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What are the drive's advantages, in your opinion?
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- Simple base components (80/20, L-angle, shoulder bolts)
- Reduced machining operations (no custom shafts, non-CNC milling)
- Simple chain tensioning method
- Quick assembly time
- Easy servicing (one bolt wheel removal)
- Lightweight
- Large baseboard area for electronics
- Less gear reduction required for 4" wheels (more efficient)
- I could see teams with some basic machining capabilities knock two of these out within the first few days a build season, then move on to bigger and better things
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Wouldn't an 1/8 wall square extrusion weigh just as much as a quarter inch L, with a much stronger profile?
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Yes, but the shoulder bolt shaft needs to be bolted to a plate with sufficient thickness, or else the plate will bend under load. Anecdotally, 1/8" wall seems too thin and will flex. Also, the L-angle leaves more space for the electronics board, and provides nice mounting flange. The L-angle looks to be plenty strong(?), and the bottom flange could be milled down to 1" or less to save weight - but that's another machining operation.
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Is the idea here that the bolts are threaded into the frame member or are they through-bolted with a nut on each side?
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It is a shoulder bolt (through-bolted) with a single nylock nut, and two washers sandwiching the plate. The above image best shows the setup. When the shoulder bolt and nut are tightened, it causes the washers to squeeze the plate tightly. The idea is that this is enough squeeze force to a) keep the cantilevered shaft perpendicular, and b) keep the shaft from sliding in the slot (the plate is actually SLOTTED for the front and back wheels to allow you to slide the wheels back and forth to tension the chain)
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My gut reaction is one of concern that the bolts will unscrew themselves, but maybe that's unwarranted.
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This is where my lack of mechanical experience shows through. I am concerned about this too, but I don't know the limitations of Nylock nuts, and threadlocker.
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This is very nice and simple but I'd be worried about the forces that cantilevered load is putting on a very small amount of aluminum. Id guess that over time either the hole in the aluminum would oval out or the angle itself would want to bend below 90 degrees. You may want to run some CAD analysis, but with me this doesn't pass the sniff test.
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The concept is that the washers that sandwich the plate distribute the load over a larger area of the plate. If this happens, there should be very little load inside the slot itself. CAD analysis is a good suggestion to see whether this works.