I’ve redesigned the cube torque tester with components that should be much more accurate and should be able to provide better repeatability between measurements.
I’ve planning on the following improvements:
The cube will be held with 3D printed parts, which I’ve ordered from Shapeways so the tolerances should be pretty good. (±0.15 mm + 0.15% of the longest axis.)
The rotation axle that supports the cube will use ball bearings to reduce the torque imparted on the cube from the holder as much as possible. Any friction from the bearing effectively reduces the torque that is transmitted to the load cell so it’s important to make this bearing as friction-free as possible.
Everything will be mounted to a ¼” (6mm) thick aluminum plate which should keep things more stable and repeatable.
I’ll be able to precisely control the stop to prevent the arm from counter-rotating, and I should be able to use this stop to slightly pre-load the load cell to make sure there is no slop in the system at all.
An extruded aluminum post will allow me to raise and lower the motor mount. This should be much more rigid than my cardboard setup and hopefully also allow me to position the motor in the same place every time. It will be interesting to see how close of a match I can get between two measurements of the same cube after removing and reinstalling the motor mount.
I’ve elongated the beam that pushes on the load cell. I suspect that I was overloading the load cell previously and using the load cell above it’s rated range is probably bad for linearity which will distort my measurements.
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