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Many (perhaps most) radio control transmitters multiplex all the "RC PWM" channels into a single physical wire, using a system called "RC PPM" (radio-control pulse position modulation). | Many (perhaps most) radio control transmitters multiplex all the "RC PWM" channels into a single physical wire, using a system called "RC PPM" (radio-control pulse position modulation). | ||
[http://www.futaba-rc.com/faq/faq-pcm1024.html] [http://books.google.com/books?id=EcbjKvhgPLsC&q=pulse%20position%20modulation] [http://www.hobbytronics.co.uk/decode-rc-control-ppm] [http://books.google.com/books?id=EWZumms67AUC&q=pulse%20position%20modulation] [http://pages.cs.wisc.edu/~bolo/rc/radio_types.html] [http://adamone.rchomepage.com/guide1.htm] [http://www.495thsquadron.org/PDF_Files/UnderstandingRC.pdf] | [http://www.futaba-rc.com/faq/faq-pcm1024.html] [http://books.google.com/books?id=EcbjKvhgPLsC&q=pulse%20position%20modulation] [http://www.hobbytronics.co.uk/decode-rc-control-ppm] [http://books.google.com/books?id=EWZumms67AUC&q=pulse%20position%20modulation] [http://pages.cs.wisc.edu/~bolo/rc/radio_types.html] [http://adamone.rchomepage.com/guide1.htm] [http://www.495thsquadron.org/PDF_Files/UnderstandingRC.pdf] | ||
Often this "PPM" signal is transferred from the a student's RC transmitter through the buddy box wire to the teacher's RC transmitter. | Often this "PPM" signal is transferred from the a student's RC transmitter through the buddy box wire to the teacher's RC transmitter. | ||
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The "combined signal" -- the "RC PPM signal" -- looks something like this | The "combined signal" -- the "RC PPM signal" -- looks something like this | ||
(based on diagram from Richard J. Prinz[http://www.min.at/prinz/?x=entry:entry130320-204119]): | (based on diagram from Richard J. Prinz[http://www.min.at/prinz/?x=entry:entry130320-204119]): | ||
[http://blog.ncode.ca/?tag=remote-control] [http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=75692&start=0] [http://users.belgacom.net/TX2TX/tx2tx/english/tx2txgb1.htm] [http://rcarduino.blogspot.com/2012/11/how-to-read-rc-receiver-ppm-stream.html] [http://www.rcgroups.com/forums/showthread.php?t=1654104&page=2] | [http://blog.ncode.ca/?tag=remote-control] [http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=75692&start=0] [http://users.belgacom.net/TX2TX/tx2tx/english/tx2txgb1.htm] [http://rcarduino.blogspot.com/2012/11/how-to-read-rc-receiver-ppm-stream.html] [http://www.rcgroups.com/forums/showthread.php?t=1654104&page=2] | ||
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Sync 1 2 3 4 5 6 7 8 Sync... | Sync 1 2 3 4 5 6 7 8 Sync... | ||
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* - low separator pulse, always 0.5 ms | * - low separator pulse, always 0.5 ms | ||
1..8 - high "RC PWM pulse" for channels 1..8 0.5 – 1.5 ms | 1..8 - high "RC PWM pulse" for channels 1..8 0.5 – 1.5 ms | ||
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The long "sync pulse" between frames is typically at least 5 ms long. | The long "sync pulse" between frames is typically at least 5 ms long. | ||
All the other pulses are no more than 2 ms long. | All the other pulses are no more than 2 ms long. | ||
Most transmitters have a fixed frame rate somewhere in the range of 40 Hz to 200 Hz. | Most transmitters have a fixed frame rate somewhere in the range of 40 Hz to 200 Hz. | ||
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When the pilot moves the positions of the joysticks on the transmitter, | When the pilot moves the positions of the joysticks on the transmitter, | ||
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The corresponding radio control receiver decodes the radio signal to a RC PPM signal on a single physical wire. | The corresponding radio control receiver decodes the radio signal to a RC PPM signal on a single physical wire. | ||
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Often the receiver includes either a 4017 decade counter[http://en.wikipedia.org/wiki/4000_series#4017_decade_counter] or a 4015 shift register -- | Often the receiver includes either a 4017 decade counter[http://en.wikipedia.org/wiki/4000_series#4017_decade_counter] or a 4015 shift register -- | ||
that chip decodes the RC PPM signal at its CLK input into to several independent "RC PWM" outputs. The various RC servos[http://en.wikipedia.org/wiki/servo_(radio_control)] are connected to those outputs with standard 3-pin connectors with 0.1" spacing. | that chip decodes the RC PPM signal at its CLK input into to several independent "RC PWM" outputs. The various RC servos[http://en.wikipedia.org/wiki/servo_(radio_control)] are connected to those outputs with standard 3-pin connectors with 0.1" spacing. | ||
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(The standardized "RC PWM" works differently enough from the PWM used to control DC motor speeds that some people say that RC PWM signals "are not really PWM signals" | (The standardized "RC PWM" works differently enough from the PWM used to control DC motor speeds that some people say that RC PWM signals "are not really PWM signals" | ||
− | [http://www.microchip.com/forums/m450082.aspx] [http://www.technobots.co.uk/discus/messages/7/387.html?1225050483] [http://www.rcgroups.com/forums/showthread.php?t=1318288] [http://www.cmucam.org/boards/8/topics/2877?r=2882#message-2882] [http://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface]. | + | [http://www.microchip.com/forums/m450082.aspx] [http://www.technobots.co.uk/discus/messages/7/387.html?1225050483] [http://www.rcgroups.com/forums/showthread.php?t=1318288] [http://www.cmucam.org/boards/8/topics/2877?r=2882#message-2882] [http://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface]. Alas, |
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none of those people give any suggestions as to what we *should* call these signals, so I call them "RC PWM signals" for lack of a better name. | none of those people give any suggestions as to what we *should* call these signals, so I call them "RC PWM signals" for lack of a better name. | ||
Perhaps I should call them "RC control signals"[http://www.mitchr.me/SS/batteriesRequired/RCcontrolTheory/] ?). | Perhaps I should call them "RC control signals"[http://www.mitchr.me/SS/batteriesRequired/RCcontrolTheory/] ?). | ||
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If two transmitters are transmitting at the same time, then yes, there will be an overlap of pulses. | If two transmitters are transmitting at the same time, then yes, there will be an overlap of pulses. | ||
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etc. | etc. | ||
[http://electronics.stackexchange.com/questions/82387/how-can-i-understand-a-servo-well-enough-to-build-one] | [http://electronics.stackexchange.com/questions/82387/how-can-i-understand-a-servo-well-enough-to-build-one] | ||
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The people at the OpenServo project have developed an [[open hardware]] motor driver circuit that fits inside a typical servomotor case. | The people at the OpenServo project have developed an [[open hardware]] motor driver circuit that fits inside a typical servomotor case. | ||
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[http://www.openservo.com/] | [http://www.openservo.com/] | ||
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== Further reading == | == Further reading == | ||
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* The original rough draft of this page was inspired by questions about [http://robotics.stackexchange.com/questions/4456/pulse-position-modulation-as-used-in-rc-controls "Pulse Position Modulation as used in RC controls"]. | * The original rough draft of this page was inspired by questions about [http://robotics.stackexchange.com/questions/4456/pulse-position-modulation-as-used-in-rc-controls "Pulse Position Modulation as used in RC controls"]. |