Quote:
Originally Posted by Kevin Sevcik
Adam,
You're probably right that this will shift the failure point of the transmission elsewhere. If it's the ring gear, there's a steel version of that. I think you're wrong that the issue is stalling the motor, though. If you ever actually manage to stall one of these things, you're going the seriously damage the gearbox very quickly. We're experiencing a failure mode very similar to fox46's in that the gearbox gradually degrades over time. I think this is a combination of the weaknesses he's helpfully pointed out and some unique load conditions. We've never stalled our 256:1 RS-775 transmission, and yet we've deformed the carrier plate twice. I'm certain this is due simply to inertial loading from our arm as we lower the arm and stop it. The stop is invariably sharp and sudden thanks to the huge gear ratio, and this creates an instantaneous load on the gearbox that exceeds the capacity of the carrier plate. I expect fox46 is actually experiencing a similar problem.
His proposed solutions will definitely strengthen the gearbox and slow the degradation process, but I think they should be coupled with programming changes designed to limit the rate of change of voltage so as to lessen the sudden shocks when motion is stopped.
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You're not sitting there stalling it, but when you first get the motor going, or rapidly change direction, the motor is stalling momentarily and putting out much more torque. As you already know, this probably isn't near full stall torque of the motor at 12V, but multiplied by the 256:1 it's still something rough.
Such high reduction p60s really shouldn't be used for arms, even with proper counterbalancing and software limits they are just waiting to tear themselves apart.
We've used our 4:1 p60s in our arm rough and hard, with aggressive cyclic direction changes and even full stall on a few occasions for a few seconds without damage.
Banebots isn't at fault here, they designed a gearbox that is mechanically nice, and very, very affordable. For people who want higher reduction but are aware the gearbox could damage itself from higher loads or cyclic loads, they offer a higher reduction. User error is not the manufacturer's fault.