Another small update.
I've changed the motor drive pulley from 20 to 30.
so the new values are:
The motor steps per deg is 222 @ X2 microstepping. 0.0045 deg per step. Mechanical
The incremental outputs from the 21bit encoder are 65535 0.0055 deg per step.
The backlash of the gearbox = 100 steps plus 45 for the elasticity of the belt.
The belt has settled in some and is now 60.
The carrier board for the DRV8825 came so I set up a test to compare to the DM556, for the spindle.
At the same voltage and current the DRV8825 performs poorly being unable to run at the same accelerations and speeds.
The difference is stark.
I have been using the DRV8825 for the brake where it has performed ok as the speed requirements are far less.
I done a lot of tests that run the batteries to exhaustion and depending on the test ran, the batteries
last between 2 and a half and 3 hours.
In comparison the Tool changers last months because the motors are turned off once a tool has been selected.
At the start I figured that a job might only take half an hour or maybe an hour at most so I would be good with the batteries if
I remembered to charge the batteries afterwards.
In part this was because the brake mechanism worked so well, it had lots of resolution and had a linear response, it also was easy
to mount, it had a lot going for it as a mechanism.
It's flaw is that it requires continuous power while the brake is in it's fully on position.
I didn't really want to change it (and didn't think that I could fit a screw mechanism in the same space) so went down a bit of a rabbit hole
looking for a toggle latch mechanism so that I could turn the motor off when it was in it's braked position.
I did find some which I 3d printed and tested none of which would hold the brake on completely
some were close as I couldn't turn the chuck with my hands but could with a 300 mm cheater bar.
In the end I went back to the linear actuator idea with a thread, see pic.
I've made the main body and fitted the bearings and made and threaded the endcap, I've also used a length of threaded rod locked it into the
housing and held the endcap to get a sense of how much force will be required for turning the threaded rod until the brake locks up, it's not a lot
and I can get away with a small stepper like the one in the pic. The stepper has a worm gear on it so I'll 3d print a worm wheel to suit. If the worm
wheel doesn't hold up I had a look and you can get module one in sets in nylon and there not expensive.
Dave
