CoreXY 2:1 belt ratio double torque and resolution ?
April 16, 2019 04:48AM
Would adding the four middle pulleys double the torque and resolution ?



Edited 1 time(s). Last edit at 04/16/2019 04:48AM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 16, 2019 06:56AM
It looks like it would do that. Are you building a large printer using small motors?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 16, 2019 07:04AM
No not really, just thinking of a smallish printer with finer steps and better acceleration. Just ideas at the moment.

Seems a waste to have the ability to go fast with normal setup (say 250mm/sec with 20 tooth pulleys) and not really be able to use it, so why not reduce top speed by 2 with the added benefit of double the resolution and torque ?
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 16, 2019 03:11PM
If it's a small printer, what's the benefit of doubling the torque?

An easier way to increase resolution (if you need to) is to use 0.9deg motors and 16-tooth motor pulleys.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 16, 2019 04:26PM
Quote
Pippy


........................Seems a waste to have the ability to go fast with normal setup (say 250mm/sec with 20 tooth pulleys) and not really be able to use it.......................,

My vote would be as DC42 says - simply use 0.9 degree motors.

On the other, you could capitalise on the speed capabilities and print at 300 mm/sec plus as I demonstrated here [somei3deas.wordpress.com] and here [www.youtube.com]

Even if you don't use multiple melt chambers to achieve high print speeds, you might find that 250mm/sec plus is very useful for non-print moves as it reduces the time that filament can "ooze" and allows you to reduce the amount of retraction needed to prevent stringing. I use 350mm/sec for non print moves even when printing slowly at 90mm/sec with a single melt chamber.

Oh and by the way, my moving mass is about 3kgs. Increasing the available torque will only allow you to accelerate a mass faster, but as the melt rate of the filament is the limiting factor then you won't be able to make use of that increase in torque in any case.

Edited 2 time(s). Last edit at 04/16/2019 04:30PM by deckingman.


[somei3deas.wordpress.com]
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 02:04AM
The 250mm/s is with 2:1 belt ratio, I forgot I'd calculated that WITH the 2:1 belt ratio change. I'm running the motors at 4 microstepping rather than the usual 16, as you get quite a bit more torque and top speed at lower microstepping it seems, plus it prevents Marlin from switching to double stepping, and the noise level is not really any different to 16 microstepping when using TMC drivers. Another reason for choosing 4 over 16 was the non-linerarity that you get with the actual real world position of the stepper motor and microstepping, the TMC look-up table in the chip really ought to be calibrated for the stepper motor in use when using u-stepping, which is mostly not done.

But, as the boost in acceleration couldn't really be used (as you've shown Ian) you guys are no doubt right about not needing the 2:1 belt reduction. Though I guess it would reduce the load on the motors by half.

That's a lovely machine you've created Ian ! and so is Marks !

V-slots and wheels sure does simplify a printers mechanics, and doesn't appear to affect resolution/accuracy etc over other methods, I guess ?

Edited 2 time(s). Last edit at 04/17/2019 03:09AM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 03:08AM
Quote
dc42
An easier way to increase resolution (if you need to) is to use 0.9deg motors and 16-tooth motor pulleys.

Yes probably easier, but it would mean buying new motors (extra cost), I have 1.8deg motors and 20-tooth pulleys to hand.

Don't 0.9 deg motors have less torque and top speed than 1.8 deg motors ? .. I've not tested 0.9's so not sure, but curious.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 03:11AM
Quote
Pippy
I'm running the motors at 4 microstepping rather than the usual 16, as you get quite a bit more torque at lower microstepping it seems

That's a myth. Going from full stepping to half stepping reduces torque (and motor heating). Increasing microstepping further doesn't reduce torque.

Quote
Pippy
plus it prevents Marlin from switching to double stepping,

That's probably worthwhile, because microstep interpolation in the TMC drivers won't work well when Marlin is double stepping.

Quote
Pippy
and the noise level is not really any different to 16 microstepping when using TMC drivers.

That's because the Trinamic drivers are interpolating to x256 microstepping. Which again makes the point about higher microstepping not reducing torque.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 03:36AM
Quote
dc42
Quote
Pippy
I'm running the motors at 4 microstepping rather than the usual 16, as you get quite a bit more torque at lower microstepping it seems

That's a myth. Going from full stepping to half stepping reduces torque (and motor heating). Increasing microstepping further doesn't reduce torque.

I've been testing various combinations of microstepping and motor current etc, the one thing I found was motor stalling with 16 microstepping as compared to 4 microstepping at the same high speed setting, I had to go from 250mm/s (with 2:1 belt ratio) with 4 microstepping down to approx 220mm/s when using 16 microstepping to prevent motor stall.

I'm using 1.7A 4mH 48mm long motors, TMC2208 drivers (UART configuring).
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 05:54AM
Quote
Pippy


V-slots and wheels sure does simplify a printers mechanics, and doesn't appear to affect resolution/accuracy etc over other methods, I guess ?

Well that kind of depends. The comment about accuracy and resolution is certainly true for OpenBuilds V-slot and proprietary Open Builds double bearing Delrin wheels running on "axels" which are supported at both ends, and then only if they are correctly assembled with the correct pre-loading on the eccentric bushes. It would not be true for "shower curtain wheels". Even so, I have seen quite a few examples of printers using OpenBuilds V-slot that have problems but they are always due to poor design with the "axels" only supported at one end, or assembly issues due to incorrect tensioning of the eccentric spacers, or the rails not being parallel.

OpenBuilds V-slot does simplify the mechanics somewhat because any frame member can also be a linear guide. On the other hand, carriages tend to be quite large compared to other types of linear guide. If noise is a concern, then using OpenBuilds V-slot is good because carriage movement is virtually silent. If cost is a concern, the OpenBuild V slot is not such a good idea. The biggest cost (which isn't obvious) is the price of the wheel kits which work out at roughly £10 a set and you need 3 to 4 sets per carriage. At the last count, my printer which now has 3 CoreXY gantries (one for the hot end, one for the 5 extruders and a third which acts as a load balancing/ force cancelling gantry) uses 60 sets of wheels which is 2 to 3 times what many people spend on a complete printer.


[somei3deas.wordpress.com]
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 07:03AM
If you really want high resolution, and have deep pockets, you could use 5 phase steppers. They usually come in either 500 or 1000 full steps per rev. You can sometimes find surplus motors with matching drivers on ebay for <$100. You have to be careful if you get motors and drivers from different sources. Some motors are wired for "pentagon" drive, and some for star drive. The drivers have to match the motor type. Not all the drivers can do microstepping, but it looks like most will do 1/2 steps.

Try this for the search: 5 phase stepper motor -4 phase -two phase -3phase -2 phase

Edited 1 time(s). Last edit at 04/17/2019 07:10AM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 07:40AM
Quote
deckingman
At the last count, my printer which now has 3 CoreXY gantries (one for the hot end, one for the 5 extruders and a third which acts as a load balancing/ force cancelling gantry) uses 60 sets of wheels which is 2 to 3 times what many people spend on a complete printer.

That's a little out of my price range winking smiley

But I'd certainly like to try the V-slot and wheels method, I do like simplicity as it's always the best route to go by.

Thank you for the info, it's invaluable !

Edited 1 time(s). Last edit at 04/17/2019 07:43AM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 07:42AM
Quote
the_digital_dentist
If you really want high resolution, and have deep pockets, you could use 5 phase steppers. They usually come in either 500 or 1000 full steps per rev. You can sometimes find surplus motors with matching drivers on ebay for <$100. You have to be careful if you get motors and drivers from different sources. Some motors are wired for "pentagon" drive, and some for star drive. The drivers have to match the motor type. Not all the drivers can do microstepping, but it looks like most will do 1/2 steps.

Try this for the search: 5 phase stepper motor -4 phase -two phase -3phase -2 phase

I never knew they did more than 2 winding steppers. You live and learn every day.

Fascinating stuff, thank you !
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 08:29AM
Quote
dc42
An easier way to increase resolution (if you need to) is to use 0.9deg motors and 16-tooth motor pulleys.

Moving to 16 tooth drive pulley would be nice because that produces 0.02mm per step rather than 0.025mm per step .. nice to have more rounded numbers, not that it makes any difference at that level with home built 3D printing really.

The reason for me was mainly to reduce motor load. The added benefit of torque, acceleration and resolution is there if ever it was required.

Edited 2 time(s). Last edit at 04/17/2019 09:00AM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 10:57AM
Another idea which might be a little less complex than your OP, and one that I have considered myself, is to replace the motor with a shaft which would hold two pulleys - one 20 tooth and the other 40 tooth. Then mount the motors to the side with 20 tooth pulleys and a short belt to the 40 tooth pulley on the shaft. That would give you the 2:1 gearing. The reason why I had considered it was not to do with increasing torque but more to do with belt tensioning. I need to do some research and maybe take a stepper motor apart but I have a nagging doubt that the stepper motor bearings might not be up to the axial loads that the optimum belt tension would produce over a long term. So remotely mounting the motors might allow a higher belt tension on the carriage without unduly stressing the motor bearings. This might, or might not be desirable. It's on my (long) list of things to investigate.


[somei3deas.wordpress.com]
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 11:12AM
Yes that's possible, though I don't think the middle pulleys in the OP are that difficult to add really.

But in another design I have added an extra support bearing for the motor because I don't like having the constant sidewards force from a tensioned belt on the motor bearings and shaft alone.

It's just a 5mm bore flange bearing.

It doesn't remove the pressure from the motor bearings and shaft but it does half it and removes the possibility of a bent motor shaft.

But yes, I like the idea of moving the motor off the main tensioned belt in the way you describe.





Edited 2 time(s). Last edit at 04/17/2019 11:25AM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 17, 2019 03:46PM
Quote
Pippy
I've been testing various combinations of microstepping and motor current etc, the one thing I found was motor stalling with 16 microstepping as compared to 4 microstepping at the same high speed setting, I had to go from 250mm/s (with 2:1 belt ratio) with 4 microstepping down to approx 220mm/s when using 16 microstepping to prevent motor stall.

That's probably because your electronics/firmware combination can't generate smooth step pulse trains at high speeds when using x16 microstepping. Smooth step pulse trains are especially important at high speeds, particularly if you have microstep interpolation enabled in the drivers. (That's one of the reasons why we stopped using double etc. stepping in RepRapFirmware. Servo drives hate non-smooth step pulse trains even more.)

Edited 2 time(s). Last edit at 04/17/2019 03:51PM by dc42.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 11:58AM
Couldn't you just get some inexpensive brass gears and do the same thing that way with less cost and complexity?
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 12:20PM
Quote
dc42
Quote
Pippy
I've been testing various combinations of microstepping and motor current etc, the one thing I found was motor stalling with 16 microstepping as compared to 4 microstepping at the same high speed setting, I had to go from 250mm/s (with 2:1 belt ratio) with 4 microstepping down to approx 220mm/s when using 16 microstepping to prevent motor stall.

That's probably because your electronics/firmware combination can't generate smooth step pulse trains at high speeds when using x16 microstepping. Smooth step pulse trains are especially important at high speeds, particularly if you have microstep interpolation enabled in the drivers. (That's one of the reasons why we stopped using double etc. stepping in RepRapFirmware. Servo drives hate non-smooth step pulse trains even more.)

But that's just not the case, from testing here.

Though yes the 8-bit board is limited due to lack of processing speed.

We get 400mm/s WITH the 2:1 belt reduction on the 32-bit board (16 micro stepping), 20 tooth drive pulley, clean stepper pulse train (on the scope), TMC2208 at 1amp, 256 interpolation enabled, 24V.

Their is a notable torque difference between 16 micro stepping and 4 micro stepping (at full motor speed), We're certainly getting more torque with 4 micro stepping, it takes more effort to stall the motors at 4 than it does at 16.

The TMC2208's are configured to switch from StealthChop2 to SpreadCycle at 1/3 the top speed (400mm/s).

We're only going from what we're finding here. Try it ?

Edited 3 time(s). Last edit at 04/18/2019 01:33PM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 12:32PM
Quote
obelisk79
Couldn't you just get some inexpensive brass gears and do the same thing that way with less cost and complexity?

Gears add backlash if you're not careful, though you can remove the backlash with careful gear selection etc.

We don't think adding 4 little pulleys is difficult or complicated, particularly if you're capable of building an entire printer.
We're actually finding such resistance against the 2:1 belt idea really strange, such a weird forum what with the other goings on.

Edited 1 time(s). Last edit at 04/18/2019 12:35PM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 12:51PM
I'm not resistive to the extra pulleys.

But like most things in life there are more than one way to solve any particular set of problems.

Additionally, increasing resolution through the use of 2:1 gears would minimize the effects of any imposed backlash in the system which should only really manifest motor direction changes, provided you aren't using terrible gears that is. Also, matched sets of reasonable quality gears don't seem hard to find at low price points. Another consideration/question, wouldn't adding the extra belt paths pose a potential concern with relation to the parallelism of the belts? In your belt design haven't you added new belt paths where the parallelism of the belt paths is critical?

I'm just here to engage in a discussion as an enthusiast hoping to learn more and share ideas. I'm not here to say your design is dumb or pointless.

Edited 2 time(s). Last edit at 04/18/2019 12:53PM by obelisk79.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 01:24PM
Quote
obelisk79
I'm just here to engage in a discussion as an enthusiast hoping to learn more and share ideas. I'm not here to say your design is dumb or pointless.

That's nice of you obelisk, good on you smiling smiley

Well, the idea's now there for anyone to try and play with. It's no bad thing to share these things. After all, it's where the fun does lay. Go forth and experiment I say !

Anyway, yes gears are OK too, though as Ian (deckingman) suggested, I'd probably go for the belt version (small drive pulley belted to larger pulley) rather than brass gears, less noisy and cleaner.

Edited 1 time(s). Last edit at 04/18/2019 01:24PM by Pippy.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 18, 2019 03:49PM
Quote
Pippy
Quote
dc42
Quote
Pippy
I've been testing various combinations of microstepping and motor current etc, the one thing I found was motor stalling with 16 microstepping as compared to 4 microstepping at the same high speed setting, I had to go from 250mm/s (with 2:1 belt ratio) with 4 microstepping down to approx 220mm/s when using 16 microstepping to prevent motor stall.

That's probably because your electronics/firmware combination can't generate smooth step pulse trains at high speeds when using x16 microstepping. Smooth step pulse trains are especially important at high speeds, particularly if you have microstep interpolation enabled in the drivers. (That's one of the reasons why we stopped using double etc. stepping in RepRapFirmware. Servo drives hate non-smooth step pulse trains even more.)

But that's just not the case, from testing here.

Though yes the 8-bit board is limited due to lack of processing speed.

We get 400mm/s WITH the 2:1 belt reduction on the 32-bit board (16 micro stepping), 20 tooth drive pulley, clean stepper pulse train (on the scope), TMC2208 at 1amp, 256 interpolation enabled, 24V.

Their is a notable torque difference between 16 micro stepping and 4 micro stepping (at full motor speed), We're certainly getting more torque with 4 micro stepping, it takes more effort to stall the motors at 4 than it does at 16.

The TMC2208's are configured to switch from StealthChop2 to SpreadCycle at 1/3 the top speed (400mm/s).

We're only going from what we're finding here. Try it ?

The TMC2208 drivers should be interpolating to x256 in either case. Is the step pulse train really as smooth in x16 mode as it is in x4 mode? Are you certain that you have the changeover to spreadCycle configured correctly, and that the firmware you are using is able to perform that changeover quickly enough when it is generating step pulses at x16? It might be better to run this test in fixed spreadCycle mode.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 20, 2019 08:52PM
Quote
Pippy
Quote
dc42
An easier way to increase resolution (if you need to) is to use 0.9deg motors and 16-tooth motor pulleys.

Moving to 16 tooth drive pulley would be nice because that produces 0.02mm per step rather than 0.025mm per step .. nice to have more rounded numbers, not that it makes any difference at that level with home built 3D printing really.

The reason for me was mainly to reduce motor load. The added benefit of torque, acceleration and resolution is there if ever it was required.

How do you get .02mm? I get .08. Isn't it 2mmx16x(.9/360)
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 20, 2019 11:08PM
Quote
shortyski13
How do you get .02mm? I get .08. Isn't it 2mmx16x(.9/360)
It is niether 0.02 nor 0.08.
20 teeth x 2mm x 1.8/360 x 1/16= 0.0125
16 teeth x 2mm x 1.8/360 x 1/16= 0.01

Edited 1 time(s). Last edit at 04/20/2019 11:13PM by piper3d.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 20, 2019 11:48PM
Quote
piper3d
Quote
shortyski13
How do you get .02mm? I get .08. Isn't it 2mmx16x(.9/360)
It is niether 0.02 nor 0.08.
20 teeth x 2mm x 1.8/360 x 1/16= 0.0125
16 teeth x 2mm x 1.8/360 x 1/16= 0.01

We're not using 16 microstepping. Plus we're using 2:1 belt reduction - reduces the load on the motor and the belt.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 21, 2019 01:19AM
Quote
Pippy
We're not using 16 microstepping. Plus we're using 2:1 belt reduction - reduces the load on the motor and the belt.
So you have effective microstepping of 1/8th.

Aside from increased belt length, it is a nice idea. I may go for a similar belt schematics in the next generation of my printer.
It opens a new way to tension the belt on Y carriage.
Thank you for sharing.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 21, 2019 12:15PM
You're most welcome Piper3d.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 21, 2019 10:56PM
This is an old pic, from an ongoing coreXYU project:

Been using 2:1 belt for awhile. Mine's a 40T to 20T pulley with a 9mm wide belt.
Reason being the main dive belt is steel core, and requires a larger pulleys throughout.
My gantry also weighs a lot, with 2 steel rails and 2 direct drive carriages, so the extra torque was needed.

While the OP with the double run looks intriguing, and worth a trial.
The longer belt runs may cause additional ringing (echo print artifacts due to vibration).
Cool idea none the less.
Re: CoreXY 2:1 belt ratio double torque and resolution ?
April 23, 2019 10:26AM
That's a lovely machine prot0typ1cal !

Do you have a video of it working I wonder ?
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