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Unread 04-01-2011, 19:47
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skimoose skimoose is offline
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AKA: Arthur Dutra
FRC #0228 (GUS)
Team Role: Electrical
 
Join Date: Jan 2005
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Location: Meriden, Connecticut
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Re: pic: GUS Team 228's Prototype Sheet Metal 6WD Chassis

Quote:
Originally Posted by AdamHeard View Post
Compared to mcmaster, they ship painfully slow (in our experience).
True. Nothing beat McMaster for speed, but we've normally received our colson order from Robot Marketplace in about a week. I don't remember, but we probably could have paid extra for expedited shipping.

Quote:
Originally Posted by Rob Stehlik View Post
Brandon,
Thanks for the info on Colson wheels. I got a sample from Mcmaster a while ago, and they do seem to be nice wheels. Obviously they were never intended to be powered, which is why they are difficult to mount hubs to. The one I got has a 1/2" bore, but this is with plastic bushings. The hub itself is 7/8", which could be broached, but now that you mention it, the plastic is a bit soft, and may not hold up well under stress. I was looking for an alternative to knurling because while we do have the tools, it seems like it would be a bit time consuming to get it right on a manual lathe.
I guess with Colsons the initial effort to mount them is offset by the benefit of never having to change treads.
Rob
Actually, making the insert plugs is very simple, and we've always made them on a manual lathe. Round aluminum stock, 6061 has worked fine, turned down to +0.005-0.007" larger than the Colson wheel's bore ID. Knurl the plug stock with a standard diamond pattern tool. This will raise the plug's OD by another 0.005" or so. Bore for your preferred axle diameter. Cut to length and slightly chamfer the edge of the plug to help with the alignment during the initial insertion into the wheel. Broach the plug for your key stock or hex broach if you prefer hex shaft. The plug is done.

If you're using 2" wide Colson wheels, the plug can be a little long to broach. One year we made the plugs in two pieces. One half was bored and broached, the other half had just the bore. That made it easy to broach and we didn't have to worry about lining up the key ways.

The knurled plug works to the advantage of the soft plastic of the Colson hubs. As the plug is inserted into the wheel the knurling cuts into the plastic forming a sort of spline mating. We have never spun a wheel off of one of our plug inserts.

To Install the plugs simply place the wheel on an arbor press, place the plug onto the wheel's bore, and press until flush. I would recommend a 3-5 ton arbor press. We've used a two ton press in the past, but that's pushing the limits of the press. The plugs are self centering and self aligning. Twelve plugs were machined in about 2-3 hours, insertion takes about 10 minutes.



As for the tread pattern cut into the wheel's surface, now that was time consuming. We built a jig and used a radial arm saw to cut a 0.125" deep tread. This modification withstood an entire year's worth of wear, and greatly improved the wheel's normally impressive traction.
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