A high torque, high precision, Strain Wave Gear (harmonic drive) based 3D printable closed loop servo actuator for use in robotic arms
Placed an order for my first batch of custom Open HD 8318 motors.
I thought this would be worth publishing a log about.
While preforming a load test I found that the flexspline will start to rachet if too much reverse torque is applied. I find this interesting, I was under the impression that the first mode of failure with this version of the flexspline would be the teeth shearing off.
I'll be working on a fix for this issue over the next few days. A few ideas in mind have are:
I've also been given a suggestion by Gabrael Levine, the designer of OpenTorque Actuator, to alter the wave generator geometry to keep a preload on the flexspline. I shall see what works best and include it in the next Open HD revision.
That brings a revised wave generator, fixed spline, and output shaft assembly. There are now 3mm dowel pins of various lengths (40mm, 14mm, 8mm) placed throughout the fixed spline as well as output shaft assembly for precise mating and added structural support.
Changes to the wave generator were primarily processes focused to make their manufacturing simpler to automate. List of component changes:
Changes to the fixed spline consisted only of two component changes and some slight procces refinement.
Changes to the (upper) output shaft assembly
Integration of the still unfinished encoder head also came with the V 5.1. Currently the encoder head is using a transmissive photointerrupter (link). I will be switching to a Broadcom reflective sensor in the future, but for now I have some stock of the EE-SX1108 and they work fine as a placeholder till then.
The only post processing that needs to be done on the parts prior to assembly (inner race, outer race, and ball cage) is polishing the surfaces and cleaning up any printing artifacts.
Pre and post processing on the races and ball cage:
The only assembly steps after post processing are: