Bizarre mechanisms

[fluppet]

I realise I might be able to find the answer to this in one of the books on Carlos site, but before I send him money I thought Id ask here.

This must be a known problem: I want to take a rotating axle with approximately constant torque/speed (e.g. an electric motor) and use it to drive another axle such that speed and torque are approximately inversely proportional.

In other words, I want to turn an axle quickly when theres little resistance applied to it, but apply a lot of force if necessary at the cost of speed.

This isnt for a crusher, so I dont need an absolutely resilient mechanism. (Although I can see how such a thing would be useful for a crusher. Mind you, if I was doing a crusher, Id start by shoving a linear actuator along a ratchet until it found resistance, which is a far more digital thing than Im looking at.)

I can think (vaguely) of various ways of doing it - something using a device like a governor as a gear (or some other CVT-related technique relying on belt drive), something based on limited slip differentials, or even actually giving the thing a gearbox. None seem very simple, and certainly not very resilient. Rather than reinvent the wheel, I thought I should ask the more mechanically minded types here for the right way to do it.

Any thoughts?

Ta,

--
Fluppet

[maddox]

Use a series wound motor, they have that build in, in the Torque/speed tabel.Easy as asking. Sheap dependable, but not that efficient.

[_jl_]

Why not a PM motor?

[fluppet]

The efficiency may be my concern - also the range of speed Im looking at. You might be right that I could just wire it up and not worry about it. I dont really have enough experience of the things to know what behaviour I should expect.

That might have made it academic, but Im still curious if anybody knows a mechanical linkage with the relevant behaviour.

--
Fluppet

[maddox]

Yes I know a suitable system. And even better, I know roboteers that have some.
The variable belt driven transmission
We have 1 that needs an external source to vary the speed.
Sam Smith-Tiberius- has some from mopeds.

[_jl_]

Christian:I know the difference!

But a PM also delivers more torque when slowed down. And, without knowing more of the application, it is impossible to say if the PM would work.

[_jl_]

Sorry for hijacking of this thread, I know you don´t want a motor, i just need to say one thing...

Christian wrote:but the speed of a permanent magnet motor is proportional to the load torque

That means, the higher speed, the higher torque.
Now, assuming that you mean inversely proportional (which I really hope you do!):

Andrew wrote:such that speed and torque are approximately inversely proportional

That is (as you can see) the exact feature he is looking for. Now it is up to the application (which I dont know anything about), to tell if a PM would or would not work.