>> 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.
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.
The behavior depends on the motors (and controllers).
Synchronous (and brushless DC) motors must run at *exactly* the RPM that
the controller demands. It will be difficult to use such motors to drive
2 wheels without a differential, unless you intend to "skid-steer" it
like some wheelchairs and lawnmowers. The controllers for such motor
must command *exactly* the right speed to coordinate two motors driving
two wheels.
Other types of motors and controllers aren't so picky. AC induction
motors, and brushed DC motors run at *about* the speed that the motor
controller requests. If the load is light, they run faster; if the load
is heavier, they run slower. This is enough to compensate for the lack
of a differential (for vehicles that don't have too tight a turning radius).
Brushed DC series motors (like the Tropica had) have the greatest
tolerance for speed differences. The Tropica happened to use two
controllers (for economic reasons), but one would have worked just as
well. The two motors can be connected in series to the same controller,
and behave themselves just fine regardless of the RPM difference between
them. Being in series, they produce the same torque regardless of speed.
They act almost exactly like a differential, including the effect that
if one wheel can't turn, the other wheel runs twice as fast, and that if
one wheel is in the air, the other wheel produces almost no torque.
If the motors are wired in parallel, they act almost exactly like a
limited-slip differential. This is better for poor-traction situations.
The motors also run twice as fast with half the torque as compared to
the series case. A series/parallel switch can thus be used change the
motors from series to parallel, which has the effect of providing a
2-speed transmission.
--
Results! Why man, I have gotten a lot of results. I know several
thousand things that won't work. -- Thomas A. Edison
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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