July 26, 2023
Description
This is a variant with finer teeth (module 0.5) and can be printed without supports.
The CircularSpline has 160T, the FlexSpline has 158T.
The gear ratio is 79:1
With the 17HS15-1684S-PG27 from OMC Stepperonline, the transmission ratio is 2121.15:1, which should be enough for clean tracking. For this motor you also need an extender: https://www.printables.com/model/304137-extender-for-stepperonline-geared-pg27-stepper
My Onstep controller has 2 TMC2130 drivers in SPI mode. With it I can track silently in stealtchop mode and for GoTo it switches to spreadcycle mode and full steps for maximum speed. You can download my config.h here:
(German) https://astrophoto.lionbit.com/3d-druck/26-keenone-eq
The Onstep controller, as published by Ken, is a WeMos R32 D1 and CNC Shield V3. https://www.printables.com/model/273808-simple-onstep-system-case-wemoscnc3
!!! Important !!!
These are precision parts with very tight tolerances, so the printer has to be set very well.
In order to ensure dimensional accuracy, you must first calibrate your printer best possible. Flow, pressure advance (klipper) linear advance (marlin) and including the shrink factor of the filament, because that makes the difference between success and failure.
To calibrate your shrinkfactor, use this: https://www.printables.com/de/model/308591-shrinkfactor-calibation
V2 is done!
V3 is done!
After many tests, i found out that the gear works best when the flexspline is completely formed by the wave generator. The thinner wall at the toothing also brings advantages and, above all, smooth running.
The 3rd variant was created.
With 20 small ball bearings that form the flexspline into an ellipse that does not allow any further freedom for the deformation of the flexspline.
Without the elliptical wave generator, I always saw an "unround" movement with the GoTo and cracking noises in the gears that came from improperly engaging teeth.
Now the gearbox runs quietly and smoothly but because of the weather I can't test on the stars :(
BOM for one unit:
The 20 M3x10 screws are screwed into WaveGenarator_A_V3.1, i drilled the threads here with an M3 tap. Unfortunately there is no space for heatset inserts or nuts
V4 is done!
This variant is a printed flexible elliptical ball bearing, it uses 42 5mm steel balls to form the thin flexible outer ring. This then forms the 158T_Flexspline_V3 in a very well-defined ellipse, which creates optimal smoothness. A little grease with PTFE also helps here ;)
How to print:
I printed the parts Wavegenerator_A_V4.x and Wavegenerator_B_V4.x with the 0.25mm nozzle and a layer height of 0.1mm to get the most accurate and smooth surface possible.
Wavegenerator_A_V4 is printed with ABS to have a hard and stable base and Wavegenerator_B_V4 with PETG without cooling and printed very slowly (33mm/s outer perimeter, 60mm/s inner perimeter) to maximize layer adhesion. The outer ring is optimized for 0.25mm nozzle and has 2 perimeters at its thinnest point, i.e. 0.5mm thick
Layer adhesion is very important here!
BOM for one unit:
WaveGenerator_B_V4.3 has slightly thicker edges for more stability. If your V4.2 works without problems, you dont need to reprint it.
22-12-2022:
WaveGenerator_A_V4.3 has no changes on elipse since V4.2, only the clamping screw is on new position to avoid warping.
Note:
Do not tighten the clamping screw too much, otherwise the wave generator will warp and it will no longer run smoothly. Check the run before you screw the two assemblies together. The hole for the motor shaft is intentionally made a little narrower so that the wavegenerator is as well centered as possible. A lot of torque doesn't work here anyway.
This short video shows the Keen-One EQ in GoTo. Also hear the sound, it just sounds clean :)
GoTo Speed was 2,5°/s with 27:1 Stepperonline Steppers.
V5 is done!
The development goes into the next and possibly last round.
This time the ball bearing is integrated into the flexspline, which makes the gearbox much more stable, some had problems with the thin ring in version 4.2/4.3, that should be a thing of the past here.
A coupling has been added, which is attached to the motor and later, when the ball bearing has been assembled, it is simply plugged onto the wave generator. The torque is transmitted via the six teeth on the clutch, which also centers the wave generator. There are very little tolerances here, as with all other components ;) But we need zero play!
I hope for feedback from you.
BOM for one unit:
The AssemblyHelper is responsible for centering the wave generator during the assembly of the balls. Snap it onto the protruding shaft at the bottom of the flexspline, then snap on the wave generator with the arrows pointing up. Now you can install the balls.
When all the balls have been installed you can simply pull out the AssamblyHelper and the ball bearing wave generator should now be stable.
See the pictures how to assembly V5, its easy!
With a small hack I was able to increase the Goto speed from 2.5°/s to more than 4°/s. This mount is now as fast as others.
I have described exactly how this works in my blog and offered an adapted Config.h for download.
(German) https://astrophoto.lionbit.com/3d-druck/26-keenone-eq
Happy printing :)
License:
GNU General Public License v2.0
Luke
