My kids want to make an actuator using pneumatics to deploy a small arm-like mechanism, but the pneumatics would need to hold the arm up for almost the entire match. I’ve never used Vex pneumatics before so I’m wondering if it is generally okay to keep the solenoid open that entire time, or would that draw too much electrical current for too long?
There is some chance they will want to lower the arm several times during the match, so they can’t really use a system that permanently locks the arm in place once the pneumatics fires.
Also keep in mind that the port that is permanently open is also the one that is open when the robot is disabled, so you will probably want to apply power to release it and keep the power on it to stay down/deployed. But there should be no issue keeping power on the solenoids for a long time, definitely not for 2 minutes.
Could you clarify this a little? Are you saying that when the robot is disabled and waiting for a match to begin that the solenoid would be pressurizing the piston?
For the kids, the ideal situation is that the piston remains unpressurized before the match. Then, when autonomous begins, the solenoid will fire, the piston will be pressurized, and thus the arm will get pushed up. During the match, the arm will remain up most of the time (the piston will remain pressurized), but there might be times when they want to de-pressurize the piston and let the arm drop down from its own weight. So would that scenario work okay with the single-acting piston? They are using RobotC.
Field control does not (and can not) disable anything connected to the digital or analog ports of the cortex. The ROBOTC competition template starts and stops the autonomous and operator control tasks, but any code you put into the pre-auton function can control the pneumatics if necessary. Be aware of the “bug” we have discussed in the past where sometimes pneumatics can fire when the cortex is first powered on.
I wrote a long post describing the issue, it’s not a “bug” in the sense that ROBOTC is doing anything wrong, just a byproduct of the way ROBOTC has to work (being a VM) and the way the solenoid driver was designed. Just turn the air on after the robot has initialized.
Is there a reason that this “bug” always seems to occur more on different solenoid cables. I had a cable that would extend and retract the piston rapidly 5-10 times while connecting but other cables wouldn’t have an issue.
The “faulty” cables didn’t seem to have any problem after the connection so it kinda baffled me.
There is a transistor in the solenoid driver cable that may turn on under just the right conditions. It’s all down to component tolerances, connector resistances, things like that. See the long explanation of this in posts #1 and #2 here. Cortex digital IO ports and the pneumatics driver
Last year, one of the guys on our team got his face plastered by our launcher while he was trying to fix something on the tray and we were trying to connect controllers to the robot. He was fine and that was definitely one of the most memorable and funniest moments from our club. Also, this past weekend, Jesse got his face grabbed by our claw when he was trying to make an adjustment to it after judging.
I guess these are the sort of reasons why were supposed to always wear safety glasses XD
