As a powerchair user, you know how your powerchair maneuvers indoors. But, do you know why your
powerchair has such inherent handling characteristics?|
The answer is, your powerchair maneuvers
the way it does because of its drive wheel pivot point. Sure, overall size and user placement influence
maneuverability, as well. However, at the heart of maneuverability is the solid science of the pivot
point, the absolute design criteria that governs a powerchair's maneuverability. If one wishes to understand
powerchair maneuverability, then one must understand the principles and characteristics of a drive wheel
Powerchair drive designations - rear-wheel drive (RWD), front-wheel drive (FWD),
and center-wheel drive (CWD) - define the location of the fixed drive wheels. (In today's market, CWD
is often used interchangeably with mid-wheel drive (MWD); however, for the sake of clarity, this article
will use the CWD designation). Powerchairs are castered vehicles, where fixed drive wheels steer casters
that rotate 360-degrees for maneuvering, turning on a defined pivot point. This pivot point is where
the drive wheel axle line and the powerbase's centerline intersect, the point around which a powerchair
turns and maneuvers.
On a RWD, the pivot point is rearward, with the majority of the powerchair ahead of the pivot point.
On a FWD, the pivot point is forward, with the majority of the powerchair behind the pivot point. And,
on a CWD, the pivot point is centered, with the majority of the powerchair atop the pivot point.
RWD and FWD pivot close to a powerchair's ends, and, as a result, intrinsically swing outward the majority
of the powerchair's length when maneuvering in 90- and 180-degree turns, exceeding the powerchair's static
diameter. A CWD, on the other hand, pivots on center, remaining within its original static diameter.
It's this principle - an offset versus center pivot point - that dictates why RWD and FWD require more
space to rotate 90- and 180-degrees (and, ultimately, 360-degrees), than a comparably-sized CWD.
Although RWD and FWD require greater rotational turning space than a comparably-sized CWD, they can
be maneuvered efficiently through skilled operation. However, it's still not possible to rotate a RWD
or FWD within its static diameter like a CWD - this is why a CWD is intrinsically the most maneuverable
platform in confined diameter spaces.|
Beyond turning diameters, pivot points also dictate handling
characteristics in tight, linear spaces, as with maneuvering in hallways.
In making a 90-degree hallway turn, the front end of a RWD must swing wide, toward wall C, then swing
into the doorway, allowing the inside rear wheel to clear wall B. The same scenario in a FWD requires
that the front wheels are positioned close to wall B, then pivoted into the doorway, swinging the rear
casters close to wall A. For the same maneuver in a CWD, the center of the drive wheel is positioned
just beyond wall B, where the powerchair then pivots the front and rear around the door frame, with near
equal lengths front and rear, without a long front or rear to swing, readily clearing walls A, B, and
C. In halls, as with diameters, a CWD pivot point decreases the space needed for maneuvering over a
RWD or FWD.|
A powerchair's overall length, of course, influences maneuverability, and keeping
all powerchair platform lengths to a minimum optimizes maneuverability, including CWDs. A 42"-long CWD
turns in a smaller diameter than a 44"-long CWD, as holds true for RWD and FWD. Further, seat location
in relation to the drive wheels is important, including on CWD, where the goal is to have the drive wheels
as centered as possible within the powerchair's true length, from the tip of the footplate or legrest
to the rearmost part of the powerchair.
Beyond subjective adjustments, however, a pivot point
is the constant that dictates a powerchair's maneuverability. No matter the length of a powerchair,
a CWD pivot point location is more maneuverable than a comparably-sized powerchair with a RWD or FWD
pivot point location. Further, a slightly longer CWD can prove more maneuverable than a shorter RWD
or FWD. Going back to overall turning diameter, a RWD or FWD requires dramatically more space to pivot,
well beyond its overall length, so while an absolute CWD can stay within its overall length (turning
within a static diameter), a RWD or FWD cannot - that is, a short RWD still requires more turning space
than a slightly longer CWD.
Beyond the defined pivot point terms, there are individual RWD and
FWD, as well as conventional mid-wheel drive (MWD), models with drive wheel pivot points located in positions
closer inward or farther outward from the traditional drive wheel pivot point conventions - that is,
some models have more optimized drive wheel pivot point locations than others in a given class. However,
no matter the individual model, the definitions of RWD, FWD, and CWD pivot points still create the principles
that govern fixed drive wheel powerchairs, and dictate that no matter inward our outward pivot points,
RWD and FWD still feature offset pivot points in comparison to CWD.
The maneuverability of RWD,
FWD, and CWD powerchairs is predictable and governed, based on fixed drive wheel pivot point locations.
It's through understanding the inherent maneuverability characteristics dictated by pivot points that
one can fully recognize the distinct handling of rear-, front-, and center-wheel-drive powerchairs.
Published 12/05, Copyright 2005, WheelchairJunkie.com