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Openning Scribler — Parallax Forums

Openning Scribler

JohnBJohnB Posts: 10
edited 2010-04-20 22:13 in Robotics
The left motor does not turn. It has a little movement and very low torque. There seems to be six screws holding the bottom on: Are there any other fasteners? If I cannot remove the cause of the binding and need to replace the motor, what should I buy and where can I buy it. Is it obvious how to remove the wheel and put it on the new motor? The right wheel works fine.
John

Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2010-04-19 19:57
    If it is still under warranty Parallax will be helpful in getting it promptly repaired.

    If it is not under warranty it is a snap to fix yourself. Just remove all six screws and the shell will come apart. There are two cables from the top half to the bottom half which you can remove to fully separate the shells. It's possible something got trapped in the wheel hub so look if there's anything in it. If not then one of the motors has likely burned out. The motors/gearbox assembly will literally fall out of the housing because they are clamped in place by the two shells. The cable to the motherboard is easy to remove.

    The motor is a standard size motor and the Solarbotics RM3 works, It is available at Solarbotics or Pololu, maybe Parallax, but I haven't noticed it on their web site. Buy more than one as a matched set produces the best results, and the motors are highly variable. It may take some fiddling to get a pair that works well together. The motor is attached to the gearbox by two screws and a retaining clip.

    Some people in the forum have replaced the gearboxes with the Solarbotics GM2 which has higher gear ratios and allows for more repeatable movement from Scribbler if you hack wheel encoders into the robot.
  • JohnBJohnB Posts: 10
    edited 2010-04-20 00:58
    Thank you for your help. Indeed it was easy to get to the motor and gear box. When the motor is removed from the gearbox, it rotates freely and the wheel attached to the gearbox rotates freely, but when the motor is reattached to the gearbox, the wheel seems to bind: at least it is much harder to rotate than the other wheel. I haven't put power to the motor yet, but I will tomorrow.
    Thanks,
    John
  • Martin_HMartin_H Posts: 4,051
    edited 2010-04-20 01:18
    A diagnostic would be seeing if you swap motors between housings. If the problem is with the gearbox it will happen with the other motor and if the problem is with the motor it will happen with the other gearbox. Then you buy a replacement for which ever is the source of the problem.

    I fix plenty of kids toys that break due to abuse or poor quality. I've had the problem that a hobby motor turns freely when you spin it by hand, but resists turning when you put it in a gearbox. In that case there was some kind of short across the terminals. The motor then acted like a dynamic brake, probably didn't do the power supply much good either. I just swapped out the motor and all the caps and the toy worked good as new.

    From broken toys I've ended up with a bunch of spare parts for other toys that are not as far gone.
  • JohnBJohnB Posts: 10
    edited 2010-04-20 20:39
    Can someone tell me if a replacement motor is available from parallax?
    Thanks,
    John
  • WhitWhit Posts: 4,191
    edited 2010-04-20 22:13
    You can ask them - but I believe Solarbotics makes a compatable model.

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