First, the Engineering Library should have several texts. Boston Gear is a good
source of gears and other power transmission products. A differential has 4 main
parts: There is a gear on each output shaft. There is an input shaft that will
normally have a pinion gear on it. There is a cage that will normally have a
ring gear on it. There are gears that rotate freely on axles attached to the
cage. The gears mounted to the cage engage with both of the gears on the output
shafts. The input shaft turns the pinion, which then rotates the ring gear. The
ratio of pinion teeth to ring gear teeth is the rear end ratio. A 4.10, for
example might have 10 pinion teeth, and 41 ring gear teeth. The ring gear
rotates the cage, which moves the cage-mounted gear(s). Because the cage-mounted
gear is engaged with both output shaft gears, both output shafts will rotate
together, and the cage-mounted gear does not rotate on its shaft. Differential
action happens if the two output shafts need to (or can) rotate at different
speeds. Then the cage-mounted gear will rotate, and one output will rotate
faster than the other. This is a good thing when a vehicle is turning a corner,
as it allows both driven wheels to maintain traction without skidding. It is a
bad thing if one of the tires does not have enough traction, because all of the
input power will go to the side with no grip, spinning that wheel, and supplying
zero torque to the other wheel. A couple of options for a light duty
differential: The rear axle from a golf cart. The rear axle, or at least the
differential from a Chevette, or similar car. (I have one from an MG Midget on
my workbench, its fairly light.)

Good luck, have fun.

Aubrey Williams wrote:
> > I am part of an engineering design group at the University of >
Maryland, College Park, and we are building a four-wheel pedal driven >
vehicle. We are investigating the possibility of using a differential > on
the rear wheels. I was wondering if anyone could explain the > operation of a
differential and explain the meaning of differential > ratios. Also, if any
good websites could be suggested. > > If we do not build a differential, I
would be interested in buying any > small, light, light-duty differential if
any recommendations are > possible they would be greatly appreciated. >
> If we do build a differential we will need gears, and any good >
references on gears would also be appreciated. Thanks > > Aubrey Williams
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