Question For Cobra Owners

[VanDutch]

Hope you can help me in setting my servo motor speeds for max torque. I find that if I am sewing slowly through thicker material the motor stalls and I have to manually turn the wheel a fraction. My motor settings are.

Speed = 1 (1-9 setting)

RPM = 10 (1-40 setting)

There is a speed reducer installed.

What settings do you use?

cheers

Frans

[VanDutch]

No cobra users out there?

[Northmount]

The slower a motor turns, the lower the torque it produces. To get the punching power (torque) you need for heavier leather, the speed reduction has to come from the speed reducer. Do you have a stepped pulley set (more than 2 belt grooves)? If so make sure the motor belt is in the largest diameter groove, and the machine belt is in the smallest diameter groove.

Tom

[rmr]

Frans

I had the same problem a few years back- was very frustrating at first- - I posted on here and several guys including Steve at Cobra contacted me and recommended I double check the bolt holding the pulley wheel to its shaft- as it was probably slightly loose and had allow3d the pulley wheel to shift upwards ever so slightly resulting in the tension on the belt to be reduced and causing the needle to stop/stall in the middle of thick layers of leather.

So I checked it out when I got home from work that night- they were spot on- tightened up the bolt - after pulling the pulley wheel assembly downward about 1/4 " to place more tension on the belt- never had the problem since then

RMR

[Greystone]

I have not had the problem but I've also been very limited in my usage and

limited to mostly softer leather bridle, chromexcel , and upholstery,

But at times up to 4-5 layers of, 5-6 an-8-9 oz and no issue,

LOVE my KING cobra

[Trox]

Hi Frans, do you have the EPS motor or the regular servo motor without needle position (Called EPS by Cobra). If you have the EPS and your machine flywheel is loose the machine will stall, because of the position sensor installed on it. It will send faulty signals to the motor to stop. Otherwise, I would need to know about your sewing thickness and thread size etc. to see if its normal or not. This motor should be powerful enough for this machine.

Good luck

Tor

[Cobra Steve]

Hi VanDutch,

The setting that you refer to as SPEED has nothing to do with speed at all. Actually it is a setting that can be used to cause a 'delay' from the time to demand power until the motor actually starts turning. On some sewing applications (not leather sewing!) some operators prefer a slight delay and that is why we have incorporated this electronic option on our motors. Your choices for this setting range from 0 - 9. You should have yours set to 0. (Hold the down button until the display reads 5.0 and then press the UP buttom once to get into the 5.1 programming mode. Press the down button once and your setting will appear on the readout. If you are set at 1 - press the down button one more time so that the display reads 0. Wait for the motor to store that setting - about 5 seconds.

Now on to your speed (RPM) setting - I suggest you move the Max RPM from 10 up to 12.

Our motors are 600 Watts or 8.3 HP - more than enough to sew up to 7/8" leather smoothly. I would check both your V-Belts to ensure they are not slipping - it sounds like at least one of them are slipping. And while you are checking everything, make sure the 'pointed' bolt on your handwheel is firmly tightened in to the groove on the main shaft of your Cobra. Then firmly tighen the other bolt as well.

If you have any other questions, please contact us.

Thanks

Steve

[Greystone]

KUDO'S n SHOUT OUT to

Steve and LMC

[VanDutch]

The slower a motor turns, the lower the torque it produces. To get the punching power (torque) you need for heavier leather, the speed reduction has to come from the speed reducer. Do you have a stepped pulley set (more than 2 belt grooves)? If so make sure the motor belt is in the largest diameter groove, and the machine belt is in the smallest diameter groove.

Tom

Hi Tom.. I have worked a lots with Servos/Stepper motors on CNC machines and the feature of these motors is that they have Max torque at any RPM range. They don't use inertia like an induction motor does.

Hi Frans, do you have the EPS motor or the regular servo motor without needle position (Called EPS by Cobra). If you have the EPS and your machine flywheel is loose the machine will stall, because of the position sensor installed on it. It will send faulty signals to the motor to stop. Otherwise, I would need to know about your sewing thickness and thread size etc. to see if its normal or not. This motor should be powerful enough for this machine.

Good luck

Tor

Hi Tor.

Yes I have the EPS motor. I will check the flywheel. Thread size is 277 and the material thickness is 8-10mm. I only have issues at really slow speeds like corners on gussets. Normal sewing it is punching through no problems.

[VanDutch]

I must say that I have had great support and communication from Greg (Dealer) Qld Sewing Machines. Yesterday I delved further and decided to try something to eliminate belts etc.

I removed the flywheel belt and the needle and free-wheeled the machine.. I found that after a number of turns the wheel grabbed(stopped) and required backing it a fraction before it would allow me to spin forward again. This is def not normal. Any ideas what this might be?

[Cobra Steve]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

[VanDutch]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

Thanks Steve.. I will do that.. Appreciate your help.

Will let you know the outcome.

BTW I love the machine.

cheers

[Cobra Steve]

Thanks good buddy!

[VanDutch]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

Steve.. checked the shuttle..all clean. Also double checked the belts and pulleys.. All tight.

[muzzleblast]

Frans, I think I share your same problem with my new C4 and am also looking for a solution.

When stitching through two layers of hard, 10/12 ounce veg tan, with 346/277 and a 25 needle, very slowly, the machine has to be hand wheeled because there is not enough torque at very slow speed to drive the needle through. Increasing the RPM setting is actually counter productive, because I am needing to run the machine very slowly, smoothly and precisely to land my stitches. Going through hard, Barge glued, double 16 ounce in a straight line at top speed is actually very easy. But, that is not the issue. (And yes, belts and pulleys are tight.)

If anyone has any thoughts or suggestions it would be appreciated.

[Wizcrafts]

VanDutch;

Try placing the stitch lever in the zero position; not moving the feed dog forward or backward. Then rotate the flywheel as before and see if the binding stops happening. If so, a clamping screw or bolt may be loose on the stitch length/direction crank arm. This can be checked from the large round cover plate on the right front and back of the head. I have heard of cases where the one accessed from the back shook loose and made it difficult to balance forward and reverse stitches. It could also halt the machine if one of these bolts backs out too far.

[Northmount]

Hi Tom.. I have worked a lots with Servos/Stepper motors on CNC machines and the feature of these motors is that they have Max torque at any RPM range. They don't use inertia like an induction motor

There is a big difference between servos and steppers on CNC machines and those used on sewing machines. My statement was intended for anybody but a CNC user. I normally say "most motors", but neglected to do so this time. Other motors such as used for traction motors don't fit the general statement either, but no one here would draw such a comparison, so I would usually be safe with such a generalization.

For your sewing machine servo, 600 W, 0.83 HP, its torque does fall off at low speed. I don't have as heavy a machine as your Cobra, and have a servo with 3:1 gear reducer followed by a 6:1 reduction pulley set. It can go really slow and punch through 3/8" of leather right from the start, and not run away because I had to give it too much juice to get started. Of course my top end speed is much reduced too, but that is the way I want it. I don't need high speed production.

There are quite a few threads here about servo motors, pulley reducers, etc. that you can peruse and see what others have experienced and done.

Tom

[VanDutch]

There is a big difference between servos and steppers on CNC machines and those used on sewing machines. My statement was intended for anybody but a CNC user. I normally say "most motors", but neglected to do so this time. Other motors such as used for traction motors don't fit the general statement either, but no one here would draw such a comparison, so I would usually be safe with such a generalization.

For your sewing machine servo, 600 W, 0.83 HP, its torque does fall off at low speed. I don't have as heavy a machine as your Cobra, and have a servo with 3:1 gear reducer followed by a 6:1 reduction pulley set. It can go really slow and punch through 3/8" of leather right from the start, and not run away because I had to give it too much juice to get started. Of course my top end speed is much reduced too, but that is the way I want it. I don't need high speed production.

There are quite a few threads here about servo motors, pulley reducers, etc. that you can peruse and see what others have experienced and done.

Tom

Tom.

I am talking about small servos & steppers that are used on CNC machines. Motors that are only $100-$200 each. some of these motors are only 6x4inch and they drive 500lb gantry's with minimal gearing.

Tom, your gearing is much higher at 18:1. From my understanding the cobra's with the speed reducer only get 9:1.

[Northmount]

Tom.

I am talking about small servos & steppers that are used on CNC machines. Motors that are only $100-$200 each. some of these motors are only 6x4inch and they drive 500lb gantry's with minimal gearing.

Tom, your gearing is much higher at 18:1. From my understanding the cobra's with the speed reducer only get 9:1.

So what's the coefficient of friction for your 500 lb gantry? FF = mu * N I'm sure that it is properly mounted, aligned, supported with bearings such that you could move it easily with your little finger (with all cables or rack and pinion removed). Try pushing a needle through the leather with your pinky. That's why you bought the sewing machine. Anyway, enough said.

Tom

[VanDutch]

Whilst we are on the subject of servos, here is a torque curve of a servo motor. Servos actually lose torque at higher RPM. Totally opposite to an induction motor.

[VanDutch]

Whilst we are on the subject of servos, here is a torque curve of a servo motor. Servos actually lose torque at higher RPM. Totally opposite to an induction motor.

03_speed_torque.jpg

In reality a True servo/stepper motor has the most torque at 0 RPM. The type of servo motor fitted is most probably not a true servo because otherwise we would be unable to handwheel when the unit is switched on..

Anyone actually know more about the motors fitted?..

I have received several PM's from owners with similar issues. I do want to make it clear this discussion is not about the machines but rather the motors. Issue seems to be the motors do not have sufficient toque to punch through thick leather at very slow speeds without additional speed reduction.

Edited May 4, 2014 by VanDutch

[Trox]

Hi VanDutch,

I understand you have the King Cobra machine with the EPS motor (position motor). I do not have the same setup as you. I use a expensive Efka servo system on my 441 machine that are strong enough without a speed reducer. I do have a regular Cobra servo/speed reducer on one of my other machines (same motor without EPS) These motors are among the most powerful economical servo motors on the marked today. Although they have had some faults on the speed control before (that has been fixed now) they have always had enough power. Very strong compared to others in the same class (price range). Its not fair to compare them to `high end motor systems as Efkas and Ho Sing that cost 1k $. If its a loose part on the machine somewhere in the needle feed a position system will stop, it reports the wrong position and the motor will stop. Or turn an extra rotation, thats the way these systems works. What ever the fault is you can rest assure you are in the best hands, Steve will make it right. And if it is a motor problem, I still think its related to the position system. The EPS motor is the same as the regular servo motor with a built on needle position system, same spec`s, power and torque. Together with a speed reducer it should have no problem sewing that on slow speed.

Good luck.

Tor