Question About Servo Motors

[particle]

So, I received my new Cobra Class 4 recently and have been playing around with it a bit. One thing that has me a bit annoyed is the lack of easy variation in the speed when you press the foot pedal. Yes, I'm well aware you can adjust the max speed on the motor. When I press the foot pedal, I expect it to utilize at least a fair portion of the travel of the foot pedal to vary the speed. Mine is so sensitive, all the speed is literally controlled in probably less than 1/8th of an inch of travel. Is this normal? It might as well be a clutch motor at this point!

The actual lever on the motor has a nice range of movement. Sadly, most of that movement does absolutely nothing to affect the speed.

And what's the point of the low-speed start mode? Why would you want the machine to start slowly, then surprise you by ripping away at full-speed and ruin your work? The only purpose I could see is if you just keep tapping on the pedal to continually make the machine crawl at low-speed until you are ready to go full-speed. Maybe I'm missing something?

Here is a video I shot that shows what I'm talking about. Please ignore my wife's runner's feet. It was an impromptu filming. She just ran a half marathon and lost a couple toe nails...

http://youtu.be/IsxufcVvKdc

[Luke Hatley]

Look at the pulley on the motor, if it is 3" or larger replace it with a 2" pulley.

I had to do that on mine.

Also there are 2 rods with an adjustment clamp on mine i had to lengethen mine for more travel for the foot pedel.

Edited May 21, 2012 by Luke Hatley

[gringobill]

That's odd that your machine is doing that. I have one that's coming up on two years old and it is not that touchy. I have to push the pedal down about 1/4 to 1/3 of it's stroke before the motor starts moving. I'm wondering if it has somthing to do with the length of the chain between the pedal and the lever, it may be too tight and needs some slack in it, Just a thought? My chain has quite a bit of slack in it and the motor is pretty controlable.

[gringobill]

I just watched your video and noticed the noise the motor is making, mine does not do that. It sounds like it is really winding up with very little pedal movement. Something sure seems to be out of adjustment. What speed do you have your motor set for? You may need to lower the max speed way down. I'm not where I can look at the speed on mine right now, but it's maximum speed is set pretty slow so I have more control.

When I want to adjust my speed, I unthread the top of the machine so I can watch how fast the needle moves when I'm adjusting the speed. The only complaint have about this machine is IMHO adjusting the speed is kind of unhandy. The machine has to be running to adjust the speed up or down and for me to do that I have to get on my hands and knees and push the pedal with my left hand and adjust the speed control with my right. Obviously I can't see what's going on above very well. However since your wife will help you making it a two person job would simplify it a whole lot.

[Northmount]

The arm on the motor usually has 2 or 3 holes in it for the foot pedal connection. Make sure it is in the hole furthest from the shaft it pivots on so it has the longest arc to travel through.

CTG

[particle]

I should have mentioned this, but forgot. When I filmed the video, I had the motor set at max speed - I was winding a bobbin. But, regardless of the maximum set speed, the lack of control in the foot pedal pressure makes the higher speeds useless. The whole point of the servo motor is to provide great control in speed when compared to a clutch motor. When you press the clutch motor's pedal down, once the clutch grabs, the machine takes off. It's very hard to control the speed. That's the same feeling I'm getting from this particular servo motor. I expected more control in the foot pedal. I should be able to use max speed on the motor if I want to, but also have access to the slower speeds by applying less pressure to the foot pedal. That's just not the case - maybe I expected too much?

[particle]

The arm on the motor usually has 2 or 3 holes in it for the foot pedal connection. Make sure it is in the hole furthest from the shaft it pivots on so it has the longest arc to travel through.

CTG

Done - that was the fist thing I changed when I assembled the machine. It came on the middle hole, and I moved it to the furthest out. Along that line - I fabricated a longer 12" arm out of a bar of aluminum I had laying around. I put holes every inch, and bolted it to the existing lever on the motor. This helped with the variation quite a bit, but added too much weight and the springs couldn't overcome it so the machine wouldn't shut off I don't feel like adding new springs to compensate for the added weight just yet. I moved it to around 6" and that fixed the shut-off problem and gave me more control in speed than stock configuration, but I removed it until I could talk with Kevin today to see if I just got a bad motor.

[Gregg From Keystone Sewing]

A 'Slow Start" option that is usually adjustable is great to allow the first few stitches to catch up, so they to do become lose or get caught back into the sewing mechanism. It's a really useful option, IMO, but you can of course turn this feature off if you like.

As for the power band, I do hear you, some have a very limited range of variable speed, as in you can go fast to slow with good control, as long as you do it withing a short range of arm movement, where having the flexibility of a larger 'power band' would make life a lot easier for the operator. This is a concern with a lot of these servo motors coming out.

[particle]

So the slow start feature helps to minimize initial stitch problems? That's interesting and good to know - the manual doesn't say anything about that as far as I can recall so I really had no idea what the benefit of the feature was.

[Gregg From Keystone Sewing]

So the slow start feature helps to minimize initial stitch problems? That's interesting and good to know - the manual doesn't say anything about that as far as I can recall so I really had no idea what the benefit of the feature was.

If you have the documentation that I'm thinking you have, then it's probally pretty limited for sure.

'Slow Start' or AKA 'Soft Start' is usually a feature found on more expesive Ho Hsing, Mitsubishi, or Efka motors, so having this option on a less expensive motor is a pretty nice feature.