# Rookie Team Claw Question

We are thinking of using pneumatics to operate our claw. Will the cylinders from AndyMark provide enough clamping force to grip the cubes?

Is it better to have one fixed arm and one movable or to make them both movable?

One fixed doable as we used that method on our forklift in RR and was never a problem and very fast…takes some of the complexity out, that decision was in our second year and first foray into pneumatics. Not sure about AM cyls I suspect they would be ok.

From our prototyping, the cylinders that are from Andymark will provide enough force. We have used split pool noodles one the arm ( one movable and one stationary) for more grip and have not dropped a cube yet.

How much are you using? Then, how long does it take to recharge your system to grab again? those are seconds you lose in the match…

Sounds like you need to do some math. The clamping force you get will depend on the working pressure of the cylinder (typically 60 psi), the cross-sectional area of the cylinder, and also how you attach it (torque and mechanical advantage will depend on both the angle it’s acting at and where the force is applied relative to the pivot point).

If you don’t have any mechanical engineering mentors, your local physics teacher should be able to help you come up with math to at least closely approximate the forces and distances you can generate with different configurations of the same cylinder on a claw.

You might also want to consider a roller claw–they’re surprisingly easy to build (though take some prototyping to get right), run off of one or two motors, and their biggest advantage is that they don’t require timing on the driver’s part–you just drive up and make contact and the cube gets sucked in. (A limit switch or other sensor to tell you when you’ve acquired a tube and thus to turn off your intake motor(s) is a good idea.)

Your questions can be answered through calculations explained in this PPT Karthik sent me the other night…

http://first.wpi.edu/Images/CMS/First/2007CON_Pneumatic_Power_Olivera.pdf

This depends on your specific use case and what cylinder you’re looking at. You may want to reference this tool while you’re shopping, it’s handy for figuring out roughly how much force you can expect from a given cylinder.

Personally I’ve always preferred to have both arms moveable as it provides more flexibility (and I’m a bit OCD so it would bother me if it wasn’t symmetrical), however, it’s certainly much simpler to make an arm that only moves on one side, so it really comes down to what your team is capable of.

Check out this prototype video, it addresses both pneumatic claw and roller. We’re going to prototype a hybrid to see if that has any advantage.

When designing the claw should we make the claw close (retract) to the size of the cube (or slightly smaller, say .5") or should we make the claw retract smaller than the cube by a few inches?

Definitely make it retract smaller than the cube, but I’d also recommend some sort of rubber or tread on it that compress a bit on the gripper itself.

How much smaller do you recommend?

You’d have to prototype and see what works best for your design.