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Unread 18-12-2012, 12:46
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Re: Elevator Design - Rack and Pinion Cascaded - 772

Aaron.

Our gear was aluminum that was waterjetted, and our gearboxes up top were custom and very light.

In our initial conversation I overlooked these differences, that really starts to affect the CG more substantially. Really depends on the game, what you're lifting, etc...

You should do the due diligence and explore other gearing methods as well. Driving the initial stage with chain or timing belt are both pretty easy. The rack gear worked great for us, but we took advantage of the waterjet rack and custom gearboxes to really make it work.

Remember, to model the cascade as single stage, the effective "weight" (in quotes as this isn't actually weight, but close enough for simple models) is = 2*(carriage weight - carriage spring force) + (2nd stage weight - 2nd stage spring force).

If geared reasonably slow for 2 550s, the 1.5 second or so range we talked about, acceleration is effectively instant and you can just look at the loaded speed of the motor and assume it travels at that speed the entire time (as John's calc does I believe). For the faster case, that .22 second range, the acceleration time does factor in more I imagine.

Madison, Jared and Bill.

We found that our bearing setup was nice enough such that misalignment was a nonissue. IF you LOCKED one motor shaft and ran the other full stall, the elevator would kick very slightly and stay in place (Still rolling smoothly, just unable to move due to the motor being locked). We had absolutely no issues with them keeping sync due to this. We tested pretty much all possible combinations; a motor unplugged, running a single motor only, running one motor arbitrarily slower than the PID loop commanded to create a power difference at all times. Nothing caused failure, it just worked.

I wouldn't say this as a blanket statement for all rack and pinion, but our lateral bearing support was able to handle this.

Linking them with a shaft to solve the problem requires a shaft large enough and stiff enough to have enough torsional rigidity due to the length of that shaft.

Last edited by AdamHeard : 18-12-2012 at 12:49.
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