On Mon, 20 Jun 2005 19:38:46 GMT, "Tom Gardner"
wrote:

This dog won't stay petted!!! I have an application that unspools wire with
a dancer operated switch controlling a @35 RPM 1/15 HP ac gearmotor belt
driving a roller that a wooden spool fits on. I know I have to use "Shaded
Pole" or "Permanent Split Capacitor" motors as a cap start motor will
burn-up in a day due to the constant on/off switching. I have three of
these de-spoolers and need to make six more. These gearmotors are about
$250 ea and I have to replace at least two a year now. Any suggestions an a
better solution? Anybody got any gearmotors they want to sell? I keep an
eye on ebay and surplusscenter.

Is something pulling off the wire, or are you feeding it into
something? If you're pulling it off, I've used pretty simple dancer
rolls activating a brake to provide constant tension. On the takeup
side, I've used the dancer - pot idea.

I developed one design needing a very constant takeup tension with
varying takeup roll size. I routed the web over a roller at 120 deg
with the roller mounted on load cells. This read web tension
directly. I used this to control a magnetic particle slip clutch
driving pinch rollers, which gave very repeatable linear torque
response to the signal voltage.

If a drip of resin fell on the web and jammed at the pinch rollers,
the sensing roller would immediately see the lower tension, and the
slip clutch controller would smoothly increase the torque on the
spring loaded pinch rollers until they swallowed the lump. The torque
would rapidly return to setpoint. I was using a PC based process
controller. This is where you get into tuning PID loops, or in this
case PI loops (if you need derivative, buy a fuzzy logic autotuning
controller). The web control worked great.

Maybe there's an idea somewhere in the above you can use.

Pete Keillor