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Originally posted by Jnadke
The bot is only as strong as the strongest material.
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Yep. I still have some concern about the polycarbonate, but it seems like a good bet. Another, slightly heavier option that I'm considering is sandwiching a 1/4" piece of aluminum between two 1/4" polycarbonate sheets.
We broke polycarbonate in a collision last year, so we're intimately familiar with its potential for failure
But, then, we were also lucky because it wasn't structural.
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With that stated, how are you going to attach the polycarbonate wheel to your shaft? Keyway? Setscrew?
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Set screws suck
I usually just design to bolt through the wheels and sprockets, as I've done for this. While a keyway is an option, bolting through the wheels circumference (or near it) has worked fine.
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Although polycarb has a very high impact strength, I am unfamiliar with its tolerance of high forces for long periods (tensile strength). If a keyway is used, will it hold as the shaft rotates and high forces are created? This is one of the things you will need to figure out.
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My biggest concern is that the rim may break between the spokes. I hope that since the weight will be distributed over 6 to 10 wheels, it won't be a considerable obstacle. We can test this.
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If you look on the first site, Polycarbonate has a maximum working temperature of 138 degrees C before it loses much of its tensile strength. Will friction approach this temperature, allowing your keyways to melt through the polycarb like butter? You'll have to find this out. It's better to figure it out now, then to figure it out when your shafts are rotating but your bot is going nowhere during the match.
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240 dF is a lot of friction
Friction is bad. I love bearings.
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One problem with 10 wheels is turning the robot.
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Turning won't be a problem