How many rules does this catapult design break? :)

[DavisDad]

Prototype @ 35' : http://simhardware.org//img/FirstTry.avi

Slow Motion Study:http://simhardware.org//img/Compound...-2_slow-mo.MP4

[wilsonmw04]

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

[Al Skierkiewicz]

Dad,
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.

[Daniel_LaFleur]

Originally Posted by DavisDad

Prototype @ 35' : http://simhardware.org//img/FirstTry.avi

Slow Motion Study: http://simhardware.org//img/Compound...-2_slow-mo.avi

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?

[DavisDad]

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.

[Al Skierkiewicz]

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

[Al Skierkiewicz]

Dad,
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?

[DavisDad]

Originally Posted by Al Skierkiewicz

Dad,
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...

[372 lives on]

how about
[R14]
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...

[teh_lol]

Originally Posted by 372 lives on

how about
[R14]
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.

[DavisDad]

Originally Posted by 372 lives on

how about
[R14]
No individual item shall have a value that exceeds $400.00...
...last time I checked the bow this came from cost around $900...

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.

[DavisDad]

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…

http://simhardware.org//img/Compound...atics30fps.MP4
http://simhardware.org//img/Compound...tics240fps.MP4

[kclark]

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

[DavisDad]

Originally Posted by kclark

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

http://www.bimba.com

You can buy direct from the "Buy Online" page.

Have fun!

[kclark]

do you know the part number you used?