Jump to content
Uwe

Show & Tell: Thumb Controller For Needle Positioning

Recommended Posts

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

Share this post


Link to post
Share on other sites

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:

post-56402-0-16487900-1455719603_thumb.j

Edited by Uwe

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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 by Uwe

Share this post


Link to post
Share on other sites

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".

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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 by Gregg From Keystone Sewing

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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 by RemingtonSteel

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...