Thursday, September 02, 2004

Project updates
The new project name is "Knewt" (knowledge in a small package) This week we explored a problem with the gears intended for the foot motors, and decided they were'nt a problem after all.
There is a 5%-7% descrepancy in the tooth pitch of the bastard gears from the surplus bins. But further testing and measurement revealed that a little wear on the aluminum gear, and the errant 7% is worn away. I'm worried about backlash, but as the foot only sees resistance in one direction, there isn't much reason to worry about it. A spring may be added at some point if play becomes a nieucance.

My method for measuring the fine dimensions on these gears was to scan them at a high resolution directly on my scanner, then import the image into CAD, in this case intellicad. (oddly enough, the photoshop PSD format was the only one that made the image visible in the workspace, jpg's and bmp's came in as icons...something I didn't expect) I then used 3 point circles to outline the id and od tooth dimensions, splitting the difference between the od's of the two gears to get the pitch. I then measured the pitch of one tooth on each gear along the pitch line, and found a 7% discrepancy. Even though these are faily high resolution images, there must be some error which I estimate to be less than 3%. So to change the diameter of the pitch circle and remove the discrepancy, I mounted the steel pinion on a drill and ran it against the aluminum ring gear for a few minutes and saw marked improvement in the smoothness of their mesh. I'm hopefull that with a proper jig and some lapping compound, the gears will mesh very smoothly....the clock builders who make alot of gears said that backing off the clearance between the gears will work.
Alternately, we'll go back to linkages...


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