## Life estimation for stepper motor gearhead life

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### Life estimation for stepper motor gearhead life

Q: For my specific application, I really need long life out of my geared motor. How can I calculate motor life with the following conditions?

1. Motor Part Number: PKP223D15B-SG36-L (PKP series stepper motor with 36:1 SH gear)
2. Speed of Output Shaft: 0.33 Rotations per second
3. Motion – Output shaft cycles back and forth 180 degrees
4. Required torque: 4.5 oz*in

A: Since the load would be handled mostly by the bearing inside the gearhead instead of the motor, the service life of motors will be longer than gearheads. For that reason, we will be basing our life estimation on gearhead life instead of motor bearing life. We have a rated life of 5,000 hours for PKP series SH gears in the catalog based on max conditions, but your requirements are far from max conditions so the life should be much longer.

The following formula calculates the service life of a gearhead:

Stepper gear life - formula.jpg (104.2 KiB) Viewed 1774 times

Where RATED LIFE (L1) = 5000 hours (scroll down below for PKP series SH gear life, or click for full image)

Stepper gear life - rated life of gearheads.jpg (121.16 KiB) Viewed 1774 times

0.33 RPS converts to 19.8 RPM; 19.8 x 36:1 gear ratio = 712.8 RPM input speed at the motor

We will be using a LOAD-TYPE FACTOR of 1.5 for frequent start/stopping via stepper motor.

Stepper gear life - load type factor.jpg (100.83 KiB) Viewed 1774 times

LIFE IN HOURS = 5000 * (3000/712.8) / [(4.5/56)^3 * 1.5] = 27,037,021.64 hours