Abused Pinion Gear

This severely abused pinion gear from 2010 971 robot drive train shows what happens when a gear is loaded too highly. The four pinion gears in this drive train wore to near failure very quickly. Here is a competition video of the robot that the gear came out of. The gears were undersized relative to the load put on them.

Click images for full size.

Here are some details about the installation and loading in the pinion gear.

  • 12 tooth, 20 DP, 14.5 degree pressure angle, 4140 steel.

  • Mated with 3/8" face width 50 tooth 4140 steel spur gear.

  • Driven by FRC CIM motor with 19 in-lb stall torque and no load speed of 5,200 rpm.

  • Under repetitive shock loading.

  • From FIRST Robotics Competition (FRC) 971 Spartan Robotics 2010 SVR undefeated champion robot.

  • Estimate that it was run hard for 8 to 20 hours. Maybe fewer. Not more.

  • Michael and Austin Schuh, Mentors for 971 Spartan Robotics, Mountain View High School, California.

You can use the above information in a gear loading calculator to compute the safety factor (also called a service factor) for the gear. If it is less than one, you are in for a short lifespan and perhaps even catastrophic failure. When you use the calculator, be sure to keep in mind that the robot was often driven at full power (max rpm) in one direction and then the power was fully reversed. This results in twice the stall torque at the no load speed.


November 7, 2010