was introduced on the cover of Mechanix Illustrated magazine in February, 1977, long
before the automotive world began thinking about manufacturing electric cars. Urba
Electric's introduction was a landmark in EV development for a number of reasons. First,
the car was ahead of its time simply by having been built at a time when EVs were
considered non-starters by car makers. Secondly, MI readers collectively purchased over
20,000 sets of plans, which sent a strong message about public enthusiasm for EVs. Third,
it was designed and built outside the automotive industry, and its development was
entirely financed with private funds. And finally, although the car's 48-volt battery pack
was little more than a copy of those used in golf cars, Urba Electric utilized
cutting-edge composite technology in its construction, and it pioneered an innovative new
concept in EV speed control and power system strategy. The car's technical innovations
inspired engineers at Delco to purchase a set of plans and build one for testing. The
Delco car later became known as GM's Drive I.
Urba Electric's main technology breakthrough was the Electromatic Drive
Transmission, developed and patented by Darrell Hillman and Foster
Salsbury of Salsbury CVT fame. This ingenious electronically controlled continuously variable
transmission (CVT) let the motor run at a steady speed while the transmission's
shift-position provided control over the car's speed from zero through 60 mph. The
accelerator pedal was connected to a device that varied a low-voltage shift-position signal
to the CVT. This caused the shift-position to track the degree of depression of the
accelerator pedal. As the accelerator pedal was depressed, the CVT smoothly up-shifted
causing the car to accelerate in unison. Meanwhile, the compound-wound dc motor ran at a
constant speed - its most efficient speed. For regenerative braking, the driver simply let
up on the accelerator pedal, causing the CVT to downshift to a lower ratio. Downshifting
at cruising speeds forced the motor to spin faster, which reversed the direction of
current flow and delivered a charge to the battery (due to counter emf) as it slowed the
car. No traditional electronic speed control was necessary.
Urba Electric's chassis is not from an existing car. Instead, it was designed from
scratch in order to keep weight down and efficiency up. The battery pack is arranged in a
reverse "T" much like the battery pack of GM's EV1. Half of the car's eight
6-volt batteries occupy the space in a tunnel that runs between driver and passenger, and
the other half runs transversely just behind the passenger compartment. The frame is made
of rectangular steel tubing. A jackshaft coupled to a differential with a simple chain
drive makes up the final drive, which is contained in a sealed oil-bath housing and
suspended from the frame at the rear. The body is made of FRP/foam
Today, the Electromatic Drive Transmission is no longer available, and plans include an
alternative speed control system. Also, the trend today is toward much higher system voltages. Urba
Electric's performance and efficiency would be enhanced by upgrading to a higher voltage.
The most simple way is to switch to12-volt batteries. And the new
Lithium batteries will significantly increase the vehicle's range.
Urba Electric plans provide a technical insight into one of the most innovative and
cutting-edge EV designs ever developed outside the mainstream automotive
field. Although the Electromatic Drive Tranmission is no longer available, an innovative machinist coud undoubtedly build one from patent drawings. That would probably require a physical search for the patent at a Patent Depository Library.
Photography for the MI feature was done by the consumate professional (the late) Peter Gowland. Peter was always relaxed and casual. You could hardly tell he was working. Peter did all the Mechanix Illustrated MiMi shots. The model in the photograph was doing toothpaste commercials at the time. But she should have been doing eyedrop commercials. She had the most gorgeous eyes ever created.
For more information on the Electromatic Drive Transmission, please see the linked page.
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