How do you control the length a piston will extention/retraction?

[Racer26]

Yes, many threads already, but I'll answer it again.

The short answer is No, you can't stop a piston in mid-travel.

The only *easy* way to do it is to mechanically block the piston from traveling any further than you want it to.

The long answer is Yes, but its a bit complicated.

In the past (Read: 2004 Off-Season, and 2007 Regular/Off-Season) 1075 has built arms that stop in mid-travel with pneumatics.

In 2004 we used 2 valves. One to switch the direction of travel, and then a second to switch the exhaust of the first. By not letting the exhaust out of the system, the piston doesn't move.

That system was plagued with large amounts of drift, but it served its purpose.

In 2007 where accuracy was paramount, we used a 3rd valve, as well as a mechanical brake. This allowed us to switch the feed side as well for added control. This reduced the drifting problem. Additionally, we used potentiometers, and some fancy code to make it all work nicely together.

Searching CD should yield several drawings of how to plumb such a system.