Catapult shafts

Hi! We are team 3031B from Barcelona (Spain)

We’ve designed a catapult with rubberbands, it has enough power but the problem is that the shafts get twisted.

This are the photos of our catapult and the twisted shafts I hope that you can help us.

Us a high strength axle.

Try to link the gears together using standoffs and a axle, and not just using the axle to drive them together.
If that doesn’t work , i would try the HS shafts.
Here’s a link:

Do you think that I should change the gear sistem?

no, for the gears on the bent shaft take 2 or 3 standoffs and put them in-between the gears, so leave the axle there and every thing else the same. IMG-20161016-WA0004.pdf (141 KB)

I agree. Do not rely on the shafts to transfer power to others gears in a system with this much torque. And even though the high strength shafts are not likely to twist like the normal shafts, they are still very likely to start spinning in the square mounting holes of the green gears. It’s best in cases like this to use the shafts only as pivots and not as power transfer elements.

thank you very much, l hope you the best in starstruck!

thank you, your idea has saved my robot!

do you know how can I synchronize the two sides ?

The easiest (best in my opinion) way is through programming. Add an optical quad encoder to each side and find out exactly where the launcher trips; hold one side there until the other side meets it, then launch.

thank you!

I had the same problem on my catapult too. What I did was I upgraded to a high strength axle and connected both gear systems to a single axle, so that the gear systems remain in sync. You do not need an encoder to keep them in sync this way. The HS shaft will also require you to upgrade to high strength gears (thicker gears).

can you send me some photos please my email is:

My team used high strength axles, and because they don’t have HS HS inserts (metal inserts for the high strength axle), the axle eventually strips the inside of the gear. We dealt with the problem by having four HS 84-tooth gears running on that axle, but I think that even with the HS axles, the gear is bound to fail.

But yes, the axle will eventually strip the inside of the gear.