# Epicyclic gearing: 3 free axes

• Cri85
In summary, the conversation discusses the possibility of using an epicyclic gearing with no fixed axis, but it is not commonly used. The speaker has two questions about this: if it is possible and what the ratio of reduction would be. The other person suggests considering all three rotations at once, which may be the reason why this mode is not used. They also mention the possibility of reducing rotational velocity without giving torque, but this would result in zero output power.

## Homework Statement

The teacher said it is possible to use an epicyclic gearing with no axis fixed but nobody use the gearing like that. I watched this video:

at time 42s it's possible to watch it. I have 2 questions:

1) Is it possible to used the epicycloidal train with no axis fixed ?

2) If yes, what is the ratio of reduction ? is it dependant of the torque ?

Maybe if you have a link ?

--

## The Attempt at a Solution

I'm looking for this case, but each time the epicyclic gearing is used with one fixed axis.

Last edited:
Cri85 said:
1) Is it possible to used the epicycloidal train with no axis fixed ?
I don't see an argument against it.

Cri85 said:
2) If yes, what is the ratio of reduction ? is it dependant of the torque ?
You have to consider all three rotations at the same time. Things like a ratio of reduction that consider only two do not make sense any more. That's probably the reason they are not used in that mode.

mfb said:
Things like a ratio of reduction that consider only two do not make sense any more.
I can set the input to the sun gear and the output to the ring gear (planets are free to turn like they want) ? Why there is no a ratio ?

In this case, it's possible to reduce a rotational velocity without give a torque on the support ?

Cri85 said:
(planets are free to turn like they want) ?
Then your output will not get any torque (neglecting friction). The free axis will rotate with the right speed to give zero output power.