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Will I damage an RC receiver, if I control servos using a BS2SX and my receiver — Parallax Forums

Will I damage an RC receiver, if I control servos using a BS2SX and my receiver

Capt. QuirkCapt. Quirk Posts: 872
edited 2006-08-23 22:55 in BASIC Stamp
I have a BS2sx and my project controls 2 servos based off of inputs from 3 other sensors. Currently the BS2SX is intended to operate·2 servos, independently of my RC system.
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But I want to expand it, to work in conjunction with the receiver and system·servos. I am planning on using a couple of Futaba "Y" connectors·between·my RC system receiver and servos·and monitor the position of·the 2 system servos using the BS2SX. Then·fine tune their position based off data from·the·sensors attached to the basic stamp.··
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My question is, will it damage the Receiver if I use the basic stamp to control the servos using the "Y" connector, since the Stamp will be sending PWM to both the servo and receiver at the same time.
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My·radio is a Futaba PCM 1024 based system.
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Thank you
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Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2006-08-23 21:39
    It's quite possible. Any time you have two drivers connected, and one tries to drive high while the other tries to drive low, you have in effect a short-circuit which can burn out one or the other of the drivers.

    Putting a 220 ohm resistor in series with the BS2 pin will prevent damage to the BS2, and probably to the RC system, but will also probably prevent the BS2 from controlling the servo's.

    Is there a reason you can't put the output of the RC reciever to a pin on the BS2, and using "PULSIN" to read the pulse width commanded by the RC reciever? That way, only the BS2 has to drive the servo's.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-08-23 22:27
    Bill,

    ·· Why can't you pipe the pulses into the Stamp then out to the Servos?· The BS2 could be set to adjust the values or just pass them through.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Capt. QuirkCapt. Quirk Posts: 872
    edited 2006-08-23 22:50
    First off, I'm programming a project that somebody else already made a board for and it only has 2 servo connections. So I figured I could change input/output status on pins 12 & 13 since the board only made use of those 2 pins and write code to prevent the pins from changing to output, if the receiver was sending an input.

    It's for a model airplane and when it's in the air, the·fuel mixture and throttle·servos I would be monitoring are not in use for about 4 of the 7 minutes its in the air. The Stamp would monitor the fuel mixtures·servos opening % and spin it's wheels until it's allowed to take over and adjust the fuel mixture according to EGT, CHT and Tachometer readings.

    So in the time that the servos are actually in use, the program will only log servo positions. Then take over completely and then shut off after the race is over and allow the receiver to take·control·for landing.

    So in a perfect world, pulse width will only be coming from 1 source at a time. But it would still be sending pwm to the receiver no matter what (that I assume is setup for output only)

    Bill

    PS It would be a $7500 pile of mush, if it took out the reciever in the air. lol
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-08-23 22:55
    Bill,

    ·· It might be possible to put a couple of resistors in between the signals coming from the receiver so that when the BS2 is outputting data it doesn't damage the receiver.· Of course this is a suggestion that you can follow at your own risk.· We assume no liability if it doesn't work.· =)

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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