My catapult had been reiterated so many times and it just won’t work. From not shooting both balls to the both top and middle flag. Also my gears sometimes skip and it has a hard time pulling back 10 rubber band even though both motors are red. With any less rubber banding it won’t shoot high enough. We have everything in high strength from the axles to the gears to make sure nothing bends. But help would be appreciated.
That is strange 2 v5 motors at that gear ratio should have no problem pulling it back, for one thing though I would replace the c-channel on the catapult holding the rubber bands to a standoff to reduce weight. As far as the skipping goes, when does it skip? As soon as it starts trying to pull or at the end of the pull?
Check that your motors are both running and that they arn’t Fighting each other
yeah, I use the same ratio you do, with 2 393’s and I can handle a ton of bands before I stall my motors
If it is not shooting high enough, etc, then check the angle of release of the balls.
If it is hitting the flag but not able to turn the flag, then check the number of rubber bands.
If it is not able to pull the rubber bands back, then 3 possibilities…
- Too many rubber bands than necessary
- Gear ratio is not correct
- Quality of build is not good
Hope it helps.
@James6555
The gear that has the catapult bar attached to it skips the bottom gear.
How do I make the quality of the build better? I am pretty average at building and there’s no one at my school who is going my route or has built a catapult. Any tips would be appreciated .
@Xenon27
Would it be okay to see a picture of your catapult by any chance? I haven’t found a close up picture of a catapult using this ratio.
sure, let me find a good one…
lol nevermind I don’t use your ratio, for some reason I thought you were using 1:7, but I see you’re using 1:5. but if 2 393’s can run a 1:7 catapult, 2 v5 motors should be able to handle 1:5 no problem.
I also can’t see anything in your catapult that stands out to me as poor build quality, it looks pretty solid. some information about how the gears slip, and possibly a video of the catapult trying to lower would be quite useful.
Thanks! I will definitely look up some videos and try and remake the catapult with a stronger ratio. Hopefully the will fix the skipping
I don’t see how this could fail tbh, but a 1:7 catapult would help maybe. I can vouch for 1:5 catapults with 2 v5 motors however, as I’ve seen them around before, so It can be done.
1 Like
The first time we used regular axle , we found that it was bent because of the stress . The bend can cause skipping of gears. We used high strength axle (big one) afterwards which worked fine.
they already use all HS axles, so I can’t see how axle flex could be the cause here.
They don’t have a HS axle on the catapult shaft. That is the one with the most stress and will bend the easiest. I imagine when it slips it’s that axle bending.
1 Like
The first picture is more recent than the second. We had more itirations but there are just two pictures that I had on hand. And both skip
a video of the skipping might be most helpful. if you take a slow-mo of the skipping, it can reveal a lot you may not have thought of.
I will try when I get to school tomorrow, as I don’t have the catapult in hand
I see now that you have all high strength in the top photo, I thought they were the same just different angles. I do see a loose screw on the right bearing of the arm shaft in the top photo. The only other thing I would change is having the rubber bands pull up, right now they seem to be pulling down and not optimally.
1 Like
Compression of gears might be more difficult with 1:5s, although it may be possible. The best option if gear skip is the biggest problem is probably to go 1:7 for your gear ratio and swap in green 200 rpm cartridges instead.
In addition, your release angle seems pretty steep, which may be the reason for why you don’t hit the flags (It’s probably undershooting?). I would consider making the angle less steep (moving the bar you use for blocking the catapult down), but not too much or else the shot will not have enough momentum going directly into the flags instead of up. this may help with your rubber band problem as well - you can trade out a little power for a little more arc.
1 Like