differentials

I was wondering if anyone knew of a good lightweight differential
(hopefully parallel) that could be used to combine the power of two
riders. I know this isn't the easiest way but this is for a
competition where innovation counts. Also how effective would using a
differential be?

Thanks

(catabong) wrote in message . com...
I was wondering if anyone knew of a good lightweight differential
(hopefully parallel) that could be used to combine the power of two
riders. I know this isn't the easiest way but this is for a
competition where innovation counts. Also how effective would using a
differential be?

Thanks

You mean like this?

http://www.davincitandems.com/dv2.html

john riley wrote:
(catabong) wrote in message . com...

I was wondering if anyone knew of a good lightweight differential
(hopefully parallel) that could be used to combine the power of two
riders. I know this isn't the easiest way but this is for a
competition where innovation counts. Also how effective would using a
differential be?

Thanks


You mean like this?

http://www.davincitandems.com/dv2.html

This isn't a differential; it's independent freewheels. A
differential would force each rider to provide the same torque, but
would let them choose cadences independently. If one rider suddenly
chose to rest, the cadence of the other rider would need to double
to maintain power, and the resting rider would still need to resist
the pedalling torque of the other rider, even though not moving the
cranks. Independent freewheels in front of the differential would
not help; you would still get the back torque to the resting rider.
My guess is it would be a very odd vehicle to ride.

I don't know if there are any commercial differentials suitable for
bicycles. You would want something light and not too wide, but still
capable of taking high torque at low RPM. It's possible to build a
differential out of flat spur gears only, rather than the bevel
gears in conventional automotive differentials, but you might need
to design and fabricate a custom one to meet your requirements. My
guess is it would be quite heavy. If you tried to build one with
chains and sprockets, it would still require one gear pair for
direction reversal, or a figure-8 chain (ugh!).

How about two fully-independent conventional drive trains, so each
rider can choose cadence and torque independently, and coast at
will? Weight should be about equal to two conventional drivetrains.
You might need some mirror-image components, if you use both sides
of the bike to keep things symmetrical, and a custom rear hub.

Good luck

Dave Lehnen

Are you asking about a differential to split the power between 2 wheels
like found on an automobile?
For a human power application the common way is a "dominate drive". Power
from the human goes to a jack shaft and from there it is split by means of
2 chains to each axle. 2 additional freewheels are either placed on the
axle or jack shaft.
The reason it is called "dominate drive" is: when the vehicle turns a
corner the outside wheel "dominates" the gear ratio and makes the pedals
harder to turn. A small price to pay for a simple , light weight system.
Biggest benefit is that in a low traction situation on 1 wheel, the other
wheel will drive.
An automotive style differential is not suitable for this reason alone.
Human power vehicles are light meaning traction can be lost easier.
The Crank-it quad has an elegant version of this system hidden inside
their final drive sprocket. www.crank-it.com
Steve "Speedy" Delaire


..

catabong wrote:

I was wondering if anyone knew of a good lightweight differential
(hopefully parallel) that could be used to combine the power of two
riders. I know this isn't the easiest way but this is for a
competition where innovation counts. Also how effective would using a
differential be?

Thanks



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(catabong) wrote in message . com...
I was wondering if anyone knew of a good lightweight differential
(hopefully parallel) that could be used to combine the power of two
riders. I know this isn't the easiest way but this is for a
competition where innovation counts. Also how effective would using a
differential be?

Thanks


I don't think you want a differential if you're combining two riders'
power. The less powerful rider will be pushed around by the more
powerful. If you gear the drivetrains together, they'll find it easier
to coordinate their power output.

The kinetic sculpture folks have a lot of experience with building
multi-rider powertrains. Google it!

Jeff

"Dave Lehnen" wrote in message
...
How about two fully-independent conventional drive trains, so each
rider can choose cadence and torque independently, and coast at
will? Weight should be about equal to two conventional drivetrains.
You might need some mirror-image components, if you use both sides
of the bike to keep things symmetrical, and a custom rear hub.

Two riders, two wheels: obvious, if not original solution, --
2 wheel drive.

Jon Meinecke

S. Delaire "Rotatorrecumbent" wrote:

Are you asking about a differential to split the power between 2 wheels
like found on an automobile?

From his description I get the impression he is looking for a
differential in reverse. Where each rider is connected to where the
wheels would be, and the driveshaft or chain comes out of the
differential box rather than into it.


Something like....

Rider1 Rider2
| |
| |
-----{differential}-------
|
|
|
|
(wheel)

With this, when one rider stops, the other rider must double the cadence
in order to maintain the same wheel speed.

I remember seeing some small differentials used in some go-carts. It
may be his best bet.

Cheers.

S. Delaire "Rotatorrecumbent" wrote:

Are you asking about a differential to split the power between 2 wheels
like found on an automobile?
For a human power application the common way is a "dominate drive". Power
from the human goes to a jack shaft and from there it is split by means of
2 chains to each axle. 2 additional freewheels are either placed on the
axle or jack shaft.
The reason it is called "dominate drive" is: when the vehicle turns a
corner the outside wheel "dominates" the gear ratio and makes the pedals
harder to turn. A small price to pay for a simple , light weight system.
Biggest benefit is that in a low traction situation on 1 wheel, the other
wheel will drive.
An automotive style differential is not suitable for this reason alone.
Human power vehicles are light meaning traction can be lost easier.
The Crank-it quad has an elegant version of this system hidden inside
their final drive sprocket. www.crank-it.com
Steve "Speedy" Delaire



I think the OP was looking for a way to have two unmatched riders
power a single wheel, rather than drive two wheels on a trike or
quad while allowing cornering. The drive you describe above, and on
the Crank-It website, would drive the slower inside wheel on
corners, while the outside wheel freewheels a little faster and gets
no drive torque unless the inside wheel slips. It probably works
fine, although the inside wheel has less traction due to cornering
forces. Both wheels always turn at least at driven speed, so it
should work pretty well in low-traction conditions.

Dave Lehnen

I rode a Crank It Quad in Vegas/Interbike this week - - Wow was that fun. Even
better was to watch Crank It's Robert Kay ride it. This is an amazing vehicle!
The most fun I've had on 4 wheels with pedals.
Bob Bryant
http://www.recumbentcyclistnews.com

"Jon Meinecke" wrote in message ws.com...
"Dave Lehnen" wrote in message
...
How about two fully-independent conventional drive trains, so each
rider can choose cadence and torque independently, and coast at
will? Weight should be about equal to two conventional drivetrains.
You might need some mirror-image components, if you use both sides
of the bike to keep things symmetrical, and a custom rear hub.

Two riders, two wheels: obvious, if not original solution, --
2 wheel drive.

Jon Meinecke

Tain't original- in fact, it's in production:
http://www.zoxbikes.com/main/zox20&26.jpg
and there's lots of homebuilts around:
http://www.ohpv.org/pir2003/theracers/pages/don008.htm
http://www.ohpv.org/pir2003/theracer...s/calvin03.htm

Jeff