Motors for DBOT corexy build



  • Hi all,

    I'm currently in the process of ordering parts for the above build. I have most of the parts I need now but am trying to nail down a choice on the steppers. For now I am going to be using 2 Z axis motors and in the future once I can print the appropriate parts, swap them out for a single motor driving the other z axis screw(s) with a belt.

    I will be running a DuetWifi with a 24V psu. The Z axis will be fairly heavy as I will be running wheels at each corner and will have a 6mm cast aluminium bed. I might also want to try motor driven bed levelling at some point which I have read may be implemented into DuetWifi in the future. To try to eliminate the Z Motors dropping out of sync after power off (before I swap the motors out) I will be using 1 start 8x2mm leadscrew.

    With all that said, my question is, is there any benefit of using 0.9 motors over 1.8 in my system? Think3dprint3d sell either but I have read that even when used on a delta, the results are debatable, so I'm not sure on a corexy. The cost is not much more over the 1.8's so is it worth just plumping for the 0.9's from the start or am I just wasting money.

    Thanks for your time!


  • administrators

    With a 2mm pitch leadscrew, your full steps/mm using a 1.8deg motor will be 100. That gives you 10um full step resolution, which is more than adequate. So I don't see any advantage in moving to 0.9deg motors. Deltas are different because the Z resolution per full step using a 1.8deg motor is typically 160um or 200um.

    I'm looking to add code to reduce the chance of the motors getting out of sync, probably in either the 1.18 or 1.19 release. The code will detect power down and turn the Z motors by up to 4 full steps so as to raise the nozzle or lower the bed so that the motors are in the correct full-step position for the subsequent power up. As long as the motors don't rotate by more than about 1 full step while the machine is powered off, they will still be in sync when the machine is powered on again. In this context, 1.8deg motors are better than 0.9deg motors, because 1 full step on a 1.8deg motor is double the amount of rotation of a 0.9deg.



  • Thanks for the info David, Is there no benefit of using them on the X/Y axis either then? I will be using 16 tooth pulleys.



  • I have been doing some research and it looks like the 0.9 is not needed at all. I am looking at these steppers in that case

    http://us.stepperonline.com/3d-printer-nema-17-stepper-motor-59ncm84ozin-2a-17hs192004s1-p-18.html

    Can anyone see any problems with these? The original BOM goes for 55Ncm and these are pretty close.

    Thanks


  • administrators

    I've never built a CoreXY printer. In theory 0.9deg motors would give you more precise positioning, but in practice I doubt you will be able to detect any difference.


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