gearbox and motor removedI took an apart a child’s toy because it looked like it had a neat gearbox in it, it did. The problem is I have no idea what type of gearbox is and I wanna see more things used with it.

It rotates both wheels forward when the motor goes in the forward direction. Thing weird thing is, when going in reverse it has one wheel go forward and one go backward is to turn the car.

  • $\begingroup$ so it has one wheel that always turns in one direction, and the other wheel that changes direction? $\endgroup$
    – jsotola
    May 25 at 6:09
  • 2
    $\begingroup$ Is there a photo? $\endgroup$ May 25 at 6:14
  • $\begingroup$ This is an interesting question, and an interesting mechanism. I too, would be interested in knowing the answer. I did try to work out what it's called, but as you probably found, there are so many results for completely inappropriate mechanisms that it was impossible to get anywhere. As with many identification question, this requires you to know what you're looking for before you can find it, which makes this an excellent question for the experts here in this community. $\endgroup$
    – Mark Booth
    May 25 at 10:56
  • $\begingroup$ are you certain that both wheels turn when in reverse? $\endgroup$
    – jsotola
    May 26 at 0:14
  • 1
    $\begingroup$ I've seen a lot of toys with a differential and a ratchet on one wheel. This 1 motor solution allows the toy to both drive straight and turn. When the motor goes forward, both wheels go forward. But when the motor goes in reverse, a ratchet prevents one wheel from going in reverse. So only one wheel reverses and the other is locked, and the toy turns while rotating backward around the locked wheel. $\endgroup$
    – Ben
    May 27 at 1:28

1 Answer 1


I don't know what this is called, but my suspicion is that this mechanism makes use of something very similar to a differential gear.

When the drive shaft is rotating in one direction, the pinion gear (green) engages with the ring gear (blue) as normal, but when the drive shaft is rotating in the other direction, the pinion gear engages with an extended side gear (cyan) instead, while locking the ring gear in place.

Since the ring gear is fixed in place, the torque going into the side gear directly would be translated via the spider gears (orange) into torque in the opposite direction on the other half shaft (red).

Animated differential gear, click through for static version if link to animated version breaks

Thanks to Mallaky for the animated gif.


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