Catapult Axle Breaking Problems

Hi guys, our seesaw catapult has twisted and broken 6 axles in one week. We shot about 3 matches worth of balls and it just kept breaking them. We think the axle is breaking because we are pulling it back to fast and the strain killed the axle, so we lowered the speed and increased the time of which we pulled the axle back, but it just broke again. It did take much longer to break, though. Do you guys know any permanent solutions to our problem?

My team faced the same issue in our original prototype, although that was just twisting. Switching to a high strength shaft should fix the problem. This may require some drilling and reworking with the high strength components, but it’s definitely worth it.

If you don’t want to drill, you can try adding a support linkage (kind of like a 6 bar linkage) with idler gears

How do you mean? Picture please?

We tried to do that, but the high strength shaft is much thicker than the normal shaft and wouldn’t fit inside bearings or motors.

Yes - the high strength shafts use high strength bearing flats, high strength gears, and require drilling through the metal to use (or linkages, as Draco mentioned). They do not interface with the motors, but adding a motor below with the same sized gear should give the same effects.

THANKS SO MUCH! This really really helps us.

                                                                                           On behalf of 815J, THANKS!!!!!!!

Glad to have been of help.

Use a screw. Less friction, less breaking, no drilling.

I don’t think a 2" screw is long enough for these purposes, and would probably break as well. Screws come with pre-made fractures, after all, which lead to fast fracture, and then to failure.

Ehhh… idk how to upload a photo and for some reason I can’t find a photo of one I already had in another season.

If you can imagine, there is a gear currently sharing an axle with the catapult. Connect a 2nd gear as an idler. Then connect a third gear. This third gear would also have a bar parallel to the catapult. Connect that bar to the catapult as a linkage and the load will be distributed among 2 axles

Ah… I see. Interesting concept.

Hmm, we use screws as joints whenever it’s possible because there’s less slop and friction. I would assume that they break less easily too because they’re thicker (and I believe they’re made of a stronger material?). But we’ve never done any testing either.