Design Inspiration

In order to win races, a race car must be operated at its performance limits. In order for the driver to push the car to its performance limits the driver must have precise control of steering, braking, acceleration and gear selection. Furthermore, this control must be applied in a chaotic environment of g-forces, speed, proximity to other racers and changing track conditions. An able bodied racer uses both hands and feet to control the vehicle. A paraplegic racer is unable to use her lower body and so those functions normally controlled by the feet must be accomodated elsewhere.

In the Hollfelder/Therkleson Hand Control System, the race car is controlled as follows:

Clutch/Gearshift
The foundation of the Hollfelder/Therkleson Hand Control System is the automatic clutch and gear select control system. The shifter is an experimental auto shift/select shift manual (ASM/SSM) developed by Ford.

The system is comprised of a standard clutch and 6-speed Tremec gearbox, but with actuation accomplished by an electrohydraulic system initiated by two thumb switches mounted on the left and right steering wheel spokes. The right switch upshifts and the left switch downshifts in sequential fashion.

All shifts are automatically coordinated with engine speed, throttle opening and aggressiveness of the driver. When driven aggressively, gear shifts are accomplished in less than 250 milliseconds.

Brake
The steering column is designed to be telescopic with mechanical linkage to the cars brake master cylinder. The driver can cause the vehicle to brake by merely pushing the steering wheel away from her body. The motion is a simple arm extension much like bench pressing. Only about 50 lbs. of force are required for full brake lockup.

The driver's upper body is restrained in the form fitted race seat with a full 6-point race harness and so the body's forward momentum under braking does not interfere with the braking movement. Braking can be applied completely independent of steering wheel rotation or throttle position, therefore, the driver is able to carry trail braking into corners.

Throttle
The throttle is drive-by-wire implemented by means of a concentric ring mounted on linear bearings about two inches in front of the steering wheel rim. The ring is in turn connected to a throttle position transducer.

The concentric ring is pulled toward the steering wheel rim by use of the fingertips of either/or both hands. About 15 lbs. of force exerted over two inches of travel is enough to go from idle to full throttle. Control is precise and quick.

Steering
Steering of the car is conventional except that a steering quickener gearbox has been added to the steering linkage to quicken the steering action by about 30%. This enables the driver to keep both hands at the 3 o'clock and 9 o'clock positions at all times while racing.

The Hollfelder/Therkleson hand control system is a custom fabrication made especially for Tiger Racing's Ford Mustang. It is not available for commercial sale. However, persons interested in racing hand controls are invited to communicate with the designer, Tom Hollfelder, via e-mail at the team address. He will be happy to answer questions and provide insight into the problems associated with hand controlling a race car.