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Ok am I just being anal or is this fine? — Parallax Forums

Ok am I just being anal or is this fine?

rwgast_logicdesignrwgast_logicdesign Posts: 1,464
edited 2013-01-15 22:23 in Robotics
So alot of you guys said I was taking things to seriously and sucking the fun out of making a Robot. Any you were right, Ive taken a few days away from it to start working with a stripped down roomba, the point of the roomba is to have a bunch of working electronics made I can easily transfer to a stingray, when the time comes.

Anyways I was cleaning up a bit and picked up the the working motors I intend to use on my from scratch bot, I turned them on to see how much the wheels will wobble due to my homeade shaft attachments. Now before flipping out and remounting them I figured Id find out if it was even necessary, or if I was just going a bit overboard. I have a feeling this is why I had a hard time getting my original bot to go straight with out encoders but im not sure. So im asking you guys is this too much wobble in the wheels or is it acceptable?

Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2013-01-15 18:58
    I've seen worse wobble on robots that work perfectly fine. Scribbler for example has a fair bit of wobble out of the factory, and my CBA robot's wheels wobble because there's play in the servo spline.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-01-15 19:54
    Wheel wobble comes in two flavors: radial and axial. Radial wobble will provide a bumpy ride, but as far as odometry and tracking go, it should average out okay. Axial wobble actually changes the distance between wheels periodically. For tracking a straight line, it's of little consequence. For differential turning, though, it could affect odometry since thae angle of the turn is related to the distance between wheels and their relative rotation distances.

    That said, however, I don't think the wobble shown in your video is of huge consequence. You're not being anal, BTW, just careful. :)

    -Phil
  • ercoerco Posts: 20,255
    edited 2013-01-15 21:52
    Your runout (wobble) is not bad, but I'd consider lower rpm & gearing for the odometry experiments you say you are interested in. Your motor is haulin' Smile in that video. I'm a fan of very low gears & low rpms for accurate navigation. http://www.youtube.com/watch?v=cAbjISH5WS4

    Lower voltage and pwm can reduce rpm but torque gets lost. There's no substitute for low gearing and high torque.
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2013-01-15 22:23
    Those motors are geared pretty low, there 6v nominal 80RPM, In the video im running them at 12v mostly becuase the wobble shows more. Ive had two of these motors haul 15 or so lbs at 3v they still put out alot more torque than needed in lower voltage/current modes. The gearing is 141:1.

    I'm glad to hear they aren't too bad, im really tired of ripping them up and re-setting the axles because I cant find the proper ID tubing. I was thinking about mounting them to an old hard drive platter, makes a really cool small round bot like a 3PI.
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