Electric sewing maching motor control with triac...would like to improve slow speed control

[Des Quilty]

Hi All, 

I have purchased a triac/diac electronic pedal to control my sewing machine. Being electronic I thought that it would work better for slow speed control than a traditional carbon disk type controller, but this isn't the case.

I've hooked the controller up to an oscilliiscope to see the output AC waveform, and it looks as if the power output jumping straight from nothing to midrange power and then increasing from there.

I've put together a little video and circuit diagram to explain what I mean and attached a poorly drawn circuit diagram.

If anybody has any suggestions how to improve the circuit to get better slow speed control I'd be all ears! 

Also it would be great if anybody knew what the resistor/capacitor pair circled in red does.

https://youtu.be/quetOZsITJA

Cheers

[Des Quilty]

Oh, forgot to mention that I'd also be interested in trying to change the AC motor for a brushless DC motor so I could attempt some position control via arduino as well as 
speed control.

Just wondering what spec brushless motor would be suitable for this? The AC motor is 70w...

[Adrian Godwin]

At the lower end of the speed control curve, there's no useful torque control, so once you've overcome friction the motor runs away. You might get some back by dropping your foot back once it's running, but a sewing machine si a rather variable load so this isn't easy. You really need electronic feedback, and modern sewing machines usually do this with a DC motor. A really expensive one might use a servomotor, working like something between a stepper and brushless 3-phase.

The triac control works better on an electric drill, because you usually start it with no load, begin drilling the hole, and then automatically increase the grip pressure as the load slows it. The industrial sewing machine in the space uses a clutch instead.

The RC network is called a snubber, and reduces the interference (caused by those fast edges when the triac switches) conducted back into the mains.

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[Des Quilty]

So I'm hearing that it would be better to concentrate on a DC motor replacement rather than trying to improve the AC motor.

There is a space restriction that the motor can't have a diameter greater than 60mm or it won't fit in the space. Perhaps a brushless motor from a RC car might fit the bill?

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[Adrian Godwin]

Brushless motors can be either with or without rotation sensors. The ones used in quadcopters usually don't have sensors. They have to generate a 3-phase rotating field in sync with rotation but this is synchronised by looking for a signal on one coil when the  others are pulsed. They work best when running smoothly at high speed : starting them is a bit of a black art. As a result, they're not very good at low speed operation. Another type has a position or rotation sensor. These tend to cost more but have an unambiguous rotation signal even at low speeds. It would be more appropriate for a low speed controlled device.

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[Des Quilty]

Good start, need a sensored one..brushless motors seem to be rated with turns, but don't have a sense for how much wattage they deliver..

Would something like this equate to a 70w ac motor? How do I work it out?

http://www.ebay.co.uk/itm/Etronix-Phaser-1-10th-sensored-brushless-motor-ETO360-10-5T-Nearly-new-/302109420085?hash=item46571fea35:g:ay4AAOSwpLNYBBMT

Thanks for the help Adrian, much appreciated!

[Adrian Godwin]

I don't know for sure. But I'd expect a small number of turns to be a high speed, low torque motor. I'd be looking for something intended for lower speeds. More turns means more flux and more torque at a lower current.

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[Des Quilty]

Cheers Adrian,

Another thing occurred to me..

If you are powering a 12v DC brushless motor producing 70w, it will need a pretty hefty amperage to power it I'd reckon, just looking at the cables on RC speed controllers they look pretty hefty, what kind of mains to 12v transformer will I need?

[Adrian Godwin]

70W at 12V is only 6A. The speed control can drop the effective voltage down so a 20V 6A laptop PSU will probably do.

Better still, find a 24V or higher motor.  Search for 'brushless motor' in the industrial section of ebay - there are a few there though I didn't check the voltage.

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[frankf...@gmail.com]

What RPM are you wanting this to run at ?

On Sunday, October 30, 2016 at 11:28:52 AM UTC, Des Quilty wrote:

[Des Quilty]

Good question, I'll have to work out the gearing. Also need to find the maximum speed of the machine. Given that its an all metal gear machine it should run pretty fast for a domestic machine perhaps 1300 stitches per min but that's a guess.

Will report back..

[Des Quilty]

The gearing ratio from the motor to the main shaft is 7:1, so 7-9000 maximum rpm would be adequate I'd reckon..

[Nigel Worsley]

> The gearing ratio from the motor to the main shaft is 7:1, so 7-9000 maximum
> rpm would be adequate I'd reckon..

At 50Hz, the maximum speed of an induction motor is 3,000 RPM - if
your motor is spinning faster than this then it may be a DC motor with
a built in rectifier.

Nigle

[Des Quilty]

Yep, I'm thinking of brushless DC motor for smooth quiet running, I'll start with just getting good speed control, especially at low speeds, then would like to introduce speed and position feedback with arduino control so it can do funky things like popping one stitch in at a time, or stable speed irrespective of varying cloth thickness. But one step at a time!

[deanforbes]

I over ordered on some encoders when you get to that point 

[Mr Ed]

If it has brushes it could well be a universal motor, running straight off AC.

-Ed

 

Nigle

[Des Quilty]

There's a trusty 60 year old universal ac motor running in the 431g at the minute..

I'm sure that it would like the beating heart of a modern brushless motor.

One of the constraints is that to fit in my Singer 431g, the diameter of the motor can't be greater than 6cm..although

I am also considering fitting a DC motor as a piggy back motor on my 1920's Singer 201k where I wouldn't have the size constraint and was considering one of these...

http://www.ebay.co.uk/itm/24v-Brushless-DC-Electric-Motor-BN34-Series-Poly-Scientific-Litton-/222298572839?hash=item33c2070827:g:F5cAAOxyJX9SH1iC

[Des Quilty]

Hello from LA!

I've managed to acquire a 110v US version of the original motor. It has an aluminium body rather than the bakelite 240v versions available in the UK (which usually break when you try and remove them from the sewing machine!). Am thinking that I can use the top half of the US motor body as a mount for my DC motor.

While I'm doing that I was just wondering if anybody knows what specifications in the motor parts (commutator/magnets etc) are tuned to make the motor work on 110v US and how they would differ in a 240v UK comparable version?

[Henry Best]

Des,

The windings will be different and the commutator/stators may be made for 60Hz, so even if it's rewound, the speed may not be the same as a UK one.

[Adrian Godwin]

If it's a 'universal' motor, I don't think it will be very different. Induction motors do run at a multiple of the mains frequency but they don't like the resistive speed control so not common in sewing machines.

--

[Des Quilty]

It is a universal motor

will be swapping out the US one for a UK version (or brushless DC possibly as discussed) so no need for a rewind..

While we are chatting, since you are rarely running a sewing machine at full speed, a small change in motor speed might not make much difference most of the time I'd reckon..

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[Henry Best]

OK, but I don't consider a 20% reduction as small.

[Des Quilty]

A picture tells a thousand words!

Here are the two armatures from almost identical universal US and a UK sewing machine motors, both output 0.7w.

The 240v version is on the left and you can see that there seems to be double the amount of plates in the commutator..

[Henry Best]

Also, from the photo the armature windings on the US one look longer, probably to get more power from the 110v supply.

I suspect that the brushes are of different sizes too, smaller on the UK one.

Somewhere on the case will be a capacitor to reduce RFI (or maybe more than one) and these will be of different types. The US one(s) will only be rated for 110V. Put 240V across it and you'll let the blue smoke out!

But I'm not clear on what you intend to do. Am I right in thinking that you want to put the UK armature in the US case, or have I got that wrong?

One other thing you mentioned is that the US case is metal. I'm not certain that a metal case will comply with UK electrical regs.

On Friday, 9 December 2016 14:09:28 UTC, Des Quilty wrote:

A picture tells a thousand words!

Here are the two armatures from almost identical universal US and a UK sewing machine motors, both output 0.7w.

[reedreb...@yahoo.com]

--------------------------------------------
On Sun, 12/11/16, Henry Best <henry...@gmail.com> wrote:

Subject: Re: [london-hack-space] Re: Electric sewing maching motor control with triac...would like to improve slow speed control
To: "London Hackspace" <london-h...@googlegroups.com>
Date: Sunday, December 11, 2016, 6:01 AM

Also, from
the photo the armature windings on the US one look longer,
probably to get more power from the 110v supply.I
suspect that the brushes are of different sizes too, smaller

on the UK one.Somewhere on the case will be a

capacitor to reduce RFI (or maybe more than one) and these
will be of different types. The US one(s) will only be rated
for 110V. Put 240V across it and you'll let the blue

smoke out!But I'm not clear on what you

intend to do. Am I right in thinking that you want to put
the UK armature in the US case, or have I got that

wrong?One other thing you mentioned is that the

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cum cand slabiciunea militara a U.R.S S. a trecut in domeniul trecutului iar situatia internationala care s-a creat cere rezolvarea rapida a chestiunilor mostenite din trecut... U.R.S S.

[Des Quilty]

Was just curious what makes a universal motor running on 240v different from the motor running on 110v supply..

I might use the metal casing from the US motor as the basis for a drive shaft mount to connect a DC brushless motor  to the sewing machine at some point, but thats about it really, just trying to learn more about motors in general..