I can speak to the Tropica as I am still working on restoring/finishing
mine. It has 2 6.7 inch DC brushed motors, one for each rear wheel. The 2
Curtis controllers are both connected to the single throttle pot. From the
factory, they only reversed the left motor for backing up, the right one was
just disconnected when in reverse. I don't know why since all it took to
"fix" that was to change the contactor for the right motor to a reversing
one and re-arrange a couple of control wires. I believe the top speed
was/is actually 72 MPH and is electronically limited buy a circuit in the
dash that looks at inductive proximity sensors set to see the "teeth" on the
cog belt sprocket on each motor. If the pulses come in too fast, the
circuit trips and locks out that motor, requiring a manual button reset
under the passenger side of the dash. As for "sharp" corners it is not a
problem as the car has a very large turning radius. I think my F350 work
truck turns sharper than the Tropica.
On the forklift side, all of the 4 wheel forklifts I have had use a single
motor driving a differential for the two drive wheels. One of the three
wheeled units was the same as a 4 wheel unit and the other one had a hub
motor in the third steerable wheel. Un-sprung weight is not much of a
problem for forklifts as many of them are operated on relatively smooth
surfaces and also at slower speeds.
respectfully,
John
----- Original Message -----
From: "Alan Brinkman via EV" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Saturday, September 27, 2014 10:16 AM
Subject: Re: [EVDL] Building a true road going solar EV.
Peri,
I am wondering if not having a differential but driving each wheel
independently with an electric motor does not create the issue that one
would expect. If you have a solid axle car, and turn a corner, one or both
wheels will scrub the road and the car will try to drive straight forward.
The Tropica electric car, also called the Zebra, the four wheeled
fiberglass sports car looking one, not the three wheeled enclosed Zebra,
had an Advanced DC 7" motor at each rear wheel. A belt drive was used to
transfer power from the motor to the wheel. The suspension was independent
at each corner. They did have two Curtis 400 amp controllers, I am not
sure if they were tied to the same throttle input, or if there was some
linking of the controllers. I know some of the more modern Curtis
controllers can be linked to the same model of controller to power a
vehicle with one throttle and two motors. The Tropica or Zebra owners did
not report any problems with making sharp corners. I wonder if
the "electrical connection" between the motors is not the "straight axle
mechanical connection" that you would suspect. Someone on the list help me
here with a more knowledgeable explanation. A mobility chair or wheel
chair has a controller or controllers that manage the speed and direction
of the two drive wheels to control steering and movement. But did the
Tropica (Zebra) circa 1996 have controllers that were just set up for
forward travel, or was there some coordination between the units according
to steering position and speed. A forklift technician may also know the
answer. Do forklifts with steerable wheels need any coordination between
two driving wheels. I suspect that the electric drive of the vehicles, not
being 100% mechanical, gives enough flexibility for turning. Also, a drive
axle with a differential with no locking device, can have one wheel lifted
or lose traction, and the other wheel loses power because it is all
transferred to the lifted wheel. I do not t
hink this will happen with two wheels, each driven with an electric motor.
One wheel with traction will keep transmitting power to the ground, and
one that has lifted will spin also. However, now you have to make sure
that you have the issue of over speeding a motor under control. The
Tropica was listed with about a 60 mph top speed, 7" motor, 72 volts of
batteries, and maybe the Curtis controller was set to limit top speed.
With one controller and two DC motors, each driving separate wheels, I
would think that cabling them in series or parallel would affect the
traction and speed of the motors.
Someone more knowledgeable please jump in............................
Alan
Part of post cut out..........
The other potential problem is *not* having a differential. With a
mechanical differential, one wheel is allowed to turn faster than the
other >when going around corners. With hub motors, that process will have
to be done electronically.
Peri
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