How can I couple two shafts along the same axis so that they rotate together, but only one shaft is allowed to drive the rotation?

Question

This question is going to have an application in aviation (to avoid doubts and relocation to other forum) but let's concentrate on theoretical mechanics here.

If I want to allow a shaft to rotate in one direction and not the other, then a ratchet would be a solution.

But what I need is a base/platform with shaft M (master) and shaft S (slave) connected to each other the way that if I rotate shaft M (both clockwise or counter-clockwise) the shaft S will rotate with the same speed and direction. But if I try to rotate shaft S in any direction it should not be possible the same way as if I tried to rotate a ratchet in blocked direction.

What is the name of a device I described?

Shaft M --> ===[Device in]=== <-- Shaft S
_______________[question ]________ <-- platform

Answer 1

One basic class of mechanism which can achieve this is a non-backdrivable worm drive, however this does come with a failry large reduction ration and so may not be suitable for your application.

It would also be achievable, in some circumstances with an automatically engaging clutch such as a centrifugal clutch or you could envisage a sytem where the master shaft has a cam lug which engages in a spiral groove to pull the shaft fowrard and engage with a dog clutch with a return spring.

Alternatively a clutch mechnism which is engaged by a governor a bit like an automatic gearbox, this could be achieved by mechanical, hydraullic or electrical means.

Of course a lot depends on the sorts of torques and angluar speeds you are looking to deliver as well as the response, stiffness and backlash that you require I've seen very simple inertial engagement mechanisms in toys etc which achieve this but wouldn't be up to precision or heavy duty applications.