AVC or active vehical control on rover

Posted by F. C. Bearsch on October 27, 2014 at 6:18am

Having done this many years ago when developing in the fastest RC car on earth challenge with my friend Wolfgang soon after Kalman had released his specs on sensors in the early 2000s I wondered when this would hit the commercial market on a RTR car. 

I am not that familer with the Rover and the capabilities, however would think that the same capabilities could be done with a ardupilot FC. From what it seems they just use a basic gimbal controller limiting wheel spin I think. 

If there has been any development this direction please point me in the right direction. Currently I was pulling out a few serpents and a few of my custom machined Nitro trucks to see which I would fit up first. Axial has something that looks amazing, the Yeti racer, thinking that the addition of Active suspension could create something quite amazing. 

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Tags: dsc, stc, active, avc, control, pixhawk, vehicle, vrbrain
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  • MikeRover October 29, 2014 at 2:57pm

    From what I've seen in the code, "STEERING" mode pretty much does this - it takes your steering input as a ?lateral acceleration? command and adjusts output accordingly.  Theoretically it should compensate for oversteer by counter-steering.

     

    I played around with a 1/10 scale car on dirt, and in AUTO mode it could stop itself from spinning out during extreme cornering - you could see it countersteering.

     

    It's been a while since I looked at it hard, so take these with a grain of salt. The problems with it at the moment seem to be:

    • Poor velocity accuracy at low speeds hinders its operation since it works out it's desired rate based on lateral acceleration or vice versa, and the speed term has a big impact
    • AFAIK, the nav loop runs at only 10Hz, which isn't fast enough to catch departures in a small vehicle
    • Adding wheel speed encoders would be a huge benefit - if you ran both front and rear wheel ones you could detect loss of traction on the rear wheels and modulate throttle accordingly.

     

    If you've got an APM / PixHawk it's worth giving it a go.

    • F. C. Bearsch > MikeRover October 30, 2014 at 6:39am
      Weight is not that much of an issue so possibly we could put a sensor on each wheel to detect wheel spin as in a full size car then add brakes to each wheel or possibly parts of the drivetrain to arrest excessive wheel spin total speed could be derived from the vector data and possibly to offload some of the computation we could use a PC board computer
    • Admin
      Thomas J Coyle III > F. C. Bearsch October 30, 2014 at 8:06am

      @Tearig,

      I suggest that you build a prototype and compare its performance against one of my autonomous Traxxas 4WD Slash rovers that incorporates active braking and lateral acceleration control as pointed out by MikeRover.

      The Steering Mode is essentially a FBW control setup and will help to keep you out of trouble, but will not totally mitigate the chance of a rollover when trying to take a turn too fast.

      The members on diyrovers have been working with wheel rpm encoders and individual wheel brakes for a couple of years, but have yet to see success compared to my autonomous rovers.

      Regards,

      TCIII AVD 

    • MikeRover > Thomas J Coyle III October 30, 2014 at 2:44pm

      Thomas, you're probably still maintaining a level of sanity in your mission planning, and running on asphalt.  If you really hammered the throttle, and/or were operatinng on gravel you might start to see the limits of the existing code :)

       

      I think it's working well for you because it's able to predict adequately when it NEEDS to slow down ahead of time, rather than having to react completely to a loss of traction.  You'd have the grunt in yours to do it - try setting up a fast, tight track and see how it goes ... no responsibility taken!! 

       

      Theoretically it should be possible to just augment rover with the wheelspin detection and modulate throttle through a similar mechanism to the "throttle nudge". 

  • F. C. Bearsch October 27, 2014 at 12:56pm
    Here is a picture of the B4 before ;)

    IMG_20140518_111337.jpg

  • F. C. Bearsch October 27, 2014 at 12:54pm
    I have messed with a few tmaxx a few years back, I know the revo better. I think the first thing needs to be a pushrod setup and shock tower assembly for all of the vechicals, if we hold to a 1/8 scale nominal size is probably easiest for me also. I have several nitro buggy or truggy pans I can convert.

    Can you post the shock length and the travel for your tmax? I will measure the hotbodies lightning and associated B4, it has a pretty good hacker c8 with a jeti esc which should be interesting...
    • Admin
      Thomas J Coyle III > F. C. Bearsch October 27, 2014 at 1:29pm

      @Tearig,

      I presently have the E-Maxx packed away in the garage. I can probably make a measurement tomorrow for you.

      Regards,

      TCIII AVD

    • F. C. Bearsch > Thomas J Coyle III October 27, 2014 at 2:20pm
      No rush, my stuff is in some sort of box also and has been dormant for some time, my neighbor is to blame.
      Associated RTR 1/8 Nitro: http://youtu.be/0TyGy6TsaRo
  • F. C. Bearsch October 27, 2014 at 7:40am

    TCIII, Yes I am aware, I never liked the racing more the can I do something part of rc... If we as a group raced it would from in doors in AC via FPV in some sort of augmented reality senerio anyway, I would prefer it to be more GranTurismo and F1 than dirt track oval crowd anyway. 

    I did order a few small linear drive thinking of making a pushrod suspension that can have adjustable travel and spring tension. Thinking out loud the linear drives can control just ride height while we could use a array of high-speed high torgue metal gear servos for each spring tension setting, open to ideas, would love the help Rob, what ever custom part I cut I will send you duplicates...

    I have several 1/8 scale buggies chassis etc, not sure if you have anything existing if so possibly we can find the overlap so we can duplicate in both locations...

    Ultimatly I think that this is the style of platform suspension however would like to do all the proof of concepts in parts I already have.

    • Admin
      Thomas J Coyle III > F. C. Bearsch October 27, 2014 at 10:05am

      Hi Tearig,

      I have a Traxxas E-Maxx 1/8 scale brushless rover that is equipped with an APM2.6.

      Regards,

      TCIII AVD

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