By: asid61
New: 23-10-2016 21:23
Updated: 24-10-2016 19:24
Views: 1159 times

CGX-116, a 576:1 Versaplanetary gear stage.
Has CAD gone too far? Probably not, considering that I almost went with a 1024:1 stage instead.
Although this design boasts several weak points, I am fairly confident it would be able to shear a 1/2" hex shaft without being totally destroyed. A steel housing and gears makes this fairly strong to begin with, and the use of 3/32" pins throughout only makes it stronger. The input shaft is approximated as a 1/4" round so that it can be plugged into a VP spline gear after boring it out.
That being said, a 1/2" hex shaft is not a good lever arm to have for many arms. Although this might survive shearing a hex shaft, it's my opinion that large arms are better off using dead axles and 1.875" mounting hole patterns to mount with.

The primary weak points of this design are the lack of significant face width on the "double-gear" (essentially 2 gears in one piece) the use of only a single 6704 bearing to take loads on the camshaft, and the difficulty in manufacturing the double gear. You could also assert that the low efficiency is a problem, but considering this is basically 2 reductions replacing 3-4 reductions, it does gain some of it back.
The double gear only has 1/8" of face width and 3/16" of face with on the 1st and 2nd reductions respectively. The use of 3/32" diameter steel "teeth"/pins and large area of contact should alleviate some or all of the risk from that.
The 6704 bearing only has a static load rating of 160lbs, and a dynamic rating of about twice that. According to some basic calculations I did it should shear the hex shaft before breaking, but I may have analyzed the system incorrectly.
EDIT: I was able to update the design to use 2 6704 bearings instead of just 1, which makes it very safe.
The double-gear is difficult to manufacture in general. The easiest way to do it would probably to turn the bore and step to capture the bearing from round stock before making one side of teeth, flipping it, then making the other side of teeth. Live tooling would be the easiest way to do it.

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