How many rules does this catapult design break? :)

Prototype @ 35’ :

Slow Motion Study:

Hard to answer the question without seeing how it’s mounted on the robot, but as a device, it looks effective and legal.

Is that part of a compound bow with camo that I see? If so, I would want to know how you modified it for this mechanism. I can’t tell much from the picture but my first response is usually one of safety and the possibility of this mechanism self destructing in firing. Is the material a laminate and is it capable of a dry fire without damage? I might have a UL safety person check this out during inspection if I was your inspector.

The only issue I see with this design is safety during transport onto the field with the robot powered. You’d need either no energy stored in the catapult arm or a safety lockout (pin?).

Other than that, its a wonderful out-of-the-box type launcher.

Are y’all going to be at GSR?

Roger that on the safety. I’ve copied the Mathews mount (“limb pocket”), prestress and string angles as closely as possible. The cylinder (this one is temporary, final will be 1-1/2 bore, 6" stroke) adds a load to string to string during a dry-fire. I think the most likely failure mode would be pieces flying of the pivot arm.

Thank you all for the feedback. This may be a secondary launcher to our already developed spinning wheel shooter. If weight allows.

Glad to hear you are thinking about that usage in the design.

I did a search and it appears that the parts you are using required no machining on your part, is that correct? More or less just a bolt on?

Hi Al,

Thanks so much for the thoughtful response. As a newbie mentor, your help is greatly appreciated.

The only parts that I made, that touch the composite bow limbs, are the “limb pockets” parts:

  1. Delrin guide/spacer for adjustible tension
  2. Ball socket (1/2 sphere washer) for bolt pivot point

If the shooter works well I may order OEM parts to eliminate doubt about the limb restraints.

I have been scrambling to get developed enough to test accuracy. If the performance pans out, I intend to make shop drawings and write up my analysis for review. Sorry I don’t have this ready now…

how about
No individual item shall have a value that exceeds $400.00. The total cost of Components purchased in bulk may exceed $400.00 USD as long as the cost of an individual Component does not exceed $400.00.

last time I checked the bow this came from cost around $900…

You can buy just the limbs for a bow depending on the company that makes it and the piece that is taken.

I paid $40 at Reedy’s Archery shop (Middleboro, MA) for a used set. The guy gave me a discount when I told him about our robot competition. He said he could get $80 used. I assume they cost about 2x that. I couldn’t find a price on-line for the limbs new.

My son and I tested the latest version of the “compound catapult” yesterday; properly sized cylinder and trigger release (couldn’t exhaust air fast enough}. We hit 6/6 @ 27.5’ (video below) until part failure. We were setting range by adjusting pressure until bow limb deflection was the same as measured by a caliper. We were cocking to about 75% of max force. We are working on the load beam/pressure transducer feedback cocking mechanism…

I’m planning on making a smaller one of these for a project for college, where did you get the air cylinder from?

You can buy direct from the “Buy Online” page.

Have fun!

do you know the part number you used?

do you know the part number you used?