You are not logged in. Please login or register.
SoliForum - 3D Printing Community → Hacks & Mods → Replacing Y-axis with direct drive..
Is there a big win in replacing the current Y-axis pulley and belt system with a stepper motor directly driving the shaft?
It seems like the shaft wouldn't move back and forth so much, a fairly constant problem on my SD4 that means realigning the belts about once a month, a very finicky thing.
What Stepper motor, flexible coupling and shaft would be required to do this?
Thanks..
Scott
Yes. It eliminates a potential source of backlash. For me, it eliminated the issue where the infill was not touching the perimeter sometimes. IMO, this is the 3rd most important mod to have a happy printing experience. (1st is glass bed, 2nd is E3D. Just my opinions). This has been covered several times on here, try the search function.
You should strongly consider adding a pillow block or two while you've got it apart. Use the stock stepper motor, just take the pulley off. 5x6 mm couplings are cheap on ebay or there are printable designs out there that may or may not work well. The shaft is 6mm. A few people have upgraded to 8mm for increased rigidity but this involves taking out the bushings and buying new pulley's. You would probably go for GT2 belts if you are doing 8mm rods, I haven't seen 8mm bore MXL pulleys out there and MXL (stock) belts are not the best anyway.
It is the single best upgrade you can make to your machine, in my opinion. The precision is freaking ridiculous, and lash is essentially eliminated at the shaft if you use the right coupler. For an idea of my printer's precision with direct drive, I can push a 6x13x5mm flanged bearing into a 13mm printed hole. It will fix a lot of issues you didn't even know were drive related. It is also not picky about the side belt tensions--as long as they are even enough that the rod doesn't slide away from the coupler, you should experience no visible lash despite inconsistent tensioning. As the motor is now at a mechanical advantage, as well, the Y axis is much more difficul to bind up.
I use this mount for the motor:
http://www.thingiverse.com/thing:593006
And this coupler:
http://us.misumi-ec.com/vona2/detail/11 … 665%3A%3A6
And a new 6mm drive shaft.
Had I done this sooner, I wouldn't have been bogged down by circles from the start. It's nice having a machine that has an accurate Y axis. Direct drive is like flipping the high quality switch!
Yes, noticeable change in the prints result, easy and very cheap to do.
Jago, that coupler from Misumi is 28 bucks. Is it really any better than the Chinese couplers on ebay for about $4? My $4 one seems to work fine.
Jago, that coupler from Misumi is 28 bucks. Is it really any better than the Chinese couplers on ebay for about $4? My $4 one seems to work fine.
It just depends on how well you can get the rods aligned. That particular one is an oldham coupler, what kind are the ones on eBay? The oldham coupler is a strong choice in my opinion, but there are many others. I like the oldham because it is forgiving of poor alignment--my motor and drive shaft are not perfectly centered, but the oldham coupler prevents varying resistance as the carriage rolls, within reason.
Part of the high cost is Misumi markup, but I spent the $$ because I knew the tolerances would be very usable. It's also not made in the U.S.--package said Vietnam, I think.
I don't know much about the different kinds, but I use this one:
http://www.ebay.com/itm/Flexible-5x-6mm … 1c2a9e9002
So its more like $8 but there are cheaper ones too.
Are there any mods or settings that need to be changed or is it strictly hardware?
Are there any mods or settings that need to be changed or is it strictly hardware?
Strictly hardware. The same motor is turning the same shaft in the same direction, you've just eliminated the belts and gears.
I don't know much about the different kinds, but I use this one:
http://www.ebay.com/itm/Flexible-5x-6mm … 1c2a9e9002
So its more like $8 but there are cheaper ones too.
That might not be bad. The helical ones are the ones you probably want to avoid since they can flex in rotation, which would wind up introducing the same kind of backlash the belt did (though perhaps not as much as the belt anyway).
mdrVB6 wrote:I don't know much about the different kinds, but I use this one:
http://www.ebay.com/itm/Flexible-5x-6mm … 1c2a9e9002
So its more like $8 but there are cheaper ones too.
That might not be bad. The helical ones are the ones you probably want to avoid since they can flex in rotation, which would wind up introducing the same kind of backlash the belt did (though perhaps not as much as the belt anyway).
Yup, jago is right that the oldham coupler is the best option (they're near-zero backlash, while also being potentially very stiff depending on the disc material), but yes they're not very common and fairly pricey. http://en.wikipedia.org/wiki/Coupling#Oldham
The helical (aka "spiral", "beam") couplers have too much torsional flexibility to be useful when used in a load-transferring application; you might find they don't offer much improvement over the belt and/or introduce more 'ringing' (vibration). They're popularly known for "zero backlash" but this assumes zero applied force! They're more often used to attach encoders etc. that need an accurate position but present no load. http://en.wikipedia.org/wiki/Coupling#Beam
Look up "spider", "plum", "lovejoy" or "jaw" couplers: which have a plastic part in the middle. They're less tolerant of shaft misalignment, but provide a little wriggle room. They're stiff enough in torsion for a printer I think. If you're not keen on the $30 oldham coupler, then maybe start here. http://en.wikipedia.org/wiki/Jaw_coupling
I'm not sure what the middle on mine is made out of - maybe brass? It's also got some magnets along the sides that help keep it all together, so even with fairly wacky belt tension it's pretty much impossible to pull it apart enough to bind the axis.
I'll be printing up a dial indicator mount soon - id like to put more numbers to my backlash and taping an indicator to the rails is only so repeatable 
I agree direct drive is the best mod you can do especially if your after functional parts that fit together. I use the 8 dollar ebay one, with the red plastic works fine enough . I'd recommend replacing the bushings with ball bearings. Pillow blocks help too especially with high tension fishing line
Grob and others, thanks for the info on the various types of couplers. I'm building another printer and was about to put a helical type on it but now I'll either get another red plastic in the middle one or an oldham. I don't mind paying for quality, I just didn't realize that the oldham type was actually better.
Just looking at a couple options here on Misumi. I am using an 8mm drive shaft.
It looks like the high rigidity clamping type is not available in 5x8, so I could get this clamping type that is not high rigidity:
http://us.misumi-ec.com/vona2/detail/11 … m+coupling
That one has a 1.1- 3 mm allowable misalignment. Sounds like a lot, I'm not sure if that is good or not for this application.
or this one that is high rigidity but just uses set screws. I could grind a flat spot into my 8mm shaft if I have to.
http://us.misumi-ec.com/vona2/detail/11 … m+coupling
Any opinions on which is better?
Edit: I just looked up the Nema 17 motor spec and it produces up to 45 N-cm (0.45 N-m) torque. That is not the stock motor, but my better replacement that I got and I'm not running it at the max, obviously, so its less than that. Even the non high rigidity coupler is rated for 1.2 N-m so the high rigidity coupler rated for 3 N-m is way overkill. I would still like an opinion if the allowable misalignment on that top one is actually too much for this application.
At the end of the day, it might not even matter which of these two I use.
This is a mod on my list, too. I had no slop for the first 6 months of ownership but have lately been observing poor finish on my walls. Noticed that there is a noticeable amount of slip is the short belt despite tightening it (can feel the belt shift forward and back against the pulley teeth when I hold the pulley and try moving the carriage). Ordered a replacement belt but I guess at best this buys me another 6 months.
It seems like the left and right top belts would suffer the same so direct drive only addresses part of the problem. Maybe since they are longer they wear out slower (pulley rubs against each belt tooth 1/2 to 1/3 as often)? Looks like the alternative here is fishing line. Or maybe a combination?
Edit: I just looked up the Nema 17 motor spec and it produces up to 45 N-cm (0.45 N-m) torque. That is not the stock motor, but my better replacement that I got and I'm not running it at the max, obviously, so its less than that. Even the non high rigidity coupler is rated for 1.2 N-m so the high rigidity coupler rated for 3 N-m is way overkill. I would still like an opinion if the allowable misalignment on that top one is actually too much for this application.
At the end of the day, it might not even matter which of these two I use.
+1 on your last sentence, they both look ok
* Set screws are ok, of course can be used without a flat as long as you button them up tight!
* Torque rating should be nice and high!
* Only worry about the maximum allowable misalignment - the plastic one is actually a bit more liberal (3 degrees / 1.5mm rather than 1.5 degrees / 0.5mm). I'd actually say the plastic one was the better option here for a flexible solidoodle frame...
* 20mm plastic one is 60 Nm/rad, while 17mm brass one quotes 1000 Nm/rad, so the brass one definitely less springy. I think both are more than stiff enough, but if you're scared of ringing, the brass one is better!
To be honest, I think you'll be hard pressed to really see any advantage to a high quality coupler over an ebay spider coupler for $5, but it would be interesting to see the results or even a comparison, so I'll leave that up to you! 
I hate ringing.
I hate ringing.
At >1000Nm/rad, evidently you do!
I've tried my search foo, but can't find a thread on this. And need to cut the rod this coming week.
Anyone able to give me a pointer?
Thanks
Scott
Assemble it all temporarily and let the rod stick out the right side. Mark it where you want it cut and pull it out. Cut it a dremel cutoff wheel or even a very good hacksaw.
unfortunately, the place where the Solidoodle is, is about 3 hours from where I am actually able to do cutting and other fabrication sort of things. :-/
I'll have to cut it to the approximate length, and then try it, take it back and cut it to the right size.
Thanks
Scott
If that was my situation I would go buy a cheap hacksaw with a good blade and cut it where the printer is. If you have never cut steel with a hacksaw it is time you try it.
Alternately you could install your motor on the mount along with the coupler and then just measure how long of a rod you need 
I Just got a rod I knew would be a little too long and let it stick out the other side. Doesn't hurt anything, and if I ever decide I need to add some kind of thrust bearing to keep the oldham coupler from falling apart, there is plenty of rod to play with :-).
I Just got a rod I knew would be a little too long and let it stick out the other side. Doesn't hurt anything, and if I ever decide I need to add some kind of thrust bearing to keep the oldham coupler from falling apart, there is plenty of rod to play with :-).
I've been having a bit of issue with this actually since switching to fishing line. I think it's an issue of tension, but my ultimate solution is going to be to put 6x13x5mm flanged bearings into the frame to replace the bushings. The fit should be tight enough that it will prevent the coupler from sliding apart. I've noticed, though, that even if it's almost completely apart, it still drives the system--I'm waiting to come back to the coupler just spinning on its own and the carriage going nowhere...
Also, does your coupler make a "clicking" noise? Mine does--not sure why! But it doesn't seem to be hurting anything.
SoliForum - 3D Printing Community → Hacks & Mods → Replacing Y-axis with direct drive..
Powered by PunBB, supported by Informer Technologies, Inc.
