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Old 2016-07-20, 01:50 AM   #10
Justin LE
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Join Date: May 2010
Location: Vancouver
Age: 37
Posts: 120
Quote:
Originally Posted by harper View Post
Another concern is the press fit pins in the aluminum plate planet carrier. I tried that on my first rendition with dowel pins pressed into a steel disc. The pins elongated the holes but the catastrophic failure was one of the planets galling on the dowel pin and seizing.
Oh no! That was the one area of biggest concern for me since I don't have much firsthand experience with press fit pins, and aluminum is way softer than steel. What was the overall radius where the planet gears were installed in your early prototypes?

I'm hoping that the fairly large distance out of my planets plus the spread over 5 of them means that the forces will stay reasonable. Quick calculation (should have done this earlier!) but we're at a 52mm radius to the pins, the most torque someone could put on the pedals is about 200 Nm, so that would be 200 Nm / 0.052m / 5 = 770 Newtons or about 175 pounds per pin.

Yikes. I might need to keep the cranks short. With 100mm cranks then a 200lb person standing with full force on a pedal would be more like 90 Nm, so about 80 pounds on the pins. Still a lot for a press fit of a 6mm dowel into aluminum., time to go hang some weights on the gears and see if I need to remachine that part out of steel instead!

-Justin
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