Pneumatics holding their position
 

After the match when the control system is disabled, will pneumatic cylinders hold thier position still? Sorry for the newbie question but my team is very experienced in everything but pneumatics.

Re: Pneumatics holding their position
 

They will hold their position assuming you still have pressure in your accumulators, at least thats what Ive always found the case to be when we've used them.

Cory

Re: Pneumatics holding their position
 

Whether or not the pneumatics will hold their position after a match depends on how the actuators are connected. If they are controlled by a double solonoid valve, they WILL hold their final position after the match ends. (provided there are no significant air leaks).

Cylinders controlled by single solenoid valves will return to the default "off" position when the match ends. (note that the default off position might mean extended or retracted, depending on how you connect the tubing).

Re: Pneumatics holding their position
 

The double solenoid valves will cause a pneumatic actuator to hold their position after a match has ended, but single solenoid valves might not. Single solenoid valves have a default position that they automatically (because of a spring, usually) revert to when power to the acutal solenoid is cut. If the actuator is in the non-default position at the end of the match, and power is cut, the valve will switch Pressure and Exhaust ports, and the actuator will change states.

Basically, the way to make an actuator hold its position after the match ends is to use a double solenoid valve.

Hope this helps. :)

<edit>Ack, a little late. I'll leave it up, anyway.</edit>

Re: Pneumatics holding their position
 

one caviot: they will only hold as described above if your system has no leaks

Ive seen bots with arms extended at the end that sloooooooowwllly drooped while the judges were scoring - if your pnuematics leak, the final resting position is what counts.

If you want something to stay put at the end, put a latching mechanism on it - something that will have to be manually released to retract.

Re: Pneumatics holding their position
 

Well it's always best to test you connections to make sure there are no leaks prior to putting it on your robot, it will be easier to find a a leak if its sprawled out over a table.

Re: Pneumatics holding their position
 

Definetly true kevin.

Building a pneumatics board to practice on makes it so much easier to put it in the robot.

Their are many ways to leave a actuator extended, retracted, or even somewhere in the middle after the power has been cut. The best way is to read the pneumatic manual on FIRST and play with the different parts. Remember the single solenoid switches back, the double stays on one side, and that air is a fluid.

Pneumatics are fun.

Oh yeah, to check for leaks get water with a little soap in it and check each part. Or just have really good ears in a quiet environment, sssssss, not best to look for in the pits or before competition.

Re: Pneumatics holding their position
 

Attached is how a Single Solenoid works, the Magnet symbol is for the ON and "Not ON" states. Top is ON, bottom is Not ON. The Orange color is exaust route, light blue is pressured route. To the direct right of the magnet symbol is the spring in it's compressed and extended states.

Note: all 5 positions in the diagram have plugs and wires. The bottom left and bottom right do not require a plug or wire if you do not intend on using the exhaust.

Re: Pneumatics holding their position
 

Yes, using a dubble solenoid valve will keep it's poition after the power has been cut at the end of the match. However, the pressure regulators relieve excess air pressure in the system. On page 4 of the penumatics manual, It describes this process as:

"Assume that you extend the cylinder of the apparatus the cylinder is attached to agaainst a wall. Then push against the wall with your robot. That would increase the preasure in the cylinder. The increased pressure will relieve out of the regulator and the cylinder will slowly retract."

Now, immagine your robot as a weight the the cylinder has either extended or retracted, which will cause a greater preassure than 60psi (if your robot weight under the cylinder is greatter than 45 pounds) on a 3/4" bore cylinder or if the robot is greater than 90 pounds under the cylinder on a 1.5" bore. In order for you to get around this problem, use a 2" bore with a robot weight under 120 pounds.

Re: Pneumatics holding their position
 

Take note that this applies when you exert force greater than the capacity of 60PSI over the given area.

For example:
Robot A using a 2" Bore cylinder retracts the cylinder to pull iteself into a HANGING position.
Robot B is using a Winch-Type mechanism and HANGs higher than Robot A.

When power is cut, Robot A will stay in position. For examples sake, let's say Robot B's winch slowly slips and it's frame begins to be supported by robot a:If Robot B's weight being rested on Robot A is more than ~40 lbs, Robot A will start to slowly sink down towards the ground, if it's only support is the Cylinder.

Re: Pneumatics holding their position
 

If you have a lot of time to test, a "5-Minute" or "10-Minute" test is a great leak checking measure. Charge the pneumatics assembly to 120psi, turn off the power, and check the guages 5 or 10 minutes later. If they still read 120, you have no leaks. If thee gauges are under 100, you have a slow leak, if the guages are under 60 psi, you have a problematic leak.

If it's your first time using pneumatics, or first time using the soap method, take about 2 oz of water and maybe a 1/2 oz. of liquid soap mixed well. Should be noticible to the touch that there is soap present, but just soap won't work well. Using a finger, dip it into the soap/water mixture, then dab around any place where a connection is made. Plugs to cylinders, plugs to tubes, plugs to T-Box's... anywhere that a leak could be. You will notice that the air pushing out of the leak will make little, but noticeable, bubbles. tighten the connection or recut the hose to fix the leak. (Note: messy cuts in hoses are usually the cause of the problem. If it doesn't cut the first time, go 1/4" higher on the tube and cut again. Tubing is rather lightweight. An extra 1-3 inches per plug is a good saftey measure incase tubes need to be cut down.

Re: Pneumatics holding their position
 

When you do your calculations, remember that the cylinder has different power capabilities in each direction. Pushing the rod out has more force because there is 60 psi acting over a larger surface area. On the retract, the surface area is reduced by the diameter of the rod, so you have 60 psi acting on a smaller surface area. Depending on the specific cylinder, the difference in cabability can be substantial.

Re: Pneumatics holding their position
 

There is leak locator you can buy which is basically liquid soap. Ours came with a giant Q-tip attached to the cap.

Re: Pneumatics holding their position
 

The soap and water thing works great, but set it up on a board to test it, and test it ALOT, ALOT, ALOT!!!!!!!!!!!!!!!

Re: Pneumatics holding their position
 

Pnuematics barring leaks and other snaffoos (sighs at two years ago's robot that leaks like a spaghetti strainer) should hold thier position as long as they have the particular valve (forget which one it is) two have a spring return and the 3rd uses air power to turn on and air power to return that would be the one you'd want to get if your objective is to stay after time is called.