Hi! Does anyone have a cad file (prefer stl or iam) for a catapult? I would like to try to build a catapult for a basketball. I would like to see some reference cad designs to see the different variations of a catapult. Thanks!
Have you checked Grabcad? Im sure there are some models on there.
You might also check out Instructables, they usually don’t have CAD but will show you pretty in-depth the design and how to build it, with lots of photos.
A few years ago I came up with this rubber band powered design, which was intended to be laser cut from 3mm plywood and assembled with hot glue. The intended audience was middle schoolers, so it’s not a particularly large or powerful device, but it might give you some ideas. For scale it gets cut from a roughly 12"x12" sheet.
I lifted the trigger from a wood catapult design on saw online; the sear is connected to the rear axle, so you rotate the rear wheels back to lock it, and forward to fire. It’s adequate for a couple good rubber bands, but there’s no secondary safety. Release angle is controlled by a dowel that the arm whacks into.
It’s all solidworks native files, which I’m happy to share. I can spin off a .step assembly, if you’d like. I’m not sure how relevent it’d be to scale up, but it’s something, I guess.
Catapults are cool and all, but have you considered a trebuchet?
Team 118’s 2016 robot is the first thing that comes to my mind:
It looks like the CAD is available to download here:
You may want to start by watching a bunch of match videos from 2014 and 2016. Those were the most recent years I recall where catapults were common (and effective). You can then look for reveal videos from teams you see in the match videos. It may also be worthwhile reaching out to those teams. They may be able to provide insights into the design that you won’t get from watching a video or even looking at a CAD model (i.e. what made their catapult good or bad). The 118 students I spoke with described the procedure they used to calibrate their catapult when it was mounted on their practice robot and how they recalibrated it when it was transferred to their competition robot, making it very accurate in competition.
I can think of 3 different types of energy sources used for powering the catapults that I saw. You may want to explore the pros and cons of the different energy sources from the perspective of your team and the resources available to it.
Oo, sorry, I haven’t really thought about that. What benefits/disadvantages would that be? Also what kind of mechanism would you need? (Motor, spring, piston)?
Generally it’s easier to launch things further with trebuchets. They also do not need springs, motor, or really anything other than a weight and a sling (bearings if you want to get fancy). They can be a bit finicky to tune the right sling length, release hook, and pivot distance, but once they are set up they work amazingly.
The most difficult part is that they require a rather heavy weight to launch, generally making them heavier than a regular catapult.
do they not also mainly work with smaller stuff? Like it might struggle with a 2016 boulder but not a 2017 fuel
Depends on size. Take a look at any videos you can find of the Punkin’ Chunkin’ competition, there’s a few good-sized trebuchets in there.
Bear in mind that trebuchets were used to try to knock down castle walls back about 500-1000 years back. They threw heavy stuff like big rocks. Just need a big enough weight, a big enough lever arm, and a big enough sling. Oh, and heavy enough structure.
Wait there’s no electronics involved? What if I want it to vary the shot power?
How would u make it so I can control power and stuff with a computer?
No, not really. They work with all size of objects, it just depends on how large your system is. A trebuchet that is able to launch the same object the same distance as a comparable catapult would likely be overall smaller, but there are so many variables in the system it is very difficult to say one way or another.
You change the weight, the position of the weight, the length of the arm, the sling, all kinds of different variables to change, many of which can be pretty easy to make configurable. Maybe not as easy as a standard catapult though.
This is something you did not mention in your OP, to which I suggest you take this as a lesson in defining your scope clearly and completely. Having this controlled by a computer brings an entire new perspective and set of answers and likely changes some of the answers already asked.
A standard catapult would likely be significantly easier to be adjustable by a control system than a trebuchet.