If you want to see a drawing of a device that utilizes a constant-magnitude force acting along a constant line-of-force to rotate a disk with constant torque, view the drawing and text at the following link...
www.bluffton.edu/~edmistonm/ConstantTorque.pdf
The sliding contact allows a variable point of attachment that allows the line-of-action to remain constant. This shows that any point of attachment along the line-of-action yields the same torque. You do not need to specify the point of attachment.
The disk could be powered by a rotary motor, and the linear motor would then be replaced with a linear bearing. If the motor has constant torque then the rod will be driven with constant force along a constant line-of-action.
Of course there is limited range of action in either of these cases, but these are actual devices that have utility in the engineering of real products.
To me, this shows a different way of thinking about force vectors, point of attachment, and torque from the way I had thought about them in the past.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu