What motors are better?

Hi i am buliding a prusa machine and want to have the best motors possible, and have one question. what motor is the best option? 1.8 or 0.9 degree steppers?
thanks

It's better to look at the power output and current pull
kthx says:
ideal steppers are ideal steppers are NEMA17 size, rated 1.5A to 1.8A or less, 1-4 volts, 3 to 8 mH, 62oz.in (44Ncm, 4.4kg.cm) or more of torque, 1.8 or 0.9 degrees per step (200/400 steps/rev respectively), for example the kysan 1124090/42BYGH4803 or the 17HS8401


if all that is equal, then you're going to get more steps per mm with the 0.9 deg per step.
I've got 88 steps per mm with 1.8 so... I duno if you're going to see much of a difference in quality with a 0.9

I upgraded from 1.8deg to 0.9deg steppers last year while still using Gen6 electronics (only 1/8 microstepping). Resolution improved in the X and Y. You probably won't see an improvement with 1/16 microsteppers (Pololu, Printrboard, etc.). But, why not go for 0.9degree motors? Twice the number of steps per revolution can only be advantageous.

Quote

Twice the number of steps per revolution can only be advantageous.

Except it will half your maximum speed, all other things being equal.

---

[www.hydraraptor.blogspot.com]

Personally I went with 0.9's. They've performed great so far. I was concerned with speed as nophead pointed out, but so far that hasn't been an issue. That's not exactly true - my extruder stepper would chatter if I set the retraction speed too high. But thats the only issue I've had with my motors. I got mine from sparkfun.com Part ROB-10846. They've got a pretty good video on steppers too.

-akhlut

i'm thinking about getting these motors
[www.ebay.com]
is there anything i should know about that would make them a bad idea?

You could use these for the axes, but the extruder needs more holding torque. These have 33N.cm but you need around 40N.cm for the extruder. Also, the stepper pictured has >4 wires. Could probably get it to work with some fiddling...

-akhlut

those will probibly run hot.

It looks like it is 6-wire unipolar motor. These can be used as a 4-wire stepper ignoring the two wires in the middle of each winding (just select the two wires with higher resistance out of the three that give you connectivity, twice).

Typical 4.4kg-cm holding torque is achieved at 1.6A but stepper drivers are going to work at 1A max (unless some cooling extra is added to your electronics). That means the torque is going to be 2/3 of the rated one. The motors of your link seem like they can do the work, and the price is good if you're based in USA.

It's true you will have to push more current to your steppers for more power (P = VI) with cheaper, not so torquey (is that a word?) motors but when you're starting out and you can find some inexpensive steppers, I'd say go for it. Sure they will run hot, but a some heat sinks on the case of your steppers will help alleviate that problem.

I started out with inexpensive salvaged steppers for my axes and one nice and strong stepper for my extruder, it turned out to work pretty well.

bdc
~Stay Calm Out There

akhlut Wrote:
-------------------------------------------------------
> You could use these for the axes, but the extruder
> needs more holding torque. These have 33N.cm but
> you need around 40N.cm for the extruder.

I really wonder if this is true anymore. I was just printing 3mm filament with a direct drive extruder for a while. The motor (SY42STH47 with 44Ncm holding torque) was running hot as heck, but it worked fine. Now, the geared extruders have as high as 5:1 gear down ratios, which of course multiplies the torque by 5. So... what's wrong with this picture? If 44Ncm motor works with direct drive, shouldn't the requirements for a 5:1 or 4:1 geared extruder be much less than that?

nophead Wrote:
-------------------------------------------------------
> Twice the number of steps per revolution can only
> be advantageous.
> Except it will half your maximum speed, all other
> things being equal.


True. Hadn't thought of that, as my machine prints at up to 130mm/sec (infill) without trouble. I did have to decrease maximum Y-axis acceleration to 2000 mm/sec^2; occasionally it would skip steps at 3000 mm/sec^2. I'm still using 1.8degree motors for the Z-axis and extruder.

ttsalo Wrote:
-------------------------------------------------------
> akhlut Wrote:
> --------------------------------------------------
> -----
> > You could use these for the axes, but the
> extruder
> > needs more holding torque. These have 33N.cm
> but
> > you need around 40N.cm for the extruder.
>
> I really wonder if this is true anymore. I was
> just printing 3mm filament with a direct drive
> extruder for a while. The motor (SY42STH47 with
> 44Ncm holding torque) was running hot as heck, but
> it worked fine. Now, the geared extruders have as
> high as 5:1 gear down ratios, which of course
> multiplies the torque by 5. So... what's wrong
> with this picture? If 44Ncm motor works with
> direct drive, shouldn't the requirements for a 5:1
> or 4:1 geared extruder be much less than that?

It depends on what you are extruding and the design of the hot end. PLA doesn't need much force if you run it hot but ABS does. I need to run my extruder motors at more than 1.3A and they do get hot and I only extrude ABS at 40mm/s. Since step sticks are limited to 1A some people must get away with less torque.

The higher the gear ratio the slower you can rewind and fast forward.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> It depends on what you are extruding and the
> design of the hot end. PLA doesn't need much force
> if you run it hot but ABS does. I need to run my
> extruder motors at more than 1.3A and they do get
> hot and I only extrude ABS at 40mm/s. Since step
> sticks are limited to 1A some people must get away
> with less torque.

I was direct-drive extruding 3mm ABS at 70 mm/s (0.25*0.5 mm print track, 0.5 nozzle), but maybe my ABS brand, hot-end and temperature combo just makes it particularly easy to push the filament. In any case I'm pretty sure that 40 Ncm isn't an absolute requirement for a 4:1 or 5:1 geared extruder.

But hey, it should be simple to calculate. If the effective driver radius is 3 mm (the usual hobbed bolt, diameter 6 mm), and gearing 4:1, a 40 Ncm motor would provide 40*4/0.3 = 533 N of force for the filament. Right? (Well, holding force, with actual driving force being somewhat less.)

> The higher the gear ratio the slower you can
> rewind and fast forward.

Yeah, that's an annoying issue with high gearing, retracts cause noticeable pauses even at minimum settings, at least for me. I'd like to go down from 5:1 to 3:1 gearing or so to get the retract working faster.

ttsalo Wrote:
-------------------------------------------------------

> But hey, it should be simple to calculate. If the
> effective driver radius is 3 mm (the usual hobbed
> bolt, diameter 6 mm), and gearing 4:1, a 40 Ncm
> motor would provide 40*4/0.3 = 533 N of force for
> the filament. Right? (Well, holding force, with
> actual driving force being somewhat less.)

40Ncm is with 1.7A into both coils and with an 80C temperature rise, which would melt your extruder.

I use 1.3A, but that is peak current into one coil. When both coils are on they get 70% which is 0.9A. Power is proportional to current squared, so I get (0.9/1.7)^2 * 80 = 22C rise. Inside my chamber at 45C that means close to 70C. Too hot to touch and probably the reason my extruder brackets fail after about 6 months.

The holding torque will be 40 * 0.9 / 1.7 = 21Ncm. My gear ratio is 39:11 and my hobbed bolt 6.7mm. That would give 222N. I think the force needed to push the filament is less than 100N, probably around 50N, so something doesn't add up.

As you say moving torque is less than holding torque. Most of the motion is slow but the fast forward is where it will fail. Also the gears are not going to be 100% efficient.

>
> > The higher the gear ratio the slower you can
> > rewind and fast forward.
>
> Yeah, that's an annoying issue with high gearing,
> retracts cause noticeable pauses even at minimum
> settings, at least for me. I'd like to go down
> from 5:1 to 3:1 gearing or so to get the retract
> working faster.

Yes if it wasn't for the fast forward and rewind you could use a much smaller motor and a high gear ratio. I have often wondered if we should move the motor up and down with a solenoid to make a lighter extruder with very fast pressure changes. The other option is to only start and stop slowly, but move the axes to match the flow rate.

---

[www.hydraraptor.blogspot.com]