Coming in a bit late to the party, but I'll try to check everything:
From OP, for future reference, in lengths more than about four inches, bar stock should only be used for tension elements. If the item will be under any sort of compression or torsion, go with angle or channel (or, though I've not designed with it, sheet metal with appropriate bends).
I'm not entirely sure where the "initial robot" ends and the "new robot" begins. For sanity's sake I'll assume everything after "We are using a spare chassi[s]" is all about the new robot.
You refer to rotating the mecanum wheels sideways, and Kevin Leonard advised negatively. Unfortunately, the graphics provided do not really provide any idea as to how the wheels/gearboxes/bearings were attached to the frame in the first place, nor how they are mounted now. Perhaps he has more info. 3946 used Mecanums for Aerial Assist (we vastly underestimated defense!), and the key elements to make mecanum work from my experience are:
- (As with any drive system) make sure that there is a solid support structure. The wheels must support the axles (and/or gearboxes), the axles/gearboxes support the beams, the beams support the joists, and the joists support the rest of the robot. The key thing is NOT to think so much about the robot chassis as supporting the gearbox/axle, as to think about the gearbox/axle supporting the chassis. (OBTW, the same is true of airplane fuselages and wings, which is where I learned this many years ago, before FRC existed; wings that fold up are no good for flying. I remember cringing when I saw the F4Us in Baa Baa Black Sheep/Black Sheep Squadron, and marveling when I later found out that yes, those were real WWII planes!)
- Keep the axles horizontal. We mounted AM TB2 gearboxes on the main beams with no bearings on the ends of the axles, and had to stiffen up those mounts considerably.
- Provide enough flexibility in the chassis and/or a suspension so that weight is equally distributed among the wheels. This one I would consider more of a "good idea" than a "hard requirement". Our practice robot for Aerial Assist (made of lumber, and the product of slamming together a wooden pickup chassis and makeshift mecanum mounts with an external control board that was almost a trailer, but was eventually "twisted around the umbilical" and "screwed to the right side" of the robot) had about four times as much weight on the right rear wheel as the front left wheel, but the drivers learned to work with it fairly quickly.
I can't figure out this quote - the bottom line is that bar stock cannot support compression or torsion, only extension. If the concept of swapping out the bar stock with cable gives you the creeps, bar stock is probably not the right answer.
Quote:
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For the elevator assembly we are going to take pieces of bar stock with 2 bearings on the sides gripping the tubing. With 4 sets of 2 bearings we believe it will slide nicely with any weight load and again the assembly is held together with 2x1 rectangular tubing.
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Ramp: can't help you there first hand - we decided early to go landfill. If you do manage to get your lift faster than your HP can feed through the chute door, I recommend the long low slope ramp used by 254 (Cheezy Poofs) on
EinsteinCarson; it elegantly coupled this impedance contrast without requiring a "Robin" style (see team 148, RoboWranglers) active stacker.
What do you mean by "webbing"? 3946 used chain, as we did not have ready access to long loops of timing belt, but we knew that we could extend 10' lengths of chain with master links as long as we needed. We used
two chains to provide torsion control in the "roll" dimension. With sufficiently robust rollers to handle this torque, this would not be necessary. We did not trust our ability to make such a system, and decided to use two chains.
Sorry, but the Ri3ds seem like years ago now. Even after I went back, I'm not sure exactly what you're talking about with Ri3d Indiana.