected to the DECODER via a pair of wires. This is called "wired remote" which can be used for underwater craft such as a model submarine or an underwater camera.
The transmitter and receiver as well as the servo amplifier can all be made using discrete components. All parts are locally available. Even the decoder can be made using transistors. It is however practical to use a shift register IC for a decoder. ICs can also be used to construct encoders in subsequent projects.
July 6, 2011
BK 0922810680
Saturday, April 2, 2011
Saturday, August 7, 2010
PULSE PROPORTIONA RADIO SYSTEM
PULSE PROPORTIONAL RADIO REMOTE CONTROL SYSTEM
I have read many descriptions of this system and today I feel that it was either that the technology was too young then and explanations lengthy or that it was intended to make it look so difficult at that time by manufacturers. I discussed the system with some friends into RC electronics and I came to the conclusion that many of us CONFUSED THE PULSES SENT BY THE TX AND THE COMMAND PULSES FED TO THE SERVOS. The problem I think was the description the command pulse was being sent from the TX which has a variable width from 1 MS to 2MS(1MS=1/1000 second). Actually, the TX sends short pulses with a duration of only .25MS to define the START and END of a command pulses created at the decoder. In modern days digital language, the TX sends clock pulses serially. It send a set of clock pulses, pause, then repeats. The number of clocks is always number of channels plus 1. Each clock is both the end and the start of the command pulse created at the decoder except for the first and last clocks. Had authors used "clocks" and not pulse in describing tansmissions, confusion would have been less. In fact, what the oscilloscope displayed as coming from the TX were small bars looking like matchsticks.For a 2 channel system, there were 3 bars and no command pulses. The duration from the first bar, to the second, then to the third is what will create command pulses in the decoder. When one stick is moved, he last two bars move to the right. When the other stick is moved, the last bar moves to the right. These bars can also be transmitted to a TV and can be seen as horizontal bars.Thus:
THE TRANSMITTER SENDS CLOCKS OF.25MS DURATION WHICH IS RECEIVED BY THE RX WHICH WILL CLOCK A SHIFT REGISTER DECODER WHICH WILL CREATE THE COMMAND PULSES FOR THE SERVOS.
THE SERVO
The servo is probaby the most ingenious system developed in the fifties. Before today's servo developed, there were crude predecessors. Immediately before it was the analog servo which had tendencies to delay and to overshoot in its response. Before analog servos were the various geared motors which did not have feedbacks to position the servo arm. ON/OFF pulses oscillated the motor at a given position.
The Mather/Spreng servo today is still the same servo in principle developed by thse two Americans in the fifties
AN INCOMING PULSE FROM THE DECODER IS SUMMED UP WITH A LOCALLLY GENERATED PULSE OF THE OPPOSITE POLARITY. WHEN THEY ARE OF THE SAME DURATION, THEY CANCEL EACH OTHER. THE RESIDUAL OF THE LONGER PULSE DRIVES EITHER OF TWO AMPLIFIER TRANSISTORS. A POSITIVE RESIDUAL PULSE DRIVES ONE AMP,A NEGATIVE RESIDUAL PULSE DRIVES THE OTHER AMP. THESE AMPS IN TURN DRIVES A BRIDGE TO TURN THE MOTOR CW OR CCW. THE FINAL OUTPUT SHAFT OF THE SERVO TURNS A POT WHICH WILL ADJUST THE LOCALLY GENERATED PULSE TO MATCH THE INCOMING PULSE TO STOP THE MOTOR. BY THEN,IT HAS TAKEN UP A NEW POSITION. THE PULSE KEEPSON REPEATING ON AVERAGE AT 6O TIMES PER SECOND.
THE DECODER
The decoder does two things: it creates the command pulses and separates them into channel ports. The first incoming clock from the RX turns CH1 port ON, the second clock OFF and turns the next CH2 port ON, third clock turns CH2 port OFF. A PAUSE is introduced before the clock frame repeats. This pause is detected and resets the decoder to begin on CH1 port again on the next clock.
MODULATION
Modulation has something to do on how the clocks are sent. In Amplitude Modulation, the amplitude of the carrier wave is varied. In RC, the CW is shut off to represent a clock. In Frequency Modulation, the frequency is shifted slightly to represent a clock. These modulations are detected in the receiver. It's amplified, filtered, shaped and sent to the decoder as clocks.
I have read many descriptions of this system and today I feel that it was either that the technology was too young then and explanations lengthy or that it was intended to make it look so difficult at that time by manufacturers. I discussed the system with some friends into RC electronics and I came to the conclusion that many of us CONFUSED THE PULSES SENT BY THE TX AND THE COMMAND PULSES FED TO THE SERVOS. The problem I think was the description the command pulse was being sent from the TX which has a variable width from 1 MS to 2MS(1MS=1/1000 second). Actually, the TX sends short pulses with a duration of only .25MS to define the START and END of a command pulses created at the decoder. In modern days digital language, the TX sends clock pulses serially. It send a set of clock pulses, pause, then repeats. The number of clocks is always number of channels plus 1. Each clock is both the end and the start of the command pulse created at the decoder except for the first and last clocks. Had authors used "clocks" and not pulse in describing tansmissions, confusion would have been less. In fact, what the oscilloscope displayed as coming from the TX were small bars looking like matchsticks.For a 2 channel system, there were 3 bars and no command pulses. The duration from the first bar, to the second, then to the third is what will create command pulses in the decoder. When one stick is moved, he last two bars move to the right. When the other stick is moved, the last bar moves to the right. These bars can also be transmitted to a TV and can be seen as horizontal bars.Thus:
THE TRANSMITTER SENDS CLOCKS OF.25MS DURATION WHICH IS RECEIVED BY THE RX WHICH WILL CLOCK A SHIFT REGISTER DECODER WHICH WILL CREATE THE COMMAND PULSES FOR THE SERVOS.
THE SERVO
The servo is probaby the most ingenious system developed in the fifties. Before today's servo developed, there were crude predecessors. Immediately before it was the analog servo which had tendencies to delay and to overshoot in its response. Before analog servos were the various geared motors which did not have feedbacks to position the servo arm. ON/OFF pulses oscillated the motor at a given position.
The Mather/Spreng servo today is still the same servo in principle developed by thse two Americans in the fifties
AN INCOMING PULSE FROM THE DECODER IS SUMMED UP WITH A LOCALLLY GENERATED PULSE OF THE OPPOSITE POLARITY. WHEN THEY ARE OF THE SAME DURATION, THEY CANCEL EACH OTHER. THE RESIDUAL OF THE LONGER PULSE DRIVES EITHER OF TWO AMPLIFIER TRANSISTORS. A POSITIVE RESIDUAL PULSE DRIVES ONE AMP,A NEGATIVE RESIDUAL PULSE DRIVES THE OTHER AMP. THESE AMPS IN TURN DRIVES A BRIDGE TO TURN THE MOTOR CW OR CCW. THE FINAL OUTPUT SHAFT OF THE SERVO TURNS A POT WHICH WILL ADJUST THE LOCALLY GENERATED PULSE TO MATCH THE INCOMING PULSE TO STOP THE MOTOR. BY THEN,IT HAS TAKEN UP A NEW POSITION. THE PULSE KEEPSON REPEATING ON AVERAGE AT 6O TIMES PER SECOND.
THE DECODER
The decoder does two things: it creates the command pulses and separates them into channel ports. The first incoming clock from the RX turns CH1 port ON, the second clock OFF and turns the next CH2 port ON, third clock turns CH2 port OFF. A PAUSE is introduced before the clock frame repeats. This pause is detected and resets the decoder to begin on CH1 port again on the next clock.
MODULATION
Modulation has something to do on how the clocks are sent. In Amplitude Modulation, the amplitude of the carrier wave is varied. In RC, the CW is shut off to represent a clock. In Frequency Modulation, the frequency is shifted slightly to represent a clock. These modulations are detected in the receiver. It's amplified, filtered, shaped and sent to the decoder as clocks.
PULSE PROPORTIONA RADIO SYSTEM
PULSE PROPORTIONAL RADIO REMOTE CONTROL SYSTEM
I have read many descriptions of this system and today I feel that it was either that the technology was too young then and explanations lengthy or that it was intended to make it look so difficult at that time by manufacturers. I discussed the system with some friends into RC electronics and I came to the conclusion that many of us CONFUSED THE PULSES SENT BY THE TX AND THE COMMAND PULSES FED TO THE SERVOS. The problem I think was the description the command pulse was being sent from the TX which has a variable width from 1 MS to 2MS(1MS=1/1000 second). Actually, the TX sends short pulses with a duration of only .25MS to define the START and END of a command pulses created at the decoder. In modern days digital language, the TX sends clock pulses serially. It send a set of clock pulses, pause, then repeats. The number of clocks is always number of channels plus 1. Each clock is both the end and the start of the command pulse created at the decoder except for the first and last clocks. Had authors used "clocks" and not pulse in describing tansmissions, confusion would have been less. In fact, what the oscilloscope displayed as coming from the TX were small bars looking like matchsticks.For a 2 channel system, there were 3 bars and no command pulses. The duration from the first bar, to the second, then to the third is what will create command pulses in the decoder. When one stick is moved, he last two bars move to the right. When the other stick is moved, the last bar moves to the right. These bars can also be transmitted to a TV and can be seen as horizontal bars.Thus:
THE TRANSMITTER SENDS CLOCKS OF.25MS DURATION WHICH IS RECEIVED BY THE RX WHICH WILL CLOCK A SHIFT REGISTER DECODER WHICH WILL CREATE THE COMMAND PULSES FOR THE SERVOS.
THE SERVO
The servo is probaby the most ingenious system developed in the fifties. Before today's servo developed, there were crude predecessors. Immediately before it was the analog servo which had tendencies to delay and to overshoot in its response. Before analog servos were the various geared motors which did not have feedbacks to position the servo arm. ON/OFF pulses oscillated the motor at a given position.
The Mather/Spreng servo today is still the same servo in principle developed by thse two Americans in the fifties
AN INCOMING PULSE FROM THE DECODER IS SUMMED UP WITH A LOCALLLY GENERATED PULSE OF THE OPPOSITE POLARITY. WHEN THEY ARE OF THE SAME DURATION, THEY CANCEL EACH OTHER. THE RESIDUAL OF THE LONGER PULSE DRIVES EITHER OF TWO AMPLIFIER TRANSISTORS. A POSITIVE RESIDUAL PULSE DRIVES ONE AMP,A NEGATIVE RESIDUAL PULSE DRIVES THE OTHER AMP. THESE AMPS IN TURN DRIVES A BRIDGE TO TURN THE MOTOR CW OR CCW. THE FINAL OUTPUT SHAFT OF THE SERVO TURNS A POT WHICH WILL ADJUST THE LOCALLY GENERATED PULSE TO MATCH THE INCOMING PULSE TO STOP THE MOTOR. BY THEN,IT HAS TAKEN UP A NEW POSITION. THE PULSE KEEPSON REPEATING ON AVERAGE AT 6O TIMES PER SECOND.
THE DECODER
The decoder does two things: it creates the command pulses and separates them into channel ports. The first incoming clock from the RX turns CH1 port ON, the second clock OFF and turns the next CH2 port ON, third clock turns CH2 port OFF. A PAUSE is introduced before the clock frame repeats. This pause is detected and resets the decoder to begin on CH1 port again on the next clock.
MODULATION
Modulation has something to do on how the clocks are sent. In Amplitude Modulation, the amplitude of the carrier wave is varied. In RC, the CW is shut off to represent a clock. In Frequency Modulation, the frequency is shifted slightly to represent a clock. These modulations are detected in the receiver. It's amplified, filtered, shaped and sent to the decoder as clocks.
I have read many descriptions of this system and today I feel that it was either that the technology was too young then and explanations lengthy or that it was intended to make it look so difficult at that time by manufacturers. I discussed the system with some friends into RC electronics and I came to the conclusion that many of us CONFUSED THE PULSES SENT BY THE TX AND THE COMMAND PULSES FED TO THE SERVOS. The problem I think was the description the command pulse was being sent from the TX which has a variable width from 1 MS to 2MS(1MS=1/1000 second). Actually, the TX sends short pulses with a duration of only .25MS to define the START and END of a command pulses created at the decoder. In modern days digital language, the TX sends clock pulses serially. It send a set of clock pulses, pause, then repeats. The number of clocks is always number of channels plus 1. Each clock is both the end and the start of the command pulse created at the decoder except for the first and last clocks. Had authors used "clocks" and not pulse in describing tansmissions, confusion would have been less. In fact, what the oscilloscope displayed as coming from the TX were small bars looking like matchsticks.For a 2 channel system, there were 3 bars and no command pulses. The duration from the first bar, to the second, then to the third is what will create command pulses in the decoder. When one stick is moved, he last two bars move to the right. When the other stick is moved, the last bar moves to the right. These bars can also be transmitted to a TV and can be seen as horizontal bars.Thus:
THE TRANSMITTER SENDS CLOCKS OF.25MS DURATION WHICH IS RECEIVED BY THE RX WHICH WILL CLOCK A SHIFT REGISTER DECODER WHICH WILL CREATE THE COMMAND PULSES FOR THE SERVOS.
THE SERVO
The servo is probaby the most ingenious system developed in the fifties. Before today's servo developed, there were crude predecessors. Immediately before it was the analog servo which had tendencies to delay and to overshoot in its response. Before analog servos were the various geared motors which did not have feedbacks to position the servo arm. ON/OFF pulses oscillated the motor at a given position.
The Mather/Spreng servo today is still the same servo in principle developed by thse two Americans in the fifties
AN INCOMING PULSE FROM THE DECODER IS SUMMED UP WITH A LOCALLLY GENERATED PULSE OF THE OPPOSITE POLARITY. WHEN THEY ARE OF THE SAME DURATION, THEY CANCEL EACH OTHER. THE RESIDUAL OF THE LONGER PULSE DRIVES EITHER OF TWO AMPLIFIER TRANSISTORS. A POSITIVE RESIDUAL PULSE DRIVES ONE AMP,A NEGATIVE RESIDUAL PULSE DRIVES THE OTHER AMP. THESE AMPS IN TURN DRIVES A BRIDGE TO TURN THE MOTOR CW OR CCW. THE FINAL OUTPUT SHAFT OF THE SERVO TURNS A POT WHICH WILL ADJUST THE LOCALLY GENERATED PULSE TO MATCH THE INCOMING PULSE TO STOP THE MOTOR. BY THEN,IT HAS TAKEN UP A NEW POSITION. THE PULSE KEEPSON REPEATING ON AVERAGE AT 6O TIMES PER SECOND.
THE DECODER
The decoder does two things: it creates the command pulses and separates them into channel ports. The first incoming clock from the RX turns CH1 port ON, the second clock OFF and turns the next CH2 port ON, third clock turns CH2 port OFF. A PAUSE is introduced before the clock frame repeats. This pause is detected and resets the decoder to begin on CH1 port again on the next clock.
MODULATION
Modulation has something to do on how the clocks are sent. In Amplitude Modulation, the amplitude of the carrier wave is varied. In RC, the CW is shut off to represent a clock. In Frequency Modulation, the frequency is shifted slightly to represent a clock. These modulations are detected in the receiver. It's amplified, filtered, shaped and sent to the decoder as clocks.
Thursday, January 28, 2010
The schematic diagram shown is that of an encoder for a transmitter.
-first two transistors form a free running multivibrator(flip-flop). Q1 is On and Q2 is Off and vice versa. There is a duty cycle of about 20 milliseconds(MS). Subsequent transistors are timer circuits triggered by the previous Q(Q=transistor). The 5k POT sets the delay when to fire the next Q. When the timer Q turns on, it send a .25MS pulse to shut off the carrier wave of an RF generator.
-So, the TX send a frame of .25MS pulses to clock a decoder at the RX. This schemactic diagram is for a 2 channel system. The three diodes send three pulses and the space between pulses is the time a channel port in the decoder remains on which the servo recognizes and positions itself.
To add more channels, add more timer Qs.
-first two transistors form a free running multivibrator(flip-flop). Q1 is On and Q2 is Off and vice versa. There is a duty cycle of about 20 milliseconds(MS). Subsequent transistors are timer circuits triggered by the previous Q(Q=transistor). The 5k POT sets the delay when to fire the next Q. When the timer Q turns on, it send a .25MS pulse to shut off the carrier wave of an RF generator.
-So, the TX send a frame of .25MS pulses to clock a decoder at the RX. This schemactic diagram is for a 2 channel system. The three diodes send three pulses and the space between pulses is the time a channel port in the decoder remains on which the servo recognizes and positions itself.
To add more channels, add more timer Qs.
Wednesday, December 2, 2009
Battery Charging
I will discuss charging Nicasds and Metal Hydrides
Both batteries have nominal voltages of 1.2V but when fully charged(peaked), the V goes to 1.4V. Thus a flight pack of 4 cells should have a voltage of 5.6V when freshly charged. the voltage drops suddenly when the V reaches 1.1V. Thus 4.4V is a critical level.
How to charge them
In technospeak, C is charging rate. Thus a charger is known to have percentC charging rate. A .10C means the charging rate is 10% of capacity(less the hr). The safest charging rate is .10 C. for example, if the pack is a 1000mah pack, the charging rate at 10% is 100ma. For a fully discharge pack, the time to restore the battery to full charge is 15 hours. It means 50% more is inserted into the battery to charge it.(15 hoursx100ma is 1500 mah). .10 is also called C10.
The enemy of the battery is high temperature. As the C rate goes up, heat build up goes up. And it is really bad to leave a battery under charge beyond the time needed at high C rates. The safest is the .10C charger.
Most of the radio sold in the market with batteries come with a 500 mah packl. And the call charger is usually a .10C charger. (You might say charger for dummies who will surely forget to unplus the charger after 15 hours.) . One other good reason why a .10C charger is used is because the pack is not really depleted before it is recharged. So, the 10C charger is safe.
Modern chargers with peak detection allows us to plug in the charger and batt anytime without worry. It dos not matter how much charge was there at the start.
We can make a very simple rugged charger like the ones used on RC cars charging a fully discharged pack. Usually, there was a 15 mins timer in those charger. Tose chargers were as high a 3C chargers.
15 mins RC chargers are no longer in voque but once in while, there is a need to make a simple rugged charger to charge metal hydrides used in model planes. Normally 7-8 cells are used. The peaked voltage os 8 cells is 8 x 1.4 or 11.2V. We can charge them in series from the car battery.
A simple rule of thumb is to charge it at 50% more opf capacity. If we use a charger that is 1C, we need a timer for 1.5 hours. or if we charge it at 1.5C, we charge it for 1 hour. The formula is rate x time = 1.5 x capacity.
For example, for a 1000 mah pack, we can charge at 1.5 amps (1500 ma) for one hour. If we want it for 30 mins, then we double the rate to 3 amps.
A good good guideline is to decide on how many packs one can afford in the field and use the longest time to charge acceptable. for example, using 4 packs, each pack lasting 10 minutes, with a rest in between. When the first pack is used, the nest 3 packs is good for 30 minutes plus rest time of 30 minutes. Then a 1 hour charger is good.
Can we charge more than 8 cells from the 12V car battery. Well, yes. Say for a 10 cell pack, we break them up into 5 cell packs. We charge them as parallel packs. After they are charged, they can be plugged together in series. Only one timer has to be used and there is no need for two chargers really.
Current is the critical parameter. The charger voltage has to be higher than the peak V of the pack. Current is calibrated using resistors in series with the right wattage.
BK
I will discuss charging Nicasds and Metal Hydrides
Both batteries have nominal voltages of 1.2V but when fully charged(peaked), the V goes to 1.4V. Thus a flight pack of 4 cells should have a voltage of 5.6V when freshly charged. the voltage drops suddenly when the V reaches 1.1V. Thus 4.4V is a critical level.
How to charge them
In technospeak, C is charging rate. Thus a charger is known to have percentC charging rate. A .10C means the charging rate is 10% of capacity(less the hr). The safest charging rate is .10 C. for example, if the pack is a 1000mah pack, the charging rate at 10% is 100ma. For a fully discharge pack, the time to restore the battery to full charge is 15 hours. It means 50% more is inserted into the battery to charge it.(15 hoursx100ma is 1500 mah). .10 is also called C10.
The enemy of the battery is high temperature. As the C rate goes up, heat build up goes up. And it is really bad to leave a battery under charge beyond the time needed at high C rates. The safest is the .10C charger.
Most of the radio sold in the market with batteries come with a 500 mah packl. And the call charger is usually a .10C charger. (You might say charger for dummies who will surely forget to unplus the charger after 15 hours.) . One other good reason why a .10C charger is used is because the pack is not really depleted before it is recharged. So, the 10C charger is safe.
Modern chargers with peak detection allows us to plug in the charger and batt anytime without worry. It dos not matter how much charge was there at the start.
We can make a very simple rugged charger like the ones used on RC cars charging a fully discharged pack. Usually, there was a 15 mins timer in those charger. Tose chargers were as high a 3C chargers.
15 mins RC chargers are no longer in voque but once in while, there is a need to make a simple rugged charger to charge metal hydrides used in model planes. Normally 7-8 cells are used. The peaked voltage os 8 cells is 8 x 1.4 or 11.2V. We can charge them in series from the car battery.
A simple rule of thumb is to charge it at 50% more opf capacity. If we use a charger that is 1C, we need a timer for 1.5 hours. or if we charge it at 1.5C, we charge it for 1 hour. The formula is rate x time = 1.5 x capacity.
For example, for a 1000 mah pack, we can charge at 1.5 amps (1500 ma) for one hour. If we want it for 30 mins, then we double the rate to 3 amps.
A good good guideline is to decide on how many packs one can afford in the field and use the longest time to charge acceptable. for example, using 4 packs, each pack lasting 10 minutes, with a rest in between. When the first pack is used, the nest 3 packs is good for 30 minutes plus rest time of 30 minutes. Then a 1 hour charger is good.
Can we charge more than 8 cells from the 12V car battery. Well, yes. Say for a 10 cell pack, we break them up into 5 cell packs. We charge them as parallel packs. After they are charged, they can be plugged together in series. Only one timer has to be used and there is no need for two chargers really.
Current is the critical parameter. The charger voltage has to be higher than the peak V of the pack. Current is calibrated using resistors in series with the right wattage.
BK
Wednesday, August 5, 2009
Tuesday, July 7, 2009
RC RADIO
July 7, 2009
Don Mathers and Dough Spreng developed the truly proportional system still in use today. Different modes of modulation were later introduced (FM) other than AM, PCM was introduced, but still, it is the Mathers/Spreng servo at work at the end. Even digital servos still use the system.
AM to FM. This is often confused, many thinking that we have to go FM once we are on the upper band. No, in fact, there were FMs on 27Mhz. FM is a modulation form to transmit information. It does not change the the Mathers/Spreng system in positioning the servo. In AM, the strength of the signal is varied to send info. In fact, in RC, the carrier wave(CW) is momentarily shut off to represent a signal. This is also practical since no extra power is use to send a short pulse. The receiver takes care of recognizing the blank and convert it to an ON signal at its output. In both AM and FM, a very short trigger pulse (.25MS) is sent at intervals. The intervals represent the time a port is ON at the decoder, which sets the servo position. This is called Pulse Width Modulation(PWM). PCM which stands for Pulse Code Modulation can be viewed by the layman as also a modulation form. Instead of the short pulse sent, the TX actually sends a binary code to the RX. The RX has a CPU which produces the command pulse for a servo (from 1 MS to 2 MS). In PWM, the TX sends the ON/OFF commands to several servos in sequence. Thus, usually,it can only send about 60 commands to each servo per second. In PCM, in as long as there is no new command from the TX, the RX keeps generating the same pulse width. So, an interference on the signal does not mean anything to the RX since it is unintelligible to it. PCM today is usually on FM. It remains a very good system against interference. But it should not be confused as to what the spread spectrum (SS) is doing. In PCM, The system is very good against unintellgible interference. But another TX on the same channel can of course interfere with one's RX. The spread spectrum takes care of this aspect. In frequency hopping (FHSS) for example, the signal is rotated among different spot channels and the sequence of the combination code is locked between the TX and the RX (called binding), and there are thousands of combinations possible, thus probability for two radios using the same code is very low. So, the SS is not an improvement on the modulation. It is an improvement on the use of frequency space. It could well be that PCM is used and transmitted the SS way on 2.4Gig. The 2.4G is just coincidental that the FCC opened up this band for wireless communication. Again, it could well be that SS were used at 72-75 Megs, or even 27 megs.
What is the Mathers/Spreng system?
Well, the best way to appreciate it is to look at the servo. In a way, this was the heart of their invention. Before them, the servo was analog. A motor is geared down to developed torque and there was a feedback pot on the final shaft. In the analog system, the pot adjusted the bias on a transistor. When an increased/decreased drive voltage turns ON/Off the transistor, the pot counters the move(opposite wise). So, the changed is canceled by the changed in the transistor bias controlled by the pot. The problem of the analog servo was delayed reaction, non-proportionality and overshoot, among others perhaps. You see, the voltage level moving was purely analog, meaning, it was on a curved path. There must be something discrete like On then OFF but sent continously and when a change is introduced, the interval between the ON/Off is changed.
The concept was an incoming pulse with a width from 1 MS to 2MS. A local pulse is also started by the incoming pulse but is inverted (positive incoming and negative local pulse). When one is longer than the other, a residual pulse remains. TX sends the trigger pulses which the decoder vonvrts to a positive pulse of a duration. The TX sends the trigger pulses on a stream (repeated). When the residual pulse is positive, the motor is turned one way. When the residual pulse is negative, the motor is turned the other way. Now, a pot (normally 5k today) is again, attached to the final output shaft of the servo and controls the width of the local pulse. It is wired so that the width of the local pulse matches that of the incoming pulse as the pot is turned which then stops the motor. By that time, the servo horn is at a different position.
How is the command pulse created?
It is created at the decoder. The TX sends two short pulses that we can call trigger pulses(.25MS). This is not the servo command pulse. It is the signal for a decoder to turn a port ON on the firsts pulse and OFF at the second pulse. This port is the servo channel port. In a hypothetical single channel system, the TX will just keep sending two trigger pulses with intervals controlled by a joystick. And since the max interval is 2 MS and there are 1000 MS in one second, the TX can send 500 command pulses per second to 1000 command pulses when the delay is at 1MS. But all of this changes when more than one channel is sent. First, the OFF trigger pulse of the fist channel can be made to be the ON trigger pulse of the second channel. Thus, only three trigger pulses are needed to create two command pulses at the decoder. However, to make sure that the first trigger pulse turns on the first port, a long inverval called a pause is introduced in the stram of trigger pulses. This must be at least twice the longest interval which is 2MS, thus 4MS. So, in a 2 channel system, the max intervals is 2x 2MS plus the 4 MS for a total of 8MS. Thus, a system can be designed to send 1000MS/8MS commands per second. A set of command pulses for the two servos is called a frame. That will be 150 frames per second. Mind you fellow modellers, if you are using an 8 channel TX and RX to control only two servos, the resolution is wasted.
PCM
Perhaps the above will make us appreciate PCM more. In PCM, the above computation becomes irrelevant.The TX in a PCM does not send pulses on merry go around such that we add all the intervals which becomes longer the more the servo channels. In PCM, it is like sending the juke box a number for a record to play and you do it only once. In PCM, the TX tells the RX-CPU to generate a pulse for a given channel only once until you had moved that joystick for a new command. There is no stream of commands to a set of servos. In PWM (or PPM), a cut in the stream sends the servos chattering. In PCM, a cut in the transmission is merel;y recognized as silence and does not mean much to the RX-CPU which is waiting only for intelligible commands to shift the pulse widths to a set of servos. PCM is truly intereference proof but not from same channel TX. That is where the SS comes in. By the way, PCM was not developed for the RC industry. It was developed for general communications works but was particularly used to send commands to the Mars probe and to send images from the Mars probe to Earth.
A short explanation of
Spread Spectrum
Let say we have 3 channels only on 72 MHZ. The way to allow more that 3 TX to be used at the same time is to make a system wherein the TX hops channels. Let us call the channels A,B, and C. Tx1 will hop ABC,TX2 ACB, TX3 BAC, TX4BCA, TX5CAB,TX6CBA. This of course is a very simplified semblance on the principle used. The pattern that the TX will adopt is copied into the RX when they are bounded(binding). Thus it is nearly impossible for two systems to cross.
The 2.4Ghz band is very high frequency of course and is not limited to RC. Wireless phones, cell phones and other services are in this band. The antenna is very short indeed as the wavelength of the signal is 300/2400 or just .125 meter or 1.25 CM. The problem at this frequency, are wires around the antenna such as servo extension cables which robs the RX of range. And that is one reason 2.4's suffer momentary cut offs. SS is good but the band gives this problem. One remedy is to wrap the extension cables around a ferrite ring.
To follow is a detailed explanation of the "hardware" of a typical TX and RX with decoder. Complete circuitry will be explained.
BK
Don Mathers and Dough Spreng developed the truly proportional system still in use today. Different modes of modulation were later introduced (FM) other than AM, PCM was introduced, but still, it is the Mathers/Spreng servo at work at the end. Even digital servos still use the system.
AM to FM. This is often confused, many thinking that we have to go FM once we are on the upper band. No, in fact, there were FMs on 27Mhz. FM is a modulation form to transmit information. It does not change the the Mathers/Spreng system in positioning the servo. In AM, the strength of the signal is varied to send info. In fact, in RC, the carrier wave(CW) is momentarily shut off to represent a signal. This is also practical since no extra power is use to send a short pulse. The receiver takes care of recognizing the blank and convert it to an ON signal at its output. In both AM and FM, a very short trigger pulse (.25MS) is sent at intervals. The intervals represent the time a port is ON at the decoder, which sets the servo position. This is called Pulse Width Modulation(PWM). PCM which stands for Pulse Code Modulation can be viewed by the layman as also a modulation form. Instead of the short pulse sent, the TX actually sends a binary code to the RX. The RX has a CPU which produces the command pulse for a servo (from 1 MS to 2 MS). In PWM, the TX sends the ON/OFF commands to several servos in sequence. Thus, usually,it can only send about 60 commands to each servo per second. In PCM, in as long as there is no new command from the TX, the RX keeps generating the same pulse width. So, an interference on the signal does not mean anything to the RX since it is unintelligible to it. PCM today is usually on FM. It remains a very good system against interference. But it should not be confused as to what the spread spectrum (SS) is doing. In PCM, The system is very good against unintellgible interference. But another TX on the same channel can of course interfere with one's RX. The spread spectrum takes care of this aspect. In frequency hopping (FHSS) for example, the signal is rotated among different spot channels and the sequence of the combination code is locked between the TX and the RX (called binding), and there are thousands of combinations possible, thus probability for two radios using the same code is very low. So, the SS is not an improvement on the modulation. It is an improvement on the use of frequency space. It could well be that PCM is used and transmitted the SS way on 2.4Gig. The 2.4G is just coincidental that the FCC opened up this band for wireless communication. Again, it could well be that SS were used at 72-75 Megs, or even 27 megs.
What is the Mathers/Spreng system?
Well, the best way to appreciate it is to look at the servo. In a way, this was the heart of their invention. Before them, the servo was analog. A motor is geared down to developed torque and there was a feedback pot on the final shaft. In the analog system, the pot adjusted the bias on a transistor. When an increased/decreased drive voltage turns ON/Off the transistor, the pot counters the move(opposite wise). So, the changed is canceled by the changed in the transistor bias controlled by the pot. The problem of the analog servo was delayed reaction, non-proportionality and overshoot, among others perhaps. You see, the voltage level moving was purely analog, meaning, it was on a curved path. There must be something discrete like On then OFF but sent continously and when a change is introduced, the interval between the ON/Off is changed.
The concept was an incoming pulse with a width from 1 MS to 2MS. A local pulse is also started by the incoming pulse but is inverted (positive incoming and negative local pulse). When one is longer than the other, a residual pulse remains. TX sends the trigger pulses which the decoder vonvrts to a positive pulse of a duration. The TX sends the trigger pulses on a stream (repeated). When the residual pulse is positive, the motor is turned one way. When the residual pulse is negative, the motor is turned the other way. Now, a pot (normally 5k today) is again, attached to the final output shaft of the servo and controls the width of the local pulse. It is wired so that the width of the local pulse matches that of the incoming pulse as the pot is turned which then stops the motor. By that time, the servo horn is at a different position.
How is the command pulse created?
It is created at the decoder. The TX sends two short pulses that we can call trigger pulses(.25MS). This is not the servo command pulse. It is the signal for a decoder to turn a port ON on the firsts pulse and OFF at the second pulse. This port is the servo channel port. In a hypothetical single channel system, the TX will just keep sending two trigger pulses with intervals controlled by a joystick. And since the max interval is 2 MS and there are 1000 MS in one second, the TX can send 500 command pulses per second to 1000 command pulses when the delay is at 1MS. But all of this changes when more than one channel is sent. First, the OFF trigger pulse of the fist channel can be made to be the ON trigger pulse of the second channel. Thus, only three trigger pulses are needed to create two command pulses at the decoder. However, to make sure that the first trigger pulse turns on the first port, a long inverval called a pause is introduced in the stram of trigger pulses. This must be at least twice the longest interval which is 2MS, thus 4MS. So, in a 2 channel system, the max intervals is 2x 2MS plus the 4 MS for a total of 8MS. Thus, a system can be designed to send 1000MS/8MS commands per second. A set of command pulses for the two servos is called a frame. That will be 150 frames per second. Mind you fellow modellers, if you are using an 8 channel TX and RX to control only two servos, the resolution is wasted.
PCM
Perhaps the above will make us appreciate PCM more. In PCM, the above computation becomes irrelevant.The TX in a PCM does not send pulses on merry go around such that we add all the intervals which becomes longer the more the servo channels. In PCM, it is like sending the juke box a number for a record to play and you do it only once. In PCM, the TX tells the RX-CPU to generate a pulse for a given channel only once until you had moved that joystick for a new command. There is no stream of commands to a set of servos. In PWM (or PPM), a cut in the stream sends the servos chattering. In PCM, a cut in the transmission is merel;y recognized as silence and does not mean much to the RX-CPU which is waiting only for intelligible commands to shift the pulse widths to a set of servos. PCM is truly intereference proof but not from same channel TX. That is where the SS comes in. By the way, PCM was not developed for the RC industry. It was developed for general communications works but was particularly used to send commands to the Mars probe and to send images from the Mars probe to Earth.
A short explanation of
Spread Spectrum
Let say we have 3 channels only on 72 MHZ. The way to allow more that 3 TX to be used at the same time is to make a system wherein the TX hops channels. Let us call the channels A,B, and C. Tx1 will hop ABC,TX2 ACB, TX3 BAC, TX4BCA, TX5CAB,TX6CBA. This of course is a very simplified semblance on the principle used. The pattern that the TX will adopt is copied into the RX when they are bounded(binding). Thus it is nearly impossible for two systems to cross.
The 2.4Ghz band is very high frequency of course and is not limited to RC. Wireless phones, cell phones and other services are in this band. The antenna is very short indeed as the wavelength of the signal is 300/2400 or just .125 meter or 1.25 CM. The problem at this frequency, are wires around the antenna such as servo extension cables which robs the RX of range. And that is one reason 2.4's suffer momentary cut offs. SS is good but the band gives this problem. One remedy is to wrap the extension cables around a ferrite ring.
To follow is a detailed explanation of the "hardware" of a typical TX and RX with decoder. Complete circuitry will be explained.
BK
Monday, June 29, 2009
WIRELESS REMOTE CONTROL
INTRODUCTION
Probably Man's age old dream: wireless remote control of objects. This was realized only in the 20th century after the vacuum tube was developed ( which was discovered after Edison invented the lightbulb). Well, Samuel Morse conceptualized and developed the Morse Code, perhaps unknowingly, stumbling into digital concept, a two state mode communication, dot and dash. Today, dot and dash is reresented by 1 and 0 which can be manipulated mathematically. It was Marconi who made it wireless. Instead of voice over the Atlantic, Marconi sent dots and dashes, using Morse's code. There were only two sounds to recognize. Of course voice followed but it is interesting to note that today, we are back to using only two distinct symbols to send voice great distances, the farthest is to the moon when austronauts were there. In reality, 0 and 1 are sent but the way it is electrically sent is on or off. On for 1 and off for 0. Voice is converted to 0 and 1's (binary) sent, then reconstructed in the RX.
The modellers were at the forefront of RC. Actually, before the vacuum tube era, a spark gap was used to transmit a wideband electrical noise. The receiver was a coherer tube, a glass tube with iron fillings. When electromagnetic energy was detected, the iron fillings lined up inside the tube in an orderly North-South arrangement, thus making the iron fillings conduct. The first public display was somehow controlling a balloon inside a building, probably looking like a dirigible. Rapid progress was made in the 30's when vacuum tubes was used to oscillate at a frequency kept steady by a crystal. A fixed frequency on a narrow bandwith was transmitted.(this was broadband by today's standard). A broadband receiver with very little selectivity picked up the propagation which at the beginning was nothing but the carrier wave of the TX. Modellers put a button on a TX and a relay in the RX. The world was "quiet" in those days (transmission wise). Later, it was found out an audio tone modulated on the CW (AM) was better. To move the control surface of a model aircraft, an escapement was developed which multiplied the force of the relay. The escapement was mechanical where rubber band was wound to generate torque on a spindle. The spindle had an dual arms caught on a latch to hold it from turning. The relay released the latch and engage it in the next arm, thus changing the positon of a horn attached to the spindle. Thus rudder was controllable to be at center, left or right by pressing the TX button. This was called "single channel" in those days and was probably like owning a I-pod today! If only we could control the elevator as well was the main wish. There were various attempts and the one that became widely acceptable was to use tones to send different commands on the same frequency. The sound discriminator in the RX was mechanical: reeds. Reeds resonant to the tone were placed on top of an electromagnet. The corresponding reed vibrating given a tone. Soon, there were 8 channels, eight reeds on top of an electromagnet. These reeds touched a contact when vibrating which turns on a relay which activates escapements. This went on for a time. In 1949, the Americans discovered semi conductors called transistors, much much smaller than a vacuum tube and did not need heaters. By the fifties, transistors were appearing everywhere. Still, tones and escapements were used. Eventually, small dc motors replaced the rubber band and the escapement itself. High speed motors were geared down to have torque to turn the control surfaces(Rudder and elevator, ailerons and throttle). These were called "servos". In the forefront of servo development was Howard Bonner(American). Bonner servos reached moddellers across the globe. But this servos were not proportional, meaning they did not move linearly with stick movement in the TX. In the beginning, they only had end switches to stop at extreme ends. In fact, a transition was a servo that was swinging back and forth to a position based on an ON/Off switcher in the TX. The rudder appeared like a dorsal fin of a fish on flight. It became known as the galloping ghost.
The first attempt at proportional control was called analog in nature. The TX transmitted a signal which can increase/decrease a voltage level. A transistor is turn on but a variable resistor connected to the output shaft of the servo changes the sensitivity of the transistor thus bringing it back to an OFF state and shuts the motor. By then the horn connected to the control surface has changed position. The problem was delayed reaction, proportionality,and overshoot. By then, two young Americans electronics buffs were working on a concept. They were Mathers and Spreng(Dough).
Probably Man's age old dream: wireless remote control of objects. This was realized only in the 20th century after the vacuum tube was developed ( which was discovered after Edison invented the lightbulb). Well, Samuel Morse conceptualized and developed the Morse Code, perhaps unknowingly, stumbling into digital concept, a two state mode communication, dot and dash. Today, dot and dash is reresented by 1 and 0 which can be manipulated mathematically. It was Marconi who made it wireless. Instead of voice over the Atlantic, Marconi sent dots and dashes, using Morse's code. There were only two sounds to recognize. Of course voice followed but it is interesting to note that today, we are back to using only two distinct symbols to send voice great distances, the farthest is to the moon when austronauts were there. In reality, 0 and 1 are sent but the way it is electrically sent is on or off. On for 1 and off for 0. Voice is converted to 0 and 1's (binary) sent, then reconstructed in the RX.
The modellers were at the forefront of RC. Actually, before the vacuum tube era, a spark gap was used to transmit a wideband electrical noise. The receiver was a coherer tube, a glass tube with iron fillings. When electromagnetic energy was detected, the iron fillings lined up inside the tube in an orderly North-South arrangement, thus making the iron fillings conduct. The first public display was somehow controlling a balloon inside a building, probably looking like a dirigible. Rapid progress was made in the 30's when vacuum tubes was used to oscillate at a frequency kept steady by a crystal. A fixed frequency on a narrow bandwith was transmitted.(this was broadband by today's standard). A broadband receiver with very little selectivity picked up the propagation which at the beginning was nothing but the carrier wave of the TX. Modellers put a button on a TX and a relay in the RX. The world was "quiet" in those days (transmission wise). Later, it was found out an audio tone modulated on the CW (AM) was better. To move the control surface of a model aircraft, an escapement was developed which multiplied the force of the relay. The escapement was mechanical where rubber band was wound to generate torque on a spindle. The spindle had an dual arms caught on a latch to hold it from turning. The relay released the latch and engage it in the next arm, thus changing the positon of a horn attached to the spindle. Thus rudder was controllable to be at center, left or right by pressing the TX button. This was called "single channel" in those days and was probably like owning a I-pod today! If only we could control the elevator as well was the main wish. There were various attempts and the one that became widely acceptable was to use tones to send different commands on the same frequency. The sound discriminator in the RX was mechanical: reeds. Reeds resonant to the tone were placed on top of an electromagnet. The corresponding reed vibrating given a tone. Soon, there were 8 channels, eight reeds on top of an electromagnet. These reeds touched a contact when vibrating which turns on a relay which activates escapements. This went on for a time. In 1949, the Americans discovered semi conductors called transistors, much much smaller than a vacuum tube and did not need heaters. By the fifties, transistors were appearing everywhere. Still, tones and escapements were used. Eventually, small dc motors replaced the rubber band and the escapement itself. High speed motors were geared down to have torque to turn the control surfaces(Rudder and elevator, ailerons and throttle). These were called "servos". In the forefront of servo development was Howard Bonner(American). Bonner servos reached moddellers across the globe. But this servos were not proportional, meaning they did not move linearly with stick movement in the TX. In the beginning, they only had end switches to stop at extreme ends. In fact, a transition was a servo that was swinging back and forth to a position based on an ON/Off switcher in the TX. The rudder appeared like a dorsal fin of a fish on flight. It became known as the galloping ghost.
The first attempt at proportional control was called analog in nature. The TX transmitted a signal which can increase/decrease a voltage level. A transistor is turn on but a variable resistor connected to the output shaft of the servo changes the sensitivity of the transistor thus bringing it back to an OFF state and shuts the motor. By then the horn connected to the control surface has changed position. The problem was delayed reaction, proportionality,and overshoot. By then, two young Americans electronics buffs were working on a concept. They were Mathers and Spreng(Dough).
Thursday, April 16, 2009
KNOWING YOUR BATTERY PACK(for Nitro planes)
Most of us put our confidence in what the label says in a battery pack. When we used to have the standard 500mah pack and later on got a 650mah pack,we falsely conclude that we have a better pack. To compound the problem, modern chargers will indicate how much capacity it has injected into the pack while charging. Another confidence booster. But there is no way actually that a charger can record how much your battery pack absorbed. What is then the best way to evaluate a battery pack? Well, many modellers do not really appreciate the discharge feature of newer chargers. This feature can give us a better evaluation of a battery pack. This is the procedure:
1. Fully charge the pack with the charger which has delta peak feature.
2. Discharge the pack at a known rate till the voltage has reached 4x1.1=4.4V.
3.Record the time elapsed.
4. The discharge rate x time elapse=true usable capacity of the pack.
Example:
You have a650 mah pack and after fully charging it, you discharged it at 650 ma. It lasted an hour before falling to the 4.4V threshold. It has a 650MAH useful capacity. Now,supposed it lasted only 30minutes, then the useful capacity is half or 325 mah.
Most of us put our confidence in what the label says in a battery pack. When we used to have the standard 500mah pack and later on got a 650mah pack,we falsely conclude that we have a better pack. To compound the problem, modern chargers will indicate how much capacity it has injected into the pack while charging. Another confidence booster. But there is no way actually that a charger can record how much your battery pack absorbed. What is then the best way to evaluate a battery pack? Well, many modellers do not really appreciate the discharge feature of newer chargers. This feature can give us a better evaluation of a battery pack. This is the procedure:
1. Fully charge the pack with the charger which has delta peak feature.
2. Discharge the pack at a known rate till the voltage has reached 4x1.1=4.4V.
3.Record the time elapsed.
4. The discharge rate x time elapse=true usable capacity of the pack.
Example:
You have a650 mah pack and after fully charging it, you discharged it at 650 ma. It lasted an hour before falling to the 4.4V threshold. It has a 650MAH useful capacity. Now,supposed it lasted only 30minutes, then the useful capacity is half or 325 mah.
Saturday, March 28, 2009
Hello guys. Sorry for the long vacation. Have been busy with RC planes. Our last topic was encoders and decoders in RC gear. Let's hightlight some points about the non- digital way of driving the servo. In the ordinary PWM system, the Tx sends about 60 frames of commands to many servos. The more the channels, the less command is given to a servo per unit time. Let's take a 4 channel system. The allocation is 2 MS for each channel totalling 8 ms and 10ms for the pause. That's 18ms divided into 1000MS in a second. At 20 MS, that would be 50 times a second. If you have 6 channels, that would have been 6 x 2m=12, plusa 10ms pause to make a total of 22 ms. There will be less than 50 c0mmands to a servo per second. Now, how does this affect the servo strength? Well, everytime a servo arm is pull out of its position, the pulses drives the motor to pull it back in. If we had more pulses, the pulling in would be finer. That is where the digital servos come in. In a digital servo, the number of pulses "correcting" the servo position is about 300 times vs 50-60 for the analog system. That is about five times. It's like a gear of 300 teeth vs one with 60. The drive is finer as it can correct a smaller error and in smaller units. The drawback is that digital servos also draw five times the current! How is this done. Well, it cannot be possibly converting the 60 pulses per second from the transmitter and convert it to 300 pulses. That is not possible. It became possible with PCM. Pulse code instead of pulse width. In PCM, the Tx sends a binary code to tell a CPU in the RX to position a servo. For example the Futaba 1024 PCM, the servo can take up 1,024 positions. And the beaty of it all, the TX only have to say it once, like sending in the code to take up the position 512 which is center. It's like the command is "Don't change position until I tell you". The local CPU will generate the pulse of 1.5MS but at 300 pulses per second. And that is why a PCM RX is immune to electrical noise since the code has to be exactly legible for it to recognize as a command. In PWM, a glitch can be read as a pulse. Theoretically, if you had switch off a PCM TX momentarily, the servos will remain in their position since no new command was received. This is not the fail safe feature in PCM. The failsafe feature is when a given setting for each of the servos at a certain moment was stored in the CPU in the RX. If the RX does not hear from the ground after X seconds, the CPU switches to this mode even when nothing was heard from the TX again. The plane took on a circling mode for example. Another thing that can be memorized by the CPU is say, a loop. Next time you press the repeat button, the plane does it again. It's like putting the music organ to recording. Pressing a button will play it again and again.
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