The following video compares a SewQuiet 5000 servo motor against a conventional clutch motor for powering industrial sewing machines.
Summary: When adjusted properly, a clutch motor is just as controllable as a servo motor, but it requires some practice, and a little more concentration.
There are modifications published on the internet for modifying an optical servo motor to make it have a “smoother” ramp-up than came stock with my unit in Spring of 2012. (This requires taking the unit apart and I haven’t bothered to to this yet.) I leave my top speed set at 600rpm, which is fine for the type of heavy sewing the (compound feed) Adler spends most of it’s time doing.
The Juki, with it’s clutch motor is a (bottom-feed) single needle unit that does light and medium weight sewing. I recently made drapes with it, and the raw speed and power of this unit (compared to the domestic sewing machine I used last time around) was intoxicating.
Clutch motors use more energy and make more noise, but they cost a lot less — especially if they came FREE with your used machine. I rather like the soothing hum it makes, as well as it’s bullet-proof feel and unstoppable performance, but that’s just the Alpha-male in me.
Each person must weigh “cost versus control” for themselves.
If buying a new machine, I would bite the bullet and not only buy a servo motor, but go all the way to a needle-positioning system. (“Pay once, cry once. Cheap out, buy again” has been my experience.)
A Juki 555-5 (clutch) and an Adler 467 (servo) were not harmed in the making of this video.