Replacement Motor - Sewing machine (Stepper or Servo?) More torque needed

[ag273n]

I have a Singer Sewing machine - model 190 - and a problem I have with it is that its motor has too much RPM and quiet low torque - as a result, its stitching too fast for me, and it could hardly rotate on lower speeds...
So, I am hoping to replace its motor with something of higher torque, and lower RPM..

I'm thinking somewhere between Servo Motors and Stepper Motors
-what can you suggest?

 

[Alec_t]

Personally I'd go for a DC motor with PWM speed control. PWM has the advantage that torque is fairly constant over a wide speed range.

 

[duke37]

I have a speed control for a coil winder using a foot pedal which is just a variable resistance. This works well down to very low speeds.

To get more torque and less speed, use a smaller pulley on the motor or a bigger pulley on the sewing machine.

 

[ag273n]

To get more torque and less speed, use a smaller pulley on the motor or a bigger pulley on the sewing machine.

i was contemplating about this earlier before i posted... The pulley in the motor is already as small as it can possibly get, and in the sewing machine, there's a part of its case that won't allow for a bigger pulley, one option is to add a third - compound gear/pulley to help with the reduction, but has sadly very limited space for it - plus the belts

 

[Minder]

The problem with increasing power, you may stress other parts of the machine if you end up over taxing it.
Traditionally the motor has been a Universal motor on sewing M/C's, Do you know the technology of this one?
M.

 

[ag273n]

The problem with increasing power, you may stress other parts of the machine if you end up over taxing it.
Traditionally the motor has been a Universal motor on sewing M/C's, Do you know the technology of this one?
M.

i'm not looking to overpower it, i'm happy with what it can sew.. what i'm not happy about when i press down the pedal is that the initial rotation feels like its stalling, then when i press harder, it suddenly bursts stitches to a speed thats a little hard for me to control. - whats ideal would be if it can still rotate even in slower speeds - not necessarily stronger. I observed i could actually stall the motor by hand if i hold the wheel holding the bigger pulley - a weak motor.

 

[Minder]

Well that explains it a little further!
The motor technology is needed in order to take it further.
AC ?,DC?, Universal? etc.
Acording to Google it is Universal.

M.

 

[Minder]

Universal motors are hard to control accurately without feedback, but if the present M/C method is a variable resistance pedal, you may get an improvement with one of the simple Triac controllers and follow it with a bridge rectifier before the motor.
M.

 

[ag273n]

yes, the one it currently has isn't too different from the picture you posted - the standard motor for Singer Sewing machines. Mine is a 220v version.

 

[Minder]

Before changing the motor I would try the Triac method, if you are able to, there are many designs out there via Google etc. And simple to build with just a few parts needed.
M.

 

[kellys_eye]

When I've seen sewing machine operators use similar systems they always, and I mean always, start the sewing by manual rotation of the wheel as they press the pedal. This gives the motor the starting torque necessary to prevent it over-speeding when you 'get your foot down'.

Could simply be a 'method' is needed rather than a solution.

 

[ag273n]

Before changing the motor I would try the Triac method, if you are able to, there are many designs out there via Google etc. And simple to build with just a few parts needed.

would you have a link you can recommend for a diagram?

When I've seen sewing machine operators use similar systems they always, and I mean always, start the sewing by manual rotation of the wheel as they press the pedal. This gives the motor the starting torque necessary to prevent it over-speeding when you 'get your foot down'.

i do this a lot. I observe on my machine, there's always a point in the one full rotation that the resistance/friction seems to be the greater than the rest of it.. There's so many parts in this mechanical thing that i dont think I'd ever figure out which is causing it. As a result, sometimes it can run on its own, and sometimes i had to push full throttle on the pedal and it still needs a push on the wheel - which is annoying.

Plus, to think the machine is about 50+ years old, its motor is probably a little worn out. One time I had to replace its power cable because it caused a short circuit - the insulation of the cable literally decomposed and caused contact on the +V and Ground..
this thing is built like a tank, its older than me and it still works! - well... like the rest of those old time singer machines - they last probably more than a lifetime

 

[Minder]

Google Triac 220v motor controller.
In place of the motor place a bridge rectifier with the AC in and then wire the motor across the bridge +ve & -ve.
The 220K with be your foot pedal pot.
M.
e.g.

 

[debe]

With the Singer universal motor you don't need a bridge rectifier with the Triac speed controller.They work on AC or DC.

 

[Minder]

With the Singer universal motor you don't need a bridge rectifier with the Triac speed controller.They work on AC or DC.

Being a Universal motor I realize that.
The motor runs that more smoothly on DC.
M.

 

[duke37]

I wonder what the difference is between using AC and DC on a universal motor. I would think that the inductance would limit the current on AC and there would be no current limit on DC so, with no losses, the speed would go up to infinity.

A low voltage DC motor will have a strong correlation between voltage and speed, I have used one on a coil winder fed with rectified AC and controlled with a SCR which is triggered when the feedback voltage is not high enough. This will be boxed when I get round to it. Presently I use a battery charger, a Variac and a variable foot pedal, this works well but is cumbersome.