Page 295 - Handbook of Electronic Assistive Technology

284 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

Front drive chairs have less directional stability than rear wheel drive; it can be difficult
to avoid ‘fishtailing’ when attempting to drive in a straight line, although with the advent
of gyroscopic assistance the effect is reduced.
There does not tend to be any problem with excess loading of castor wheels, as opposed
to the situation with rear wheel drive chairs.
The fact that the drive wheels are at the front enables the person driving to turn much
more tightly around a sharp corner. The flip side is that the back of the chair swings round
in a full arc so the person must have the insight to allow for this, not only in terms of
the physical restrictions of the building, but with regard to people who might be in the
vicinity.
These can be an effective solution for particularly heavy people where the centre of
mass of the occupant is pushed forward.
Front drive chairs do not have problems with ‘beaching’ when driving onto steep vehi-
cle access ramps, as compared to mid- and some rear drive chairs.
The overall weight of some of the larger front wheel drive chairs can be considerable,
which can cause problems with some lifts, ramps and vehicle tie-down systems in terms
of the weight rating.
One particular difficulty associated with front drive chairs is that if the person stops
with the side of the chair up against a wall, they cannot drive forward to get away from the
wall – a reversing manoeuvre is required. This is the same to some extent with mid-drive
chairs although the castor wheels tend to be set inboard of the drive wheels, which gives
room to turn against a wall with the rear wheels while driving forward.

Comparison of Wheel Layouts With Respect to Space
Requirements for Turns
Historically, powered wheelchairs were considered less manoeuvrable than manual chairs.
Since they were bulky and the control systems less advanced, they required more circula-
tion space, but this is no longer always the case with the products available today. A person
with upper limb weakness may gain more independence in the home by using a compact
powered wheelchair than struggling to manually self-propel (Harpin, 2003). The techno-
logical advances of the past 15 years emphasise this point all the more.
In daily manoeuvres it is rare that a wheelchair user will perform a 360-degree turn,
but they are likely to revolve through 180 degrees frequently. This makes the width of
the turning circle similar across the three wheel layouts (Fig. 9-6), but the depth of the
turning circle is still greater for front and rear drive chairs, thus the importance of
assessing the home environment and the driving habits of the person are underlined
once again.
A very common manoeuvre will be the 90-degree turn, so the wheelchair’s ability in
this regard will be vital and far more important than the 360-degree turn. Fig. 9-7 illus-
trates how the drive wheel configurations are broadly comparable for the 90-degree turn,
with perhaps the front drive chair having the widest turning circle and the rear drive being