Sewing machine motor torque and speed

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I have a perfectly good and robust sewing machine (Jones Zig Zag semi-industrial thing) with only one problem - the electric motor and foot operated speed control is a bit dicky. So I wondered if replacing them with a 12V DC motor and electronic speed control might be better than repairing the ancient 230V ones. Mechanically and electrically this is within my scope, but I realise that I don't know the speed range and expected torque as seen at the machine's 'flywheel'. I can arrange gears or (as now) a belt and pulley speed reduction.

I think the speed should be around 200rpm at full welly, and around 0.6Nm, but does anyone know? And is the idea a good one or stupid?
 
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I would say the idea is not impossible but the problems could be both physical and economic. Low voltage DC motors tend to run around 2500 rpm,the Chinese build Ebike hub units mostly 24v and 36v with internal gearing to around 12: 1 ratio for a 26" wheel so 200rpm rated from 200watts upwards and these can be throttle or pot. controlled through a purpose built unit, hub size from 100mm dia.x 85 mm width. possibly 2kgs . A lot of the older secondhand bikes have much bigger and heavier hub units ,but you may find suitable units on used childrens scooters and they are sometimes 12v. Prices for new Ebike hubs in China are around $70 hubs $15 controllers $5 throttles so say £60 + shipping and vat etc add £80.

http://elifebike.com/peng/pic.asp?ModID=PicS224&TypID=S210032

The best answer may be a 24v dc 2500rpm motor with a small pulley and drive belt these can be seen in the scooter section of sporting goods on Ebay for around £15 and use a voltage converter and suitable controller.
 
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Typical domestic sewing machine motor is 90W, 6000rpm it seems.
There are lots of 12V drill motors that will do 90W, but usually intended for short bursts, while a sewing machine can be running for long enough for a small motor to get hot.
Looking at mine, I guess the reduction is between 10 and 15 to 1, so machine rpm might be up to 600?
Industrial might be faster?

The 12V motor of that sort of rating that springs to mind is a blower motor from a car heater. Last one I messed with drew 14A at full chat. Obviously with lots of fan cooling!
Such a motor will be bigger than a mains sewing machine motor, so the belt will be longer, I wonder if belt stretch becomes an issue?
 
SWMBO has her old Singer out at the moment. The motor is marked as being 75 watts.

It must be easy enough to count up the number of stitches it makes in, say, 10 seconds. Then work out the ratio of the gearing to estimate the RPM at the motor.
 
I'd consider a brushless motor. You would need a hefty power supply or to run from the boat main supply but an RC electronic speed control would give smooth speed control from a few hundred rpm to flat out.

To run off nominal 12v a motor rated at around 500 revs per volt would do the job. If the power required is under 300watts then there are plenty of off the shelf motor and esc combinations available.
 
Just a hint, but I seem to remember Jabsco water puppy motor being mentioned as a conversion option for a Singer.May have been on this forum.In a bit of a rush right now so it may even been the links kindly posted by others.
 
jdc said:
I have a perfectly good and robust sewing machine (Jones Zig Zag semi-industrial thing) with only one problem - the electric motor and foot operated speed control is a bit dicky. So I wondered if replacing them with a 12V DC motor and electronic speed control might be better than repairing the ancient 230V ones. Mechanically and electrically this is within my scope, but I realise that I don't know the speed range and expected torque as seen at the machine's 'flywheel'. I can arrange gears or (as now) a belt and pulley speed reduction.

I think the speed should be around 200rpm at full welly, and around 0.6Nm, but does anyone know? And is the idea a good one or stupid?
Click to expand...


Some of the foot controls are krap.......... It might be worth simply replacing that........ we had to replace it on SWMBO's Frister_Rossman. I cant say what's fitted as my daughter has the machine now.
Our new Pfaff does have a better foot control ... better than the old F-R one ever was.
 
My last on board sewing machine was rugged s/h Japanese but 110v so....so good that it was worth fabricating a hand crank that clamped onto the flywheel.
So, is it really worth the bother of rejigging the power source and foot pedal or is the OP intending a lot of use?

I currently have a machine with a extra heavy flywheel for smoother handcranking when leccy not on tap..

A friend converted the saloon table into a foot crank set up for their sewing machine by cutting a slot and adapting an old singer foot treadle but that is perhaps a tad extreme..
 
Many thanks

Many thanks for all the replies and good suggestions. If all was in good order I'd probably keep it all as is, but I have to do something even if only to replace the cables since the insulation has gone hard and perished. So I thought 'why not 12V'. It's a peculiarity of my boat that I have 230V only when the generator is running.

I think reading the nominal power rating of the mains motor fitted to an existing sewing machine is not that relevant: for instance it's marked 0.5A on the existing 230V AC motor, but if I put the max normal torque I believe reasonable (about 1kgF at about 6cm radius on the flywheel) and multiply by the max speed of around 200rpm that's equates to only about 12.5 Watts - and no way can I get it up to 0.5A x 230V = 115W unless there is a comparatively huge start-up torque to overcome. Neither is speed of the motor when running under zero load of that much direct relevance: mostly sewing machines are operated well below max speed and fine control at low speed with good torque is more important I'd imagine. What I propose (supposing I bother changing from a 230V system at all) is to use a speed servo (which is just a small tachometer in the feedback loop) for good speed control irrespective of load. It's a standard and respectable control technique.

As for a source of 12V DC motors, I'd have thought that a permanent magnet motor with brushes would do fine. I like the idea of using one from a pump, but there are loads in a modern car, in particular the windscreen wiper motor. The lifetime need not be that high: a sewing machine will probably be used only for a few tens of hours a year actually stitching so I think that almost any electric motor will be robust enough provided it develops enough torque.

Critique welcome!
 
Given that 99.999% of sewing machines are 240 or 110v, it is reasonable to assume that spare 240/110motors are available everywhere. These will be designed to have the right torque characteristics.

If the rating is 115W max, then there are 200W inverters on ebay for <£15, which also gives you some e.g. phone or laptop charging as well.
 
How do you get your 1kgf?
I think my machine works pretty hard when shoving a big needle through 4 layers of canvas, but I wouldn't be able to guess the torque.
I'm sure the flywheel helps a lot.
I would not expect the motor to be ever so efficient, whether it's 50 or 75% does not make much odds.

Wiper motor might be a good call.

Not sure about your control system, it will deliver max current in the event of a jam, rather than stalling it may break the needle?
Maybe a feedback system that controls torque up to a certain speed, then limits speed might be ideal. Not exactly my field, but there are lots of sophisticated PWM control circuits out there.
You may gather I give my machine a hard time making covers etc.
 
I think the main reason your estimate of the power is so low is that sewing machines go faster than 200rpm.
At least when SWMBO is driving!
 
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