Solution: Variable position of cylinder in compliance with <R74>

[Roboman01]

Okay, I see what you're saying. Still, a valve that applies pressure to both ports in the middle position should only allow for three positions, unless you use an electronic regulator on one side. If you use an electronic regulator, you might as well just use the system described in the initial post - it will save weight and reduce complexity.

[PAR_WIG1350]

Originally Posted by Roboman01

Okay, I see what you're saying. Still, a valve that applies pressure to both ports in the middle position should only allow for three positions, unless you use an electronic regulator on one side. If you use an electronic regulator, you might as well just use the system described in the initial post - it will save weight and reduce complexity.

There are three states, not three positions: extending, retracting, and stopped. [there are 5 states if you include full extension and complete retraction]

[Roboman01]

Originally Posted by PAR_WIG1350

There are three states, not three positions: extending, retracting, and stopped. [there are 5 states if you include full extension and complete retraction]

If it's a 3-position valve that is center pressure, then you can only have three possible positions of the cylinder, without adjusting the regulator. If you use a center-closed valve, like I show in the schematic I posted, theoretically, you can have an infinite number of cylinder positions.

[wilsonmw04]

Originally Posted by Roboman01

If it's a 3-position valve that is center pressure, then you can only have three possible positions of the cylinder, without adjusting the regulator. If you use a center-closed valve, like I show in the schematic I posted, theoretically, you can have an infinite number of cylinder positions.

what's the difference between half and and say 3/4?

[Al Skierkiewicz]

Originally Posted by Roboman01

True, but negative pressure is a vacuum, and vacuums are not subject to the rules.

I think you are missing the true meaning of this...

G. For the purposes of the FRC, a device that creates a vacuum is not considered to be a pneumatic device and are not subject to the pneumatic rules (although they must still satisfy all other appropriate rules). These include, but are not limited to, venturi-type vacuum generators and off-the-shelf vacuum devices (as long as they are powered by provided or permitted motors).

The storage is what is under discussion and storage is most definitely under the rules.

[Roboman01]

Originally Posted by wilsonmw04

what's the difference between half and and say 3/4?

That's irrelevant, for the purposes of this discussion. All I'm saying is that with a 5/4 3-position valve with center pressure, you can only move the cylinder to a total of three positions - out, in, and a predetermined spot in between the two extremes.

I think you are missing the true meaning of this...

G. For the purposes of the FRC, a device that creates a vacuum is not considered to be a pneumatic device and are not subject to the pneumatic rules (although they must still satisfy all other appropriate rules). These include, but are not limited to, venturi-type vacuum generators and off-the-shelf vacuum devices (as long as they are powered by provided or permitted motors).

The storage is what is under discussion and storage is most definitely under the rules.

Even though my team probably won't decide to use this system, I'll bring it along with me to St. Louis, to have it looked over by an inspector.

[cjwmam]

That's irrelevant, for the purposes of this discussion. All I'm saying is that with a 5/4 3-position valve with center pressure, you can only move the cylinder to a total of three positions - out, in, and a predetermined spot in between the two extremes


I am not sure why you say this will not work. but all I seen on our robot was I could stop and start cylinder any where in the 30" stroke. only used standard regulater on none shaft side of cylinder.

[Roboman01]

Originally Posted by cjwmam

That's irrelevant, for the purposes of this discussion. All I'm saying is that with a 5/4 3-position valve with center pressure, you can only move the cylinder to a total of three positions - out, in, and a predetermined spot in between the two extremes


I am not sure why you say this will not work. but all I seen on our robot was I could stop and start cylinder any where in the 30" stroke. only used standard regulater on none shaft side of cylinder.

Are you sure it's a center pressure valve? Also, when you were moving the cylinder, did you need to adjust the regulator to change the position of the rod, when it was not at either extreme?

[PAR_WIG1350]

Originally Posted by Roboman01

Are you sure it's a center pressure valve? Also, when you were moving the cylinder, did you need to adjust the regulator to change the position of the rod, when it was not at either extreme?

The requirement to hold the piston in place doesn't change as the piston moves along the cylinder, stopping it half way is the same as stopping it one third of the way out. The sum of the forces must be 0 to maintain constant motion or to stay at rest. If the regulator is set at a constant setting that balances the forces resulting from the pressure pushing against the 2 surfaces of the piston, which have different areas, then friction will quickly bring the cylinder to a stop and keep it there. The accuracy of such a system decreases with momentum.

You seem to be confusing volume or surface area of the inside of the cylinder with force exerted on the piston. The force exerted on the piston is what matters, the other two are irrelevant.

[Roboman01]

Originally Posted by PAR_WIG1350

The requirement to hold the piston in place doesn't change as the piston moves along the cylinder, stopping it half way is the same as stopping it one third of the way out. The sum of the forces must be 0 to maintain constant motion or to stay at rest. If the regulator is set at a constant setting that balances the forces resulting from the pressure pushing against the 2 surfaces of the piston, which have different areas, then friction will quickly bring the cylinder to a stop and keep it there. The accuracy of such a system decreases with momentum.

You seem to be confusing volume or surface area of the inside of the cylinder with force exerted on the piston. The force exerted on the piston is what matters, the other two are irrelevant.

According to the schematic symbol, it would appear that the two cylinder ports are tied together, and pressure is applied. Wouldn't this cause the cylinder to creep back to a position around the midpoint? In any case, it would appear that using a center-pressure valve for this application is not generally accepted in industry, according to the Norgren Valve Guide. From page 225, section 3: "3. 3-POSITION - Inlet Open to Cylinder Ports
a) Equal pressure supplied to both sides of the piston creates an
unequal force, due to rod area differential, which causes the
cylinders to extend. Many times a regulator will be installed in
the blind end cylinder line to drop the blind end pressure and
equalize the force (we all know this would be an improper
application of a regulator). The application of full-line pressure
to this regulator during normal cylinder cycling leads to
premature regulator failures.
b) Cannot be used to support vertical loads."

It would appear that is causes unnecessary and undesirable strain on the components.

[cjwmam]

Are you sure it's a center pressure valve? Also, when you were moving the cylinder, did you need to adjust the regulator to change the position of the rod, when it was not at either extreme?

Yes it is center pressure valve, I started with closed center but could not dump all air from system so went to presure center. once set you do not need to adjust regulator. you can stop & start at any point. up or down the stroke with only powering silonoid on one side or the other

[Roboman01]

Originally Posted by cjwmam

Yes it is center pressure valve, I started with closed center but could not dump all air from system so went to presure center. once set you do not need to adjust regulator. you can stop & start at any point. up or down the stroke with only powering silonoid on one side or the other

I see. Still, that is an improper application of a center-pressure valve, as my previous post stated. You could easily blow out your regulator with that setup. According the the Norgren Pneumatics Manual, the only way to properly jog a cylinder is to use a closed-center valve.

[PAR_WIG1350]

Originally Posted by Roboman01

The application of full-line pressure
to this regulator during normal cylinder cycling leads to
premature regulator failures.

In FIRST, the lifespan of the components is not generally an issue, as long as it gets through the season (sometimes, even shorter lifespans , such as a single event or match) are also tolerated in FIRST.

It is not proper to:

• Use AC light or limit switches to switch DC current.
• Use the 90c to fill a tank with a volume exceeding one gallon.
• Do A LOT of other stuff that we do in FIRST.

[Roboman01]

Originally Posted by PAR_WIG1350

In FIRST, the lifespan of the components is not generally an issue, as long as it gets through the season (sometimes, even shorter lifespans , such as a single event or match) are also tolerated in FIRST.

It is not proper to:

• Use AC light or limit switches to switch DC current.
• Use the 90c to fill a tank with a volume exceeding one gallon.
• Do A LOT of other stuff that we do in FIRST.

Still, according to the manual, the proper way to jog a cylinder is to use a center-closed valve. Since there is a way to do this legally, as far as I can tell, there really is no reason why you shouldn't do it the proper way.

[wilsonmw04]

Originally Posted by Roboman01

Still, according to the manual, the proper way to jog a cylinder is to use a center-closed valve. Since there is a way to do this legally, as far as I can tell, there really is no reason why you shouldn't do it the proper way.

Center locking valves are not allowed this year, that's the whole purpose of this crazy thread.