this was also a long time coming
Worthy of note: those numbers are bullshit. The counts per rev on the motors isn't vaguely right, there's a 9:1 gearmotor between the motor and the ballscrew, and the ballscrew calcs aren't even incorporated. And uhh obviously the motor and the ballscrews aren't even physically connected.
But that's the software, cheerfully controlling a servo motor to a tenth of a micron.
The backlash of the gear motor is under 3 arc minutes, or under 0.05 degrees. The backlash of the GT2 belts is 2.7 arc minutes, or also under 0.05 degrees. two of the axes are 4mm/rev ballscrews, one of them is 2mm/rev. .1 degree at 4mm/rev is 0.0011mm, or 1.1 microns.
The machine originally used closed-loop control via Heidenhain glass scales that were totes stolen by the brigand that sold me the machine. With that closed-loop control the machine managed 1-micron precision. I can buy Mitutoyo scales that will work with a module for the servo pack that will get me to within 0.01 microns, or "a coronavirus." I don't think it'll take that. To assume mirror finish for any waveform you need half the wavelength. Visible light starts at around 370nm, so half of that is 185nm, or around 0.2 microns. The motors, for their part, are 24-bit encoders, so 0.0013 arc minutes per pulse or 0.077 arc seconds. 0.073 nanometers per pulse at which point you acknowledge you're measuring absolute fucktons of noise. 4600 pulses just in the combined backlash of belt and gear motor.
But I've taken this creature from "is it possible" to "do I want it."
I got the motors to wake up yesterday. They appeared in SigmaWin and I could jog them. I choked up like I was watching the end of Babe. I've got at least one dead servopak; I paid $190 ea for them because the local guy told me they were $3k and fuck him. I could buy another for $190 used or $400 new out of China or, apparently $1100 out of any scrupulous North American distributor who isn't giving me the fuck-you price. I found this out when I inquired about getting mine fixed and was told they won't fix it if it'll cost more than 70% of the new price or "around $800."
Here's a $4500 mill. Like that surface finish? Here's its stepper motor. A B C D, baby! Mine have 1500 parameters, life-cycle monitoring and not one, not two, but five thousand-page manuals. Which allow fancy moves like this fucking voodoo at 3:30.
I'm literally at "the plane flies." It's not ready for passengers? I wouldn't take it across the Atlantic? But the proof-of-concept has proven out and this fucker IS GOING TO WORK.