A Few Vex Pneumatics Questions

Our team recently bought a Pneumatics kit and we were wondering about a few things. We can’t find a whole lot of documentation except the tech sheets by looking up the part numbers. These still don’t provide us with much useful information.

Some things we’re starting to question:
The pressure regulator. We understand what it does (hint in the name), but does it just take trial and error to find the right adjustment? We obviously don’t want to blow anything up, but we have no idea where to stop turning the knob.

Pushing or pulling. We’ve seen so far that the cylinders (We have two double acting and one single acting) have a better pulling speed than the pushing speed. The force is fairly similar, but many applications we were thinking of would be more productive with a push. We did find a work around of just changing angles so it’s not a problem, but we were just curious. Is there a way to change this? We had a few guesses as to why this was happening, but we’re still not quite positive on anything with this kit.

Thanks in advance

Start with:
a) the regulator turned to minimum pressure (That’s usually counterclockwise, but check the regulator instructions or labelling.),
b) full system pressure on the regulator inlet, and
c) something that will allow a small flow (An untightened fitting comes to mind, but don’t leave it so loose that it will launch.) and a pressure gauge on the regulator outlet.

Turn the regulator slowly until the gauge on the regulator outlet maintains the desired pressure.

The output pressure of the regulator will vary slightly as a function of flow and inlet pressure, but probably not enough to matter to you (except, of course, if the inlet pressure isn’t above the desired outlet pressure).

If your problem is that you don’t have a pressure gauge, you can use a cylinder coupled to a force gauge. At equilibrium (after the transients have been settled and the piston is not moving (but not because it’s at the end of its stroke)) the force on the piston is equal to:
(pressure on high pressure side - pressure on low pressure side) * piston area] -(piston static friction).

Good Luck,
Eric

If you want to apply a specific amount of force to something (e.g. enough force to lift a basket), you can turn the pressure regulator valve all the way off and fill the pneumatic cylinder and pistons at 100psi (the max for the pneumatic system). Than open the solenoid and start turning the knob on the regulator until the pistons have enough pressure to achieve what you are trying to do (e.g. they lift a basket).

If you are trying to have the pneumatics do something more dynamic, like shoot a ball, it is more trial and error. You could do calculations based on the force of the pneumatic pistons at different pressures and the amount of force that you need to move the balls, but I have found that no matter how good your calculations are, the calculated pressure and the actual required pressure will vary a lot, because of friction and air resistance.

Keep in mind that do to the inefficiencies of the pressure regulator that you may lose more air with it than without it.

A lot of the robotics teams that I have seen don’t use the pressure regulator, because it adds one more thing to the robot that can go wrong. Unless you are trying to apply a small amount of pressure a lot of times, I would attempt what you are doing without a regulator and see if that works.

The single acting piston has a spring in it to pull it closed after it is fired, so the firing speed of the single acting piston would be slower than the double acting piston, because the single acting spring is working against the spring.

Also, if I remember correctly, the fitting on the top port of the double acting cylinder is a flow-regulating one? (Looks like a right angled one with a screw inside) Forget how it works, but you could swap it out with a standard straight through fitting, or remove it altogether, if you need more pushing power.

@Eric and Kendalls Thanks for all of the advice. We got the regulator working after running through the things you both said.

@k.gen04 We ended up doing this just before we rechecked the forums. We swapped the flow meter to the other port and got it doing exactly what we wanted. Thanks for the advice!