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Re: (ET) Elec-trak Digest, Vol 11, Issue 119
Today I think cog belts are about the most efficient and quietest.
Personally I like the idea of a direct drive electric motor on each wheel.
While this increases unsprung weight it's the most efficient. On low speed
vehicles unsprung weight isn't the problem it is on race cars. To go off
topic a bit but stay on the subject line I've been looking at electric zero
turns with an electric motor on each rear wheel. This makes the most sense
to me. My zero turn has hydro drive, it works fine but eats power, is noisy
and uses too much gas if you ask me. I see Cub has an electric zero turn now
and it looks like Hustler's isn't going to make it.
Rob
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Message: 3
Date: Fri, 21 Jun 2013 09:08:01 -0400
From: Max Hall <mhall maxmatic com>
To: "David Roden (Akron OH USA)" <etpost drmm net>
Cc: Elec-trak <elec-trak cosmos phy tufts edu>
Subject: Re: (ET) I was wondering
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Trucks used that rig more often than not 100 yrs ago... a transaxle/diff
about amidships and chain drive to the (sprung) rear wheel hubs. Good
stuff! Example:
http://www.txtransportationmuseum.org/photos/hist-wichita-truck/wichita-truck-03.jpg
The Italian three-wheeled Ape ("Bee") used that system as recently as the
60s. e.g. http://www.vespaape.com/ape/myape_00.jpg
Suspension can be a real pain... just ask the guys who built the Seep (GPA
- amphibious Jeep) and the DUKW! The LARC guys just used lower speeds/big,
big low pressure tires...
Low speed is engineering simplicity. Road speed is wicked.
And as others have mentioned... you get to play an awesome game with TWO
e-motors in a drive train. (At least, series-wound motors.) Parallel/series
"differential" characteristics mentioned already, and also: in series, both
motors get ALL the current, but about HALF the voltage, of the controller
output... high torque, low speed. In parallel, each motor gets about HALF
the current and ALL the voltage of the controller output... high speed, low
torque. Two "electrical gears."
On Sun, Jun 9, 2013 at 9:30 AM, David Roden (Akron OH USA)
<etpost drmm net>wrote:
On 8 Jun 2013 at 17:29, Geof Thompson wrote:
> If two motors were connected in series, but with opposite polarity.
> Then mounted end to end, what would happen if they were used as a rear
> axle? would they act like a differential or would they work like a
> posi- trac. or would they just not work at all?
In terms of the way they drive the wheels, DC motors in series will act
like
a conventional differential. DC motors in parallel will act more like a
limited slip differential.
The amount of "slip" with parallel motors will depend on the type of
motors.
I think that series motors might be more tolerant of differing rpm going
round corners, but PM motors tend to be more rigid about voltage vs rpm
and
might fight you more. Not having tried it, though, that's just a guess.
How you make this idea into a usable drive axle is another matter. I
don't
see how you could just bolt two motors together and make a drive axle.
Other folks have mentioned the issue of reduction gearing. Even if the
speed were correct, I'm not sure that conventional motor housings would
have
the mechanical strength necessary to handle supporting vehicle weight over
rough ground.
Another concern in a road EV would be the large unsprung weight at each
wheel. That probably wouldn't matter much, if at all, with something like
a
tractor.
What would be more likely to work would be to forge an axle and mount the
motors outboard, driving the wheels through chains or belts. Bob Beaumont
did something like this in the Tropica roadster in the 1990s. The rear
wheels were on trailing arms. It used two motors, each with its own
controller. Each motor drove one rear wheel through cogged-belt
reduction.
It worked, but it was a fairly expensive setup compared to one motor
driving
a conventional differential.
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End of Elec-trak Digest, Vol 11, Issue 119
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