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Thread: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

  1. Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    Can the Roboard capture (read) PWM from an RC receiver?

    The Roboard documentaion for the "RC Servo lib" says it has
    "Capture mode (for reading RC servo’s position feedback)"
    but I am not sure if I understand what is meant by the term
    "RC servo position feedback"?

    My application is to have the Roboard in an RC airplane and
    have the Roboard read the servo commands from the traditional
    RC receiver. If the Roboard decides that the RC receiver is in
    failsafe mode it will overide the commands from the RC receiver
    and use GPS to guide the RC airplane back to the position of the
    pilot on the ground. Some people call this "pigeon homing".

    Thanks. John Elliott (Seattle)

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    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    I believe the capture mode is for the higher-end digital servos that support a serial communications protocol, in other words, it uses an entirely different strategy than PWM and is not for reading in an RC pulse.

    I think you'll have a hard time reading the length of an inbound RC-pulse on the roboard since programming in real time under an operating system such as Windows is quite difficult. Personally, I'd also be afraid to use PC-based failsafe.... seems more likely to fail than the device it's monitoring.

    Any reason not use a true embedded controller, where real-time programming is easy, and the hardware/software is typically very robust?

    -Fergs

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    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    Take a look at the Ardupilot project. It sounds like it may do what you want and is a real-time system.
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    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    Seconded and thirded. There's a reason I have to build watchdogs into my critical PCs. I don't think I'd _ever_ consider having a PC *be* the watchdog.

    Welcome to the forum, btw!
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  5. Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    I was afraid that might be the case.

    I was hoping to use a PC based controller since I have done most of my programming on PC's in Windows and DOS, so it would be much less of a learning curve. A true embedded controller would probably be a better solution.

    Thanks. John Elliott (Seattle)

    Quote Originally Posted by lnxfergy View Post
    I believe the capture mode is for the higher-end digital servos that support a serial communications protocol, in other words, it uses an entirely different strategy than PWM and is not for reading in an RC pulse.

    I think you'll have a hard time reading the length of an inbound RC-pulse on the roboard since programming in real time under an operating system such as Windows is quite difficult. Personally, I'd also be afraid to use PC-based failsafe.... seems more likely to fail than the device it's monitoring.

    Any reason not use a true embedded controller, where real-time programming is easy, and the hardware/software is typically very robust?

    -Fergs

  6. Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    I looked at the Ardupilot and it does look pretty capable. I may have to switch over to the Ardupilot.

    I have already ordered a Roboard so I will look for another work around to get PWM input.

    Thanks. John Elliott (Seattle)


    Quote Originally Posted by jes1510 View Post
    Take a look at the Ardupilot project. It sounds like it may do what you want and is a real-time system.

  7. #7

    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    Have you looked at Windows Embedded CE ? It is a real time OS, is compatible with the RoBoard, and programs very much like Windows and DOS. You can even run .NET and MS Robotics studio applications. There is a learning curve involved in building an OS image, but the payoff is an extremly small footprint Windows OS.

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    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    You've still got drivers goin' on, and from what I've seen, it just doesn't smell mature enough for me to consider it fault-tolerant. Even hard-realtime isn't necessarily fault-tolerant by nature... Just a total "IMHO" though.
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  9. #9

    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    I've used WinCE on robots needing real time processing and it worked well. No crashes or hangs, either.

    I've also written custom drivers under WinCE. Again, there's a learning curve but it is a great driver development environment. You get remote source code level debugging while your driver is running within the OS. WinCE ships with many, many drivers. Custom drivers are often not needed.

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    Re: Can Roboard capture (read) PWM from an RC receiver (RC Servo lib)?

    Custom drivers would be needed for the RoBoard's servo control...

    And RoBoards drivers have not proven to be particularly robust at this time.

    [shrug]Not my plane that falls out the sky, crashes into a group of school-children, and explodes in a nitromethane fireball...
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