pneumatic catapults

[jvdiv]

We built a pneumatic catapult for RI3D on 'Snow Problem. We used a pair of 0.75" bore 7" stroke cylinders with high cv valves (Norgren v60). The black tanks are at 60 psi. The catapult is gravity return, top of the cylinders are left open. The distance from the pivot point to the piston mounting point is 6.5". The length from the pivot to the center of the cradle is 20.5". I would be happy to answer any questions.
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[Cothron Theiss]

This is a bit of a tangent, but what do people typically use as the fulcrum in the catapult? Do you just drill holes and run a strong bolt through, or do you incorporate bearings and go with something a bit more engineered? In 2014, we had an excessively overpowered kicker (A poor design led to us putting a dangerous amount of power into that kick.) that ended up bending several rods we were using as fulcrums. The hardstop was actually between the fulcrum rod and where our surgical tubing was mounted, so when the kicker arm hit the hardstop, the kicker arm applied a pretty large amount of side loading on the intended fulcrum rod because the corner of the hardstop began acting as the fulcrum whenever it hit the hardstop.

So long story short, what methods do you all use to mount the catapult arm and/or use as a fulcrum?

[Peyton Yeung]

Originally Posted by Cothron Theiss

So long story short, what methods do you all use to mount the catapult arm and/or use as a fulcrum?

This year we used steel rod through bushings for both the cylinder end pivots as well as the arm pivot.

3/4" bore 5" stroke cylinders i believe.

[GeeTwo]

Originally Posted by Cothron Theiss

So long story short, what methods do you all use to mount the catapult arm and/or use as a fulcrum?

This year, we used ball bearings, more out of the simplicity of doing so with versaframe than any requirement. Most years, we have used steel bolt(s) with bronze bushings.

[adciv]

Originally Posted by Cothron Theiss

So long story short, what methods do you all use to mount the catapult arm and/or use as a fulcrum?

Piano Hinge. Works great for a lot of applications.

[BrendanB]

Originally Posted by Cothron Theiss

So long story short, what methods do you all use to mount the catapult arm and/or use as a fulcrum?

Ours was made an added this year during our third district event so we drilled a 1/4" hole, threw a long bolt through the lexan frame of the catapult, and used some round 1/2" OD 1/4" ID tubing from Vexpro as spacers. The frame was pretty rigid so we made the spacers have a slightly loose fit. Just enough to keep it steady but allowed it to pivot freely.

Had it been a made in our shop we might have used bushings or bearings as a pivot.