Issue with 136:1 Sub-Micro Plastic Planetary Gearmotor – Stops Spinning in One Direction

Support Motor controllers/drivers and motors
1

Hi Pololu Team,

We are currently using your 136:1 Sub-Micro Plastic Planetary Gearmotor (6Dx19L mm) in our sand robot project, running the motors at 6V. However, we’ve been encountering a recurring issue during field tests in sand that has resulted in multiple motor failures.

Symptoms:

IMG_6041
IMG_60411920×2560 652 KB

IMG_6040
IMG_60401920×2560 377 KB

IMG_6042
IMG_60421920×2560 682 KB

IMG_6043
IMG_60431920×2560 544 KB

IMG_6044
IMG_60441920×2560 701 KB

IMG_6045
IMG_60451920×2560 688 KB

IMG_6046
IMG_60461920×2560 748 KB

IMG_6047
IMG_60471920×2560 792 KB

  • After some usage in the sand, a motor will slow down and eventually stop spinning in one direction, while it continues to spin in the other direction.
  • Occasionally, using a plier to manually rotate the output shaft helps it spin again temporarily, but this fix doesn’t last.
  • Eventually, the motor will completely stop working in that direction, while still working (sometimes less smoothly, or even stop working as well) in the opposite direction.

This issue has damaged several motors, and we would appreciate any insight into what might be happening and how we could prevent it.

Thanks in advance for your help!

Best regards,

2

Hello.

It is hard to tell for sure from your pictures, but it seems like the brushes are failing from some combination of being worn out or bent. That type of failure can occur in a way that the motor still works for a while longer in one direction before completely failing, especially in applications where the motor spends most of its time spinning in one direction but not the other.

We do not have the lifetimes for these well characterized, and in general, the lifetimes can depend on many different factors, but if you are seeing rapid failures like this across multiple units, that probably indicates the load is greater than what the motors are designed to handle. A a general recommendation for brushed DC motor operation is to limit the load so the motor draws 25% or less of the stall current.

- Patrick