UC300ETH: UCBB Vs UB1 breakout board ?

[Neale]

I don't know if this is just an academic quibble, but is there an issue with the concept of two steppers driving a single, very rigid, axis with no possibility of adjusting their relative position? I'm thinking that the typical micro-stepping driver (although possibly not the latest and greatest) will reset to the nearest full step at switch-on, and there is no reason to suppose that the "full-step" positions on both steppers will align. In the case of the typical both-ends-of-a-gantry setup, there is enough give to allow for this (and we are taking about quite small mis-alignments - a full step with a 5mm pitch screw is only 0.025mm) but auto-squaring takes this out anyway. But if this dual-drive Z axis is going to be much stiffer, is this an issue? Maybe this will be addressed at initial setup?

I believe that some newer stepper drivers will maintain micro-step position across switch off/on, which might help.

[JAZZCNC]

I don't know if this is just an academic quibble, but is there an issue with the concept of two steppers driving a single, very rigid, axis with no possibility of adjusting their relative position? I'm thinking that the typical micro-stepping driver (although possibly not the latest and greatest) will reset to the nearest full step at switch-on, and there is no reason to suppose that the "full-step" positions on both steppers will align.

I agree with Neale on this (even though I'm probably talking myself out of a sale...Lol), the motors will always jump to the nearest full step on startup or when drive powers down and you won't know if they both go the same way. Over time this will accumulate and twist up the axis. Loosening the coupler will only work that one time and without some way to home each motor to a known location, you will need to loosen the coupler every time to be accurate or at least every other power down/up.!.

[routercnc]

OK sounds like I will have to do some testing on the steppers and see how they behave over multiple startups (w/o couplers connected).

[routercnc]

Not so keen on 2 motors off one driver.

Also for step alignment I will loosen one coupling, turn them on, then tighten the coupling. I think this will get the motors aligned internally.

Here is the machine as a reminder:

[routercnc]

Hang on. Is this any different to how I have been running this machine for several years? I have 2 identical stepper motors wired the same way to identical stepper drivers. They have their own step/dir signals but as these are slaved they should be the same. When I first built it I aligned the motors to full step with loose couplings and have not touched it since. Z axis sounds smooth as the day it was built. Only difference with the update is running off the same dir and step outputs.

[dazp1976]

I've only just really started wiring mine up. Hasn't turned out as well as I wanted. Everything is bigger than I thought and the box I got is a bit tight. Uc300 stacked on Ucbb.






I also have a second Ucbb that will go on the stilts between the existing bb and 300. This is in case I end up going to full servo control on all axis.

[JAZZCNC]

Hang on. Is this any different to how I have been running this machine for several years? I have 2 identical stepper motors wired the same way to identical stepper drivers. They have their own step/dir signals but as these are slaved they should be the same. When I first built it I aligned the motors to full step with loose couplings and have not touched it since. Z axis sounds smooth as the day it was built. Only difference with the update is running off the same dir and step outputs.

If you haven't been homing each motor then Yes, it's exactly the same. I can't see how the motors won't have jumped in opposite directions at some point and if you haven't got reference marks to check against then it could be very hard to see. It would be a random occurrence and you could have just been lucky that it's not twisted up enough to show up.? Still, it wouldn't be my first choice if I'm honest.!

[routercnc]

@dazp
Wow that is busy ! Funny how you always seem to need more space than you originally think.

@Dean
I hear you. I might have been lucky all these years but I could always add a pointer on the rear output shaft of each motor and periodically check they are in the same position after homing.

[Kitwn]

If you haven't been homing each motor then Yes, it's exactly the same. I can't see how the motors won't have jumped in opposite directions at some point and if you haven't got reference marks to check against then it could be very hard to see. It would be a random occurrence and you could have just been lucky that it's not twisted up enough to show up.? Still, it wouldn't be my first choice if I'm honest.!

Surely the mechanism will relax mechanically every time the machine is switched off and turn the motors back to the same starting positions. There may be a small twist at switch-on but it won't accumulate over multiple on/off cycles.

routercnc,
Thanks for the reminder pictures.
Sounds like you're talking yourself into a redesign to have a single motor and belt for Z as you have for X (or s it Y?). Was there a good reason for not using the same technique?

Kit