6.6:1 Gear Reduction Study

UPDATE 2024/04/21:

Here is the promised link to the Limited Slip Torsen differential, for which this study was a test.

UPDATE 2024/04/17: 

I have learned a lot while printing this. With the Bambu Lab P1S and 3DJakes PCTG Filament I can achieve steady tolerances of 0.15mm (used in the model, except for the Axle 2 (yellow) Spacer, which is -unnecessarily- 0.2mm) and potentially even below for a snug fit. Of course dialing in the filament in the Slicer is mandatory first.

Also what works tremendiously well is C-Clips, which seem to also fix the gears quite well against the opposite shoulder and preventing them from wobbeling.

Downside of having a modular system for sure is the need to have one side being able to slip into the gears which weakens the smaller side of the axle. Fixing the Axle 1 (blue) with a C-Clip resulted in a predetermined breaking point when mounting or unmounting, so again not ideal. But as this is only a proof-of-concept and not a final gear assembly, I would neglect this.

More to come soon. A Limited Slip (Torsen Type 2) Differential for a roughly 1/8- 1/10 scale crawler is already in Onshape, waiting to be finalized and published.  I am true to my dogma and made it fully 3d printed - no screws whatsoever (yet) needed.

And I even have some thoughts to make it a LS Torsen Diff with option to fully lock the diff via Servo. I will keep you posted and link the model once finalized. [Link added on top!]

UPDATE 2024/04/10: slightly longer outter C-Clip for Axle 1 for better grip on the axle.

With creation of an RC Crawler in mind,  I made a pilot/ design study for a 6.66:1 Gear reduction. As Plastics are not exactly the best material to transport torque at high speeds, the whole assembly was intended to be as modular as possible while retaining structural integrity when assembled. This would allow me to change worn parts on the fly without the need to spend hours of printing.

The gearbox study consists of three axles, starting with a Helical Gear (16T, Axle 1, light blue) onto a Shaft containing a 40T and a 15T Helical Gear (Axle 2, yellow) and a final third Axle with again 40T (grey).

As there is quite some flex needed to assemble these Shafts into the Chassis, I strongly advise to print it with flexing Material like PETG. I did use PCTG w. 0.12mm Layer heights. The Helical Gears benefit from multiple walls to make the gear teeth and the underlying structure solid.

All Helical Gears are Module 1 with a Pressure angle of 25deg.

The Gears are held in place on the shaft with C-Clips. There is another C-Clip for Axle one (which can be turned with a cordless Drill). Here is a picture with removed Gears. Pls note the spacer between the two gears on Axle 2.

For clearance, one of the 40T Gears has a slightly larger Chamfer and that gear needs to sit on Axle 2 to avoid touching the Tapered C-Clip on Axle 3. That is certainly a design flaw which could have been avoided:

After some tests with the shaft parts where the gears sits on I have settled with a Pentagon shape to transport power to the gears.

Final Assembly: