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Unread 16-05-2011, 21:23
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Re: Mecanum Einstein this year

Quote:
Originally Posted by apalrd View Post
We (33) built a live-axle drive inspired by team 254. We made bearing blocks and cam tensioners out of 1/4" plate and cut them on a waterjet, but the bearing blocks were seriously just three holes in a line and not hard to make by hand. The shafts were lathed by hand (we used keyed shafts since they were easier to machine), and the wheels, hubs, and transmission components all came from Andymark. If you simplify the design, it isn't hard to make.

The Cheesy Poofs transmission, on the other hand, is quite difficult to replicate as basically all of the gears are custom-made by them.
It's more about their overall design rather than the WCD-sliding blocks or their custom gears (which I suspect *could* be COTS gears if they chose).

3.5" wheels -- they can't go smaller because of the large gear on the shifting shaft
They can't make the first stage reduction greater because of CIM spacing (2.55 or 2.6" between CIMs) and the internal shaft spacing of the large gear on the first stage. The AndyMark super shifter runs into this same issue.
So they're 'stuck' with 18 ft/s, in a sense. All in the name of removing the 3rd gearing stage from the transmission to increase efficiency.

Then
- For any sort of decent acceleration, they need incredible efficiency on the overall drive train since it's only 4 CIMs (unless there were other motors hiding under the CIMs...)
- Weighing only 100 lbs + battery, bumper, lightweight minibot helps acceleration too

So their strategy, at 18 ft/s for an 'open field' where defense rules were constricting and effective "anti-flow" strategies forbidden, was actually a great idea in hindsight. 7 ft/s would help them get through the average defensive robot in a pinch, though the tradeoff was lack of torque -- which did get them into trouble once.

I'll admit, I didn't count gear teeth, and a bit of this is reverse-engineered estimation; so I don't know the true numbers for their gearing itself. Yet if you design a 2-reduction 2-stage gearbox (I tried the week after champs) you'll see that it's not quite as easy as slapping COTS parts together. So most of us wouldn't be able to do it quite like they do.
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