Hello everyone, I was making a catapult for the new season Level Up. When it launches, it does not go very far (a foot at most). It is not that the object that I’m launching is heavy, because it is a little bit lighter than the official bean bag. I was wondering if it was the winch or the rubber bands. When it releases the arm, the winch creates a little bit of friction. Also, I have a tensioner, which limits the amount of rubber bands. Also, even if I remove the tensioner, adding too many rubber bands makes the back of the robot bend. Please let me know if I can fix this issue without removing the tensioner, or if I need to sacrifice the tensioner. Note that I am not that experienced, and this is my very first time building a catapult, so any general tips about building a catapult will be very much appreciated. I also only have the education kit so some materials are limited.
I don’t see a hard stop, maybe you could try and place something to stop the catapult at a 45 degree angle? And yeah you probably need more cross bracing than just standoffs. They work, but having actual beams running through is probably a better choice.
Thank you for the response! Actually, I have a hard stop at an 45 degree angle because of the rope part, but please let me know if that doesn’t work. Also, just checking that the standoff that you’re talking about is the one holding the rubber band, correct?
My experience from Rapid Relay is that more rubber bands will make the catapult more powerful. Because of what you said about the tensioner, I understand that that might not be an option, but that might be your problem. Another thing that could be causing this is an unstable frame. Too much movement in your frame/catapult could be absorbing some of the energy from the launch. If you notice this, I would recommend attempting to minimize the motion of your robot/frame.
I could be wrong, but it looks like your rubber band is very close to your fulcrum. That could cause your catapult to be weak, since the band doesn’t have enough mechanical advantage.
Thank you for the reply! When I placed the rubber band further, it launched so much farther, and I am so grateful that you wrote this. However, It looks like the frame is near its limit before the pins start to pop, and it is not at its distance of throwing that I am satisfied with. Is there anything I can do to make it go farther without placing the rubber band even farther? Or should I put the rubber band to its absolute limits?
If there’s room in your design, you could place your fulcrum farther in. Also, if your pins start to pop, you might want to add some triangular bracing to your catapult. It looks like a lot of your catapult is held together by standoffs, so you could place some beams for filler with 0x3 or 2x2 pins through them.
For IQ, use standoffs to brace everything, and add supports when you can. Connecting beams together where possible can help stabilize them against each other. I noticed in your drive specifically, there’s a lot of empty space, so you might be able to put supports there.
You could also try adding more tension (add more rubber bands) and dedicate a separate motor for the winch. Also make sure you use a slip gear, so the forward motion isn’t connected to the motors when released (might break motors, and motors add more friction).
Generally, structurally, beams are better, but it does depend on the situation. Standoffs are lighter and take up less space. We usually try to keep our structure from being spaced out on different layers, because stacking a ton of beams is annoying, heavy and unnecessary. I would say that short ones are fine (0.5x - 2x pitch, though it depends on the application), but the long ones put your robot at risk of falling apart.
Also, if something is sticking out, you should usually put a beam to triangular brace it.
Thanks for the reply! Sorry for saying it not clearly. I mean like how, like a right triangle, or like anything else. If it’s possible, an image will be so helpful. Also, I always watch your videos on youtube which has helped me a lot last season!
Just connect three beams together, and try to use a equilateral triangle, since it is the strongest. The winch that I mean is the mechanism that pulls the rope back. You can connect 2 motors together giving more force to pull back more tension from the rubber bands (add more for more tension). You can also give it a gear ratio (2:1 or 3 : 1) for more torque.
