Talk me out of wanting 0.9° stepper motors for X and Y

[Matthew]

According to the "Motors and Drivers" section of the following article, changing to 0.9 degree stepper motors increases the printing resolution in quite a noticeable way: https://hackaday.com/2016/07/06/build-a-3d-printer-workhorse/

Are there any reasons I wouldn't want to do this upgrade for the FT-5 R2? Am I missing something??

[Ron]

I can only tell you what did or didn't work for my printer.
I have some high quality 0.9 degree NEMA17 motors left over from a past project.
They have winding resistances and currents that are surprisingly similar to the ones that FT supplies.
Their torque curves are different though (see below).

So I tried one on the original FT-5 non-geared extruder first.
Failed miserably.
Couldn't get anywhere near enough torque out of it.
So I scrapped my thought to try them on the X, Y or Z axes and made other plans.

I changed to a geared (E3D Titan) extruder instead which has approximately a 3:1 reduction ratio (it doesn't equate to the exact gear ratio because of a difference in the extruder gear diameter).
Tons of torque, no real problems. Very happy.

Then I changed the driven Z pulleys (on the leadscrews) to 40 tooth versions.
Now it has a 2:1 reduction ratio with the stock motors and motor pulleys.
Worked like a charm and I now routinely print with 0.1mm layer heights (and I have tried smaller ones).
I simply couldn't do that before.

In general you won't get as much torque from a given 0.9 degree motor as from its 1.8 degree counterpart, all other things being equal.
Unless you spend a ton of money on super precision (ultra small rotor to stator gap) versions.
They will run out of torque at lower stepping speeds, and probably don't have as much to start with.
A Titan (or similar) setup and a pair of 40 tooth pulleys is a whole lot less expensive.

Quite a few of the "hackaday" articles are interesting.
But you have to ask yourself who wrote them, if they actually tested what was in it, and in this case was it written for a smaller (lighter weight component) printer setup?
Were they running the resulting printer slower, assuming it was even built?

FWIW........
Your experiences may vary.
There definitely are people who run 0.9 degree motors on FT-5's.
My particular motors just weren't remotely powerful enough at the same driver currents (or even higher).
Am I willing to invest in different ones as a test? No.
I am very pleased with the setup I have at the moment.

[Matthew]

Thanks for your reply Ron. Hmm, doesn't less teeth result in higher precision? As I understand it, 40 tooth pulleys would actually result in lower resolution than 20, not more.

https://www.prusaprinters.org/calculator/

https://nutz95.wordpress.com/2014/12/02/reprap-how-to-choose-your-pulleys-for-your-3d-printer/

[Ron]

Exactly the opposite is true.
I think you may be putting the tooth counts in the wrong places.
Or there is something wrong with the calculators.

With the stock setup the motor pulleys and leadscrew pulleys are both 20 tooth.
This is a 1:1 drive ratio.
So when the motor moves 1 step (or microstep as you wish), the leadscrews will move by exactly the same angular amount.

However when doing what I did (stock 20 tooth motor pulleys with new 40 tooth leadscrew pulleys) it takes two steps of the motor to move the leadscrews the same amount as if everything was "stock".
So this is a 2:1 drive reduction ratio.
Therefore the effective resolution of the motor is doubled (increased).
Instead of 400 steps/mm on the stock vertical it now becomes 800 steps/mm.
This is more accurate (higher precision) and is exactly what you would be trying to accomplish by going with 0.9 degree motors, except that instead of having less net torque, you have double the torque......
On the Z axis the increase in step speed to get the same linear speed is of no importance.
On X or Y it might be somewhat of a concern because you would be shifting upwards in the torque/speed curve of the motor.
That said, with 24 volt drive to the motor step sticks, it really doesn't matter.

I hope that helps.

[Matthew]

Oh, it does look like I was mixing things up, oops! I am still pretty new to this. I'm also distracted by a screaming toddler and barking dog. Thank you for your patience and detailed replies Ron, I really appreciate your help. Wow, so this would accomplish basically the same thing for a lot less money. Awesome tip!! Thanks Ron!

[PaulS]

.i run .9 motors but have duet wifi board and 2 amps to each so plenty of power. I am betting it would be far cheaper to go with 1.8 motors and a few pulleys to change gear ratio not to mention the extra torque you get by design. If you don't have a high end 12v supply (i use gaming rated pc PS) highly recommend 24v all sorts of advantages.

[Ron]

I totally agree.

It gets you a lot more torque and resolution for the buck on the Z axis.
For X and Y all is not lost though.
You can also change from 20 tooth to 16 tooth motor pulleys which should gain about 25% on resolution with a corresponding gain in torque at the belts.
However, without a 24 volt PSU you might have to reduce the maximum X and Y speeds a bit.
That was another mod I was planning to try one of these days, perhaps in conjunction with an "H" drive conversion.

With a stock FT controller board and "normal" step sticks a 24 volt PSU makes all the difference.
I am very happy I converted mine to 24 volts a while back.
With the more exotic step sticks such as TMC21xx it is borderline mandatory because of how they operate, particularly so for TMC2100's.

[Matthew]

Finally completed my FT-5 R2 build yesterday! Now it's just tweaking and modding. I'm using 16T on X and Y, but I still think I might change to 0.9 motors at some point for those two axises. For now it's working fine though, thanks again for the ideas Ron. I used 40T on the leadscrews, but I forgot about the belt loop length (doh!), so I came up with a temporary solution:

Might change to 2mm single-start leadscrews with 20T pulleys at some point though. My prints look good except for warping/curling. I need to figure out a part cooling fan. I skipped stock and instead installed a Titan Aero with E3D pancake motor, so I'm still working out what I'm going to do for a part cooling fan and BLTouch.

[Ron]

There are 16t motor pulleys for X and Y in my printer's future for sure (parts on order).
However I am also looking at doing an "H" drive conversion based upon the really positive experiences I had with an Ender-4 printer recently.
It will take a lot of mass out of the X gantry assembly.

What you did for Z looks great by the way.

[PaulS]

and here i was expecting some big long math formula showing why you dont need them if you gear thingsproperly lol

[Ron]

Go ahead, mock me...........

I really do like what @Matthew did, and I highly recommend the 40 tooth pulleys on the lead screws.
With the gear reduction a single motor is certainly powerful enough to do the job on Z, even with the lower currents our typical step sticks are capable of.
A slightly longer belt would get it back onto the right hand idler, but frankly it's probably just fine as it is.

Mine still has the dual motor setup and my fancy 1350mm belt setup (photos posted elsewhere) mainly because I am far too busy right now to pull a motor out.
But I will one of these days.
I'll keep the open center area I have now though because that's where my bed heater wires neatly coil into (by plan).

[PaulS]

Me? mock you. @Ron... never, well maybe lol but not in this case. ! have 40 and 60 tooth gears on their way now because of your math lesson . and i have .9 motors already