articulating arm help

[AustinSchuh]

Originally Posted by HarveyAce

Should we just use two there and use a cim to power the arm?

You can still use the BB for the arm, but understand that the BB will not like being anywhere near stall for any significant period of time. This means that you should design the torque that the motor needs to apply to keep the arm up to be significantly less than the stall torque (1/4 or less of the stall torque. I don't have a good number for this). Adding a second BB if it looks like it'll take much torque on the motor to keep the arm up will help. It wouldn't hurt to also put a fan blowing across the motor to cool it when it isn't spinning.

971 used 2 FP motors in a single joint arm in 2008, and it worked just fine. We had way too much power in the joint, which meant that the motors weren't loaded very highly.

[Joe Ross]

Originally Posted by Alan Anderson

If you intend to use the motor alone to hold the arm up, without any mechanical counterweight or spring-loading, be cautious. You'll be running the motor at or near stall a lot of the time. A CIM can handle that for a while, but it will get very warm and you might want to consider a way to cool it off during or between matches.

A Fisher-Price or Banebots motor will not handle that kind of abuse well at all. They rely on an internal fan to keep their windings cool, and if they're not turning, neither is the fan. You'll melt something in short order, followed by smoke. Nearby veterans will sniff the air and nod at the familiar smell of a fried motor.

We've successfully run fisher price and banebots motors stalled at between 5-10% in order to keep mechanisms in place. The trick is to design the mechanical system such that only that little power is needed. If you do need much more then that, your motors will burn.

[MrForbes]

I agree with Joe, you can make a little motor live when driving an arm, but you need to be very careful to make sure it's not going to need to do much work to move the arm, and very little at all to hold it still. We did this in 2007 and it worked fine, we used a gas spring to support the weight of the arm itself, so the motor had very little work to do.

This year we're going to try out a window motor or two for the arm. We will again counter the weight of the arm with a springy type thing. We are also going to add some reduction between the motor and arm, both to slow the arm movement (1/4 second for full arm travel is a bit too fast!) and to reduce the load on the motor. And we have a plan for a nifty way to do this but still allow for that clutch thing that Alan was hinting at. The drive has a built in clutching ability, and it's cheap and locally available. And we've used it before for a different application...we know the slipping part works, which is good because we seem to be unable to get limit switches working