The steering of a standard traction kite is effected by adjusting the relative lengths of the right and left kite lines.  A kiteboarder does this by pivoting a bar, with the lines attached to either end, about an anchor point.  We do this by winding the left and right lines around separate, coaxial spools.  We need a solid but cheap way to adjust the relative lengths of the left and right kite lines, differentiating this relative length from the sum length.  A planetary differential provides for such control, and they're fairly easy to find, as 3 speed hubs.  We use a Sturmey Archer (S/A).  If you get a whole bunch and consolidate the parts, you should get a handful of good ones.

I'm not sure yet how to couple chainwheels to the hub of the S/A, and then mount the axle in pillow blocks so it can rotate.  Maybe all that work would be as much as having something custom fabricated.  In any case, this can provide a mechanical means of steering without additional stress on the lines.  We use a 4/3 chainwheel gear ratio to counter the 3/4 ratio of the outer and planet rings in the S/A, so that a stationary sun gear results in a 1/1 ratio of spool rotation.

If we only allowed one of the spools to exert force on the D/R subsystem, there could be substantial torque on the sun gear when the other spool had a much greater torque exerted on it.  So we couple both to the spool that relays back to D/R, with freewheel couplings.  If they were both directly
coupled, we couldn't steer (the spools would be locked into a given relative position).  But a freewheel is fine, as we never want the spool going to the D/R to push the kite spools (or vice versa).  Picture the spool corresponding to the rear wheel of a bicycle, and the bike's chain wheel corresponding to kite's chain wheels on each side coupled by freewheel.  The one on the side of the steering wheel has the standard orientation, the one opposite the steering wheel is reversed.

To Do:

  • Acquire or construct spools
  • 2 pair of Spool and chainwheel coupled together, rotating about common fixed axis
  • 1 Spool and 2 chainwheels freewheel coupled (with reversed rachetings), rotating about fixed axis
  • Sturmey Archer, pillow-block mounted with freely rotating axle
  • Sturmey Archer configured internally, with chain wheels coupled to both outer ring and planet ring
  • Steering mechanism (wheel, but really to be safe a stepper motor that can be operated from a safe distance) on sun gear of S/A
  • Chain tensioners for each of the chains, on low tension side, between transmission spool and kite spools
  • Framing

Two hand-drawn versions of the diagram: