A 3D printed strain wave gear, using a HTD 300-5M-20 and 608 bearings. The belt has 60 teeth, for 30 revolutions of stepper the outer gear rotates once, resulting in a -30:1 gear ratio.
Bill of materials
|HTD belt||1||300-5M-20 closed loop, 300mm circumference, 5mm tooth pitch, 20mm wide
|bearings||4||608, OD 22mm outer diameter, ID 8mm core, and 7mm wide|
|3D printed||1||PLA, not the best material, but forgiving|
|set screw||2||3mm nuts with set screws|
|screws||4||M3 screws to attach stepper to gear|
Using the parametric design I printed exactly the STL output. The parametric model was designed and mainly checked against an HTD 300-5M-20 that I used here. I added space for nuts on the wave generator and set screws. To assemble the wave generator 3D-printed pins for the bearings with a spot for snap rings.
|HTD Belt||Tooth spacing / depth|
|8M||8mm / 3.38mm|
|5M||5mm / 2.06mm|
|3M||3mm / 1.17mm|
|The picture shows the
belt teeth against a
So far is seems that
3M belts require the
gear to be too precise
and don't deal with
forces, 5M seems
like a good mix for
Using a 20mm wide belt, gear parts should be less than 10mm each when the sides are assembled there isn't friction between the two halves.
I used a Arduino MKR1000 using the Timer5 library, controlled by the Blynk app. The sketch controlled a DRV8825 stepper module. I can make details available upon request. Here is the configuration of the Blynk app:
I can feel there is more torque on the gear output. What is an effective way to measure torque? I have 5M and 8M and belts of different diameters.
I would want the stepper speed and current to the controlled/captured at the same time. A current sensing resistor supplying the input of an op-amp, conditioned, then captured by the ADC, should work but is there an easier/better way?
A laser diode mounted on the gear output pointed at a wall would allow measurements to find the effective repeatable resolution. Then finding out what force results in what loss of resolution or repeatability.