High-Speed Tracking - WheelchairJunkie.com

Warning: This article on power wheelchair programming is for informational purposes only, and is not an endorsement of altering any power wheelchair's programming. Programming of a power wheelchair should only be performed when necessary to meet an individual's clinical needs, and should only be performed by a provider or clinician intimate with a specific individual's needs. Improper power wheelchair programming can be hazardous.

Here's an elementary math question for you: What's the shortest distance between two points?

Of course, the answer is, a straight line.

Indeed, a straight line isn't only the shortest distance, but also the fastest - including when it comes to power wheelchairs. And, if you want your power wheelchair to run as fast, smooth, and predictable as possible, optimally-programmed high-speed straight-line tracking is the key that unleashes its fullest potential.

How Power Wheelchair Steering Effects Speed
Power wheelchairs are different than many other "vehicles" in that power wheelchairs aren't mechanically steered via a steering wheel or handle bar directly linked to the wheels like a car or motorcycle. Rather, power wheelchairs are steered via an electronic joystick that directs two motors, one on each drive wheel. If a power wheelchair is directed to turn right, for example, the right motor slows down, while the left motor maintains speed, and the power wheelchair then turns to the right, accordingly.

What's important to recognize, then, is that for a power wheelchair to maintain its absolute maximum speed, the joystick must be held precisely dead-center-forward - directing both motors to propel absolutely forward - as even the slightest right or left joystick movement at full speed can cause the power wheelchair to slow one motor, immediately losing speed and veering.

Disability Often Prevent a Surgeon's Hands
Of course, many with disabilities simply don't have the steadiness of a surgeon's hands to keep a power wheelchair's joystick dead-center-forward at, say, 8mph all of the time. Those with Parkinson's or cerebral palsy can struggle to keep a joystick precisely positioned due to tremors and spasms, and those with muscular dystrophy or multiple sclerosis can have difficulty maintaining a joystick's position on rough sidewalks, where a lack of muscle control prevents counteracting bumps and jars. In fact, even those with seemingly unaffected coordination can struggle to keep a joystick in its ideal dead-center-forward position outdoors, at high speeds.

The Mission: Tracking Straight and Fast
The goal, then, for a user is to be able to drive his or her power wheelchair at full speed, as accurately and effortlessly as possible, optimizing speed and safety. How is that accomplished, though?

The answer is, through astute programming. When programming a power wheelchair to a user's dexterity and coordination characteristics, the goal is to have the joystick remain responsive to intentional steering, while ignoring unintentional movements at full speed, and although these two needs seem contradictory, they actually work together. In simple terms, unwanted movements - no matter a single twitch of the joystick or constant tremors - are split-second movements of the joystick from dead-center-forward to side-to-side, and the objective is to reduce the joystick's responsiveness to those split-second, unwanted movements without effecting deliberate steering.

To achieve this ideal, one has to concentrate on fine-tuning three foremost parameters that affect how quickly a power wheelchair reacts from dead-center-forward joystick movements to veering side to side (and the exact parameter names vary slightly among electronics brands):

Turn Sensitivity: Dictates how rapidly the joystick responds to right and left joystick movements. With a value from 0 to 100, the higher the value, the more sensitive the joystick is to movements.

Turn Speed Rate: Defines how sharp of a turn the power wheelchair enters, specifically at full speed when transitioning into a turn. With parameters from 5 to 100, 5 would dictate a large sweeping turn, and 100 would dictate an immediate, sharp turn upon movement of the joystick.

Tremor Suppression: Reduces the joystick's response to sudden or continuously-jerky movements. With values from 0 to 100, 0 is no suppression, and 100 is maximum suppression.

Beginning with Turn Sensitivity, it's one of the most underutilized programming parameters, one that can dramatically improve a power wheelchair's handling predictability, especially at high speeds. For users who find the power wheelchair over-reactive at high speeds, where the slightest joystick movement affects tracking, decreasing Turn Sensitivity can make handling feel far more "stable." By decreasing Turn Sensitivity, the power wheelchair won't react to one's every twitch of the joystick, relying more on deliberate gross movements. The power wheelchair will still respond deliberately, and even slalom, but won't have the "twitchiness" that frustrates some users.

Turn Speed Rate also increases high-speed tracking predictability. At top speed, a power wheelchair that enters a sharp turn at the slightest joystick movement is difficult to control at best, dangerous at worst. Remember, at top speed, one is almost always driving in relatively straight lines, such as on sidewalks, merely making sweeping turns as needed, so while at low speeds indoors high turn rates are preferable for sharp turns into doorways, they're not so ideal outdoors, and can prove detrimental if programmed too high. A lower Turn Speed Rate can make top-speed handling far more manageable.

For even more predictable, forgiving handling, Tremor Suppression proves a valuable tool. Many mistakenly believe that Tremor Suppression is only for those with certain disabilities, or that it "deadens" responsiveness, but that's truly not the case. Incrementally adjustable, slight tremor suppression can benefit many users by, again, removing "twitchiness" at full speed, so that slight unintentional joystick movements or bumps in the road are ignored by the electronics, but full functionality remains (and, tremor suppression does not effect emergency "slam braking" on most systems). Nevertheless, if set too high for some users, tremor suppression can make the power wheelchair feel less responsive, so it should be cautiously adjusted incrementally to a user's abilities and preference.

How "Tracking Technologies" Don't Correct for Joystick Movements
Many consumers believe that "tracking technologies" make a power wheelchair "drive straight." And, they do - but only when the joystick is held dead-center-forward. Where tracking technologies come in is namely when obstacles or uneven surfaces are encountered, with the joystick dead-center-forward, the power to the motors automatically adjusts to prevent the power wheelchair from veering off course (and it's especially used in "latched drives," as with sip-n-puff or head switches). However, tracking technologies do not compensate for joystick movement, so if one twitches the joystick to the right, the power wheelchair still will veer to the right. Therefore, even if a power wheelchair features a tracking technology, high-speed programming optimization per individual needs still often must take place.

Putting High-Speed Programming in Its Right Place
It's important to note that this article's topic only relates to top-speed handling of a power wheelchair. Most high-end power wheelchairs feature individually-programmable Profiles (or Modes), where a profile can be programmed specifically for high-speed outdoors use - and that's the profile where the method of applying these settings would best apply (lower-speed, indoor profiles typically require different settings for optimal handling).

The Devil's in the Details
I have fun with my colleagues and peers in that although they're using power wheelchairs identical to mine, I can always beat them in a straight-line race, often to their noting that I must have "souped-up" my power wheelchair. In fact, in accordance with my own needs based on cerebral palsy, all I've done is optimized my Turn Sensitivity, Turn Speed Rate, and Tremor Suppression settings to my specific coordination, increasing my top speed from 8.2mph to 8.6mph. Again, though, what's intriguing is that my motors haven't changed; rather, I'm simply able to steer them the most efficiently.

And, steering a power wheelchair the most efficiently is truly the objective for all users, where predictability, ease of handling, and safety are key. No matter if it's at low speed indoors, or racing down a sidewalk outdoors, the perfection is often in the programming.