# Do three-way differentials exist?

**URL:** <https://boards.straightdope.com/t/do-three-way-differentials-exist/421507>\
**Category:** Factual Questions\
**Created:** [October 4, 2007, 3:42pm UTC](https://boards.straightdope.com/t/do-three-way-differentials-exist/421507 "2007-10-04T15:42:51Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Chasing\_Dreams](https://avatars.discourse-cdn.com/v4/letter/c/258eb7/32.png) [@Chasing\_Dreams](https://boards.straightdope.com/u/Chasing_Dreams)\
**Post date:** [October 4, 2007, 3:42pm UTC](https://boards.straightdope.com/t/do-three-way-differentials-exist/421507/1 "2007-10-04T15:42:51Z")

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I’m in the process of designing a robotic hand for a class project and I’m wondering if three-way differentials actually exist. Are they just made up of two regular differentials? Can anyone point me to a site that sells them?

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**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\
**Post date:** [October 4, 2007, 6:52pm UTC](https://boards.straightdope.com/t/do-three-way-differentials-exist/421507/2 "2007-10-04T18:52:11Z")

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I’m not sure exactly what you are looking for, but I suggest you try [Digikey](http://www.digikey.com/) or [Square D](http://www.squared.com/).

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**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\
**Post date:** [October 4, 2007, 7:22pm UTC](https://boards.straightdope.com/t/do-three-way-differentials-exist/421507/3 "2007-10-04T19:22:16Z")

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Ask your calculus professor. (Sorry, I thought from the title this would be a math question.)

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**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\
**Post date:** [October 5, 2007, 12:28am UTC](https://boards.straightdope.com/t/do-three-way-differentials-exist/421507/4 "2007-10-05T00:28:22Z")

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The outboard spoilers on the B-1b wings are driven by three redudndant motors driving a single shaft via two differentials. If a three-input differential were known, we would have used it. The two differential solution caused trouble due to less friction in one of the channels.