Abnormal Cycloidal Gears (ACG) present a number of advantages over traditional Cycloidal in some situations, as was covered in this post: Abnormal Cycloidal Gear profiles
So I designed this concept model to get more familiar with such profiles. It is the same design as the Dual Cycloidal gear train from earlier, but uses an ACG profile based on a simple trapezoidal tooth shape. This allowed to increase the eccentricity from 1.2mm to 2.7mm, for the same 39:1 reduction ratio.
Seeing the promising much larger tooth contact area, I then designed a robust version with bearings that passed a 16Nm test with flying colors (in the Results section below).
The concept model's Fusion360 CAD model (very messy), STEP and 3MF files are on Github and MakerWorld
Feel free to copy, remix, whatever (non-commercially)
Happy cranking to all !
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Printing
Settings
0.4mm nozzle, 0.24 layer height
2 walls, 3 top, 2 bottom
Normal Auto support, 10° Threshold Angle
CAD
Diagram (same as Dual Cyloidal):
Assembly
1. Glue the shaft together
2. Assemble the pin-disc, shaft and back disc. Position the dimples on the disc and shaft as shown in the pic:
3. Insert the front disc, dimple aligned with the shaft's, on the right side:
4. Glue the front pin-holding disc in (forgot to add spacing, don't press too hard, so that the discs can still freeely move when rotating the shaft)
Done. Time to go brrrrrrrr...
Test Results
A robust version of this drive, with shaft + disc bearings and 2.5mm of eccentricity, was 3D printed with PLA filament. It passed the lift test effortlessly.
Not only did
it deliver 16Nm of torque continuously (40Kg / 87lbs pull), but it also survived both half a dozen low
400rpm drill speed pulls and a couple more at 1500rpm. Not even the Sunless Wolfrom planetary design, which had fared best so far, passed that high speed test with
PLA without severe damage. 
Moreover, the design didn't include any disc-pin bearings and I had forgotten to install the captan drum's shaft-exit bearing, so friction and losses were unnecessarily high.
But it still uneventfully lifted the load each time. In addition, the pulls were
vibration-free and silent, when the traditional planetary Wolfrom design was vibrating and really noisy.
Worst tooth wear was limited to a ~40° wide section, likely due to the last couple of pulls when the disc pins started melting:
Can't believe that the disc pins took so much abuse and
melted, but without breaking:
Conclusion: this is a winner. Once printed with Nylon, and with proper disc-pin bearings, it should perform smoothly and reliably for a relatively long time. ABS might even be an option for lighter loads, and would be much cheaper.
Voila, c'est fini. J'ai trouvé le graal pour mon application type tir à la corde, sweet !
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Posts in the Gear Train series:
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