Keep Motors energised when changing assignment

sotpurk

@Phaedrux It would be very expensive for me to swap the motors or attach brakes to the same. As a last resort, I'd much rather move to external drivers since an enable pin would solve all my issues, but to do that I'd have to buy a 6XD or 4 1XD boards which would result in about the same price so yeah still quite expensive. And either way would result in more points of failure.

And since this is something that possibly could be done in software, I'd much rather do that.

deckingman

@sotpurk It sounds to me that having 80Kg of mass that can fall if power is not applied to motors, is a somewhat hazardous thing to do. You say you have 4 lead screws so I assume that they auto rotate when power to the motors is lost. That must be due to using very course lead screws which have a steep helix angle. In which case, I can't help thinking that a better solution to all your problems would be to use finer lead screws with a shallower helix and which will not auto rotate. The knowledge that 80Kgs of mass can come crashing down if power is lost for ANY reason, would certainly scare the crap out of me.

sotpurk

@deckingman I'm not using leadscrews, I've made a custom chain + sprocket assembly that the gantry runs up and down on.
There's a 10:1 worm gearbox between the sprocket and motor. I figured a worm gearbox would not be back-driven but I seem to have selected a lower ratio than required. My current solution to that is to switch the sprockets to smaller-diameter ones or switch the gearboxes to a higher ratio.
I'm leaning toward the latter.

Even still assuming the gantry doesn't fall down, I'd like for it to be rock solid in place when the entire actuator-based leveling happens which takes us back to the previous issues.

P.S.: The mounts are only printed to test and will be CNC'd later on.

deckingman

@sotpurk Sorry but there are too many contradictions for me to keep up. In your OP, you stated that when motors are de-energised, the 80 Kgs of mass falls and you want to prevent that happening. My point is that when power is lost for any reason, that 80Kgs of mass is still going to fall. So to my mind, this is a mechanical problem which requires a mechanical solution. Preventing the motors from de-energising when you re-map them isn't going to help if power is lost for some other reason.

sotpurk

@deckingman I apologize if my description was confusing.
I will fix the gantry falling by replacing the gearboxes so the gantry falling when power is lost isn't an issue.

The problem is only when reassigning the axes while the machine is powered on do the motors lose energy. Now the axis won't fall when that happens even if the motors are not energized, but since it'll be probing the weight is going to be shifting and I would like to have no lost steps.
And since it's an industrial environment I can't rely purely on the worm gears when probing hence it's important that the motors are energized.

TL;DR: What happens when power is lost is not the concern here, but keeping the motors energized while probing is.

o_lampe

@sotpurk Maybe it's as simple as adding a capacitor to the enable pins? Just to cover the short time gap between assigning and energizing...
IMHO the enable pins aren't time critical part of the motion planner, so adding a bit of delay won't harm.

I remember having all drivers on my DIY Duet2 extension board permanently enabled and IIRC the DUEX5 only has one enable pin for all drivers as well.
@T3P3Tony am I right?

T3P3Tony

@o_lampe @sotpurk AFAIK to kepe the motors enabled when switching between assignments would need a firmware change so I am moving this to the firmware wishlist.

sotpurk

@o_lampe Oo that's neat and would solve the issue. Thanks.
I just checked the schematics. All the enable inputs seem to be tied to a single pulled-up line from the MCU.

I'll try this out as soon as I get a chance. Thanks again.

dc42

@sotpurk the enable/disable of individual drivers is done using SPI commands to them. The global enable pin is only used to prevent the drivers being enabled before they have been initialised and for emergency stop.

o_lampe

@dc42 @sotpurk
A dropping bed because of pushing the emergency button sounds like a nightmare.
Is there a way to mask which motors should stay enabled during a reset?
Maybe use M569 for it? Would it be NIST compatible?

T3P3Tony

@o_lampe if the bed has to remain still during a firmware reset (different issue from what the OP was discussing with axis remapping) then the correct solution is to use brakes on the motors, or potentially in some situations geared motors.

sotpurk

@T3P3Tony @o_lampe
Yes, have ordered new gearboxes(worm) with higher ratios to mitigate this issue.
The problem with the motors de-energizing when changing assignments still remains though.
I messed around with the firmware but couldn't produce any results.
It seems to be a firmware limitation as was said before and to move forward I've ordered a 6XD with drivers so that I can control the enable and power separately; hopefully that should be enough to get the levelling logic working reliably.