Possible to Adjust Speed

[ligerbots]

Hey,
I was wondering if anybody knew of a relatively simple method of adjusting the speed or volume of air flow into the piston? Basically allowing the piston to shoot out real fast or to slowly shoot out.
Thanks for your help!

[Mark McLeod]

There are flow control fittings used for this purpose.
http://www.alliedelec.com/Images/Pro...s/499-1574.pdf

[willson.thomas]

Any methods for changing the speed during a match?

[Tom I]

From my unprofessional experience with pneumatics, there's no way of adjusting air flow during a match. you can adjust it manually that mark was talking about, but thats a little hard to do when your robot's on the field!

Think of a piston as a light switch... not a dimmer switch! A light switch, on/off

[Ted Weisse]

You can do this by using multiple Directional Controls (DC) and multiple Flow Controls (FC). To obtain three different speeds you could use two DCs and three FCs. Remember to only flow control the out flow of the cylinder and not the in flow. Connect the cylinder port to the "P" of DC1 (DC1-P) and FC1 to DC1-A. Connect DC1-B to DC2-P, then FC2 to DC2-A and FC3 to DC2-B. With this arrangement whenever DC1 is de-energized FC1's setting will be used and therefore that speed. With DC1 energized and DC2 de-energized you will get the speed based on FC2's flow setting and thus with both DC1 and DC2 energized you will obtain FC3's setting.

This is fairly easy to program since the DCs are basic binary on and off devices.

If you need more speed settings just add more DCs and FCs in the same "logic". You will have one less DC than FC's. If you wanted say 6 different speeds you could do it with 5 DCs and 6 FCs.

ted yz

[DavidGitz]

There are a few threads on this already, but we are thinking about using a servo attached to one (both?) of the flow control valves on a piston. Not ideal I know, but it won't require many parts.

[Al Skierkiewicz]

Originally Posted by DavidGitz

There are a few threads on this already, but we are thinking about using a servo attached to one (both?) of the flow control valves on a piston. Not ideal I know, but it won't require many parts.

David,
A servo won't give your the range you would need. The flow control valves are needle valves that may require a few turns to get to the desired flow rate.

[Teched3]

Looking at your problem from a different perspective, you might want to try two air feeds to the same cylinder port, since piston speed will be dependent on amount of air flow. Opening a second feed to the cylinder can increase your piston speed, as it may fill the cylinder more quickly. Limits are imposed by inlet/outlet port size and available pressure, and you should test the concepts by prototyping. Then you can manually adjust each feed to fine tune your speed.

[DavidGitz]

Originally Posted by Al Skierkiewicz

David,
A servo won't give your the range you would need. The flow control valves are needle valves that may require a few turns to get to the desired flow rate.

Al - This is true, but we only need a relatively small deviation in pressure. Thanks though!

[Racer26]

Originally Posted by DavidGitz

Al - This is true, but we only need a relatively small deviation in pressure. Thanks though!

Also, you COULD gear the servo up to get more spins out of it. Dunno if the servo would have the oomph to do it is all.

There are better ways to do it using multiple valves. 1075 has in 2004, and 2007 built multi-position pneumatic arms, which could be stopped in mid-travel. by pulsing a feed line, you can cause it to slow down

[Culvan Van Li]

You could put a motor and encoder on the pressure valve then control the position of the motor. It's almost trivial with the Jaguar using CAN. The biggest difficulty would be ensuring your start point is where you want it. You could run it to a stop of some sort to make sure you have the position correct.

Another option is to control the duration signal letting the air in. If it takes 250ms for a full stroke, then having an "on" signal that is shorter than that will reduce the power it has when it reaches the endpoint. This is probably the simplest method and requires the least parts, but it requires more fine-tuning to make it work as desired. It might be possible to even pulse width modultate the air intakes to achieve an overall slower speed. Perhaps you would have it forward for 20 ms and backwards for 10 ms and repeat that pattern until it reaches the desired position. This will use more air since you are using the air to oppose the movement of the pneumatic cylinder.

Andy

[trilogy2826]

Try searching for "proportional pneumatic valve" on google. There are many different flavors. A common unit I have used for prototyping air actuated brakes on very large robots is a proportional flow control valve such as:
http://www.ascovalve.com/Common/PDFF...PosiflowR2.pdf

We have prototyped this in our system with general KOP pneumatics and it works well to control velocity of the cylinder.

One lesson learned: Make sure you double check the signal voltage before ordering parts.

[Taxi Quinn]

Can Anybody please private message me and tell me how to post my own thread?

[aziobro]

Is it legal to use more than one valve? This would allow twice the flow rate into the cylinder.
Would you have to make sure that the Cv was smaller?

[Al Skierkiewicz]

aziobro,
The limiting factor is still the volume you can pass through the actuator port.