ZrX wrote: ↑07 May 2024, 21:51
This is cool!
Been thinking about a microscrew motor also, but it needing some kind of adapter has been a problem, even if I have a 3D printer.
What's the track 0 sensor accuracy with such motor?
Hi ZrX, thanks for the praise.
It was your thread using microstepping for reading the alignment disk that got me going in that direction.
Though I should have listened and abandoned microstepping earlier. I tried a really long time fiddeling with different reprap stepper boards and parameters (current, voltage, # of microsteps, and the myriad of orther stuff you can configure in the Trinamic chips)
For the accuracy: I believe it's pretty high repeatability, but I haven't run extensive tests.
What I did was scanning over a disk and just looking at the raw flux timings.
I basically did a histogram in 100ns steps, then I only counted how many of those fields are not zero. That gives me sort of a "noise level" for any "track" I read. Narrow bands will have a low number, wide bands or pure noise will have a bigger number. I also think I cut off at some timings and used a logarithmic scale or sqrt, can't remember now - it's been a while. Just don't take the noise level numbers literally.
From left to right are native 1270TPI steps, to the top the noise level.
Before each read, I did a search to track 0 twice.
Green and Gray are the same 96tpi disk, read twice with re-insert, Red is another 96 TPI disk.
The valley ground would be track-center, the peaks would be the middle inbetween tracks.
Tests were done shortly after the other, so it's not accounting for temperature drift, etc.
But with automatic track-center detection the sensor accuracy is really not that important any longer either.
Edit: and I forgot to mention, the panasonic drive board track 0 detection was a bit unreliable, so I intercepted the raw sensor signal and am reading that directly on the arduino driving the stepper board.