Twenty years ago, there were very few differences between the designs of powered wheelchairs—most were simply iterations of manual wheelchair design. As the powered wheelchair market grew and products developed, powered wheelchairs began to evolve. Eventually, consumers, clinicians, engineers, and manufacturers recognized the need for product differentiation. Moreover, as more manufacturers of electric powered wheelchairs emerged to address the specialized needs of the consumer, manufacturers wanted to have their products be distinguishable from those of other manufacturers (41,42).

Powered wheelchairs can be grouped into several classes or categories. The most common groupings are based on the functions provided by the wheelchair and the intended use. A convenient grouping by intended use is primarily indoor, both indoor/outdoor, and active indoor/outdoor. Indoor wheelchairs have a small footprint (i.e., area connecting the wheels) that allows them to be maneuverable in confined spaces. However, they may not have the stability or power to negotiate obstacles outdoors. Indoor/outdoor powered wheelchairs are used by people who wish to have mobility in the home, school, office, and community, but who stay on finished surfaces (e.g., sidewalks, driveways, flooring). Both indoor and indoor/outdoor wheelchairs conserve weight by using smaller batteries. This often results in reduced range.

Some wheelchair users want to drive over unstructured environments, travel long distances, and move fast. Active indoor/outdoor wheelchairs may be best suited for these individuals. The active indoor/outdoor-use wheelchairs include those with suspension systems and the use of a power base design is increasing. A power base separates the seating system from the main chassis of the wheelchair. With power bases, the main chassis consists of the motors, drive wheels, casters, controllers, batteries, and frame. The seating system (e.g., seat, backrest, armrests, legrests, footrests) is a separate integrated unit. Often, seating systems from one manufacturer are used on a power base from another manufacturer.

Indoor/outdoor powered wheelchairs can be further divided into categories by the design of the seating system. The simplest form of seating system is a linear seating system. A linear seating system refers to a planar seat and back with fixed angles and orientations. For people who have low sitting tolerance or who need to change posture to perform some activities of daily living, a reclining seating system may be beneficial. A reclining seating system allows the angle of the backrest to be changed (e.g., from upright to reclined). For people with very low sitting tolerance, severe spasticity, or homodynamic problems, a tilt-in-space seating system may be appropriate. Tilt-in-space systems allow the backrest, seat, and legrests to tilt as a unit, without changing their orientation with respect to each other, but as a unit change with respect to the wheelchair’s chassis. Changing the user’s position in space has other advantages besides assisting with posture and sitting tolerance. Stand-up wheelchairs assist users in performing many activities of daily living. Stand-up wheelchairs may have some physiologic benefits because of the user’s upright posture, and have been reported to provide psychologic benefits to the user. Some people cannot use stand-up wheelchairs because they do not have the range of motion or their bones may be too fragile. However, some of the benefits of a stand-up wheelchair can be obtained by using a variable seat height wheelchair. The most common function of variable seat height wheelchairs is to provide seat elevation, although some wheelchair models come with both seat elevation and lowering. Lowering may extend to a few inches from the floor, while rising can be as high as 3 feet (91.44 cm) from the floor to the base of the seat.

People with severe disabilities might need power wheelchairs for mobility purposes. Individuals who have a moderate level of trunk control can use conventional power wheelchairs. Conventional power wheelchairs contain a standard seat system. Alternative seating systems have been designed to provide customized seating in the standard power wheelchair seat. Power wheelchairs are distinguishable by their integrated frame and seat. Their appearance is most similar to that of a conventional wheelchair. Power wheelchairs may use a range of drive wheels from 8 to 20 inches (20.32 cm to 50.8 cm) in diameter. Either belts or gearboxes may drive the drive wheels. All powered mobility systems are generically lumped under the title “powered wheelchair.”

Power bases are simply powered wheelchairs consisting of a power drive system on a mobile platform. Power bases are developed for those people with minimal trunk control who need a customized seating system mounted to the base. Power bases also tend to offer higher performance (i.e., faster, more torque). A significant advantage of some power bases is that the position of the wheels can be changed with respect to the seat. This permits adjustment of the handling of the wheelchair without losing some of the power. The power base includes all wheels, the motors, the batteries, and most often the controller. Seating systems can be developed without modifying the power base which provides locations suitable for mounting seating hardware.

Another means of providing powered mobility to a manual wheelchair is to use in-wheel motors. In-wheel motors are wheel hubs made from a motor. The hub is much larger than that of a standard manual wheelchair so that the motor is of sufficient size to provide function power. In-wheel motors use a battery pack, which attaches to the frame. The most common means of attaching the battery is to use a small bag slung under the wheelchair. In-wheel motors are commonly made with quick-release axles to simplify transport. Either a joystick or switches can be used to control the motors (i.e., right and left side) to provide electric powered mobility for a manual wheelchair. One must exercise some caution when converting a manual wheelchair to an electric powered wheelchair. Manual wheelchairs are not designed to accommodate the additional weight, and this may reduce the stability, durability, and ease of propulsion when in the manual mode. The speed possible with a powered unit is also likely to be greater than that possible with a manual chair. Moreover, powered wheelchairs drive much differently than manual wheelchairs. A skilled manual wheelchair rider may pop the casters over small bumps without noticing. However, when the chair is converted to being electrically powered, the caster may be damaged in short order. When used properly, with appropriate training and awareness of the trade-offs, power conversion units can provide valuable assistance.