Life on Wheels (56 page)

The Wijit system is a set of wheels with geared levers one grasps in order to push forward and pull backward in a motion similar to rowing a boat (Figure 4-6). There is no contact with the wheels or handrims. The Wijit handles can be shifted into forward, neutral, or reverse modes. Pulling the handles inward toward the body brakes the wheels (www.wijit.com).

The handrim is the circular tube mounted just away from the wheel. You grasp it—and often will simultaneously grasp the tire with your palm—to push the chair. You grasp the handrim by itself to brake the chair while you are rolling.

The basic handrim—circular in cross-section (if you slice through it)—remains the standard that comes by default when you order any chair. They are typically made of aluminum with an anodized, gray coating that is smooth enough not to burn your hands from friction as you brake, but not so slick that you can’t slow yourself effectively with minimum grip force. Other options include plastic, foam, or powder coatings. These coatings increase the “gripability” of the handrim but are more easily damaged. Plastic handrims can be very hot when braking and might seriously burn hands that lack sensation.

Standard handrims require the rider to have a reasonably strong grip, but there are other designs that allow for less gripping ability. Low level quadriplegic riders who use a manual chair can elect to use special handrims with added “pegs” or knobs that help compensate for the wheeler’s limited grip capacity.

Handrims come in different sizes: in general, the closer the rim is in size to the diameter of the wheel itself, the less force you will have to apply to get the chair moving from a stopped position. Imagine how much force you would have to apply to a handrim about the size of the wheel hub, and you’ll get the idea. Some users choose a smaller handrim because, once you are in motion, it is possible to maintain more contact with the smaller handrim, to even get some motion out of the upward movement of your arm— which is otherwise impossible. This is the standard approach for racing wheelchairs. Manual chair riders with only one arm can get a chair designed with a dual handrim on one wheel, allowing either or both wheels to be controlled with one hand.

The design of the handrim has gained considerable attention from chair designers recently. Essentially, the design of the frame has reached relative maturity, so this is a good sign. Designers are getting down to details, and the handrim turns out to be a meaningful component in the efficiency of your use of the manual chair. Its recent evolution indicates that wheelchair design is getting extremely refined.

Natural-Fit™ handrims from Three Rivers (www.3rivers.com) are not circular in cross section but, instead, are a couple of inches wide, providing more surface area to grasp (Figure 4-7). They also provide a surface between the rim and the wheel, which is typically open with a standard handrim. The wheeler can place her thumbs in this curved surface—which is available with a plastic-coated surface—for more “traction” between the hand and the wheel during the push. Braking is made easier because there is more surface with which to make contact as you grip. They also limit the need to grasp the tire, so your hands don’t get dirty or as calloused— not to mention the occasional contact with something objectionable you might roll through! Natural-Fit handrims can be installed on most standard wheels.

The design of the Natural-Fit handrim came out of the Human Engineering Research Laboratory at the University of Pittsburgh, led by engineer and chair user Rory Cooper. Three Rivers was able to build its business with support from a federal grant intended to help assistive technologies make the transition from the laboratory to the commercial marketplace.

Another wheelchair user and designer of note is Peter Axelson (yes, that’s really his name!) of Beneficial Designs (www.beneficialdesigns.com) in Reno, Nevada. Their design, the FlexRim Low Impact Wheelchair Pushrim uses the standard circular handrim, but it is fused to a flexible, rubber surface between the handrim and the wheel. When the handrim is grasped, it actually flexes slightly, independent of the wheel, reducing the actual impact forces on your hands as you push. It is also possible, as with the Natural-Fit, to lay your thumb in the formerly open space between the rim and the wheel for additional grip and freedom from contact with the tires.

These two designs also protect you from the possibility of jamming your hand or thumb on a wheel brake because your hand is only on the rim and not on the tire where the brake makes contact. For those with long enough arms—and therefore a long enough stroke such that you might make contact with the handbrake—this is an extremely painful experience!

Wheel locks, also called hand brakes, are used to prevent a manual chair from accidentally rolling when you want it to remain stationary. The fact is, not much of the world is truly flat and level. Given the much improved engineering of manual chairs, they will move even on the slightest sloping surface—which can be in your house or anywhere out in public.

Some chair riders have eschewed the use of brakes altogether, to the absolute horror of their therapists who subscribe to the belief that a wheelchair must be locked whenever you make a transfer to or from the chair. Just the act of reaching for an object on a table is enough to send sufficient force through your body to your wheels to cause the chair to shift, especially in a hypersensitive rigid frame chair. If you are working at a desk, leaning forward on your arms will cause an unbraked chair to roll backward—and so make you exert your back or have to grab onto something to stabilize yourself to keep the chair from moving out from underneath you.

Use of a hand brake also aids back support. Since you don’t have to worry about the chair moving, you can rest your weight against the chair back with confidence.

The standard brakes are a lever placed on the frame just ahead of the tire. When engaged, the brake makes firm, physical contact with the tire and, thus, prevents the wheel from turning. Another design, called a “scissors lock”—meant to solve the thumb-jamming problem mentioned above—mounts just under the seat but engages the tire to lock it in the same way as the standard lock. It is less convenient to reach and requires bending the wrists substantially to engage and release it. It is not possible to apply your body weight to engage it, but some users prefer how this design moves fully out of the way of the wheel when not engaged.

Some brake designs are engaged by pulling backward on the handle rather than pushing forward, for people who have more optimal muscle capacity in that direction. There are also brakes that can be mounted lower on the frame for people who don’t mind leaning over more, or who are more likely to be assisted, with the brake being operated by the helper.

Brakes that lock against the tire require adjustment, as the support bracket can slightly but gradually slide along where it is attached to the frame from the force of the brake against the tire. And, as your tires lose air (a continual process that needs your attention at all times), the wheel locks become less firm.

To resolve this problem, several companies have developed disc brakes that lock the hub of the wheel rather than push something into the tire. Accessible Designs, Inc. (www.accessibledesigns.com) offers disc brakes with a variety of controls. It is possible to have four different settings of braking force or a single electronic switch that will lock both wheels, for instance.

The downside of disc brakes is that, by locking the hub, the wheel can still move somewhat according to the flexibility of the spokes of the wheels. With some of the ultra-lightweight wheels with fewer spokes, the chair might not feel as stable in the locked position, as you adjust your position in the chair while stopped. This is very much a matter of personal choice.

The major choices for a power wheelchair are the drive type and the control system. You will need to think about speed—and about stopping. You will need to consider types and sizes of batteries. Finally, you will consider safety and torso stability issues. Figures 4-8 and 4-9 show the various features found on power chairs and contrast some of the design differences.

Power wheelchairs have the drive wheels placed either at the front or the back of the chair, or in an increasingly popular “mid-wheel” design, placed immediately under the seat. Each type of wheel drive entails a different style of operating your chair, and it takes a little while to adapt to the feel of it. If the type of drive is right for you, your skill and comfort using it will become increasingly refined, despite any early awkwardness you might experience.

With a frontwheel drive system, you have the sensation of pulling the chair behind you. This sense of pulling means that, in order to operate a frontwheel drive chair, you need greater sensitivity to the chair’s movement and control. Frontwheel drive chairs are very agile—capable of making full rotations in a smaller area of space. But, because frontwheel drive takes a little more skill to operate, ability and training issues must be taken into account. People with cognitive difficulties might not be able to safely use frontwheel drive.

One advantage of having the larger drive wheels in front is that you may be able to traverse a change in surface more easily—going over a curb, for example. The larger wheels make contact with the curb first, pulling the smaller casters along behind.

If you need a tilt system, you will want to consider whether a frontwheel drive chair will be stable. The tilt system may cause the front wheels to come off the ground, making the chair difficult to operate (Figure 4-9).