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sgsdragons
01-22-2005, 06:53 PM
Our team is trying to set up the pneumatics so we can use multi-positioning. We are having trouble. Can anyone please help us with this? Thanks


SGS Dragons

activemx
01-22-2005, 07:43 PM
Pneumatic cylinders only have 2 positions. Either you can have them in or out. I know some teams have tested multipostioning, try a search.

Ralph Lambert
01-22-2005, 08:54 PM
There were a number of good posts on this subject last year. You hook up a solenoid to your actuator as though you were going to just go with two positions. You then plumb the exhausts of this solenoid together and feed that combined exhaust to another solenoid. When you want to stop the actuator at a mid position position you close the second solenoid and that pressurizes the exahust side and stops the actuator in mid stroke.

henryBsick
01-22-2005, 08:57 PM
There were a number of good posts on this subject last year.
100 of them (http://www.chiefdelphi.com/forums/showthread.php?t=23934&highlight=pneumatics+positions)

sgsdragons
01-22-2005, 10:08 PM
Ok, Thanks everyone for the help. We got it to work and it seems to work fairly well. We are going to need to do a little work w/programing however. Thanks.

SGS Dragons

Matt Fultz
01-22-2005, 11:51 PM
Chris Fultz and I sat down last year with a proposed idea on these Forums for multi-positioning, and made it work. There is a white paper here:

http://www.chiefdelphi.com/forums/papers.php?&categoryid=2&action=display&perpage=10&sort=date&direction=DESC&page=3
7th down on the page

If you have it figured out, this may not help much, but it really worked for us.

russell
01-23-2005, 03:05 AM
So has anyone mad much luck using the magnetic switch things to make the cylinder stop somewhere along the length? Like we are looking at using such a system for autonomous stuff, and I would like to have two pre programmed stop points along the cylinder so we would essentially have four different positions we could put it in.

Jeffrafa
01-23-2005, 05:36 AM
Chris Fultz and I sat down last year with a proposed idea on these Forums for multi-positioning, and made it work. There is a white paper here:

http://www.chiefdelphi.com/forums/papers.php?&categoryid=2&action=display&perpage=10&sort=date&direction=DESC&page=3
7th down on the page

If you have it figured out, this may not help much, but it really worked for us.
That powerpoint depicts it rather well, although the second solenoid blocking off the outputs can be eliminated, thus simplifying the system. You can do this by using dual solenoid (three positon) valves in which the center position is blocked, then you can cut off the exhaust air from coming out by not enabling either valve. We did this successfully last year for two of our cylinders, our boom to hang and a caster that picked up one end of our robot to help us turn.

So has anyone mad much luck using the magnetic switch things to make the cylinder stop somewhere along the length? Like we are looking at using such a system for autonomous stuff, and I would like to have two pre programmed stop points along the cylinder so we would essentially have four different positions we could put it in.
I have not tested using magnetic reed switches combined with multi-positioning, although it is possible - just expect a rather large margin of error. The reed switch would only sense it briefly before it passed by, so you would half to plan for this in programming. Also expect that it will be a little ways past (possibly even a couple inches) depending on your cylinder, pressure, and if you use flow controls.

If the cylinder wern't using flow controls and was moving too quickly then you might have issues with the reed switches never seeing the piston go by, but as long as you had it at a reasonable speed this shouldn't be a problem.

I wouldn't try and use reed switches combined with multi-positioning in order to operate something during autonomous because it wouldn't be all that accurate or dependable, instead I would say you would want to use actual three position cylinders.

Nitroxextreme
01-23-2005, 01:09 PM
couldn't you use a needle valve with a servo to control the flow rate and their for control the length but limiting air going to it

Mr. Ivey
01-27-2005, 02:46 PM
As I said last year, 2 double acting solenoids, one to control the actual piston throw, make that solenoid's exaust common, as in put fittings on the EA and EB ports, T them together, then put it through a pilot controled check valve. On solenoid 2, plug either port A or B, and then control the check valve with the solenoid. It works in the most brilliant way. I've done it, and it works great. Either that, instead of staging a piston like this, just find where you want to stop the piston in mid throw, and get 2 pistons that equal the total throw you want, with one the place where you wish to stop, the other is the whole stroke.
ivey

BillCloyes
01-31-2005, 03:00 PM
couldn't you use a needle valve with a servo to control the flow rate and their for control the length but limiting air going to it

Perhaps...but the flow control valves we have had in the past (and the ones this year look the same) have needed to go through like 5-10 rotations (screwed in/out) to go from full open to full close....

Granted you could hack the servo...or gear it up...but you would probably lose the high resolution that I'm guessing the was the draw to using a servo in the first place...

Hope this helps
-Bill