Thursday, March 8, 2012

Easier letting out of line, proof of concept.

While dreaming of getting my bike rolling in a couple of months I struck on a way to take up the slack thrown out by the take up reel in the designs I have show so far. I just modelled the idea in proof of concept form on my existing version 2 winder - in modelling clay.
Proof of concept model of a dual drum capstan (Operator's view).  Feeding line out causes the line to hop up on  the larger drum to prevent slack line from building up and getting tangled.
The basic idea is to use the first fair lead from capstan to the take up reel to cause the line to jump up onto a second capstan drum profile that has a diameter just larger than the top layers of string on a full take up reel. The jump happens only when there is enough slack to make it possible, and then the line stays on the bigger drum as long as the line is unwinding.

When the capstan is used to wind in, the line is guided back onto the smaller drum almost instantly, and only a small amount of slack builds up for the few turns it takes for the line on the large drum to be unwound again. That smallish bunch of slack could be handled with a tensioning spring arrangement - unwinding with the single size drum would produce slack as long as the reel unwound and no spring could control that.

 So, I tried it out with modelling clay tonight and it works!

Some notes:

  • Clay is ideal for the prototype, but I'll have to use something heftier for the real thing. The tension to pull line off the reel is driving the line into the clay.
  • The profile of the large drum should be level or slope toward the smaller drum so the string will travel toward the kite-side fair lead smoothly. As it is the line over-runs itself regularly and cuts out bits of clay.
  • The positioning of the take-up side fair leads is now more important. I just drilled another pair of holes for the eye screw, but it seems the best position is between those holes. C'est la vie.
  • The natural positions for the fair lead screws seems to be angled further toward the axle than they have been. I have not hidden the screw threads on them yet, and the line keeps getting caught down there.
  • I didn't notice before but the combination of a reel mount a bit skewed from the axle axis and the slipper clutch does some level winding!  I'll look into this more later.
Next Steps

Build another capstan out of a pair of disks of 3/4" plywood and try that.  I want a unit tailored to my 8" halos so I can unwind and wind with little trouble.

Experiment with different fair lead positions.

Add some way to slow the line as it goes out.  I can brake on the drum or support disk for now, but something more elegant might be needed for large line tensions.