BRAKING

There’re few things more mysterious -- and complex -- on a powerchair than its braking. To make it even more confusing to consumers, the industry uses scientific terms like “dynamic braking” and “electromagnetic brakes,” never explaining how the systems work. However, by breaking the concepts down to the fundamentals principals of powerchair braking, you can better understand how your chair operates, increasing your control over your wheels.

Powerchair braking occurs through mechanical and electrical means. The most clear cut is an electromagnet that, put simply, locks onto your chair’s drive shaft, preventing the wheel from turning (called a "parking brake" by some manufacturers). Electricity releases the magnet, so when you push the joystick, the magnet clicks loose from the drive shaft, and when you release the joystick, the magnet reattaches, locking the wheel. When driving, the brakes, then, actually consume a small amount of energy, keeping them released.

Of course, the need for electricity to release the electromagnet explains the sudden “lock up” that occurs with a loss of power -- no electricity -- and the magnets set to their natural, mechanically locked position. (The million-dollar question of how to prevent lockup in a power failure, but still slow the chair to a controlled stop, remains.)

Your question may be, then how come when I’m driving my chair, it slows automatically before the all-or-none magnets set? And that’s where the advanced, electronic part of the system comes in. The chair’s electronics sense when you release the joystick, and send feedback -- or reverse motion into the motors, you might say -- slowing the chair. Much like on old E&Js without braking when we had to put the chair in reverse to slow and stop, modern electronics “dynamically” put electricity to the motors slowing the chair for you (the amazing part is how it works no matter what direction you’re traveling).

Most advanced, programmable electronics allow you to adjust both “brake delay” and “dynamic braking.” Brake delays typically range from 1 to 10 seconds, and determine how quickly the magnets set after the joystick is released. For example, on my own Bounders, I use a 10-second brake delay indoors because there’s no need to have the brakes set each time I return the joystick to neutral -- it eliminates the annoying “clicking” sound that the locking magnets make, providing stealth operation. On wheelchair lifts, however, I use a mode with almost no brake delay so there’s little coast when I stop. Overall, a medium brake delay setting works well for most, eliminating jarring stops while maintaining safety.

The second parameter setting is dynamic braking, the force at which the electronics slow the chair. If the dynamic setting is too low, the chair will coast out of control. On the other hand, if it’s set too high, the chair will skid to a halt the minute you release the joystick. Again, using my own chairs as an example, I use high dynamic braking on slow speeds for precise stops on ramps and lifts, and outdoors I use no dynamic braking, allowing the chairs to run free and fast. Conventional logic says that the faster the chair, the more dynamic braking you’d want; however, it’s much safer and predictable to run a low braking level on a fast chair -- trust me, you don’t want your 12mph chair skidding and tossing you from its seat every time you decelerate for a stop light.

Brake parameter settings can make or break a chair, having a profound impact on how your chair handles. Personally, I like lower braking levels on most of my programs because the chairs flow more naturally. My friends, however, think my freewheeling chairs are suicidal, as they prefer more conservative settings. It’s up to you to find the settings that work best for you. So, pick up a programmer, find a large, level area -- ideally away from plummeting cliffs, high-speed traffic, and deep bodies of water -- buckle your seat belt, and have fun adjusting your brakes.