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LoboCNC

Anti-Backlash Compound Planetary Gearhead

by LoboCNC Apr 15, 2019
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I think this is similar with your previous actuator, https://www.youtube.com/watch?v=sdRGrTHq4hA .
On that video, body40 part is divided into two parts(grey one and yellow one), so it can move flexibly.
But when I printed body40, I found it consit of single part, so It do not move flexibly.

On this model, the flexible ring is still relatively stiff - just enough give to allow for tiny variations in the gears. Also note that the there is a tiny 1-layer gap beneath the ring gear and the bottom surface, and the gear needs to be flexed ever so slightly to break it away from the bottom,

How do I know if this is printed correctly?
Should body40's structure move slightly, but visibly?

Yes, you should be able to see just the slightest movement in the ring gear if you insert a small flat screwdriver blade into the flexure and pry very gently.

Printed everything in about 5 hours but can't assemble. Either Sun, or orbiter gears are way to big to fit. Are you sure you scaled everything down from original project?

I printed using Cura and Octoprint on Ender 3 and everything fit together like a glove. I did use 0.3mm nozzle and 0.06 layer height.

The STL files posted are the same ones I used for the assembled unit shown. It could be that you are over extruding some, making the parts not fit. Also, you have to be very careful to assemble the planet cluster gears as described, aligning the fiducial marks, otherwise it won't go together.

Printed all together, 100% infill, 0.4mm nozzle, 0.15mm slice, 200C nozzle, 60C bed, 100% speed, 100% fan. Everything came out looking perfect, i see marks for planetary alignment but i can't fit everything in, orbiters seems overpressurized.

How much clearance is exactly in planetary?

The gears were designed with maybe only 0.002" clearance, which is essentially zero clearance when you're talking about 3D printing. The flexing ring gear, however, is what allows it all to work. That said, the assembly is still pretty tight and you still need to clean up any surface irregularities before assembly.

Any chance you could post a STEP file of this one? I want to see if I can fit a brass coupling on the shaft and then have it attach to the sun gear.

For some reason,saving this as a STEP file in Solidworks blows up to 0.5 GB file. Instead, I've posted as a parasolid file. Hope you can read it.

Excellent. Thanks. Imported fine into Fusion 360 as parasolid.

There are no arrows for alignment on the planetary gears, so is it not as important on this design to align those planetary gears as accurately when you place them into the final assembly? It appears to be ok from the build I did, but it would seem you still would need to line these up well. I'm just doing it by visual eyesight but alignment arrows would be nice.

Orientation is still important. The original arrows were a little hard to get aligned, and on this design, there was no good place to put them on the ring gear. Instead, you'll notice that on the larger cluster gear, one tooth has the top beveled, and on the ring gear there are 3 pairs of adjacent teeth with top bevels. In the 3rd photo, you can see where I marked these with a Sharpie. There's a little more detail about the alignment in the Assembly section of the Thing Details.

Wow, you just keep upping the ante. This anti-backlash design looks great. Printing one right now.

Thanks! For the smallest actuator, this upgrade is pretty well necessary because it's really hard to get the tiny gear teeth running smoothly enough for the tiny motor. Hopefully, though, I'll have time to do anti-backlash versions of the medium and large actuators as well.

Where did you get the 4mm balls?

I got Delrin (acetal) balls from McMaster Carr. I am actually using 5/32" balls, but they also sell 4mm. You can also use steel balls which are a little more widely available.