Dual Z stepper motor sync with linear rail carriages
Posted by imotion
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Re: Dual Z stepper motor sync with linear rail carriages October 11, 2019 05:12AM |
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the_digital_dentist
There's another option- use one motor and belt the two Z axis screws together. They will never get out of sync because they can't (at least as long as the set screws in the pulleys are tight).
Why make it simpler, cheaper, better ? So much fun trying to fix issues one creates
Edited 1 time(s). Last edit at 10/11/2019 05:14AM by MKSA.
"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
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Re: Dual Z stepper motor sync with linear rail carriages October 11, 2019 05:51AM |
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MKSA
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the_digital_dentist
There's another option- use one motor and belt the two Z axis screws together. They will never get out of sync because they can't (at least as long as the set screws in the pulleys are tight).
Why make it simpler, cheaper, better ? So much fun trying to fix issues one creates
The idea is that the parts purchased will be re-purposed in any future builds. For that reason, certain selections were made (eg. the length of linear rails and motor sizes etc.) which may have exceeded the immediate requirements to get only what I was working on into an operational capacity. Had I not done so, likely half of the purchases made would be unsuitable (or insufficient in some capacity) for reuse, based on equipment requirements listed for the builds I would potentially go on to make. That includes a belt-driven Z axis, which WAS purchased - but like I said, the belt supplied was too short and another stepper motor was able to make use of the assembly and provide the dual-Z action I was seeking. Done.
"Simpler, cheaper and better" is debatable when a kit is completely dependant on a single component that isnt included. Generally, people just dont assume that coordinated design considerations were made in the first place - they assume only that poor design considerations were made. But I dont blame people for not thinking outside the box when they live in one.
I agree with the fun part, though. But only because I dig mechanical crap so much I have a trade and engineering degree in the field.
Edited 2 time(s). Last edit at 10/11/2019 05:58AM by imotion.
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Re: Dual Z stepper motor sync with linear rail carriages October 11, 2019 08:49AM |
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imotion
While I will always consider a belt driven dual Z axis, I have the same confidence in a grub screw being able to maintain the grip required to clamp a pulley to a leadscrew (unless it has been ground flat in that spot) as I do when it comes to the use of 2 seperate steppers.
Something about a motor on one side just doesnt give me the feeling that the gantry is being raised in equilibrium. I am pondering whether to throw a belt across the top and retain the motors on the bottom (both sides) to force it in sync six ways from sunday. Remembering these are pancake steppers, a bigger motor placed on one-side would most likely foul on the gantry before the nozzle was able to reach the bed - which was placed as low to the bottom of the frame as possible. Not that any loss of Z is a big problem, but the low profile bed is an important aspect of the design intended to minimise negative effects associated with non-coreXY designs (where the bed does not have to move back and forth whatsoever)
I don't know why a bigger motor placed on one side would cause a problem for the X/Z axis. This is the Z axis in one of the printers I built- the single NEMA-23 motor drives the two screws using a belt. It's about as asymmetric as you can get, but it doesn't matter - it works fine and I never have to make any adjustments to the X axis unless I take it apart which I've probably done twice in the last 5 years. The motor I used is a small NEMA-23 part- you can get NEMA-17 motors with the same holding torque. I used the NEMA-23 motor because it was already on-hand. I don't know why you'd want to use pancake motors unless you really have no space available. I like to eliminate potential problems in a design by overbuilding (yes, my printers tend to be heavy and even ugly, but they work reliably). If you're not sure how much torque you'll need to move the Z axis, use a big enough motor so that you don't have to worry about it and move on to the next problem. Refinement can come later, after things are working well. Building a machine to be duplicated 1000 times might get you thinking about minimizing parts cost by using just-right sized motors, but building a one-off machine doesn't require that sort of effort.
Here' the 695 mm Z axis in my corexy printer- entirely belt lifted. If you're into symmetry, the motor/worm gear is located at the center of an 8mm shaft that turns the two drive pulleys. This has been working well with minor changes for the last 3 years. The small, 2A, NEMA-23 motor came mounted on the 30:1 worm gear reducer that holds the bed position even when power to the Z motor is off. I operate it at just over 1A and it barely rises above ambient temperature and still has plenty of torque to lift the bed assembly and about 4 kg of print (which will never happen).
Recently, I have changed to glass core belts, larger drive pulleys, flipped the bed lifting brackets, and redesigned the belt clamps. A little lock-tite on the pulley set screws (and flattened shaft) ensures that they aren't going anywhere.
Neither of those printers has any sort of bed sensing other than an endstop switch to set the Z=0 position. Both can be transported across town in my car, stood back up, and started printing without adjustment.
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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Re: Dual Z stepper motor sync with linear rail carriages October 22, 2019 03:08AM |
Nice. I am starting to lean more and more towards a belt at the moment. I cant really find a lot of information about how reliable (long term) the prusa i3 slam-the-x-axis-into-the-top-of-the-frame-to-align calibration method is, I would prefer something which didnt degrade over time (if that is the case). That is the current objective at the moment, however (after I tweak the firmware to perform that maneuver), before coming back down to level the bed with a sensor.
As for pancake steppers, my bed arrangement was carried out to keep the bed as low as possible, for a number of reasons. You can see how low it is now with the pancakes before the bracket bottoms out on the motor. If I were to switch to a single motor, its not hard to see where the coupling would sit and where the new, lowest possible Z would be about 1 inch higher and I would need to space the bed that much higher as well, raising that center of gravity I want to keep low.
What I didnt think of until now was mounting a bigger (single) Z axis stepper motor at the top of the frame in the center, between the 2 leadscrews (with belt pulleys on both). Not sure of the best way to do that so it's out of the way of a direct drive extruder and filament roll.
Not a *huge* fan of floating/hanging leadscrews, but cant see that causing too much of a problem. I assume something that can support the screws at the bottom would exist, like a bearing that isnt a through-hole.
But I couldnt agree more with building stuff right the first time. My mistake was not doing 1 thing at a time - mind you, not neccesarily possible in my case - it always feels like a forever wait for the next part to arrive and I wonder how much longer until I can use the thing.
Edited 2 time(s). Last edit at 10/22/2019 06:29AM by imotion.
As for pancake steppers, my bed arrangement was carried out to keep the bed as low as possible, for a number of reasons. You can see how low it is now with the pancakes before the bracket bottoms out on the motor. If I were to switch to a single motor, its not hard to see where the coupling would sit and where the new, lowest possible Z would be about 1 inch higher and I would need to space the bed that much higher as well, raising that center of gravity I want to keep low.
What I didnt think of until now was mounting a bigger (single) Z axis stepper motor at the top of the frame in the center, between the 2 leadscrews (with belt pulleys on both). Not sure of the best way to do that so it's out of the way of a direct drive extruder and filament roll.
Not a *huge* fan of floating/hanging leadscrews, but cant see that causing too much of a problem. I assume something that can support the screws at the bottom would exist, like a bearing that isnt a through-hole.
But I couldnt agree more with building stuff right the first time. My mistake was not doing 1 thing at a time - mind you, not neccesarily possible in my case - it always feels like a forever wait for the next part to arrive and I wonder how much longer until I can use the thing.
Edited 2 time(s). Last edit at 10/22/2019 06:29AM by imotion.
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