Mulit-postioning with pnuematics this year?

[KenWittlief]

Since we are allowed to use more than what we have been limited to in the past, there is something Ive been wanting to try for a while, maybe this year we can.

Ive always wanted a way to be able to use a pnuematic cylinder with more control than full out or full in.

If we use extra valves on the exhaust side (the ones we dont normally put fittings on) couldnt you pressurize one side and have the cylinder go all the way out, then pressurize the other side, and have the cylinder goto the CENTER position?

if you had a position sensor, and you used the flow restrictors, couldnt you control the amount of air in each side (using more than one valve) to position it anywhere between the two extreems?

Anyone ever play around with this or try it?

any thoughts? seems like it would be perfect for controlling the position of an arm, infinitely variable.

[Rob Colatutto]

You are correct. My high school team did this in 2001 and 2003 for our arms. The system lets you stop the piston where ever you want. We never had any sensors on it but you could easily do it with some on there. The way we had it set up was, run from the regulator into a double solenoid, then the air would flow dirrectly to the extension connector (front) on the piston, but then the retraction (back) air flow would be routed through a single solenoid to with its relief valves looped together. This allowed us to stop the pneumatic at any position with some fancy programming, but you would have to ask an old 263 programmer how to do that. One thing to watch out for is the lever arm's weight on that pneumatic. We had a slight drifting problem with the arm when we had 10 pounds on the end of it 4.5 feet from the pneumatic. With the right calculations this can be solved though.

[Rickertsen2]

Originally Posted by KenWittlief

Since we are allowed to use more than what we have been limited to in the past, there is something Ive been wanting to try for a while, maybe this year we can.

Ive always wanted a way to be able to use a pnuematic cylinder with more control than full out or full in.

If we use extra valves on the exhaust side (the ones we dont normally put fittings on) couldnt you pressurize one side and have the cylinder go all the way out, then pressurize the other side, and have the cylinder goto the CENTER position?

if you had a position sensor, and you used the flow restrictors, couldnt you control the amount of air in each side (using more than one valve) to position it anywhere between the two extreems?

Anyone ever play around with this or try it?

any thoughts? seems like it would be perfect for controlling the position of an arm, infinitely variable.

The setup isn't ideal, but you can prolyl bootleg it to work. The cylinders are fince for this, and it is done all the time but not with this type of valve. You will also need some position feedback(I don't think the reed switches will work. They are probably not fast enough.). If you try what you describe above, i would be interested to hear the results.

[maxgebhardt]

Originally Posted by Rickertsen2

The setup isn't ideal, but you can prolyl bootleg it to work. The cylinders are fince for this, and it is done all the time but not with this type of valve. You will also need some position feedback(I don't think the reed switches will work. They are probably not fast enough.). If you try what you describe above, i would be interested to hear the results.

well, even if the new postion switches won't work at high speed, you could try and tighten the valves to slow the speed of the extention as much as possible. my qustion is do you damage the solenoid?

[Andrew Dahl]

can we get a diagram of this



dahl

[KenWittlief]

I havent thought this through all the way, or tested anything , so Im reluctant to draw up a schematic. Someone might take it and base their design on it, only to learn much later that it wont work for some reason.

The basis idea I have is this. The pnuematic valves work buy releasing the full pressure in the line (60psi) to one end of the cylinder, and venting the other side open to the room - so its like one end of the cylinder is always disconnected.

The big valve they give us also has fittings for the vent outputs - so you could connect those to another set of valves

that would allow you to control the 'open' end - and instead of releasing all the air, contol how much is released

the second valves would not be connected to the pressureized line at all - they would be vent control valves

so when you pressurize one end of a cylinder, then switch it the other way, the first end will not loose all its air, unless you open the additional vent control valve - and depending on how long you leave it open, the air in that side will be allowed to vent out, a little, a lot, or all of it

and that should control how far the cylinder moves towards the other end, a little, a lot, or all the way.

[geo]

Does anybody has a picture or diagrams?

Last time I tried to control the position of a cylinder with a double solenoid and I attached other one in the relase end. It worked. But sometimes the cylinder retracted slowly even I close the relase end.

[Andrew Dahl]

working on it- i think i found the digrams that we used to create it on the 2001 bot



dahl

[Jedi Padawan]

Ok so if I'm getting this right you are wanting to use one cylinder in multiple positions?? is this possible even with the magnetic cylinders?? I was thinking of that but wasn't exactly sure if that was going to be possible without doing something that might "modify" it.

[Rob Colatutto]

Originally Posted by Jedi Padawan

Ok so if I'm getting this right you are wanting to use one cylinder in multiple positions?? is this possible even with the magnetic cylinders?? I was thinking of that but wasn't exactly sure if that was going to be possible without doing something that might "modify" it.

Its possible without any modifications at all.

Last time I tried to control the position of a cylinder with a double solenoid and I attached other one in the relase end. It worked. But sometimes the cylinder retracted slowly even I close the relase end.

We had the same problem at first last year untill we discovered a leak on our pneumatics system right after the storage tank. As long as there are no leaks and the system can hold over 60psi before the match starts you will not have a problem.

[ngreen]

yes, this is very possible. We used a pneumatic lift last year that could stop in multiple positions.

I drew a fast diagram in paint of how we did it last year.

Basically it involves routing all exhaust from the double solenoid through a single solenoid and putting a stop or loop on the NOT ON state of the solenoid. Make sure you stop the exhaust of the single solenoid too. Then you can program the single and double solenoids to work together. When you push one button on the joystick the single solenoid kicks on to allow the exhaust to escape to atmosphere, and when it is released the solenoid will switch to the pressured side and stop. We used two buttons, extending and retracting but made so they would trigger on side of the double solenoid and put the single solenoid into the ON state. With a little more programming you could probably be pretty exact as to when you stop.

I'll include the diagram. Any questions just ask.

I added a picture of last years robot in a halfway position. The cylinders are behind the yellow fiberglass poles.

[KenWittlief]

Thanks for the photo and diagram

and I have to say, nicely done! Your bot looks super - this would be an ideal way to actuate and arm moving up and down to grab something like

oh, I dont know, a 30" diameter ball?

[maxgebhardt]

if some of you have doubts, and the pneumatics system assembled, I used a basic demo to convince my superiors superiors that it works. if you have the plastic tube snap connectors on the exhaust, just take a plastic tubing T bracket and make a snap in, snap out stopper by leaving one end open and looping a tube in the other two. then plug it into the exhaust valve to stop the cylender mid stroke, then remove it to let it finish. it proves it can be done if anyone has any doubts, and your too lazy to rig up a solenoid.

I'm still wondering if someone can tell me if backfeeding like that causes issues with the solenoid...

[ngreen]

We used the system all last year and still use it when we do different presentations and we have never changed either solenoid so I am pretty confident that there is no problem with backfeeding. Make sure there is no leaks to the system and if will work really pretty good. Like I said, we used a buttons that the actuator length changed as long as you held the button. We used a 8" stroke and slowed the speed of the actuator by only opening the valve to them only a quarter turn. By using programming you could open for increments of time (which means a specific distance) by pressing a button once. If I remember right the actuators may have a little more give than when not using it but it was not a problem for us. A note about the single solenoid: When not powered it returns to a not on side. Any questions please ask, or set a pneumatic board up on a piece of plywood with switches from Radioshack to control you solenoid to test. Pneumatics are very easy to implement and add and their are many resources avaliable from FIRST. I'm very excited about getting to use the rotary and magnetic piston actuators this year. If they don't use the rotary actuator on our robot I might convince them to order them for me the play with. I personally think they would work great for arms for the 30" ball.

[pras870]

I've actually been looking for a way to do this for the past 2 years. I have a pretty firm grasp on pnuematics from the past 2 years, but I still fail to see how this could be done

I've also found, that amazingly, pneumatics actually weigh less then a motor driven assembly. Our team has always seemed to have a weight problem, and I'm always looking for a way to incorporate pneumatics instead of motor driven for the fact that they weigh less and are actually more reliable, but I've always been under the assumption, with the materials first gives us, you can only open and close a cylinder in 2 positions (full and closed).