My next task is to figure out how to design a method of hooking them on to my belt.

Thanks for sharing this idea. This seems to have some "leg" (no pun intended). It would seem to work equally well sitting and standing with the monopod being extensible.

I was thinking that if someone doesn't have an old tripod they'd like to sacrifice, you could use a telescoping trecking stick or a suitable camera monopod instead. Might take a bit of engineering to secure it to the mount, but would seem to be an alternative.

Personally, I'm interested in giving this a try...

One of my Megatars has one, that was custom built by a luthier out in the Pacific North West somewhere.

It's ebony, with a graphite rod [I think] and it picks up the hardware inserts on the back of the body.

I am 6ft 7in, and I could play this thing standing up, or also seated as it is completely adjustable - see pictures !!

Somewhere I do have the blueprints for it, as the previous owner of the Megatar was a design engineer...

It works great !!

It seems that the stick would tend to rotate. What is keeping it oriented properly – perhaps your hands or the shoulder strap?

I think it depends on the center of gravity of the contraption. Where's the rotation coming from, after all? If you just stood the stick up on a pole and let it go, it wouldn't rotate, it would just fall over (don't try this!). It's when you give it a push to the left or right of its center of gravity that it begins to spin. That can happen if there's a part of the contraption which is to the left or right of the center of mass, which projects and bumps your body. Or it can happen if the center of mass is in front of the instrument, so that holding it at certain rotations puts the center of mass to the left or right of your hands. Center of mass behind is probably ok, since that would at least be stable in a fretboard-up position. But if it's balanced right, it will only rotate if your fingers turn it.

I've attached a photo of today's progress.

I just noticed something in pone of your earlier posts (post 5 on the first page).
I think it shows that on your Stick the belt hook doesn't screw on to the thicker part of he Stick where the block sits? I can't see any screw holes on that flat bit for the hook's mount, but there do seem to be couple of screws in the thinner part of the beam?

Do I have that correct?

For those of use with belt hooks mounted on the flat thick part of the beam, the hook mount's screws might provide an alternative (simpler) fixing point?