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Transmission test

A project log for FilaMecanum

3D printed hub, filament tires, Mecanum motion.

Daren SchwenkeDaren Schwenke 05/26/2019 at 03:290 Comments

Ran into some issues with my transmission.  After assembly and during some initial testing it became obvious something was amiss.  Well, a couple things.

First it was loud.  Way louder than the original.  This was traced down to a sun gear which was nicking the output ring teeth, and that the sun gear itself was rubbing on the input ring.  The latter, because both parts were PLA, actually caused it to fuse to the input ring housing eventually.  Ooops.  

I have remodeled the sun and idler gears with angled top faces and I adjusted the pin height for the sun.  Solved.

The second issue was I had too much gear tooth clearance (in the code as backlash).  I had printed the planets on the conservative side of extrusion for the best quality of the gear faces, and then I decided to heat treat them so they shrunk more in the process. 

I was absolutely loving how well they were turning out, and so I decided to do 6 planets per transmission.  24 of those planets were needed then, and due to the small nozzle size I used they took a long time.  Like 2 hours per 3 gears?  I have decided that I am not reprinting those!

I was able to correct for this though, by just reprinting the sun and idler gears with zero backlash allowance.  The gear train is still a bit loose, but it is stable and it will work now without failing.

FYI, nylon gears seem to be a lot stronger when printed with a 0.4mm nozzle than they are with a 0.2mm nozzle.  I think this has more to due with just the mass of the extruded plastic than anything else.  More plastic has more latent heat, which will heat the substrate more, which then bonds better when your melting temperature is so high.  

If I had to do this again, I would probably use less teeth so I could go back to a larger gear profile, larger nozzle, and larger layer height.  Lesson learned.

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