In article ,
"N_Cook" wrote:

Many thanks for that.
Seems more black arts than science. I assume the black fibrous block under
the arm in pic 008 is someone's retrofit damper like the Millenium Bridge in
London.
http://www.taylordevices.com/papers/damper/damper.html

Ha, I hadn't heard that bridge story! The little scrap of scotchbrite
pad is to soften the metallic clang of the dancer arm, but in normal
operation it doesn't hit there, anyway.


I think I would make the sprung arm out of lighter materials as I would only
need it for 40AWG/45SWG type gauges and so less inertia there.
Do you find a problem with dirt or grime on the felt pads causing
irregularity problems at these light tensions ?

The pads are replaced as needed, but they don't tend to collect dirt.


I was wondering if a servo system for spool unloading to zero tension is a
way to go. Inductively or optically, somehow monitoring the sag in an
unsupported section of the supply wire. When in optimal band then spool rate
say 5 second average speed. More sag then proportional down to zero speed
and too little sag then proportional up to some system limit.

I think the less technology, the better. We built a custom take-up
winding machine for a fibre optic manufacturer, and it was fairly
sophisticated, with a PLC controlling everything. If I had to do it
over, I'd just use a dancer arm...

I think one key to the success of this machine is the substantial
distance from spool to bobbin. Nowhere is there any slack wire beyond
the idler pulley, but the distance and widely spaced tensioners may
allow some imperceptible stretching, and of course the idler pulley
moves up and down slightly on the end of the dancer arm, which moderates
dereeling variations.