Show & Tell: Thumb Controller For Needle Positioning

[Constabulary]

is that the Flux Capacitor 2.0?

[gigi]

Another solution for driving the machine could be an asynchronous motor and a frequency inverter + pedal.

[Uwe]

I tried the 3-Phase motor and variable frequency drive, but abandoned the idea (I used the pedal for the Arduino project). While the pedal control is super smooth, 3-phase motors of similar constant torque are huge, heavy , and expensive. And there's no easy way to do needle positioning. Here's a picture of my test gear for VFD, just for size comparison:

Edited February 17, 2016 by Uwe

[TZBrown]

You certainly laid it all out there in a complete package

How does the stepper motor torque compare to servo motor torque? 3 Nm vs ?

With the coding all ready done, and the shopping list, it would not be hard to replicate.

If the torques are similar to a servo motor, or better, the costs would rival a servo motor and speed reducer combined to refit a machine.

[Uwe]

I've not seen a single sewing servo motor actually state the torque it produces, just marketing terms like "more torque" and "high torque". The stepper motor manufacturers always state the precise torque their motors can produce for both turning and holding still, because it's a key metric for their applications in CNC machines.

I ordered the 3Nm motor just based on a guess and because it was affordable (the 13Nm motor runs $140) . The 3Nm turned out to be plenty, actually, especially with the 2:1 pulley ratio, which provides 6Nm or torque at the main shaft. 6Nm is about 4.5 ft lbs of torque. Imagine installing one foot long lever handle on the handwheel and hanging a 4.4 lbs weight on the end. That's pretty good twisting power.

One of my next little science projects will be measuring actual torque the different motor types apply at the main shaft at slow speeds, where we leather workers need it the most.

Most CNC class stepper motors make 200 steps per revolution. They take each tiny step at full speed and max torque and then hold on to that new position with equally strong force until you tell it to make another step. The overall speed is determined by how rapidly you tell the motor to take the next tiny step. If you tell the motor 200 times per second to take a step it will make one full revolution per second, or spin at 60 RPM (a slight generalization because the motor control box subdivides those steps)

When my stepper motor stops after letting go of the pedal, I actually cannot turn the wheel by hand because the motor holds on to that exact position with full force. I can't overcome that holding power by gripping the main shaft pulley with my hand. Which is also why I need the thumbwheel to gradually move the needle a small amount when the motor is powered is on. The thumbwheel is not really a fancy feature, but rather a required element of this setup.

Edited February 17, 2016 by Uwe

[spongocoel]

This is absolutely fantastic! Thank you for documenting everything so well. I've done a little bit of Arduino programming, and I hope to be able to integrate that more with some old sewing machines in the future - in my mythical "spare time".

[BigMatt]

It is like magic! Can you program it for different ratios between the thumb wheel and the needle cycle on the machine? If so, I would just make it a 1:1. Other than that, I don't see how it can be improved on.

[Gregg From Keystone Sewing]

On 2/17/2016 at 3:05 PM, Uwe said:

I've not seen a single sewing servo motor actually state the torque it produces, just marketing terms like "more torque" and "high torque". The stepper motor manufacturers always state the precise torque their motors can produce for both turning and holding still, because it's a key metric for their applications in CNC machines.

I ordered the 3Nm motor just based on a guess and because it was affordable (the 13Nm motor runs $140) . The 3Nm turned out to be plenty, actually, especially with the 2:1 pulley ratio, which provides 6Nm or torque at the main shaft. 6Nm is about 4.5 ft lbs of torque. Imagine installing one foot long lever handle on the handwheel and hanging a 4.4 lbs weight on the end. That's pretty good twisting power.

One of my next little science projects will be measuring actual torque the different motor types apply at the main shaft at slow speeds, where we leather workers need it the most.

Most CNC class stepper motors make 200 steps per revolution. They take each tiny step at full speed and max torque and then hold on to that new position with equally strong force until you tell it to make another step. The overall speed is determined by how rapidly you tell the motor to take the next tiny step. If you tell the motor 200 times per second to take a step it will make one full revolution per second, or spin at 60 RPM (a slight generalization because the motor control box subdivides those steps)

When my stepper motor stops after letting go of the pedal, I actually cannot turn the wheel by hand because the motor holds on to that exact position with full force. I can't overcome that holding power by gripping the main shaft pulley with my hand. Which is also why I need the thumbwheel to gradually move the needle a small amount when the motor is powered is on. The thumbwheel is not really a fancy feature, but rather a required element of this setup.

Great stuff, really amazing UWE.  I've got one motor supplier who provides both nominal and maximal torque for example here a DC1550 motor with nominal 1,9Nm, Maximal torque 8Nm.

I have no idea how to apply that to a real world application, but I can tell you this motor is very powerful!  

You can visit this items product page here; https://www.efka.net/en/products/electric-motors/dc1550/

Edited March 15, 2018 by Gregg From Keystone Sewing

[johnnyblaze]

Uwe,

I'm planning to do something similar to what you did here.  Looking closer at the photo of the foot pedal, I see what appears to be the splined shaft where one of the plug jacks was.  Did you add another potentiometer?   I don't see anything on your wiring diagram.

Regards,

John

[Uwe]

I think that spline shaft belonged to a second potentiometer that was originally wired in series with the pedal-driven potentiometer. It’s only used to offset pedal volume in the original music application of the pedal. It’s not used for the motor control modification.

[RemingtonSteel]

Uwe, I have always been fascinated with CNC machines, as well as Arduino, but I have never had the time to play with either. So this may be a dumb question, but can a stepper motor be put in neutral so that zero torque is used to hold the motor shaft in place?  If yes, couldn't you have a switch that would do just that so you could use the hand wheel if so desired?

Regardless, an awesome project that makes me want to find the time to learn both. Well done. I am glad this thread was revived or I might have missed it.

Edited November 28, 2019 by RemingtonSteel

[Gymnast]

4 hours ago, RemingtonSteel said:

can a stepper motor be put in neutral so that zero torque

yes, if you put a switch on the wires to the motor Windings. With zero current to the stepper motor, I think most of them will provide zero torque. But it can be somewhat problematic for the electronics, when you switch on again. So perhaps the software do have a nicer way of doing it.

I got a question too. With CNC machines with stepper motors, you normally can run into problems with a skipped steps. So they will have a way to go to a end stop electrical switch to reset the software and counter of steps in the sofware to make a right position. I suppose you can get similar problems with a sewing machine, when you want a needle positioner function. I think you need some other positioner on the sewing machine main shaft to reset the position counter in the software. Perhaps the positioner function shown in the video is just a command of a known number of steps forward.

[HikeLite]

Hi Uwe,

Here's some other Arduino source code for controlling the speed of a Teknic ClearPath servo motor with a guitar volume pedal:
  https://github.com/HikeLite/

Regards

[littleJ]

Sometimes, I get caught in a rabbit hole, this was definitely a fun one. This forum was a godsend in researching this.

• I just started sewing leather
• My machine came with a brushed servo; too fast even on slowest speeds/hard to control
• Bought a brush-less servo from eBay; too fast and too touchy for me, and I wanted a needle position sensor
  • The motor's lowest setting was 500RPM ( a friend's Consew [I think] brush-less servo can be set as low as 100RPM)
  • The motor has a hall-effect potentiometer, not optical gradient, and it felt...uncalibrated?

Then I found this thread. Uwe, thank you so much for sharing this with us. I've always wanted to learn how to work with an Arduino and big steppers and your guide was PERFECT for following along.

My thoughts:

• The foot pedal control is extraordinary and really needs to be experienced to truly appreciate.
  • The speed control is very precise and the acceleration feels perfectly linear: I know what to expect from each minor foot movement
• The button/knob rotary encoder - to be determined
  • I fried mine after trying to permanently solder the wires on after testing, so that (critical) part is on its way.
  • I think the knob may also need a software de-bounce added.
  • More to come
• The downsides
  • Noise, as Uwe said, the noise was quite substantial, but I would also like to add some sound-deadening between the table and motor mount.
    • I would also like to look at the code which does the foot pedal calculations. I think some of the motor noise may be half-steps+resistence on the needle
  • Vibrations
    • Do I need to be worried about vibrations damaging the machine?
  • Thickness
    • interested to hear Uwe's experience was with running multiple layers through. I need to investigate further to see what was occurring when going through 3 layers of 3oz chrome tan. At this point in the testing, I just walked away as I didn't want to damage my machine.

Overall, I reallllly want to make this work, but I want a working machine more.

pics
https://ibb.co/p3tX7sP

 

Edited March 19, 2022 by littleJ