Pneumatics Issue

VEX Robotics Competition Discussion VRC
#1

Hi everyone,

My team is having problems with our pneumatics. We are currently using two pistons that clamp down to lift mobile goals. They have been working well for months, however, they randomly stopped working. They close correctly, but when we try to open them, they don’t have enough pressure to do so. As soon as we try to open them it feels like all of the air is lost. We checked thoroughly for a leak but found nothing. If anyone has any tips, it would be greatly appreciated!

#2

are they single or double acting cylinders? (also can you post some pics?)

#3

double acting cynlinders

#4

Are there any rubber bands on the claw?

#5

Yes so that it can close. We tried removing them and still had an issue

#6

Try using a soap water solution to check for leaks, a teaspoon of dish detergent and a cup of water.

There is always potential of the pneumatic cylinders becoming damaged: disconnect one end and ensure that the cylinder rod slides in and out easily.

2 Likes
#7

If you are able to disconnect the piston from the claw for testing, that will let you test just the actuator with no load.

A couple of other things to test:

  • Do they work both directions right after you pump up the tank? If so, you may be losing air (check for leaks as mentioned).
  • Are you using the regulator (On page 5 of the VEX Pneumatics instructions)? If so, the lock nut on the adjusting stem can loosen, allowing it to back out and lower the regulated pressure.
  • Do you have the flow control fitting on one end of the cylinder (On page 2 of the instructions, the fitting with the right angle and the funny screw in the end)? If so, screwing that in too far will make the piston not want to move in the actuator.
  • Are the screws in the bottom of the solenoid (through the metal plate) starting to loosen up? You should not feel ANY movement if you hold the top of the solenoid in one hand and the metal plate at the bottom in the other. If there is any, you need to carefully tighten the two tiny Phillips screws (use something like an eyeglass screwdriver).
  • Is one of the pneumatic hoses between the actuator and the solenoid kinked? Just like when you kink a garden hose, kinking a pneumatic hose blocks flow.
  • As @kmmohn pointed out, is the actuator damaged? This can happen if your mechanism places any sideways force on the piston, causing it to bend slightly. With nothing connected to the piston, you should be able to move it in and out smoothly without feeling it catch on anything.

Best of luck!

3 Likes
#8

Hi back! Along with the good advice above, I’d like to offer a general recommendation to post titles that concisely convey the observations you’re dealing with. Something like “Double-acting cylinders failing to retract after clamping, unexpected low pressure observed.” A good reason for being specific about your observations is that a forum user who has fixed a recognizable problem is more likely to engage. Time spent tailoring a request to your audience can speed things up in general. It takes practice like everything else :slight_smile:

#9

Are you using the 90 degree fittings by any chance? Those are actually flow control fittings that affect how fast the air can flow out of them. You can adjust them with the screw on top.