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.
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.
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
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
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.
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
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
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.
Published 12/09, Copyright 2009, WheelchairJunkie.com