Re: Mulit-postioning with pnuematics this year?
 

When balancing the forces, don't forget to factor in any load on the piston.

Re: Mulit-postioning with pnuematics this year?
 

Ok some good objections have been raised here- if anyone hasnt been following the problem, let me state it simply

if you put 60 PSI in one end of a cylinder (say to raise an arm) and then switch its valave the other way, and use an additional valve to close its exhaust vent

then the air in that cylinder has no way to get out. If someone grabs that arm and pulls it down, the air in the bottom side will be compressed past 60 psi - maybe WAY past 60 PSI

OK - this IS a serious problem, but I think I have the solution. The regulator that is use to set the pressure to 60 PSI is designed such that IT will vent air if pressure exceeds the setting on the output side

if you have setup the pnuematics as they are normally used, and someone pulled down on the raised arm, the air that is compressed in the cylinder above 60 PSI would vent out the regulator (backwards)

so the solution for the mulitposiitoning system would be to have an additional (extra) regulator between the vent connections and the blocking valve, with the output of the regulator towards the cylinder. This will release any pressure above 60 psi in that side of the system, even when the blocking valve is closed.

If you take this approach I think you will want to have your pnuematic design WELL documented so you can explain to the judges exactly what you have, and why its safe.

Ive taken the liberty of editing Ngreens diagram to show where the extra regulator would be added - note the arrow -the regulator is connected backwards, and the input side is not used.

also note the regulator will not show pressure all the time, so you will have to adjust it to 60 PSI when the vent side is charged.

Re: Mulit-postioning with pnuematics this year?
 

A good thought, but I believe you will get into a cycle where you will keep increasing the pressure, then relieving it, then increasing, then relieving - eventually the cylinder will be all the way extended.

This may be a problem best solved and understood with a layout board and a few pressure gages.

Re: Mulit-postioning with pnuematics this year?
 

Im not sure what you mean in your last post?

I see this being used to raise and hold an arm up-so there will be a steady load on the cylinder

and the operator will hold the valve open long enough to raise of lower it where they want it.

why would it end up eventaully extended all the way? do you mean by itself?

Re: Mulit-postioning with pnuematics this year?
 

I can see the loop thing happening so that it would be extended all the way, and I think that the way to handle this is to just reduce the overall pressure to that portion of the working system. You would have to use another regulator for Ken's idea, so why not keep the rest of the bot at 60 psi and have this part at say 50 (to be overly conservative). I'm interested in this idea and I'd like to know if anyone has any coding tips on it. As for whether or not the parts can handle more than 60 psi, I believe the tanks are rated at 120 and the pistons at 60 (correct me if wrong), so I would not suggest consistently and purposely running them higher.

Re: Mulit-postioning with pnuematics this year?
 

I think maybe you want it the other way, if I understand the concern.

if the vent regulator is set at 60 psi, and the main regulator is set at 60psi, then when you goto switch the direction of the cyliner, the vent regulator will spill all its air, because its being pushed backwards with 60psi from the main supply

if this is the perceived problem then you would want the vent set at 60, and the main regulator at a little less - so that it cant force the vent side to release its air. To make this system work you have to be in control of when the vent side lets air out, through the second single valve - you dont want the extra regulator venting air unless the system has been externally stressed.

I cant wait to try this!

Re: Mulit-postioning with pnuematics this year?
 

I understand the idea of putting a regulator on the ehaust to prevent the pressure from jumping, however, wouldn't that mean that if the cylender was extending, then multi positioning would fail, because when the pressure would normaly jump above 60 psi, than it CANT, so the cylender would slowly extend rather than hold still. this could cause the arm to slowly extend and slowly drop the bot to the floor if it had tried to pull up to the bar...

Re: Mulit-postioning with pnuematics this year?
 

there would be no reason to use this approach to pull up to the bar - to do that the cylinder can extend all the way at once - no need for mulipositioning

this proposed idea is more for an arm to get the 2X ball - you could infinately adjust the position of the arm, by slowing leaking the 'vent' valve - and once you close it, it should stay where you left it.

Re: Mulit-postioning with pnuematics this year?
 

well I was hoping to use it on the ball and/or the bar, since my team captain is a bit hesitant to raise the robot more than 6" to 1' in case the bot drops.

Re: Mulit-postioning with pnuematics this year?
 

you only need to raise it enough to be 'off' the floor - no extra points for airspace :c)

Re: Mulit-postioning with pnuematics this year?
 

We set up this multi positioning system the way it was prescribed in that funny little drawing. It was a success. After putting a few flow controls in different places to adjust the speed and everything, it was great! It's not very hard to program it. If you set it up and look at it, you'll see that it's somewhat simple. We had an extra guage on the portion of the system that was being "looped." It does indeed sometimes go a little over 60. However, it was only a couple of PSI and you can give up a few from your main regulator to take care of that and you won't lose that much force.

A suggestion to improve the design... If you put an air tank in series with the exhausts that lead into the single solenoid, it will dampen the effect of opening it and allow you to better control the movement. You would have to precharge it in order for that to work, but I just wanted to throw that in there in case anyone was having trouble getting it to work well. The flow controls are the best way to go.

Anybody plan on using this?

Re: Mulit-postioning with pnuematics this year?
 

Our team built a system just like the one in Ken Wittlief's diagram.
Instead of stopping, when the single solenoid is closed, the piston slows down considerably, but does not stop.
- We have done all that is in our ability to stop leaks.
- is it possible, then, that we are loosing pressure through the main pressure gauge? That is, the one limiting the entering air to 60 PSI?
Thanks!
Dina.

Re: Mulit-postioning with pnuematics this year?
 

try increasing the setting on the secondary regulator, the one that expells excess pressure on the vent side. If you have it set to 60, and your main regulator set to 60, then I can see the second one venting on you when you switch directions

you might need to have the secondary one set to 60, and the main one set to 50 or 55

or maybe the other way around? try it and see what happens.

Re: Mulit-postioning with pnuematics this year?
 

Chris is correct here and I hope everyone read his post. It is my opinion that any team which is using this (really cool) way of multi-positioning cylinders should have the "actuation" pressure limited to 54 PSI. This ensures that the system is not DESIGNED to operate with pressures within a cylinder greater than 60 PSI.

Yes, sometimes cylinders may get "overpressurized" by some external force (another robot, wall etc.) but your pneumatics system should not be designed to take advantage of this. (In the same way you would not use a motor to compress air in a large cylinder and use it to pneumatically power a smaller cylinder at higher pressures than 60 PSI.)

Note that if you have 66 PSI in a line in your system at some point, you could USE that higher pressure by connecting another valve and another cylinder... I think we would all agree this is not legal.

So I think that we need to take precaution and design systems which never have actuation pressures (within a cylinder) greater than 60 PSI. And has already been pointed out, be sure that you include the LOAD on the cylinder as well.

-Mr. Van
Coach, 599

Re: Mulit-postioning with pnuematics this year?
 

We would all agree that using the 66PSI wouldn't be legal, but I don't think you will get a consesus that just having it there as a side-effect of use is illegal.