I wanted to follow up and show a project I have been working on. I bought each of the sewing machine motors that were discussed above, the "Enduro" motor
https://smile.amazon.com/Enduro-Sewing-Machine-Motor-Electric/dp/B079P8RQRQ/ref=sr_1_2_sspa?ie=UTF8&qid=1543944064&sr=8-2-spons&keywords=sewing+machine+servo+motor&psc=1
and the Consew CSM-1000 (aka CS-1000)
https://smile.amazon.com/Mophorn-CS1000-Machine-4500RPM-Industrial/dp/B07HFTMR8Z/ref=sr_1_14?ie=UTF8&qid=1543944064&sr=8-14&keywords=sewing+machine+servo+motor
that Ssonerai showed.
As Ssonerai suggested, the Enduro motor seems to be more of a simple DC motor whereas the CSM-1000 seems to be a true servo motor. When it is running, even at low speed, you would be hard pressed to stall it out by grabbing the pulley. When you do, the controller just gives it more juice, increasing the torque while maintaining the rpm.
The CS-1000 is much smaller and lighter weight, so I kept it and returned the Enduro - it was basically the same size and weight as the Penn State motor.
Both motors use a Hall Effects system to control the speed. I did some reading up on that technology and got to wondering if I couldn't replace the Hall Effects control with a simple potentiometer as a speed control. The short answer is Yes
There are a couple of connectors on the back of the motor control housing, the smaller 6-wire connector goes to the original speed control, even though only 3 wires are used. The Red and White wires are the +5v and common and the Yellow wire is the wiper. Using the original speed control, I found that when the motor stopped, there was 1.00 VDC (using a multimeter) between the White and the Yellow lead at the connector. As I increased the speed, the voltage increased to 4.21VDC at 4500 rpm.
So I hooked up 1kohm variable potentiometer as shown in the pictures below and VOILA, I was able to control the speed of the motor.
One thing to keep in mind if you try this yourself, is that without that 1 volt signal at zero rpms, the motor control will give you an ER-4 error, which basically means it thinks the foot pedal is not connected. So with the potentiometer connected, turn it down to where the motor stops running, but not all the way to the left. Then, when next you power up the motor control box, it will sense ~1 volt and allow you to increase the speed of the motor by turning the potentiometer to the right.
I also found the the speed readout on the motor control box is reasonably accurate.
One other quirk about the speed control is that it will only speed up the motor in 100 rpm increments, not in a smooth ramp up, so that may be a show stopper for some of you.
Finally, the CYA section - I am neither an Electrician nor and Electronics Engineer, so I cannot be responsible for any damage to you or your motor if you should try to do this. But I have tried to document what works for me.
The next phase of the project will be to try to document the missing P-XX values and what they do. I have asked the seller and they have promised, in turn, to ask manufacturer, but I'm skeptical that I will get any info back from them.
Hope this helps,
Gary