Originally Posted by Gringo
After reading Dan's letter, I had to go look at my machine. My motor is a clutch type (it says easy clutch) and it has variable speed from one stitch at a time to probably 200 mph. We have three machines and all have the same type motors. 2 Chandlers and a Pfaff. The only ones I've seen that are single speed are the old leather machines from the shoe shops and they are really slow. If it only has one speed you are going to want to change it for sure, you need variable speeds. Just push pedal down by hand an see if it speeds up as you push down.
If they are clutch motors, they are AC motors running the whole time the switch is turned on and they are going at full speed, whatever that is. The only thing that makes them go slower is skill at engaging (slipping) the clutch. Like Gringo said, the treadle can be adjusted somewhat so that the treadle requires more of a push to get it going full speed, but the clutch motor is still either on or off.
The servo is a DC motor (same principle as a variable speed drill) and is only on when you press on the treadle, so you won't even hear it unless you are sewing. I can adjust my servos so that if I want to, pushing down on the treadle all the way will only make one very slow stitch at a time, but I have the same power as if the motor was going full speed. My motors are Reliable SewQuiet 3000's.
BTW, speed and power are two different things. With regular AC motors, a 1 hp motor produces 3 ft. lbs. of torque at 1750 rpms. A 1/2 hp AC motor produces 1.5 ft. lbs. of torque at that speed. As you go slower, torque increases. If you go above 1750 rpms, torque will decrease.
Servos are DC and have constant torque throughout the speed range.