Knowing the language of power-wheelchair design and a bit about how their features change performance can make finding the correct chair considerably easier. Since most people only have a new chair of this type every five years, it is important that it fully meets the person's needs. Let's start with some basics.

Drive-wheel Location

Placement of the drive wheels—those turned by the power chair's motors—determines how the chair will steer and handle. A rear-wheel-drive power chair is a traditional approach that provides good directional stability while going forward.

These chairs handle uneven terrain well. They steer about an axis between the rear wheels, so they require some planning when turning to anticipate where the front end will sweep. However, the driver can see the front of the chair and make adjustments. Power-soccer players often use rear-wheel-drive chairs because it helps to increase the impact with the ball and provide ball control.

Front-wheel-drive power chairs are similar to flipping the seat around 180° on a rear-wheel-drive chair, but the driving dynamics change radically. Front-wheel-drive chairs are harder to drive straight, as small sideways disturbances (uneven surfaces, being pushed, hitting an object, initiating a turn) are amplified. This behavior is sometimes known as "fishtailing." Manufacturers compensate for this by using sensors to measure the rotation of the drive wheels, and then adjusting the motor power, using closed-loop control.

With a front-wheel-drive chair, the rear end swings to the side when turning, so it requires some planning to know where the rear of the chair will move to, but it allows for quick turning. These chairs are good at climbing obstacles as the drive wheels, which tend to be larger, face the front and help to power over objects.

Mid- and center-wheel-drive chairs are growing in popularity. They are easily recognizable by their six wheels—two casters in the rear, two casters or antitip wheels in the front, and the drive wheels in between.

Mid-wheel chairs turn about the center of the line connecting their axles. Because the drive wheels are closer to the driver's center of mass (located around the hips), the point about which the chair turns nearly coincides with the user's center. This makes driving the chair intuitive for many people.

Because the drive wheels are in the middle, the front and rear sets of wheels need to be suspended (i.e., held in place by hinges and springs) so the drive wheels have solid contact with the ground; otherwise, the drive wheels could lift off the ground at the end of a ramp, for example. Some people note that mid-wheel-drive chairs feel like they rock back-and-forth as speeds change or when on uneven terrain.


The authors take a closer look at seating functions, seating hardware, and control interfaces. Read more in the May PN.