using a current sensor to "brake" a motor

[Max Lobovsky]

We are looking at different ways to hold our winch in place (ie not backdriving). In the spirit of minimizing moving parts, i thought up a scheme where a current sensor is placed in series with the motor after a victor. During testing, the current neccesary to just hold the winch in place will be measured. Then, the computer will be programmed to hold that current when the winch has no commands to move. Because the system has a good amount of friction, i think we can get enough accuracy with this system. If anyone has tried this, id like to know. And yes, i realize that the power is cut at the end of the competition......

[Joe Johnson]

The only thing you will have to stop your robot is dynamic braking and friction at the end of the match (after your robot is disabled).

I would not count on dynamic braking. If you need it to keep from falling, I suppose you will be unhappy as some time in the season.

My 2 cents.

Joe J.

[KenWittlief]

that is a neat idea - you would be slightly powering the motors backwards to keep the winch motor stalled and not turning

but if you know the power will be off at the end, then what is the application you have in mind?

I recommend that every team that is planning a doing a chin up have some sort of self latching mechanism that locks into place, once you are off the ground, so that it will stay put when power is cut.

another thought: if you are planning on using this during a match for some reason, use a variable control on the OI, a potentionmeter - that will allow the driver to adjust how fast the winch pulls in, and it will allow it to be powered just enough to hold it in place - I still dont know why you want to do that, but it can be done.

[Joe Ross]

As others have said, once the robot is disabled, any current that you are applying will be shut off.

However, your idea is a good one. In 2000, we found that by applying the tiniest amount of current (just outside the deadband of the victors), we could stop our dual fisher price system from backdriving.

[Max Lobovsky]

Originally Posted by KenWittlief

another thought: if you are planning on using this during a match for some reason, use a variable control on the OI, a potentionmeter - that will allow the driver to adjust how fast the winch pulls in, and it will allow it to be powered just enough to hold it in place - I still dont know why you want to do that, but it can be done.

That is what we want to do, its part of our big ball lifting mechanism (a forklift as I'm sure u guessed). I just dont want an operator to be constantly fidgeting with the speed control teying to hold it steady. What i was thinking, was the a joystick to be calibrated so that an input of 127 (neutral) corresponds to this current feedback system. 0-127 would be from 0 current to holding current (winch letting out, slowly), and 127-255 is more than enough current (winch pulling in)