According to John Doe :

I haven't found anything that looks usable at McMaster Carr, unless
I'm overlooking something. Can a flexible drive shaft be made from a
simple spring, like inside a rotary tool flex shaft? Whatever stuff
used for flexible shaft screwdrivers?

The core of a flexible shaft is alternating layers of clockwise
and counter clockwise windings, so a simple spring would either expand
in one direction (and bind) or contract in the other direction, and
rattle around inside the buide.

If you want flexible shafts to build from, try picking up a
speedometer cable -- unless you need more torque than that can carry.

The shaft will be driven by an 18 to 36 V DC motor (up to maybe 700
watts). Not sure the RPM, typical DC motor. Bent 90° in about 3".

That's a pretty sharp bend for a flex shaft to handle the likely
torque from that motor. Are you sure that you won't do better with a
set of bevel gears?

Enjoy,
DoN.

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