ParaMedical Technologies



The WCDA device uses a simple inexpensive linkage mechanism for actuation. A full-size rendition is shown in Figure 1c for 24 inch wheels, by far the most popular.


Figure 1c


Figure 2c illustrates the WCDA assembly in detail. Actuating the lever causes the brake pads to clamp onto the grip ring, with the WCDA device stabilized by the support column secured to the hub assembly. This hub assembly is simply substituted for the standard hub assembly using a longer axle bolt.

Figure 2c

The details of the linkage assembly within the enclosure is shown in the Figure 3c. Depressing the lever moves main linkage to which it is secured about the the lever pivot and expands the retraction spring. The cross linkage is rotatably secured to the main linkage and moves in the same direction. The purpose of the cross linkage is to equalize the force applied to the grip ring by the two friction pads. This is accomplished through the two actuation linkages which pivot the two beams on the which the two friction pads are secured, thereby clamping the WCDA device to the grip ring.

Figure 3c

Many different linkage arrangement are feasible to obtain the objective shown in Figure 3. The linkage shown is one of the least complicated.

The hub assembly illustrated in Figure 4c shows the standard wheelchair bearing retainer with the longer axle bolt accommodating the extension shaft with its polymeric bearing. The support race secured to the support column is free to rotate upon the polymeric bearing. The spring retainer keeps the support race from sliding of of the bearing. The purpose of the limiter is to prevent the WCDA device from rotating to the ground when unattended.

Figure 4c

The manner by which the WCDA device can be simply detached from the wheelchair without any tools required is shown below. This feature is particularly important in narrow or crowded areas. Figure 5c shows the WCDA device as properly installed on a wheelchair.

Figure 5c

By shifting the WCDA device axially the spring retainer is depressed as shown in Figure 6c. The WCDA device can then be removed.

Figure 6c

Figure 6c shows the WCDA device fully separated from the hub assembly.

Figure 7c

Reversing this procedure reattaches the WCDA device to its proper position.


To adapt an ordinary wheelchair to accept the WCDA device requires that the two main wheel retention bolts be replaced with longer bolts that retain the two drive extensions as shown in Figure 8.

Figure 8c


The WCDA device requires no high-precision components. Except for the injection molded handle and lever shown in Figure 8c the materials of construction are largely commercially available sheet or tubing of stainless steel or equivalent materials.

The polymeric bearing could be, for example, a polymeric coated aluminum cylinder or a solid graphite-filled nylon cylinder, both readily available. The standard bicycle brake pads would have to be machined to conform to the grip ring, but the manufacturer could have the pads molded to the correct configuration.