BE8108 gearbox

As mentioned last time, I’m working on a parallel track to accelerate my quadruped development efforts.  The current plan is to try and use a BE8108 class brushless motor, with a planetary geartrain mounted mostly inside the existing bounds of the motor.

Here’s a rough exploded view of the CAD model:

Key takeaways are:

  • The rotor and stator of the existing motor are disassembled, with the original back half of the stator discarded.
  • The rotor has its center drilled out.
  • All the non-gear/shaft/bearing parts are currently designed to be printed in plastic as a fit and function test.  That means things are thick and most holes that would be threaded instead have a big hole for a heat-set insert.  I’ll switch them over to aluminum once I get things basically working.
  • Metric modulus 0.5 gears are used; everything is stock with the exception of the 100 tooth internal gear which has a reduced outer diameter.
  • Bearings are used to interface all the rotating components.
  • The front plate mounts to the original stator and the internal gear, and acts as the primary outer housing.
  • Absolute position is measured via magnets attached to the planet input and a ring shaped PCB.
  • The back plate supports the back of the rotor.

If this looks an awful lot like Ben Katz’s model, that’s because it is!  The basic mechanism is the same, and a lot of the features are similar-ish just because it was easier to make something that looked roughly the same where it didn’t matter.

More details to come…