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Unread 07-05-2015, 01:26
AustinSchuh AustinSchuh is offline
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FRC #0971 (Spartan Robotics) #254 (The Cheesy Poofs)
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Re: Sheet Metal Fabrication vs. Using Channel

Quote:
Originally Posted by TheModMaster8 View Post
I accept you challenge.
Drive bases have a lot of mixed loads. Cantilevered wheels put a torque on the tubestock. Even drive bases which support both sides of the wheel shaft have torques put on them when one corner lifts up on something, or you have high lateral acceleration. I-beams are very strong in the direction of the I, not in the orthogonal direction, and definitely not in torsion. Check the torsional strength of an i-beam. Drive bases aren't their target application.

I challenge you right back to draw up a sheet drive base and a tubestock drive base and use CAD to weigh both of them.

I'm willing to bet you can get the weight of the tube stock drive base significantly lower (a couple pounds) than the sheet base for a comparable strength. I've been comparing our chassis weight against 254 and 973's for years, and they have consistently come up a couple pounds lighter than ours.

With sheet metal, there is a minimum flange length. If you are going to make a structure (like we do) which is a tube holding your wheels, you need 3/8 - 1/2" of material on each side of each bend. That's 4" of material just in the corners, not including any material used to connect those sides together. Overlapping flanges to attach 2 pieces of sheet together just add to that number. Compare that to the 6" of tube perimeter in a 1x2 that is traditionally used on a WCD, and you are going to have a lot of trouble doing better than the 1x2.

We do a sheet metal drive base because we have sponsors who are sheet metal shops and we know how to work with it. We can design in our superstructure mount points and bumper mounts, and get a bunch of parts back while we continue designing the superstructure that only need to be riveted together to have a robot. I really love our drive bases, but getting the weight down that last little bit is one of those things that we struggle with and end up just giving up on.