Differential Claw/Arm

Hey guys, I built a differential that shares the power of two motors between the arm and the claw. This could allow you to use


Wait whoops sent that too early

It alllows you to save a motor and use it for something else. Here is the picture:

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In case you dont know, a differential is a motor sharing technique that uses the vectors of the motors to create different outputs. If both of the motors spin the same way, the gears in the back lock up, moving the arm. If they spin opposite directions, then the four-bar locks up, moving the gears in the back, powering the arm. It is a very efficient design, and it can definitely be used in competition.

Sorry the gears in the back power the claw

Nice bot! You should upload a video of it running. (Maybe on YouTube, or Dropbox or something)
Also, what do you plan on using the extra motor for?


Ok i will do that, the extra motor could be used for an Omni-directional drivetrain (most likely an h-drive). My team currently uses one and we find it very helpful for tiny micro adjustments when approaching the riser.

Here’s a video of it working:

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That looks great! You might want to speed up the claw a little bit with a chain.

Also, I don’t quite get how the claw moves. Which direction are the motors spinning to get the claws to move?

The motors move in opposite directions. Someone named T Mayer on YouTube made a great video explaining it, here’s his explanation:

Go to 2:22, thats the design that I based it off of


He’s actually on the forum, too. @TaranMayer


Your robot looks awesome! can you explain how it works? To be honest, ratchets confuse me.

Glad I could be of assistance. That video was several months in the making.


Thank you, it was very helpful


There is no ratchet involved, it is simply a differential. While it looks complicated at first, it is actually quite simple to make. It involves freely mounting the arms to two gears that are interlocking, and then attaching the motors on the gears through a 1-5 gear ratio (this can be changed, but this is just my personal preference). The motors should be attached to the arm on the outside.

For the claw, just mount a chain on one of the gears that the arm is mounted on, and then chain it to the claw. Make sure not to put the gear reduction here, as it will move the claw as the arm moves up and down. Here’s a quick drawing of how it should work:


Makes more sense now. I couldn’t tell that the 60t gear wasn’t directly connected to the four-bar in the other shots.


just a suggestion, try to fit that motor on the side inside the robot, since that motor might go out of the size constraints.