servo motor startup speed

[fibersport]

Are there any servo motors that actually have a zero speed startup?  I bought from a supplier a few years ago but it doesn't start at zero, the controller says 200 I think, not sure if that is truly 200 rpm or not but it isn't zero.  I see conflicting specs on some of them saying the speed range is 0-4500 - but will it actually start at 0 rpm? 

[Tastech]

 I remember watching a youtube video where this guy worked out how to make a servo motor variable speed  without a reduction wheel . From memory he used a specific motor which i believe was a consew brand . What he did was quite genius in that the tweek was counter intuitive and used a simple piece of paper . The basic principle of what he did was fooling the machine . The motor speed is activated with a beam of light . When the light beam is broken the motor activates . The way it is on a standard motor is a piece of metal cuts the beam and it activates the motor . What the guy did was to either replace or extend the metal with a simple piece of copy paper . For some reason the paper cutting the beam makes the motor start of slow like the accelerator on a car . I have made a half arsed effort to find the video over the last couple of weeks but i would like to do it to mine so i will have a good search and if i find it i will post it . In the meantime if anyone else finds the video please post it as i am sure 50% of us will find it handy .

[Northmount]

2 hours ago, fibersport said:

0-4500 - but will it actually start at 0 rpm

Just semantics, but 0 rpm is stopped, not running. 

The question really is, what speed does it start out at, and does it have enough torque to punch through the leather?

[Wizcrafts]

This must certainly be a digital servo motor and probably an early design at that. When servos first appeared on industrial sewing machines, they either started rotating at 100 or 200 RPM. Cobra came up with a variable density transparency that replaced the existing light blocker attached to the control lever on the left side of the motor. Some folks made their own variable density filters with pencil strokes on clear plastic. I got the filters from Cobra and they worked well for about a year, then began to have a hiccup as the motor started up. About that time, the new style analog motors made their appearance and I bought one for every machine in my shop. These motors have a knob that is attached to a pot or a rotary switch that limits the top speed. I usually set mine about three steps up from the minimum setting. The startup from zero is totally smooth.

I get my analog servo motors and speed reducers here.

[Gump]

I have 2 Sewquiet servos, and startup is as slow as you would like no matter motor what setting you use right up to max.

[Uwe]

The short answers is NO, none of the brushless sewing machine servo motors you can buy today can do 1rpm, which is what you’re implying by starting from 0rpm. 1rpm means you’ll wait a minute for the motor to make a full rotation, three minutes or so for the machine to make a stitch. Not really practical.

The spec on most servo motors should really read: 0rpm, then 300rpm-2000rpm. There is generally nothing between 0rpm and 300rpm.

Most servo motors I have worked with have a starting speed of 300rpm, some can start at 200rpm, very few can start at 100RPM (including the 1,500 Watt motors I’ve been buying.) None of the motors I’ve seen can start slower than 100rpm. With a small pulley, that 100rpm starting speed translates to a stitch every two seconds or so on the big 441 style machines. That’s all I want, personally.

The minimum starting speed is kind of a design feature inherent in servo motors, and the controllers that drive them. While it’s technically possible to make a servo motor start veeeery slowly (or one tiny step at a time), the sewing machine motors on the market here in the US are not designed that way.

 

Edited September 12, 2023 by Uwe

[dikman]

Tastech, that method of speed control adjustment was used in early servos and as far as I know stopped being used some time ago. They tend to use Hall effect sensors these days, which work on a magnetic field variation to generate an electrical signal. It's pretty hard to tinker with these.

[fibersport]

Perhaps I should have worded my question along the lines of a slow ramp up in speed from 0 rpm to whatever maximum might be. 

I do realize that 0 rpm is stopped but one has to start somewhere, and I know what revolutions per minute means - and really why would anyone want to sew at 1 rpm?    Wizcrafts you seem to understand my initial question, starting at 200 or 300 rpm is what I have but not what I want.  It's that initial start up speed that I'm trying to lower.  A clutch type motor could be made to start up slow by slipping it but I don't sew enough to be able to master that technique even though I've driven vehicles with clutches for decades, slipping a clutch on a sewing machine just eludes me!  

Thanks for all the suggestions and comments, nice to have a great brain trust from which to tap in to once in a while.

[chisel]

12 hours ago, Tastech said:

....In the meantime if anyone else finds the video please post it as i am sure 50% of us will find it handy .

If these aren't the videos then hopefully they will help.

https://www.youtube.com/watch?v=X6CCxv3i4No

https://www.youtube.com/watch?v=wu2OT9MtzMc

 

[Tastech]

Chisel , They are the videos i was referring to . I now realize that the new servo motors are of a different type and this modification is not applicable .

I guess the only option is to reduce the motor pulley size or fit a speed reduction pulley .

In relation to speed reduction pulleys . Why are they so expensive . ? There is nothing to them really .By the time i get one sent to Australia i am looking at over 300 bucks . Twice the cost of a servo motor .

I need about 5 of them .As i am also a mechanical engineer i might just make up my own using off the shelf components and maybe just a little machining. I think i can do it for under 100 bucks a piece .

The way i see it i will need 2 pulley wheels of different sizes , shaft to suit .( might need machining ) 2 bearings and the bearing housings  , some grub screws  and maybe 2 hours .