spring loaded launcher

Has anyone given any serious thought to a spring loaded cannon? I’ve been toying with the idea on and off for the last few days, but I actually sat down and worked it out today.

I’ve had everything revolve around a cauking mechanism that uses a cam. Think of a flat egg shape with a bite taken out of the side. Put it on a motor with the shaft centered toward the larger side. Now, have a spring loaded plunger that is in direct contact with the cam. As as the cam rotates, it gets longer and pushes out. If you rotate far enough, you get to the “bite” and the tension on the spring is suddenly relieved. If you keep rotating, it will retention and you can start over again. (Crude drawing attached)

The ball needs 13J, so with 4" displacement on the spring, it’d need roughly 60lb of tension. I don’t know how to do the exact math because of the oddly shaped cam, but it’ll take between 0.3 and 1.3s (most likely close to the middle of those) using the FP motor.

I think that the advantage of this is that it is easier to mount on a turret than the much liked roller throwers. I also think that it might be more consistent (barring wear on the spring).

I think I’m going to build a prototype tomorrow.



Make sure that you do not exceed the maximum allowable potentiel energy stored in a spring… (don’t know what it is… 20 foot pounds maybe?)

there isn’t a maximum spring tension rule. if there is then i’ve missed it, could you please quote the rule itself…i’ve looked and saw nothing.

it does say that if the tech inspectors think that your mechanism is unsafe they may not pass your robot.

This is the rule you are talking about, and there is no maximum and it only applies at the begining of the match.

<R02> Energy used by FIRST Robotics Competition robots, (i.e., stored at the start of a match), may only come
from the following sources:
• Electrical energy derived from the onboard 12V and 7.2V batteries
• Compressed air stored in the pneumatic system, but only supplied by the compressor included in the kit,
and stored at a maximum pressure of 120 PSI in no more than two Clippard Instruments tanks.
• A change in the altitude of the robot’s center of gravity.
• Storage achieved by deformation of robot parts. Teams must be very careful when incorporating springs
or other items to store energy on their robot by means of part or material deformation. A robot may be
rejected at inspection if, in the judgment of the inspector, such items are unsafe.

It seems to me that your firing speed would be slow, If you have to crank it back every time. If you fire every .3 seconds, its not so bad. But if it is closer to 1.3, then you may have a speed problem. And if you gear it so the cam moves fast, then you might not have enough force to reload the spring.

our team proto typed a spring cannon and it takes a lot of force to pull the springs we used back. also the distance the ball went would only be good if you shot into the lower goal.

if it doesnt work get a bigger motor… or get more motors… or both… btw that is an aggressive cam in your illustration lol