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Author Topic: "The Transmission They Said Wouldn't Work" - Popular Science, April 1971  (Read 1219 times)
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Phoenix, Arizona USA
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I found this interesting article in the April 1971 issue of Popular Science, and decided to put a little writeup about it on my site:

http://www.phoenixgarage.org/show_article/152

I found it to be really interesting, and I hope maybe someone might implement it on a future project. Enjoy!

smiley
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It's wonderful... NOT - It addsm more complexity for no more functionality. You need a slip ring setup to get power to the motor. High current and something more to maintain. I don't see any benefit, other than it is different. An improvement would be to make it simpler and with fewer parts. Thus you have a fixed motor drive a differential and the differential drive the 2 axles. Fewer moving parts and less rotational mass.
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I must admit, I thought it was a cool idea. But I think there is a reason why it hasn't caught on... Just because it works doesn't mean it's better.

Because there is no speed reduction gears means you need a high torque motor which means high capacity batteries and motor controller. I suppose the hydraulic way is better in that way (you can easily change the flow rate), but I'm sure a hydraulic motor on each wheel would be simpler and do the same thing. If you had 2 hydraulic motors connected in parallel, and you stop one, I'm sure the other one would spin 2x as fast (essentially acting like a differential).

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So how about having a motor for each wheel and feeding their brushes/armatures in series (and field coils in parallel) so that the back-EMF is proportional to the sum of the individual motors' back-EMF which is turn is proportional to the sum of shaft speeds of each motor - instant differential action without gear losses (mechanical gears are not greatly efficient, typically).

Not so good with brushless motors though (but the Kidera scheme can't be brushless anyway).
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Because there is no speed reduction gears means you need a high torque motor which means high capacity batteries and motor controller.

That's done all the time with direct drive motors. What's cute about this system is the implicit continuous differential. What's not cute about this system is the complexity of creating a spinning motor, and the problem of offsetting one of the axles to reverse the direction of rotation.
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Not so good with brushless motors though (but the Kidera scheme can't be brushless anyway).

Why not? Wouldn't it just be one extra power connection to route via a slip-ring or similar?
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Because there is no speed reduction gears means you need a high torque motor which means high capacity batteries and motor controller.

That's done all the time with direct drive motors. What's cute about this system is the implicit continuous differential. What's not cute about this system is the complexity of creating a spinning motor, and the problem of offsetting one of the axles to reverse the direction of rotation.

The inventor's original goal was to use hydraulics, and not an electric motor; I still find the electrical version interesting, though there is probably a good reason why this system isn't used in practice (many of the issues brought up here, likely). The issue of offset, though, could be eliminated with a proper gearbox (using three 45 degree bevel gears).

I am certainly enjoying the discussion about this invention, though - which was my intent...

smiley
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Not so good with brushless motors though (but the Kidera scheme can't be brushless anyway).

Why not? Wouldn't it just be one extra power connection to route via a slip-ring or similar?

My point is that using slip rings means it isn't brushless!  Brushes are common to slip-rings and commutators.
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Not so good with brushless motors though (but the Kidera scheme can't be brushless anyway).

Why not? Wouldn't it just be one extra power connection to route via a slip-ring or similar?

My point is that using slip rings means it isn't brushless!  Brushes are common to slip-rings and commutators.

Listen - I didn't just fall off the turnip truck. smiley-sad

The motor itself would be brushless; motors with commutators (or even slip rings in the case of some AC motors) have brushes which are kept in place against the commutator/slip rings via spring tension. These brushes (and springs) are attached to the case of the motor; if the case spins at a high enough speed, then the brushes can be retracted away from the commutator/slip ring via centrifugal force.

In using a brushless motor, there wouldn't be any brushes to retract - however, slip rings and brushes would still be needed -external- to the motor to carry the current to run the motor to the motor. These rings and brushes would not have any such forces exerted on them; they are wholly external to the rotation of the motor case.
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