Quote:
Originally Posted by Jon Stratis
A thought for this...
Disconnecting the motor from the wheels with the deadman switch will lead to the cart coasting to a stop, potentially over a long distance carrying a lot or momentum (150 lb robot + 50 or more lb cart...) - in other words, it can defeat the purpose and still run over a little kid. Instead of going that route, use some Jaguars to control the drive train. Set the Brake/Coast header to Brake, so when it stops, the motor actually helps the cart slow down faster. Hook all the limit switch inputs up to a limit switch sitting behind a slot. Slide a card into the slot will close the circuit, allowing the cart to move. If the card is pulled out, the circuit will open, and the Jaguars will immediately stop, with no programming needed on your part!
This can separate your two issues nicely, which might let you use an easier solution for pushing the cart around than if the solution had to solve both problems at once.
Oh, another idea I just had... a similar limit switch/slot concept, except the limit switch would activate some pneumatic cylinders, which would push some wooden skids straight down into the floor. Set it up so they can lift the cart wheels + robot completely off the floor. Now, the deadman switch serves two purposes - it stops the cart immediately, and while in your pit it can give you a more stable working surface that won't roll around!
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I very much agree with your first idea about disconnecting drive motors, very good observation.
I think your second idea could introduce a serious safety hazard. Pneumatic components that always return to one state when de-powered can actuate at un-intended times. If they are explicitly switched you might run into other issues. For example, the cart's battery could run low and the pistons could then actuate unexpectedly, causing the whole cart+robot to raise/lower without warning. If the skids default position were 'deployed' down, and there was an issue with the cart, it might come to stop in a hurry in a queue or pit lane, which would be most inconvenient.
The idea of using skids to stabilize the cart for working is good, but I would not rely on them as a safety mechanism, nor would I have them pneumatically actuated.