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Wheeled 'Bot — Parallax Forums

Wheeled 'Bot

ajwardajward Posts: 1,129
edited 2013-01-23 03:32 in Robotics
To add to the ever growing list of unfinished projects, I've started working on a wheeled vehicle (ultimate purpose unknown!). Salvaging parts from a Newbright r/c "monster truck", I'm adapting the wheels to fit on a Futaba servo.
Using my Dremel tool, I'm milling out the shafts of the drive wheels to fit a 35mm servo disk.
IMAG0500.jpg


I want to use steerable front wheels, but I'm not sure where to start. Any suggestions? Thanks.

Amanda
IMAG0500.jpg
1024 x 612 - 42K

Comments

  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-01-02 14:28
    Why not use the steering system from the monster truck? It should not take much to modify to your needs and should already be set up to be controlled by a servo or other motor.
  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-03 10:18
    ajward wrote: »
    I want to use steerable front wheels, but I'm not sure where to start. Any suggestions? Thanks.

    Amanda, have you ever seen Arrick Robotics ARobot http://www.arrickrobotics.com/arobot/ ? It uses three wheels with a front drive wheel and rear wheel steering controlled via a servo. It might be worth look at their pictures for some ideas on how their mechanism works. The mechanism isn't Ackermann steering http://en.wikipedia.org/wiki/Ackermann_steering_geometry so in tight turns one or both of the wheels will skid sideways. Also a single drive wheel eliminates the need for a differential which would be needed with two drive wheels.

    When I built a four wheel drive robot I punted on all these difficulties and used skid steering like a Bobcat.
  • ajwardajward Posts: 1,129
    edited 2013-01-21 00:38
    @NWCCTV Yup, I thought of that, but it was a little narrow. Initially, that wouldn't be a problem, but at some point I want to power the front wheels with their own servos.

    @Martin_H The Arrick concept was interesting. I've wondered about the possibility of a 3-wheeler with one wheel providing propulsion and steering!

    Anyway, my initial idea was something like a 4-wheel drive car (I like the idea of a wheel on each corner for stability). I've tried skid steer with 4WD and tracks and the results have been spotty. Not an insurmountable problem... just need to find some torquey motors.

    I've got some sketches going for an Ackerman-ish steering setup, but adding servos to the mix is going to require some advanced cobbling skills! :-)
    Another thought was using articulated steering. Not sure how effective it would be, but an interesting exercise for sure.

    Haven't been real active lately. I managed to break a rib doing some "acrobatics" in the bathroom. :-| Still pretty uncomfortable, but the doctor prescribed some excellent pharmaceuticals so the pain is manageable! ;-)

    Back to the drawing board.

    Amanda
  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-21 07:11
    Amanda, wheels can make a big difference in skid steer performance. I used a set of Tamiya spike tire set in the video below:

    The spikes help with lateral skidding during the turns, but you can still hear the servos complain during the turn.
  • TtailspinTtailspin Posts: 1,326
    edited 2013-01-21 07:55
    Turn back Amanda, turn back before its to late...
    http://forums.parallax.com/showthread.php/134532-Casters-end?
    http://forums.parallax.com/showthread.php/136102-Roombas-Revenge?



    -Tommy
  • ercoerco Posts: 20,255
    edited 2013-01-21 09:10
    @Martin_H: Gordon's "Carpet Challenge"? What's that? Where's the thread? How'd I miss?

    @Amanda: I have an ARobot, bought used. Kinda clunky and there's so much play (backlash) in the steering linkage that I dismissed it as an accurate dead reckoning platform. It looks good on my shelf, but I've never even been tempted to fire it up. IMO a PITA WRT consistency.

    Oh how I wish there was a snappy acronym for consistency. :)

    If accuracy and consistency are of primary interest to you, it's hard to beat a solid 2 wheel diff drive chassis with encoders. Treads and 4WD skid steering aren't suitable. TTYTT I'm building a Vex mecanum wheel bot chassis now. Extremely maneuverable and great fun to watch in operation, but the jury's out on how accurate those wheels are for odometry.
  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-21 11:03
    erco wrote: »
    @Martin_H: Gordon's "Carpet Challenge"? What's that? Where's the thread? How'd I miss?

    I think this was discussed in my 4x4's build thread. My 4x4 is modeled after Gordon's Rigel design. After Gordon's original wheel supply ran out, he took it out of production due to the inability to find a suitable replacement. I noticed that the Tamiya spike tires looked similar to his original wheels and figured that they might work. Gordon said the real challenge was how well a 4x4 worked on carpet which limits the ability to skid. So the carpet challenge was born and the spike tires worked like a charm. I believe Gordon is considering bring the Rigel back into production as a chassis kit like his Ardbot as a bring your own wheels kit.
  • ercoerco Posts: 20,255
    edited 2013-01-21 12:14
    Cye was the original spiked-wheel robot. On my shelf next to ARobot, but the difference was that Cye was the ultimate in dead reckoning, even on carpet. Great robot, one of the best.
  • ajwardajward Posts: 1,129
    edited 2013-01-23 02:37
    My wheeled 'bot, Wilbur, is moving about under his own power, tho' not quite where I want him to be. Right now, just a front wheel drive vehicle. Actually a powered front axle dragging a trailer. The goal is 4 wheel drive and articulated steering. I was trying to come up with Ackerman style steering, but thought the articulated would be easier to build.

    The first test (after making sure he was even going to move) was to run a figure eight. It's     not a pretty run, but that's okay... gives me something to tinker with! He's also slow, but speed really isn't a requirement... just want the darned thing to work!

    http://www.flickr.com/photos/81065424@N00/8407021907/in/photostream

    Amanda
  • ercoerco Posts: 20,255
    edited 2013-01-23 03:07
    Wilbur Wheelbot worx wunderfulley!
  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-23 03:32
    erco wrote: »
    Wilbur Wheelbot worx wunderfulley!

    Agreed.

    BTW erco you are either up early, or really late.
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