Servo Does Not Vary From Top Speed.

[FoxyD]

I have just replaced a clutch motor on Brother B755-mkIII with a servo. The make has been over-labelled but model is WR561-1 and has awful instructions translated from Chinese. If I set the top speed to 1000 RPM or more, then the speed will vary with the treadle depression but with a lower top speed the treadle acts like an on/off switch, delivering the chosen top speed with no variation with treadle travel. The accelerator control is a magnetic wiper moving near to a 3-lead electronic sensor. Can anyone suggest how I can get variance at lower speeds?

[Colt W Knight]

I could be wrong -

Do you think this problem is because your motor doesn't have enough torque to turn the pulleys at the lower speeds when you are feathering the pedal? A lot of machines need different sized pulleys to run at slower speed with adequate torque to sew.

You can try pressing he pedal and helping the pulley get started to check.

Edited April 3, 2015 by Colt W Knight

[FoxyD]

Thanks for your reply. I don't think it could be torque because there was no leather under the needle when it does this.

[biglew]

look at this... maybe it will help. It made my motor run a bit of smoother curve

[FoxyD]

Thanks so much for that. Unfortunately the servo in that video runs on an optical sensor. My servo is magnetic so the adjustments suggested in that video cannot be applied...

[Gengle100]

Foxy D I just acquired the same servo motor, but I did not come with instructions. Any way you could send those my way?

[TomG]

There is a servo motro out there - I think it's a Consew 500 - That uses a Hall Effect transistor. These are actually a semiconductor that energizes with a magnet. So, it's either on or off. You can't do variable speed with those via the foot pedal.

The ones with the optical controller, like the one on the video, are able to be variable speed. I Think the COnsew motor I got to replace the hall effect one is a 550 or 1000? I'd have to look.

I will tell you that the paper vane didn't work super well. It was fine at first, but as it sagged over a short period of time, it's range and control points changed. One of the isses is that the light on the optical interruptor is way too bright. It makes the control of how much light hits sensor very touchy. And it is so bright that a piece of paper with pencil marks doesn;t work. I used a piece of plastic gift card I cut into a ramp and played with that with some success.

I ordered a couple of replacement vanes and did some cutting and filing, but although I did get a variable speed, it was still too touchy for my tastes. But it at least made it consistent and I didn;t have to worry about the paper sagging.

Still better than the clutch motor.

[Constabulary]

My preference is the 750 Watt JACK Servo that College Sewing in the UK sells but I use it in combination with a 3:1 speed reducer. The lowest motor speed is 200 rpm but the SR slows it down very well. For my purposes they work very well. AFAIK they are also magnet controlled.

I have 2 of them and I´m quite pleased. But I admit - the instructions manuals are a pain!!!

[FoxyD]

Foxy D I just acquired the same servo motor, but I did not come with instructions. Any way you could send those my way?

Soon as I find it amongst my junk I will post it up for you.

[Trox]

Hi, I once had the same problem with my 600 W (220v single) Cobra servo motor. Then they sent us an fix, a small black tape piece in an envelope. I put the tape bit in place and the servo worked just fine. Very good low speed control, but I lost some of the top speed. That must have been a couple of years ago now, but it still work fine; no changes yet. The Cobra motor looks very similar to the motor in the video (different color only). I remember it was very sensitive to the color shades on the paper modification I tried before the fix arived. With lighter color, more top speed and less low speed control. So the best fix for the optical sensor is something dark that reflect less light.

I just wanted to mention that the fix worked fine for me. However it will not help for the motor in question here, with the magnetic speed control. Perhaps posting some pictures will help, there might be similar motors out there of other brands that work fine (or worse). That's likely since it's a Chinese product. It will also help others to know what to stay away from in the future. We should have a topic about different motors, where we could compare them to each other. That would be very helpful for the future. Thanks

Tor