Spur Gear Differential

A few people expressed interest in seeing the spur gear differential I'm
building for my grandson's pedal car so I put some photos up. They can be
found here
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The text editor wasn't being very cooperative when I did this so there is no
write up there yet. You can tell the size by comparing to the six inch scale
included in the photos. The pinions are 1" OD and the side plates are 3.6"
OD. The bearings on the output shafts are 6204. It will be enclosed in a
16ga "can" and sealed with a small amount of oil and a sprocket or toothed
pulley will be bolted to the side of the pinion carrier as the input.
Richard Coke
Reply to
Richard Coke
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Way cool, Richard. Pretty work, too. Thanks for posting the pics.
Harold
Reply to
Harold & Susan Vordos
With myself having 2 children not sure how I would find the time to do that. Wow very nice work.
Reply to
Wayne
That's awesome. I take it the one that Northern Tool sells for $63 (with axles) was not adequate?
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Or, "I just like to make gears!" >;-} David
Reply to
David Courtney
Clean. A better forum for posting, with no text problems, is
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Dweller in the cellar
Richard Coke wrote:
Reply to
JR North
Lots of well done parts here, great work.
Can you explain how it works? When I think of a differential, I think of one driven input shaft able to split power to either of two output shafts. Is the planetary assembly the input shaft? How does it hook up to the output shafts in the other pics? Or am I totally off base here?
Karl
Reply to
Karl Townsend
The ones Northern sells look like Tecumseh axles. They are fine but are too heavy for this application. This one is for a pedal car for my grandson. It will be a scaled down version of the car I built for myself. You can see it here if you want to.
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And, yes, I like to make gears. :-)
Richard Coke
Reply to
Richard Coke
Yes. A sprocket will be bolted to the side of the planetary carrier and connected via roller chain to the pedals. The short shafts extending from each side with the bearings on them are the output shafts. The planetary carrier floats on those shafts. The bearings will be mounted in the frame and the shafts will be extended out to the wheels. It's easier to see how it works if you compare it to the more common bevel gear type. Just picture the side gears being changed from bevel to spur and each spider gear being replaced by a pair of pinions that are meshed with each other only in the space between the side gears. I first saw that type in a Cletrac style steering transmission for an old crawler. It took me a while to figure out that "yeah, that really is a differential".
Richard Coke
Reply to
Richard Coke
For all who would like to get a spur gear differential, there is a similar unit used on Snapper walk-behind lawnmowers. You might get one from a mower with a blown engine -- cheap. The differential/axle assembly is almost ageless, having been produced for over 30, and the design and some early production are still going strong. To see an exploded view, go to:
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JWD
Reply to
JWDoyleJr
This one?
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Ron Thompson Was On the Beautiful Mississippi Gulf Coast, Now On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA
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The ultimate result of shielding men from the effects of folly is to fill the world with fools. --Herbert Spencer, English Philosopher (1820-1903)
Reply to
Ron Thompson
Interesting! How do you calculate the gear reduction of this?
wwm
Richard Coke wrote:
Reply to
Bill Martin
Hmm... In a symmetrical open differential, that is, one that has side gears of the same
size and it has no limited slip elements added, there is no reduction in the common
sense of the word. In an auto rear axle there is a reduction and direction change
stage at the input provided by the ring and pinion gears but it has nothing to do with
the action of the differential. Now the interesting thing about a differential is that
the sum of the outputs will always be 2 times the input speed. For example if the
input is turning at 1 RPM and the load on the output shafts is equal, the left shaft
will be turning at 1 RPM and the right shaft will be turning at 1 RPM. If you continue
the input at 1 RPM and unbalance the load on the output shafts by completely stopping
the left shaft so its output is 0 RPM and also remove the load from the right shaft it
will turn at 2 RPM. Another way to look at it is to lock the carrier and rotate one of
the shafts 1 RPM clockwise. The other shaft will rotate 1 RPM counterclockwise. In
this case the _difference_ is 2 ( 1- (-1)). If you use the shafts as inputs and the
carrier as the output it becomes the mechanical analog of an electronic differential
amplifier with a gain of 1.
In an earlier post I mentioned a Cletrac style steering transmission for an old
crawler. They have an interesting arrangement with two sets of planetary gears on each
side. When the steering brake is fully applied to one side that track doesn't come to
a complete stop. The brake actually operates on a planetary carrier and the track on
that side slows to about one-fourth to one-tenth (depending on ratios of the gear sets)
of the input speed. The other side speeds up to 1 3/4 to 1 9/10 of the input speed. When
no brake is applied it's just an open differential. More modern tracked vehicles have
much more sophisticated systems that allow them to spin around their own center by
having multiple inputs and travel at higher speeds while maintaining stability but they
are still just a big box full of heavy duty planetary gears.
Marks and Machinery's have some information on epicyclic gears and there is lots of
stuff on the net. I really like to work with them but sometimes the ratios aren't
readily apparent. It's usually 1+ something or 1- something. I hope that somewhere in
this rambling is the answer to your question.
Richard Coke
Reply to
Richard Coke
On 25 Apr 2004 04:37:56 GMT, snipped-for-privacy@aol.com (Richard Coke) shouted from the rooftop:
Very nice. Olds used a planetary diff in the original Toronado FWD transaxle.
-Carl "An honest man doesn't need a long memory"- Jesse Ventura
Reply to
Carl Byrns
Exactly!
Reply to
JWDoyleJr
Did it use helical cut gears? I'm guessing that it did since they are much quieter than straight cut gears. Somewhere I saw a limited slip diff. that used the axial thrust of helical gears as the sensing and/or locking mechanism... only a vauge memory, can't remember where. Just to be a little bit pedantic, as far as I know _all_ mechanical diffs use planetary gears. Even a bevel gear diff. is a planetary system. The axis of the spider gears is a right angles to the axis of the side gears but it is still a planetary arrangement. It has the advantage of having fewer number of parts than a spur gear system to accomplish the same thing.
Richard Coke
Reply to
Richard Coke
The Torsen differential does something like that.
howstuffworks.com has some good info about it.
-- --------------------------------------------------------------------------- Jim Wygralak | PGP (or gpg) signed messages get a free ride past my spam snipped-for-privacy@visi.com | filters. Public key available on request.
Reply to
darus
That's beautiful work, Richard.
Reply to
Artemia Salina
Thanks Richard, you covered it in the first sentence.
bill
Richard Coke wrote:
Reply to
Bill Martin
What, if any, are the advantages of this type of differential over the type used in the auto industry?
Ted
Reply to
Ted Edwards
One advantage is that a home shop type can make the components. Bevel gears are not possible to make with conventional equipment because the tooth form is not a constant.
Harold
Reply to
Harold & Susan Vordos

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