[Rob]

Originally Posted by ZZII 527

Thanks so much for your efforts to analyze and solve this problem over the past few days, Dr. Joe. My team is in the "fortunate" situation of having a 12:1 single CIM drive system, but I am worried about our arm which is driven by the 256:1 42mm transmission with FP motor. While I don't anticipate the motor ever being driven to anywhere near stall, I tend to think that impulsive loading from the arm itself is the thing to watch out for.

I can easily imagine a large arm changing directions in a matter of milliseconds, hitting a dead stop, or gaining momentum before a chain engages and suddenly yanking on the drive shaft with much more torque the the FP could supply. And at 256:1, the gearbox would have very little give from backdrive at those time scales. A good test might be to short the motor terminals (worst-case scenario with Victor e-brakes on?) and drop a weight from an arm attached to the shaft. I bet it could do a lot of damage.

If this is the more likely way to get failure, then there are a bunch of ways for teams to alleviate the problem, many of which were mentioned in previous threads (gas springs, limit switches, etc.). Do you think this could be the more dangerous culprit, or am I missing something important?

You are probably right to be concerned about shock loading in your arm possibly causing damage. There are many ways shock loading can occur such as the arm hitting hard stops, the arm hitting another machine or field element, or a rapid change in direction caused by the operator or a control program.

You may be able to use software to alleviate shocks associated with rapid changes in direction by using an accelleration and decelleration curve. This will dampen the responsiveness of your arm, but will also reduce the shock loads that the system experiences.

Another option could be to install a clutch in the system somewhere between the arm and the BB gearbox. Check out page 993 of the Mcmaster catalog for a start at some off the shelf type options. The clutch would simply slip if torques that are too high are applied (like shock loads). Keep in mind however that this could wreak havoc on feedback systems that are attached to the arm.

Another possible solution similar to the clutch would be to link the drive system to the arm through a spring which would be strong enough to transfer "normal" loads but would absorb strong shock loads (I think team 571 did something like this on their 2004 machine to absorb shock loads through the arm).

Good luck everyone,

RAZ