A Classic EV Design With Advanced FeaturesThis vehicle was the test bed for proving out the CVT speed control system for EVs. It was featured on the cover of Mechanix Illustrated magazine. Plans include 14 - 17 x 22 inch drawings & a 32-pg booklet.
Urba Electric 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 composite.
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 to 12-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 could undoubtedly build one from patent drawings. The patent is available from…. .