# Is there a way to add together the rotations of two spinning gears, which are spinning in opposite directions, into one rotation?

Two gears are spinning is opposite directions, I would like a third gear to spin in one direction (the direction is not important), and this third gear must be the sum of the motions of the two gears. The speeds of the two gears can vary. If they were spinning at constant speed, this would be easy for me, however they are always changing.

• What do you mean by "sum of the motions of the two gears"? That doesn't seem to make sense when talking about gears.
– hazzey
May 24, 2016 at 13:02
• I think what you're looking for is a differential. en.wikipedia.org/wiki/Differential_(mechanical_device) It spins a third gear at the average speed of two input gears. With the addition of other gears, more complex operations are possible. May 24, 2016 at 13:16
• @hazzey - Sorry, I am not mechanically trained, I meant that the speeds of both gears are transferred onto the third gear. If the two gears were spinning at 1 radian per second, the third gear should spin at 2 radians per second, or there about; the first two gears drives the third, basicallly.
– maou
May 24, 2016 at 14:29
• @maou the output will be $\frac{in_1+in_2}{2}$ but it's easy to add a 2:1 gear to double the output again. May 24, 2016 at 16:13