general gear question

[jms814]

Hi!
Our VEX team is just starting up for the year again (this is our 3rd season, last year we did FTC...) and we realized we've had a few of these gears (see picture) floating around and never actually did anything useful with them. Anyone seen anything cool/done anything cool/know what type of maneuver they could help with?
Just wondering!
thanks :)

Jess Scolnic
Lower Merion HS, PA

[Quazar]

Hi!
Our VEX team is just starting up for the year again (this is our 3rd season, last year we did FTC...) and we realized we've had a few of these gears (see picture) floating around and never actually did anything useful with them. Anyone seen anything cool/done anything cool/know what type of maneuver they could help with?

Hi Jess,

This is a differential (http://en.wikipedia.org/wiki/Differential_(mechanical_device)). This is usually used for "car style" robots, to allow the drive wheels on each side to spin at slightly different speeds when going around turns.

You use it with three of the bevel gears installed inside it. Generally, you drive the outer differential gear from a motor, and the axles that come out of the sides each have a wheel attached. Have a look at this Inventor's Guide Insert (http://www.vexrobotics.com/docs/inventors-guide/advanced-gear-kit-6-7-07.pdf) (page 3) to see what I mean

A differential can also be used to make a mechanical adder (or subtractor). To do this, you run it "backwards", so that you have two inputs shafts and one output shaft. The output shaft will spin at a speed that equals the sum (or difference) of the speeds of the two input shafts.

I personally haven't had much need for them, but they are pretty indispensable if you actually need one, since it would be fairly hard to make a differential from Vex metal (the spinning casing is hard to make both light and strong).

Cheers,
- Dean

[MarkO]

Hi!
Our VEX team is just starting up for the year again (this is our 3rd season, last year we did FTC...) and we realized we've had a few of these gears (see picture) floating around and never actually did anything useful with them. Anyone seen anything cool/done anything cool/know what type of maneuver they could help with?
Just wondering!
thanks :)

Jess Scolnic
Lower Merion HS, PA

More links:
Differential with sprocket (http://www.vexforum.com/showthread.php?t=1482&highlight=differential)
differential (http://www.vexforum.com/showthread.php?t=486&highlight=differential)
Differential frame-uses?? (http://www.vexforum.com/showthread.php?t=1485&highlight=differential)

[jms814]

wow thanks for your speedy replies--all of that really helped!!

[ManicMechanic]

This guide (http://www.vexrobotics.com/education/VEX_Machinations-071108.pdf) has step-by-step building instructions for a project that uses the differential gear (the Tricycle Drive (http://www.vexforum.com/gallery/showimage.php?i=2041&c=8)).

[John V-Neun]

Here are some differential robots I built. Diffs can be used in some REALLY cool ways with a little creativity.

http://www.vexforum.com/gallery/showimage.php?i=756&catid=member&imageuser=3
http://www.vexforum.com/gallery/showimage.php?i=757&catid=member&imageuser=3
http://www.vexforum.com/gallery/showimage.php?i=761&catid=member&imageuser=3
http://www.vexforum.com/gallery/showimage.php?i=762&catid=member&imageuser=3

That last one is my favorite, it was a blast to figure it all out and get it built.

-John