GerryR

@Samalan made it a math lesson, but I have a center finder.

7/8 + 24-1/2 = 25-3/8 ...you got ahead of yourself. 24-1/2 + 3/8 = 24-7/8

Definitely handier, if you have one. Alternative methods are good to know.

He got his ruler at a discount, only 11" long!

For shorter lines, you can use a compass and swing an arc on both sides of the line from both ends with the compass set at a distance greater than half the line length. Connect the intersections of the two arcs on each side of your line, and you have a line perpendicular to the original line directly thru its center. Helps if you don't have a ruler. For longer lines, make a compass from a piece of string and a pencil or marker.

Cooling, you can run a servo at very low speed (its just a motor), but you have to current limit so you don't over-heat it, and when you current limit, you lose torque. By requiring a minimum start speed, you assure that someone can't run at very low speeds for any length of time and destroy the motor. At that minimum speed, the cooling design parameters are met. (A stepper motor is designed to remain stopped with the current being sufficient to hold the designed load and not destroy itself, though many systems drop to a lower current when stopped, as you don't usually need the full current to hold the load when stopped. Many DC servo systems do the same when the load is stopped by current limiting. That is not necessary on a sewing machine and would be more expensive to implement.)

You can run the 550 watt motor from the 750 watt control unit. The other way is not advisable (750 watt motor on a 550 watt controller) unless you know you won't exceed the 550 watt load.

In the system I have (AC-VFD), the motor is spec'd at 35-459 RPM, 10-90 Hz. That is the output from the 5:1 reducer (gearmotor). I have a 1-1/2" motor pulley going to a 7" drive pulley for another 4.67 reduction giving 7.5 RPM at the machine at 10 Hz (minimun specified operating frequency for the motor), which amounts to 0.125 revs.per second or 1 revolution every 8 seconds. But that is not the point. The point is that when I hit the pedal, and the motor starts to move, I am easily in the safe operating zone of the motor, 10 Hz minimum. It would be absurd to run the machine at 1 stitch every 8 seconds for any length of time. The idea is to keep the motor happy and stll be able to do some controlled slow stitching. Just my $.02

Keep rambling, good info!!

Yes, but that would defeat the purpose of a softer start, which you are trying to achieve.

Those optical filters are nice, but they defeat the purpose of starting the motor at the so-called required minimum speed, which is probably not necessary in most instances.

Yes, I stated that both motors would generate the same amount of heat and meant power; that is where the heat management comes into play, and like you stated, the choice of materials used.

Power is power, so if it requires a certain amount of power to pierce the leather, both motors, whether 9 coil or 12 coil, will generate the same amount of heat. It all depends upon the heat management of the motor design, so "should get rid of the heat better" is up for grabs until the longevity of the motor is proven. 12 coils will distribute the heat better, but it is still within the confines of the motor housing.

Torque from a motor depends upon current in the windings and the number of poles (basically, I'm not a motor expert) so without a speed reducer of sorts, the motor has to be very robust to maintain high torque at slow rpm and cooling is paramount. The speed reducer gets the motor rpms up where cooling is better, current is lower and torque is higher because of the gearbox. As far as the OP is concerned, I don't understand why he can't just tell us his new motor/system specs; why all the mystery?

I know, I just wanted him to say it. I still prefer VFDs with 3-ph gear motors over DC systems. JMO, YMMV.