Can you use a compound gear for a catapault?

My kids built a variation of the fling catapault that they want to throw 2 balls with. With the gearing in the instructions there is too much tension in the rubber bands and it won’t shoot. So then they built compound gears and now the arm will lower but not fire. How can we fix this?

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Take a picture of the system if you want more feedback


You need some way to disengage the gear teeth

Did I hear 2-ball catapult?

Here you go…


I would change your category to IQ.

Fling does have a compound gear…??? I’m assuming it’s a choo choo… Should be obvious why it’s not cycling because something is hitting something else.

fling catapult…?
are you referring to trebuchet?

but they work quite similarly to the usual catapult.


I assume they are referring to Fling, the hero robot designed to play the VIQC game, Pitching In.

Like what’s been stated prior to this, for us to help pictures or videos are actually pretty necessary. Based off your description we have no way of giving you any advice that may actually be useful to you or your kids.

You say that with the gearing in the instructions there is too much tension in the rubber bands and it won’t shoot. Do you mean the catapult arm won’t go down? Won’t release? Doesn’t have enough torque to stretch the rubber bands? The gearing in Fling was chosen to be able to lift the whole robot for a hang, I would assume that if your mechanism doesn’t have the torque required to stretch rubber bands, the mechanism was built incorrectly. Though I cannot tell for certain without seeing the robot.

I’m also not sure what your question about compound gears is. Check out this attached image. It shows what a compound gear actually is.

It is honestly just multiple gears all fized together. Fling accomplishes a compound gear by having two gears on the same shaft rather than be stuck together.

To simply answer your question in the title of this thread: Yes! You can build a catapult using compound gears! However, we don’t know the geometry, or the gearing, or the rubber band orientations… We’ll just need a bit more info to help you out any further than that.

EDIT: I have also changed the tags of the original post to better fit this discussion.