Can you stop a pneumatic pump at half shaft
 

Pneumatics are strong so our team wants to use them in a certain mechanism. I need to know if there is anyway to stop the shaft halfway or not (for a secret reason). Anyway, I've tried putting two valves on each side but that doesn't work at all. So I am asking people smarter than myself (anyone), can you stop a pneumatic at half shaft without just cutting the shaft (cuz that would be cheap)

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http://www.chiefdelphi.com/forums/sh...threadid=16464

Wow. 10 topics down in this forum.

(Oh, and by the way - if you were to cut a piston rod, you'd have a paperweight in cylinder's clothing. Think about it.)

No there is no way to do that, you should order pistons that have the length that you require.

thanx for the thread. although the method they use is a little far-fetched and probably not worth it for our teams needs.

use a limit switch to sense when the cylinder is half extended and then close the valve.

the method for hooking up the solenoids is actually quite easy, i can make you a graphic showing the hook up if you want.

~Pyro

There is one way to control the pressure released electronically but it is a bit costly. I don't know the part number for the device but I'll find out for you. We were looking into it a few weeks ago but never went to far since we don't have much money and didn't really require it. I forget what it is called.. I'll post the info tomorrow if I can find it.

What about oscillating between on and off positions every 27 milliseconds when at the desired length? Done through programming, of course.

That's possible (sort of like PWM) but it would be putting a lot of strain on the relays to switch that fast as well as the solenoids. I wouldn't recommend it. They weren't built to handle switching like that.

I'm having trouble finding the record of that electronically controlled valve, sorry...

It's also probably illegal based on the strictness of FIRST's no-pneumatics-that-didn't-come-in-the-kit rule. Correct me if I'm wrong, but I don't believe we are allowed to buy anything (except suction cups) that deal with the pneumatics.

Actually, I think you're right. I forgot about that rule...:D

I doubt you could do it by pulsing the circuit, you'd be able to control the amount of air in the cylinder. If the load were to increase or decrease then the cylinder would expand or contract. If you really need to stop a cylinder mid length you could put a servo-lock on it. Similar to what some teams use to release spring loaded mechinisms.

I can tell you're a rookie team because they don't realize how long of a delay there can be with limit switches. By the time the brain signals the valve to cut off the air, the cylinder is most likely already fully extended. You could use a flow control to slow down the air. However, you would have considerably less force because the cylinder wouldn't be fully pressurized. Your best bet is a servo limit or an additional cylinder.

Try this solution...
 

Couple a piece of threaded rod parallel with the rod of the cylinder attached to the same component as the rod end, but free on the other (cylinder) end. You can then make a stroke limiter that can either stop the cylinder at a fixed ( albeit adjustable by using a nut and a jam nut on the threaded rod ) stroke, or by using a gate mechanism actuated by one of the small servos you could turn the stroke limiter (gate) on to stop it at one distance or off to allow full stroke operation of the cylinder. Adding more "gates " would give you the possibility of having a few stroke lengths. Hope this helps you out , or at least opens another door for you.

Good luck

Short answer is yes.

Depending on what you're using it for, this is possible, but it requires the use of the single solenoid valve upstream of the double solenoid valve. The Input into the single solenoid must be set on one of it's outputs (the other output MUST be plugged), and the output to the double solenoid comes out of the first valve's input. Next you must plug the release output of the single solenoid so that your piston stays in one spot. With all this rigged up, you can use the single solenoid to stop the flow of air to the double solenoid at any time, and with the press of a button, you can stop your piston wherever you want, no matter what direction it is doing.

This is only useful if you have a single solenoid valve sitting around gathering dust and you also have a Spike relay to use. Also, I don't believe the piston stays where it is once power is taken away.

E-mail me if you want some clearer directions, and once I get ours working totally, I'll know a little better (our problems are to do with the wiring of it, not the actual air flow).