Another Speed Reducer Question

[hercules]

I have read a lot of the posts regarding speed reducers and servo motors. I still don't have a full grip on the subject.

First question is - what is the downside to running just a speed reducer with the clutch motor?

Second question is - what is the downside to running just a servo motor without a reducer?

Third question is - what is the deal with servo motors and braking / non-braking?

Last question is - if running at crawling speed all the time, will the machine oiling system still work okay?

Thanks a lot.

[dikman]

1) None really (unless you want maximum speed, of course). It will give you better slow speed control.

2) None really. A speed reducer with a servo will give increased torque at slower speeds.This type of setup can give very slow "walking" speeds.

3) Not sure what you mean. When you take your foot off the pedal the motor stops.

4) If you have an auto oiling system, the chances are very high that it won't work too well at constant slow speeds. It has been suggested that in such a case it's a good idea to regularly wind a bobbin at normal speed, to circulate some oil.

[TinkerTailor]

Everything Dikman said plus:

1. physical constraints. Clutch motors tend to be bigger and some have had issues with getting everything fitting nice under their table. Depending on table configuration some have trouble fitting a speed reducer with a servo.
2. When i got my 5100 it was set up on the middle pulley of the speed reducer, and I found my servo did not like the lowest couple of speeds. It has a speed adjustment from 0-40. Anything under 6 and it got notchy. It no longer slowly ramped up speed as you pushed the pedal. I could do stitch by stitch at 5 but had to run it above 7 for smooth control. It was like it had 3 speeds, not a gradient. It sewed almost a as slow as 1 stitch a second, but would jump between speeds. With my reducer on the little pulley, I run the speed at 18 and can go 1/2 stitch a second, and control it smoothly. I can also do 3-4 stitches per second pedal to medal, no speed change. Plenty for my work. If i need more my motor is only at half speed.
3. My motor has a brake, and if i take my foot off too fast when i am pedal down, the pedal travels up too far and it brakes, shaking the whole table. It actually stops just fine without the brake and i would like to turn it off in the servo controller, but do not know how. My techsew servo is designed to brake when you heel the pedal i think
4. Do a weekly Pedal Metal Maintenance. Unthread the machine, turn up the speed, Crank some heavy metal with a whole bunch of double kick drums and try to play along with your machine. Crappy eastern European electronica works as well, if you must........just stop putting it in youtube videos people..

[hercules]

Thanks for the replies. It's sounding to me like if the goal is slow, fine control then you really need BOTH a servo and a reducer. Otherwise, one or the other would be disappointing.

Would the reducer alone simply be too slow to run up to speed when desired? Is that why the combination works better?

[dikman]

It will still run up to speed quickly, the reducer will have minimal effect on that, what it will do is limit the maximum speed depending on the pulley ratios.

You don't necessarily need both, it all depends what you're trying to achieve. Those who are trying to get really slow speeds generally aren't worried at losing their high speed so it's not an issue. If you still need fairly high speed then it's going to be a balancing act, juggling servo speed settings and pulley sizes. I've also replaced the handwheel pulley on a couple of my machines with larger pulleys. This is another way of adjusting speed and ratios without fitting a reducer. For example, my Pfaff has a servo, fitted with a 1 3/4" pulley and the handwheel has been replaced with an 8" pulley. This gives very slow control but it is a little notchy (glad you mentioned that, TT, I thought it was just my motor) so I'm going to experiment with a larger pulley on the motor and adjust the servo settings to see what difference it makes.

The relatively low cost of servos these days has been a boon to us newbies as it makes it so much easier to control what are often high speed machines, without having to try and master a clutch motor (I still remember the "excitement" the first time I put my foot on the pedal of my first industrial Singer - scared the daylights out of me!!!). In fact, I've just ordered my third servo, for this particular machine.

[hercules]

Okay, I think maybe from what I'm hearing I will try the servo first. Maybe that will do it. Then I guess I could always add a reducer later. I can control pretty well with the clutch, but I do a lot of hand-wheeling in the turns and corners. It would be nice to just run it all the way. Oh and by the way, with the servo, since the pedal acts like a rheostat why can't you just set it for its maximum rpm and just pedal in what speed you want? In other words, why limit the speed at all - just use the pedal like the gas pedal in your car, right off idle or all the way up.

[TinkerTailor]

Servos have a narrower range of speed at the pedal. Can't get all the way slow and all the way fast at the same time. Have to pick a range. Guys who have servos with a dial control instead of clicky buttons for the speed like them because they can reach over and adjust the speed range without looking and doing the clicky clicky dance....

[dikman]

Mmm, I can only speak about my servo(s), but there is a setting for the max speed, and this determines the sensitivity at low speed. If I want very slow speed control then I need to set the max speed lower than it's capable of. Conversely, if I set it to its max speed then the slow speed control is touchier. Like everything in life, it seems, there are always tradeoffs. No big deal for me as I'm looking for slow speed control.

Which machine do you want to put the servo on?

[hercules]

I have a Consew 206 RB1. I have also read where some will set the speed at a certain range then just floor it. I guess that would be an okay way of avoiding runaways.

When I release the pedal on the clutch motor it stops. Does the same thing happen on the servo, or does it "coast" down?

[Constabulary]

I have set my servos to 2700 rps max speed and the speed 3:1 (150mm : 50mm) reducer doest the rest. I´m using JACK Servo motors from College Sewing with 750Watts I have no problems all with the speed control. Both are brushless servos.

Servos stop as well when you step off the pedal. The brush type motor have a mechanical brake and the brushless have a magnetic brake AFAIK.

Edited January 22, 2016 by Constabulary

[Cobra Steve]

We use a ball bearing driven speed reducer on all of our equipment along with a full brushless digital servo motor, meaning that there is NO mechanical brake that will wear out and need to replace. With our system, when you take your foot off of the pedal the current stops and so does the motor. I have never liked servo motors with the mechanical brake because it costs extra money to replace and repair. We try to keep it as simple as possible for the customer.

[Davidstryingtosew]

I use 3:1 reducers with 1275rpm clutch motors. works great for me. I personally like to hold the handwheel and feel the clutch slipping. But I'm sure the same thing can be done by setting the belts loosely with a servo. I had a servo motor and just didnt like fussing with it. But it was a cheepo motor, so I cant really compare between it. I am planning to buy a quality servo motor next month to try it out again. Just need to save more money. The clutch motors are huge and getting everything set up can be a challenge, but not impossible. You may have to drill new holes and move the motor location, but thats it. I have a video of a Juki 562 with a reducer/ clutch motor and a 2" pulley on the motor. It doesn't show the set up, but you can see how the machine behaves: https://www.youtube.com/watch?v=n3H_SHMAn-Q

[Evo160K]

The Singer 45K53 that I purchased recently came with a servo motor, something new to me. So while searching LW and the internet recently for information on operating and controlling servo motors, I came across these outstanding videos on modifying the speed gradient on servo motors. They made a huge difference.

It will be better if you watch the first video before the second, the second will make more sense.

http://www.swflholsters.com/358/sewing-servo-motor-diy-smoother-speed-control-mod-paper-gradient/

Edited January 23, 2016 by Evo160K

[hercules]

I saw those videos as well, but am a little confused. Is the stock configuration a piece of transparent material with shading, or what? And is he changing the transparency, the shape, or both?

[Evo160K]

Hercules,

My Singer and servo were pre-owned, the servo had an obviously modified card in it, so I don't know what was in there originally. I suspect the card shown at 10:44 of the first video is what they look like from the factory. It appears to be a piece of paper or card. After spending some time making and shading a card to my liking, I learned the less light getting to the "receiver" end of the light beam, (the top I believe), the faster the machine will run, and since the beam is round you can't just block out the light by cutting a straight edge through it.....that may not give you the gradient/control you want. So he seems to be changing the transparency by shading with a pencil and changing the shape. Good thing about it, with patience you can set your speed to start and progress any way you like. It's really quite amazing how you can modify your servo.

[Darren Brosowski]

As we are talking about the ultimate ratio between the motor and machine shaft you also need to consider the balance wheel.

Industrial machines like the 206RB usually have 2 1/2" to 3" machine pulleys but a 45k has a pulley three times or so the diameter so it runs at one third the speed for the same motor.