Quote:
Originally Posted by RyanShoff
I wish we could find a way to safely use 3-position solenoids with a closed center. They allow a cylinder to be stopped in the middle of travel.
|
What's unsafe with how we would use them now? It shouldn't cause any sudden changes when you disable. You will likely need flow control valves to slow down the cylinder a bit so you can accurately stop it.
You can have a similar effect with two "FRC typical" latching double solenoid valves. On the first valve, you connect output A to the cylinder, and plug B's exhaust port. You do the same thing for the second valve.
When the first solenoid is at "A", and the second is at "B", the first solenoid pressurizes one side of the cylinder and the second vents.
When that arrangement is switched, (1st on B, 2nd on A), the cylinder goes the other way.
When both are at "A", you get the somewhere in the middle position.
When both are at "B", you get no pressure. Both of these states can be desirable.
The rule as it is now says "one and only one compressor". Karthik is right, "one and only one" means only one.(
http://en.wikipedia.org/wiki/One_and_only_one). If you're not using the first compressor to ever put air in your robot, then you're in violation of the rule. There is a single unique compressor that is allowed to fill your robot.
There are a few things that I think are currently unsafe/have room for improvement with the pneumatics system.
1. Teams using valves that aren't double acting. When you go to emergency disable the robot, many things suddenly move. We had a few close calls with articulating wheels in 2012. You'd be walking around the robot when suddenly the laptop controlling it would go to sleep, and suddenly all the wheels would move up and the robot would fall to the ground.
Also, when a ref e-stops you, your single acting solenoids can change state, possibly launching a ball straight into a poor volunteer.
2. The pressure switch. We need a transducer that tells us the actual pressure and we need to be able to use that sensor to control the compressor. The large cycle range of the switch is not ideal for some teams. There are teams whose autonomous program just runs the compressor as soon as auto mode starts. Although the pressure never exceeds 120 psi, they can (and do) fail inspection.
There are teams out there who have their relief valve set below switch pressure. This way, the compressor is always running. A poor solution to a problem that doesn't need to exist.
Our auto mode left us with about 94 psi. It would be really nice to have the option to start the compressor to get us more pressure before our next shot.
This could also give us the ability to refill our tanks between matches without having to let out enough pressure to get the compressor to start.
3. Clarification on "reusing" air. Must we dump all air before we refill for our next match? We've been told yes and no. We've also had four back to back matches where there was not physically enough time to do a full refill.
4. Tiny stupid detail, but if R79 applies to ALL air, then you must use your robot's compressor to fill your pneumatic tires or balloons.