I used to have one of these on an I-17R.
The universal 3 axis joint for the pole seems to be free in all 3 axis. I assume the writing force is being taken by the line running to the "beam loops" rather than the pole. Is this correct?
Yes.
If so what stops the line from running free ( or just slacking) and the pole from pivoting downards? Is it just the small stopped knot in the line? Are you then not able to dynamically adjust the angle of the pole since it is determiend by where the knot in the line is?
The knot keeps tension on the line, and the pole angle is - as you said - predetermined by the knot location. I think my instructions said to tie a big knot, like a figure 16 or something.
Is the righting line a single loop, starting tied off to one end of the pole, traveling through a beam loop, then across the cross beam, through the 2nd beam loop and then comming back to tie off on the pole again?
This is exactly how mine worked.
One word of advice: when using this system be careful with your fore-aft movement, or you can pinch the pole against your dolphin striker.
Geoff