Rover Only Forward and Reverse Responding with Pixhawk/Sabertooth Build

Posted by Robert Kyamoto on November 5, 2015 at 8:48am

I am having difficulty connecting a pixhawk to a sabertooth motor controller. I am going from the SBUS on a FrSky X8R receiver to the RC in on the pixhawk. then from channels 1 and 3 to the sabertooth motor controllers signal 1 and 2. The sabertooth is configured for skid steer. In the radio config page of mission planner, I am able to calibrate all the channels, but the motor controller only responses to forward and reverse, no steering. I have included a picture of the test setup below, dipswitch positions, mixer and input settings on Taranis, and mission planner skid steer settings. Any help you can give me would be greatly appreciated. Thank youRoverSetup.JPG?width=750

Pixhawk channels 1 and 3 to sabertooth controller. Signal, Power, and Ground wires on each cable

RoverPowerOn.JPG?width=750System powered on

Dipswitch.JPG?width=750Dipswitch for Skidsteer

TaranisInputs.JPG?width=750Taranis Inputs

TaranisMixer.JPG?width=750Taranis Mixer

SkidSteer.JPG?width=750Skid Steer Mission Planner

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Replies

  • Admin
    Thomas J Coyle III November 5, 2015 at 5:30pm

    @Jake,

    Try checking the reverse box next to the roll (steering) channel on the MP radio calibration page.

    Regards,

    TCIII AVD

  • Admin
    Thomas J Coyle III November 5, 2015 at 12:39pm

    @Jake,

    I have alerted our ArduRover firmware Developer, Grant Morphett, to your issue and hopefully he can reply soon.

    Regards,

    TCIII AVD

    • Developer
      Grant Morphett > Thomas J Coyle III November 5, 2015 at 10:19pm

      Hi.  As I understand it you have the throttle on the throttle stick but you want it on the elevator stick presumably so it self centres and your rover stops.  This is certainly how I have it.

      If your throttle stick is already moving the rover correctly and you just want a different stick on the transmitter to do the same thing the easiest thing to do is make the change on your transmitter.  Your throttle will be outputting on a certain channel (I would guess 3) so simply move that output channel to your elevator stick.  Does that sound ok or have I mis-understood something?

      Thanks, Grant.

  • Chris Card November 5, 2015 at 11:04am

    @ Thomas.

    For the sake of curiosity...

    I guess that using a Sabertooth dual output motor driver for skid steer that there are conceivably three different ways to accomplish the skid steer control setup.

    1.  [Skid steer output]  Use normal aircraft or RC-car TX with throttle for speed command & aileron/rudder or steering wheel (Car TX) for steering and let the Pixhawk controller perform the mixing and the Sabertooth drives the two motors from independent signals provided by the Pixhawk.

    2.  [No skid steering selected]  Use normal aircraft or RC-car TX with throttle CH for speed command & aileron/rudder or steering wheel (Car TX) for steering and allow the control signals pass-through the Pixhawk without mixing and have the Sabertooth perform the skid steering mixing functions.

    3.  [Skid steer input]  Use a TX with the differential mixing done on the TX and the Sabertooth drives the two motors from independent signals provided by the Pixhawk.

    i guess that the first one would be the more straight forward choice as all the mixing control and the servo trims etc. are setup in one place [ so to speak ] , where as the other two involve mixing on another device, be it before or after the Pixhawk.

    Does what I wrote 'square-up' correctly? ...gramer notwithstanding...

    Chris

    • Admin
      Thomas J Coyle III > Chris Card November 5, 2015 at 12:00pm

      @Chris,

      And the correct choice is #1 if you are going to go to the expense of buying a Pixhawk in the first place.

      Regards,

      TCIII AVD

  • Admin
    Thomas J Coyle III November 5, 2015 at 10:39am

    @Jake,

    Did you try swapping the PITCH and THROTTLE parameter numbers in the RCMAP?

    Regards,

    TCIII AVD

  • Admin
    Thomas J Coyle III November 5, 2015 at 9:56am

    @Jake,

    Try swapping the Pixhawk output channels 1 & 2 to the Sabertooth motor controller.

    Take a look at this thread on ArduPilot.com concerning a similar problem to yours and the eventual solution.

    Regards,

    TCIII AVD

  • Chris Card November 5, 2015 at 9:23am

    It looks like you are using the Sabretooth drive to accept a throttle and a steering signal.

    The drive by default will try to auto calibrate to the r/c signal each time it is powered on. Also there is a time-out feature if there is no signal.

    Your dip switch settings are correct, but you will have to use the DeScribe setup software to change it to accept a fixed range of PWM signals.

    Check out page 14 of the manual.   HERE     There is a check box on the RC tab that will force it to use the fixed PWM range.

    I don't know if that defeats the loss of signal time-out feature or not.

    Chris

    http://www.dimensionengineering.com/datasheets/Sabertooth2x25v2.pdf
    • Admin
      Thomas J Coyle III > Chris Card November 5, 2015 at 9:52am

      @Chris,

      I have never had to reprogram a Sabertooth motor controller, as you have described, to get it to work with the Pixhawk's servo outputs.

      However, the Pixhawk will not output a PWM signal on its servo outputs until it is armed. Therefore I always arm the Pixhawk before I apply power to the Sabertooth motor controller in order for it to see a PWM signal on its two inputs.

      Regards,

      TCIII AVD

    • Chris Card > Thomas J Coyle III November 5, 2015 at 10:21am

      @Thomas,

      I haven't used a Sabertooth with APM or Pixhawk, I've actually only used the 2x60's, with potentiometers or with the kangaroo feedback controller to make big R/C controlled servo motors.

      Your experience in these matters trumps my suggestions.

      Chris

This reply was deleted.