Spur gear diff rotation.

A bit of help needed.

Here is a picture of a spur gear differential I nicked off the 'net.

My question is, if shaft A is held stationary and cage B is rotated clockwise, which direction would shaft C move?

Logic and intuition tell me clockwise but I may be missing something!

Cheers

Steve

Logic and intuition win through! Shaft C will rotate in the same direction as Cage B (i.e. clockwise in this case) but at twice Cage B's speed.

The second shaft will go clockwise. It is easier to consider the case where the cage is stationary first and what is labelled as fixed goes anti-clockwise at rpm X. Then you will see that shaft C goes clockwise. In order to then see the case where the first shaft is fixed everything else has to go clockwise at whatever rpm X you imagined the fixed shaft to be going in the first case plus what it was doing in the first case. So the cage is rpm X plus zero clockwise and the output is clockwise amount plus rpm X.

Martin C

Thank you Chris but I don't understand why the rpm is doubled.

In a differential whatever speed one side is slowed by is added to the opposite side.

Thanks for you help. I am ok with a bevel diff, (here's one I made earlier - **LINK**), I'm just finding it hard to get my head around the spur gear type. It's the fact that there are two gears counter rotating transmitting the power rather than a single bevel gear.

Using the picture above. If cage B is fixed and shaft A is rotated once clockwise, I presume shaft C will rotate once anti-clockwise, the same as a bevel diff?

If so, would putting an idler gear between the two small pinions reverse that?

Cheers

Steve

If I understand it, the two pairs of "contra rotating" pinions are not actually in mesh. The two meshing with the shaft A gears drive the cage round. The two meshing with the shaft B gear are driven by the cage and drive shaft B.

Presumably you could add more pairs at right angles if you wanted to transmit more torque.

Hi Peter, this animation shows the pinions in mesh. **LINK**.

Steve