Is a direct drive catapult feasible?

We’re planning on putting a catapult on our robot and I have an idea of how it would work but I want to know what you guys think. I’m worried it wont have enough power to launch to the far zone. A link for a quick sketch of mine is below, let me know what you think.

The surgical tubing provides enough force so the motors must work at about 75% capacity to hold the arm down so that it can get an object, then they reverse at full power to fling the object with 175% the power of 4 motors. Which is hopefully enough power to fling the object from the top of the fence to the far one. It needs to have enough power to throw them over and still clear any objects in the way (bouncing into the far zone isn’t enough). The object leaves the catapult when it is 180 degrees vertical and a few inches above the fence.

The Sketch

Tbh I think you should just test with parts. You can do all of the Math perfectly and it still may not work with the actual parts

I agree but I just want to know if anyone has tried something similar and if this idea is just never going to work. Only if a lot of people tell me its definitely not going to work I won’t build it.

Is the surgical tubing your equivalent of rubber bands? If so, is there a reason why you picked it as opposed to tried and true rubber bands? This is quite the creative use of levers to help your propulsion, and I think it would work, but you would have to be very space aware. Good Luck!

Well… surgical tubing is basically the latex tubing.
It is tried and tested as well.
In fact, before the “discovery” of better quality rubber bands, it had always been latex tubing :slight_smile:

Think it is about the application itself. There are times when rubber bands is definitely more suitable than latex tubing, and vice versa.

@meng Huh. TIL. I didn’t know surgical tubing was used. What are the advantages of using it over rubber bands, and when should one not use it? Thanks!

Do you plan on having the torque of the motors hold the arm down while you scoop up a star? If so, keep in mind that the motors will heat up if they are kept in a stalled condition with speed values set above about 20 (out of a max of 127) for more than just a few seconds, and their PTCs will trip out fairly quickly. If you plan on relying on friction holding the arm down, then consider how that friction might also affect your launch.

Surgical tubing lasts much longer and is more reliable than the vex rubber bands… you can also easily tie it to be any length… thats about it in my opinion… and about the catapult i don’t know if that will be enough considering that teams like wingus and dingus had to have something like 6 motors and surgical tubing to launch a ball full court… If build right it may work though

Based on a little teensy bit of prototyping from a while ago, I don’t it will work. You need more rubber bands than a direct driven catapult can pull back; the stars are just too heavy. The direct driven catapult was good for NbN with light objects and extremely high rof, but this year we have heavier objects and more time to pull back a catapult between shots.

Yep, the tubing has a more consistent and linear pull. It’s just more reliable than rubber bands.

Just using nothing but net as a frame of reference, I remember wingus and dingus used a 6 motor elastic assist, direct motor drive to full court shot a ball.

Considering the ball was like 1/4th the weight of a star, a star catapult with the same capabilities would only launch the star a 1/4th of the distance, meaning you could launch a star about 4 feet across, maybe 3 feet high. If you want to launch two stars, it would probably only go about 2 feet across, 1.5 feet high. So in my opinion, it probably wont be worth it

I built a demo catapult using elastic tubing, but I found that it seemed to work much better with an equivalent amount of rubber bands. Obviously it was not super standardized testing and other factors could have been at play, but my experience shows that latex tubing is a “continuous” kind of pull, whereas rubber bands are more of a “bang.” In my case, I needed the “bang”, so I switched to bands. Depending on how you want your catapult to work, you might want the “continuous” instead. Try both and see what works.

After A bit of thought I’ve decided a Choo-Choo Mechanism Is probably the way I want to go. So I’ll try that first