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Two stepper z-axis January 14, 2016 05:27PM |
Registered: 10 years ago Posts: 293 |
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Re: Two stepper z-axis January 14, 2016 10:58PM |
Registered: 8 years ago Posts: 8 |
i doubt it is technically possible for them since this would also mean they could "miss a step" if used alone which would possibly mess up the whole print, no matter which of the motors it is.
i was more afraid that the connection between the motor and the threaded rod may slip, but not anymore because i observed them a long time and rhey stayed always in snync
(to make this easier for me i attached a cable tie to each threaded rod which i didnt cut entirely at a position where they wouldnt disturb the Print - bothy stayed always in sync so far)
i was more afraid that the connection between the motor and the threaded rod may slip, but not anymore because i observed them a long time and rhey stayed always in snync
(to make this easier for me i attached a cable tie to each threaded rod which i didnt cut entirely at a position where they wouldnt disturb the Print - bothy stayed always in sync so far)
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Re: Two stepper z-axis January 15, 2016 04:01PM |
Registered: 9 years ago Posts: 126 |
I have heard a lot of people complain about this as one of the design flaws of the the Prusa, That being said I never really made sure that mine was exactly lined up in the first place and i have never had any issues. I would guess that any small discrepancies in alignment manifest themselves as a bed that is not level, and can be fixed by simply leveling the bed.
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Re: Two stepper z-axis January 15, 2016 06:57PM |
Registered: 10 years ago Posts: 293 |
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Anonymous User
Re: Two stepper z-axis January 16, 2016 10:37AM |
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UniTrader
i doubt it is technically possible for them since this would also mean they could "miss a step" if used alone which would possibly mess up the whole print, no matter which of the motors it is.
i was more afraid that the connection between the motor and the threaded rod may slip, but not anymore because i observed them a long time and rhey stayed always in snync
(to make this easier for me i attached a cable tie to each threaded rod which i didnt cut entirely at a position where they wouldnt disturb the Print - bothy stayed always in sync so far)
Of course it can happen ! It is a major drawback of stepper motors. Luckily, 3D printers use them in a conservative way, don't require extreme accuracy and they are cheap and easy to control.
But it can be a serious issue on the Z axis, as out of sync means binding, leading to excessive wear if not serious damage to the guide rods.
ANd don't correct by leveling the bed, just correct it !
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Re: Two stepper z-axis January 16, 2016 01:54PM |
Registered: 9 years ago Posts: 126 |
I see what you are saying about the z axis binding. I definitely could see that it could cause issues, but I have never seen issues with it. I might worry more if I had leadscrews, but I still have threaded rod which have plenty of play. I could also see it being a much bigger issue with a longer lead thread, where the motors mechanical advantage is greatly reduced. But for now I'm not just going to make sure it's close, but not necessarily perfect. I don't really care if it is within 1/10th of a mm perfectly level.
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Re: Two stepper z-axis January 16, 2016 01:54PM |
Registered: 9 years ago Posts: 126 |
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Anonymous User
Re: Two stepper z-axis January 16, 2016 03:55PM |
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Re: Two stepper z-axis January 16, 2016 06:38PM |
Registered: 8 years ago Posts: 7 |
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MKSA
Much more expensive, complex and not required. Two lead screws, timing belt and one stepper.Quote
AudaciousTuddle
I will also advocate a closed loop control system, I would love to see a encoder on the motor. That solves all these problems.
Belt issues or second stepper issues, either way there are issues, the second stepper imo is the lesser of two evils.
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Re: Two stepper z-axis January 17, 2016 04:36AM |
Registered: 9 years ago Posts: 3,525 |
There are designs for 1 motor z axes for the i3 lovely one on thingiverse but a bit complicated [www.thingiverse.com]. I'm working on a super simple one with 2 pullets and a belt. Not sure if one motor without gearing will have enough power but I can substitute in a geared motor. Will post pics when parts arrive.
For what it's worth I think the 2 motors definitely Utley go out of sync over time.
Edited 1 time(s). Last edit at 01/17/2016 04:37AM by DjDemonD.
For what it's worth I think the 2 motors definitely Utley go out of sync over time.
Edited 1 time(s). Last edit at 01/17/2016 04:37AM by DjDemonD.
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Re: Two stepper z-axis January 17, 2016 06:31AM |
Registered: 11 years ago Posts: 444 |
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Re: Two stepper z-axis January 17, 2016 08:11AM |
Registered: 9 years ago Posts: 126 |
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DjDemonD
There are designs for 1 motor z axes for the i3 lovely one on thingiverse but a bit complicated [www.thingiverse.com]. I'm working on a super simple one with 2 pullets and a belt. Not sure if one motor without gearing will have enough power but I can substitute in a geared motor. Will post pics when parts arrive.
For what it's worth I think the 2 motors definitely Utley go out of sync over time.
Here is a link that might help you in your designs. [en.m.wikipedia.org] Those equations will help you calculate how much torque you will need. Also if yours works with a belt, then you don't need gears, just make your pulleys different sizes to get the mechanical advantage you are looking for.
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Re: Two stepper z-axis January 17, 2016 09:52AM |
Registered: 9 years ago Posts: 3,525 |
Thanks. I wasn't planning to drive it from the belt, my idea is to replace one motor with a pillow bearing to support the tr8 leadscrew and leave the other motor in place. Since I have bearings supporting the tops of both leadscrews, I plan to join the two leadscrews at the top with 20t pulleys and a closed belt. There will have to be a spring loaded idler to tension the belt once it's installed.
Edited 1 time(s). Last edit at 01/17/2016 09:52AM by DjDemonD.
Edited 1 time(s). Last edit at 01/17/2016 09:52AM by DjDemonD.
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Re: Two stepper z-axis January 18, 2016 07:49AM |
Registered: 9 years ago Posts: 1,873 |
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AudaciousTuddle
I would guess that any small discrepancies in alignment manifest themselves as a bed that is not level, and can be fixed by simply leveling the bed.
Nope, not that simple. If the X-axis is not square to the Z-axis then everything you print will be out of square to exactly the same extent. For the amount of error that is possible before the Z axis binds up it may or may not matter to you, depending on what you print and what your expectations are.
I used one motor and a belt in a triangle config. No problems with power using a standard nema 17 motor and leadscrews with 8mm pitch.
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Re: Two stepper z-axis January 18, 2016 08:34AM |
Registered: 9 years ago Posts: 126 |
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JamesK
Nope, not that simple. If the X-axis is not square to the Z-axis then everything you print will be out of square to exactly the same extent. For the amount of error that is possible before the Z axis binds up it may or may not matter to you, depending on what you print and what your expectations are.
I used one motor and a belt in a triangle config. No problems with power using a standard nema 17 motor and leadscrews with 8mm pitch.
Ok I see what your saying, I guess that I haven't run enough parts where the xy angle was crucial enough to matter, most of my parts tend to be under 25mm tall, and 1 degree just doesn't matter that much at 25mm. i also design in a lot of allowances, which would cover a lot of the printers imperfections.
On a different note, 8mm seams like a really long lead, do you have problems with holding torque? (I.e. Does the axis drop when you turn of the power?) or do you have some sort of mechanical advantage with your pully system?
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Re: Two stepper z-axis January 18, 2016 08:54AM |
Registered: 9 years ago Posts: 1,873 |
8mm lead is fairly standard on the lower priced lead screws. It looks like less because it's a 4-start thread. You get a very small drop when the Z stepper is powered off, probably the difference to the nearest full step position, so you do need to make sure the Z stays powered up after homing. If I take the belt off, the Z axis will just about fall under gravity, but it took a lot of work to get it to run that freely - I didn't do a great job on the design of the Z axis. Live and learn!
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Re: Two stepper z-axis January 18, 2016 10:53AM |
Registered: 9 years ago Posts: 3,525 |
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Re: Two stepper z-axis January 18, 2016 01:36PM |
Registered: 9 years ago Posts: 126 |
so apparently I'm ready to upgrade. I just found these [www.ebay.com]. Im going to try to upgrade to these now. I have two sets on the way.
Edited 1 time(s). Last edit at 01/18/2016 01:46PM by AudaciousTuddle.
Edited 1 time(s). Last edit at 01/18/2016 01:46PM by AudaciousTuddle.
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Re: Two stepper z-axis January 18, 2016 01:36PM |
Registered: 9 years ago Posts: 126 |
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Re: Two stepper z-axis January 18, 2016 01:36PM |
Registered: 9 years ago Posts: 126 |
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Re: Two stepper z-axis January 18, 2016 02:07PM |
Registered: 9 years ago Posts: 3,525 |
What motors have you got? I think you would be surprised even with TR8 leadscrews, as long as the leadscrews and smooth rods are well aligned a pair of standard 1.8 deg steppers work just fine, and thats not with the current set to a level that heats the motors. I am waiting to see if a single motor will be able to manage but plenty of people with corexy machines are lifting a z carriage with 2 or 3 leadscrews driven off 1 motor, might have to be geared 3:1 or similar with belts/printed gears, but should be doable.
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Re: Two stepper z-axis January 18, 2016 02:11PM |
Registered: 9 years ago Posts: 1,873 |
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Re: Two stepper z-axis January 19, 2016 03:16PM |
Registered: 9 years ago Posts: 126 |
I'm not worried about them not having enough torque, I just don't like the idea of them slumping when the power is cut off. I don't want it to cut the power after a print and have the still hot, hot end embed itself into my print. I want one that will hold its position when it is not powered.
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Re: Two stepper z-axis January 19, 2016 03:22PM |
Registered: 9 years ago Posts: 1,873 |
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Re: Two stepper z-axis January 19, 2016 07:47PM |
Registered: 9 years ago Posts: 126 |
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Re: Two stepper z-axis January 19, 2016 08:23PM |
Registered: 9 years ago Posts: 1,873 |
[edit - I messed up by a factor of 10 in the original version, update to more rational numbers below]
I guess the advantage of those fine pitch screws would be more freedom to choose layer heights. With 8mm lead I'm limited to multiples of 0.04mm, which doesn't bother me when I'm using 0.2, 0.24 and 0.28, but might be a bit of a pain if you regularly want to work around the .1mm area and you're stuck with either 0.08 or 0.12, which is a pretty big jump. Maybe give the ones you've got a go and see how it works out? The trade off will be reduced travel speed, but that's not such a big deal in Z.
Edited 1 time(s). Last edit at 01/20/2016 10:07AM by JamesK.
I guess the advantage of those fine pitch screws would be more freedom to choose layer heights. With 8mm lead I'm limited to multiples of 0.04mm, which doesn't bother me when I'm using 0.2, 0.24 and 0.28, but might be a bit of a pain if you regularly want to work around the .1mm area and you're stuck with either 0.08 or 0.12, which is a pretty big jump. Maybe give the ones you've got a go and see how it works out? The trade off will be reduced travel speed, but that's not such a big deal in Z.
Edited 1 time(s). Last edit at 01/20/2016 10:07AM by JamesK.
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Re: Two stepper z-axis January 20, 2016 09:51AM |
Registered: 9 years ago Posts: 126 |
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Re: Two stepper z-axis January 20, 2016 10:06AM |
Registered: 9 years ago Posts: 1,873 |
Yes, you're right - brain fart. Reading through my previous comment you can see it's not self-consistent, .2 .24 and .28 being 0.04 apart, not .4. Principle still applies, except makes more sense with the decimal in the right place: stuck with 0.08 or 0.12, which is a pretty big jump". You want to stick to whole steps for the layer heights to reduce the potential for one of the causes of Z wobble. It's still worth using microstepping on Z for the quieter motion, but it's best to keep layer heights to multiples of the full step distance.
Sorry for any confusion caused by the previous post.
Sorry for any confusion caused by the previous post.
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Re: Two stepper z-axis January 20, 2016 10:11AM |
Registered: 9 years ago Posts: 126 |
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Re: Two stepper z-axis January 20, 2016 12:53PM |
Registered: 9 years ago Posts: 3,525 |
It's not much of an issue with fine leadscrews or 0.9 deg steppers. With 2mm lead and 1.8 deg motors the full step distance is 0.01mm so all obvious layer heights are multiples of your full step distance, but with 8mm lead it is worth bearing in mind. It's not particularly limiting though 0.12mm should be indiscernable from 0.1mm but will print 20% faster and have fewer layer artifacts (assuming 1.8 deg motors and 8mm lead).
Edited 1 time(s). Last edit at 01/20/2016 06:10PM by DjDemonD.
Edited 1 time(s). Last edit at 01/20/2016 06:10PM by DjDemonD.
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