Work In Progress: MoCo Dolly

The underside of the modified carriage, showing the anti-backlash Acme drive nut and its mounting bracket, one of the Acme lock collars, and one of the thrust bearings. Note that the off-center position of the bracket (shifted tailward) permits the carriage to run over the lock collar and thrust bearing at the head end, so that the carriage doesn't have to stop two inches short.

This is proving to be the locus of some trouble at the moment. Due to a slight (but non-negligable) runout error in the Acme rod, the drive nut drives the carriage in a helical motion (up and down and right and left as it goes), making the camera wobble. Need to tighten up the sliding bearings and work some of the runout out of the rod...

The runout problem was subsequently addressed by mounting the drive nut to a new bracket which slides along the base of the IGUS slider, and drags the up-standing leg on the black bracket (cut down to a 4mm tab) as it goes. The tab fits into a gap on the new bracket which is small enough to not allow any noticeable backlash, but loose enough that the wobble from the Acme rod isn't transmitted to the carriage (and to make it more gearheady, the tab is tapered and rounded slightly so that there is theoretically only ever point-contact between it and the new bracket). The original problem boiled down to the nut transmitting off-axis translations to the carriage - the new arrangement only permits it to apply force in the axis direction. Problem solved.

Now, if I were an uber-gearhead, I would have drilled a hole in the little tab and press-fit a ball bearing in it to ensure there was only ever point contact...