Sunday, November 10, 2024
Mod. 4 Fails
The Mod. 4 axis was a multiple fail. Its improvements were good, there just weren't enough. Actual frame rigidity was not good. The NEMA17 coupling was a press-fit sleeve with the drive screw bolted onto the end. Unfortunately this tended to set an angle to the screw thread and everything wobbled.
After some time I realised that I needed to hold the drive shaft in the collar flexibly. So I put a fixed nut on the drive shaft, and the motor turns the shaft. The nut hole is tapered, allowing it to be firmly grabbed, yet allowing it to move to re-centre rather than eccentricity driving the shaft.
The OpenFlexure stages avoid this by having a gear between the motor and the drive shaft, and that absorbs any wiggle.
The nut trap in the drive end of the pivoting arm has a lose cavity for the nut. This allows the nut to rotate partially. Tighten it, and the nut is hard to insert. The solution again is a conical nut trap. The temporary solution: Jam it in with a bit of copper wire to take up the slack.
Finally, lubrication is very important, particularly if you can't find brass nuts.
I may insert a pair of vertical flexures into the Mod.5 lifter bar to see if this will remove any residual sideways wobble and/or try making the other flexures slightly more rigid.
I may need more anti-backlash tensioning but that may need to wait for decent springs.
