Hi @mcdanlj I was thinking of something like these multiturn or Continuous turn pot from my local supplier.
Here are encoders Shaft encoder from same supplier.
Your 330mm is very similar to my builds on 132 column dot matrix mechanics. If you sacrifice 10mm, you could use a 10 turn pot on a 16 tooth GT2 pulley for 320mm at best resolution, or 400mm for full width plus. There is an APP note to ‘improve’ the ADC resolution by oversampling and skewing the input with a DAC. This yields 1-2 more bits. I also have STM32F373 that has 16 bit ADC.
Our Rand i through the floor andtrades 15 to the $, so ODrive is out of my budget, someone could always send me a dozen to test :wink;. I’ve got a few STM Nucleo BLDC boards I plan to use in the next round. I blew 2 and have now replaced them.
A problem with encoders is they are incremental so some errors can go undetected. For example any break in LED light (could be dust or power glitch) will be accepted and lead to erroneous positioning by any number of steps until the fault clears. It is undetectable.
Some can be fitted over the shaft, and that is an option. Unfortunately the 10 turn pots I have in mind come with shafts. I have fitted these as the distal end pulley.
On occasion I have set acceleration a shave too high and had my belts slip on T5 pulleys . Motor shaft is OK but not perfect. I got some 100mm ALPS pots from RS for a smaller machine, but they were nowhere near linear (though marked as such). I need to go back there.
I have thought of backlash, but my initial idea is to take baby steps first, and only correct when more than some limit out of sync. e.g. 0.5mm.
The ARM has many analogue inputs (12-30) and up to 4 ADC channels that can be used simultaneously. You could fit a 10 turn pot for coarse measurement and one or two continuous rotation pots 180 degrees out of phase to cater for the gaps / steps at the zero positions. Even preset pots will do if you replace often - they are rated for 10K or 100K revs. There’s no sense in over resolution on a printer that won’t ever do much better than 0.2mm. I always remember the Rolls Royce specification for BHP on their cars ‘Adequate’. Adequate for cruising at 100MPh in 1928.
I’ve got lots of ideas, but no time to implement them! Please pm me crowse on my gmail account.
I’ve got a proof of concept ready for firmware and testing.
Tomorrow I am off to an ST ARM training session on the new 2.4GHz devices that I hope will resolve my wiring nightmare. … Ever tried wiring 4 gantries of 4 gondolas in a 500mm cube?