[jreuter]

We smoked an RS-550 motor last night, and were not near the stall point, as far as I can tell.

This is somewhat puzzling. We used the RS550s a couple years ago with no issues, so I thought I would throw this out here to get some opinions.

Here's what we have:

Banebots RS-550 with a 25:1 gearbox, driving a 3" diameter timing belt pulley which raises our elevator.
The design load is supposed to be around 30 lb, but we have some binding, as I will show below.

Banebot RS-550 spec
19300 RPM Free speed RPM
70.55 in-oz Stall torque
85A Stall current

When connected to 25:1 gearbox
772 RPM Free speed RPM
1763 in-oz Stall torque
85A Stall current

We were running the elevator up at roughly 8 feet in 2 seconds, using a 3" diameter pulley with a 1:1 timing belt between the pulley shaft at gearbox
Belt speed = 4 ft/sec
Pulley/gearbox RPM = 306 RPM (4 ft/sec/(pi * 3" diameter)*60 sec/min * 12 in/ft)

This is 40% of the free speed RPM.

From the motor curves:
The motor current should be roughly 51A (60% of stall current)
The motor torque should be roughly 1057 in-oz (60% of stall torque)

With a 3" diameter pulley, and ignoring gearbox efficiencies, this should create a lifting force of 66 lb (1057 in-oz/1.5" radius/16 oz/lb).
(Clearly we have some binding to get rid of.)

Even so, this is just over the normal, max power operating point of the motor.
Any ideas why this motor smoked?

-Jeff