Author Topic: Choosing stepper non captive leadscrew motor  (Read 4974 times)

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Offline smileTopic starter

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Choosing stepper non captive leadscrew motor
« on: November 23, 2023, 05:57:09 pm »
Hello,

I need to choose non captive leadscrew motor, however I do not know how to properly do it.

I tested several online calculators like these below:
https://www.daycounter.com/Calculators/Lead-Screw-Force-Torque-Calculator.phtml
https://www.vcalc.com/wiki/vCollections/Leadscrew-Torque-lift

I need motor of Nema 17 or Nema 23 size with a push pull operation, the force will be ~15Kg
Leadscrew will be (as big diameter as possible) Tr11x2mm


I plan to use chinese cycle controller like HF020, photo below:

 

Offline Doctorandus_P

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Re: Choosing stepper non captive leadscrew motor
« Reply #1 on: November 27, 2023, 06:13:40 pm »
Nema 17 is probably too small.

I have a small CNC machine with 112mm long Nema23 motors and 1605 ball spindles, and t can push around 700N at low speed before the motor stalls.

Calculation is fairly simple, but also inaccurate because of unknown properties.

For calculation, imagine a sheet of paper wound around the spindle, then unwind it until it is flat. The thread will have left an impression on the paper in the form of a slope (for TR11x2 this will be an (effective) diameter of 9mm, an effective (average) circumference of around 9 * pi = 30mm and a vertical rise of the 2mm pitch.
From that slope and the friction coefficient yo can calculate a force on the circumference of the thread.
And from that force you can calculate the required torque.

But both the friction coefficient and the real torque of the motor have large tolerances, so you have to compensate for that too. And with stepper motors (especially without feedback) you want an extra decent safety margin. and add some too for sub optimal lubrication or when the lubrication dries out or washes away or gets dirty etc.

Why do you want a big diameter? Efficiency goes down with larger diameters.

------------------------------
Also, I've been punching in some numbers in the calculators you found:
Lead: 2mm
Load: 150N
Friction: 0.15
Mean Diameter: 10mm

and both calculators suggest a torque of 0.16Nm and this should be well within the range of a Nema17 motor.
« Last Edit: November 27, 2023, 06:18:35 pm by Doctorandus_P »
 

Offline Infraviolet

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Re: Choosing stepper non captive leadscrew motor
« Reply #2 on: November 28, 2023, 03:28:52 am »
You don't have to buy a stepper with a leadscrew for its shaft. You can buy a stepper with a normal D shaft, then use a coupler to attach a leadscrew. depending on the type of coupler you might be able to find convenient places t insert thrust bearings around it to take any forces applied along the shaft without them acting on the stepper's own D shaft. This takes mroe space than a stepepr with a leadscrew shaft, but gives you a lot more options for picking the motor you want and the screw you want independently of each other.
 

Offline smileTopic starter

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Re: Choosing stepper non captive leadscrew motor
« Reply #3 on: November 28, 2023, 08:14:53 pm »
But I need the non captive leadscrew motor because I want to use it like the linear actuator



The linear actuator is not suitable because it adds length of the body where the linear shaft is housed. This increases the length of whole assembly two times.
The non captive leadscrew motor will be mounted on moving part, the leadscrew will be stationary. No added length increase.

This is for miter saw project. The type with linear rods extending to the back of the saw. No added length is priority.
 

Offline smileTopic starter

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Re: Choosing stepper non captive leadscrew motor
« Reply #4 on: November 28, 2023, 08:43:56 pm »
See positions image for intended positions.

 

Offline H.O

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Re: Choosing stepper non captive leadscrew motor
« Reply #5 on: December 02, 2023, 09:30:25 am »
Linear force is one thing but what about speed?
Remember that the torque produced by a stepper motor decreases with increased speed.
 

Offline Infraviolet

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Re: Choosing stepper non captive leadscrew motor
« Reply #6 on: December 05, 2023, 03:01:45 am »
smile: now you describe it like that...

Have you looked up CARRIAGE style linear actuators?

https://uk.rs-online.com/web/p/electric-linear-actuators/1774521

That's an example, there will be cheaper ones and a wide variety of different lengths and strengths available from other sellers.

This sort of thing is pretty slow though.

Combining your own lead screw with a normal stepper via a shaft coupler, look how it is done for typical 3d printer Z axes, is still a good starting point too.
 

Offline smileTopic starter

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Re: Choosing stepper non captive leadscrew motor
« Reply #7 on: December 06, 2023, 11:03:29 pm »
Quote
Have you looked up CARRIAGE style linear actuators?

well Yes, these are not suitable because it doubles the length of the leadscrew used. The hausing of device with motor is stationary taking extra 400mm lenght, the leadscrew extends another 400mm, this makes stupid lenght of 800mm !!!!

With captive stepper, the lenght is not increased except motor dimensions about 75mm
 

Offline Infraviolet

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Re: Choosing stepper non captive leadscrew motor
« Reply #8 on: December 08, 2023, 04:00:18 pm »
Carriage ones don't double the length (look at the picture in my example link), piston style (like your image in Reply #3) ones do. A piston style one can go from the closed length to the extended length, where L_closed is a little more than L_extended/2 . A carriage one can go right from one end to the other, the actuated item hanging off the carriage and getting from nearly at one extreme end to nearly at the other extreme end. A carriage one adds some lumps to either end, but nothing close to doubling the length.

A normal D shafted stepper with a shaft coupler and your own leadscrew attached to the coupler would be barely longer than a stepper with a leadscrew as its built-in shaft of the same lead-screw length.
« Last Edit: December 08, 2023, 04:02:55 pm by Infraviolet »
 

Offline smileTopic starter

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Re: Choosing stepper non captive leadscrew motor
« Reply #9 on: January 02, 2024, 10:30:00 pm »
Chinese sellers suggest this stepper 5A, nema 24 size

https://ae02.alicdn.com/kf/Sce2a6e84f2dc4fe3ae549fd5fccc7ae8S.png

What about thrust (push/pull power in Kg) with Leadscrew Tr12mm Lead 4mm, they do not seem to have smaller Lead Leadscrw?

Anyone can help?
« Last Edit: January 02, 2024, 10:44:07 pm by smile »
 

Offline MarkT

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Re: Choosing stepper non captive leadscrew motor
« Reply #10 on: January 06, 2024, 02:12:57 pm »
NEMA 23, not 24.  Standard sizes for steppers are 8/11/14/17/23/34/42 (and probably some larger one's I've never seen!)

Incidentally despite the NEMA sizing, most steppers are actually metric sizes that are close to the nominal deci-inch sizing implied by NEMA
 

Offline langwadt

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Re: Choosing stepper non captive leadscrew motor
« Reply #11 on: January 06, 2024, 02:43:35 pm »
NEMA 23, not 24.  Standard sizes for steppers are 8/11/14/17/23/34/42 (and probably some larger one's I've never seen!)

Incidentally despite the NEMA sizing, most steppers are actually metric sizes that are close to the nominal deci-inch sizing implied by NEMA

there's also NEMA24, fits the same hole pattern as NEMA23, but body is 60*60mm instead of ~57*57mm
 

Offline nctnico

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Re: Choosing stepper non captive leadscrew motor
« Reply #12 on: January 07, 2024, 10:18:00 am »
Linear force is one thing but what about speed?
Remember that the torque produced by a stepper motor decreases with increased speed.
Not necessarily. Torque depends on current. If you use current drive, then you can keep the torque constant even though the back EMF increases.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline smileTopic starter

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Re: Choosing stepper non captive leadscrew motor
« Reply #13 on: January 07, 2024, 03:12:18 pm »
On my first post there are few torque calculators, however  I'm too stupid to use them.
IN my case the torque push/pull will be max 15Kg (actual 8-10Kg) tested with a scale, will the motor be able to provide this?

The Lead is 4 I wanted lower but they say it not available for this motor size. Screw diameter is 12mm should be plenty.
« Last Edit: January 07, 2024, 03:14:25 pm by smile »
 

Offline H.O

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Re: Choosing stepper non captive leadscrew motor
« Reply #14 on: January 07, 2024, 03:19:59 pm »
Linear force is one thing but what about speed?
Remember that the torque produced by a stepper motor decreases with increased speed.
Not necessarily. Torque depends on current. If you use current drive, then you can keep the torque constant even though the back EMF increases.
Exactly, torque depends on current and as the speed increases there's not enough voltage to help the drive overcome the inductance in the windings and push the correct amount of current into thru the windings. Motors that have high inductance (=many turns of wire in the windings) produce more torque for a given current but the torque drops off faster than for a motor with less inductance becasue the drive is not able to "change" the current thru the windings fast enough.

So for a specific application a motor with 2.5Nm holding torque might produce MORE torque at the desired speed that a motor with 3.5Nm holding torque.

Just look at a speed/torque diagram of any step motor from any manufacturers.
 

Offline H.O

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Re: Choosing stepper non captive leadscrew motor
« Reply #15 on: January 07, 2024, 03:23:52 pm »
On my first post there are few torque calculators, however  I'm too stupid to use them.
IN my case the torque push/pull will be max 15Kg (actual 8-10Kg) tested with a scale, will the motor be able to provide this?

The Lead is 4 I wanted lower but they say it not available for this motor size. Screw diameter is 12mm should be plenty.

A 4mm pitch screw with 20% effeciency will give you aproximately 300N of linear force for every Nm you put "into it".
 


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