Show & Tell: Thumb Controller For Needle Positioning

[TinkerTailor]

That's not even close to accurate. Mine came set up with a servo and a speed reducer and I can run that one stitch at a time. The motor price did not rival that of the machine head. I would hate to think of trying to be precise with a treadle on that type machine.

He is talking about the kind of stepper motor Uwe used in his project. They cost alot more than a servo. No normal sewing servo motor is arduino controllable,.....yet.

That would require some scoping and reverse engineering to do, and in the long run is not as configurable.

Hey Darren, while a treadle would work for most, some of the leather workers around here have issues with the lower body, and are unable to operate a treadle. This hand control system could prove immensely valuable to someone with special needs. Ever seen a hand control converted car? Not a cheap process but if that is what is required to get your mobility back, you do it. I agree that this is a limited market project, and Uwe is fully aware and has stated such. He does not care it appears, this is just for fun primarily but with known potential for actual usage.

Sometimes you take the path that you know is a dead end, just to see the sights along the way.

[gottaknow]

As I stated before, the push button needle positioner isn't something new. It has been used in factories for at least 40 years. It's an option on new Juki control boxes including their new direct drive top shaft mounted motors. You can't really judge its value until you've used it. Granted, these are high dollar control boxes with around 100 programmable features that you'll never find on any of the aftermarket control boxes talked about in this forum. I don't have to tweak speed controllers with cardboard and tape. I can see the benefit of the jog feature on leather machines as it gives absolute control. I don't care how skilled you are with a treadle or your hand on a hand wheel.

Regards, Eric

[Uwe]

I put together some more details on the Arduino step motor drive setup for those who are interested. I know this is not everybody's cup o' tea. Feel free to ignore if it chafes you or you prefer a clutch motor or a treadle.

A few pictures to show the overall setup:

The stepper motor itself is quite small, actually, considering how powerful it is ( 3 Nm torque):

The pulleys are XL type timing pulleys with 20 teeth (motor) and 40 teeth (machine) for a 2:1 ratio

The motor is mounted using a bracket in the original belt slot. I used rubber pads to reduce vibration noise somewhat:

The motor drives the machine with a 11mm wide (XL size) timing belt:

The thumb dial and rotary encoder

The controller bits still set up in a test configuration, not yet neatly packaged:

The Pedal is actually the most expensive part at $65. It also needs a return spring.

The main parts used for this project ran about $225 total:

Step Motor (23HS45-4204S) $50

Motor Bracket $15

Arduino Uno R3 $10

24V 250W Power Supply $20

Step Motor Controller (ST-M5045) $35

Pulleys & Timing Belt $25

Thumb wheel & Encoder (Adafruit) $5

Pedal (Ernie Ball VP Jr. 25K Ohm) $65

I've made a shopping list on Amazon (large pulley in the list has a 10mm bore, my machine takes 12.7mm, i.e. 1/2") The prices don't quite match up because I had ordered some bits through Ebay directly from China at a lower cost.

The Arduino Sketch Software Code is available as a text file to import into an Arduino Sketch window. The Code is commented to explain what's going on.

The wiring diagram (also available in high res) - there went five hours of my life ...

[stelmackr]

Thanks, I'll have to drag out my old programming books....

[dikman]

Very impressive bit of work, Uwe. (Don't take this the wrong way, but the closeup of the thumb dial isn't pretty (!) and the soldering on the next one looks a bit so-so (or is that just the photo?)). Nothing personal, I just tend to notice these things.

[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