Page 291 - Handbook of Electronic Assistive Technology

280 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

As an observation, it is noted that some wheelchair manufacturers have responded
to these problems, not by moving the centre of mass backward and unloading the cas-
tor wheels, but by making the castor wheels/forks/stem bearings sturdier. This does not
address the root cause and may, ironically, reinforce the problem in some situations by
forcing seating suppliers to push the person even further forward because, with the feet
tucked back due to tight hamstrings, as is so often the case, they are more likely to clash
with the castors if the wheels are larger.
A kerb climber (Fig. 9-3) can usually be added to lift the front castor wheels when
ascending a footpath from a road. One is needed where the axle centre of the castor wheel
is below or only fractionally above the top surface of the kerb, or in other words, simply
driving the chair at the kerb will most likely result in a dead stop. A kerb climber can help
in these situations; however:

• In general only fairly low kerbs can be climbed, so it is best to find a dropped kerb
where possible.
• Some individuals struggle to master the skill of kerb climbing because one must be
aligned to hit the kerb square on and have the commitment to keep the joystick (or
whatever access method is being used) pressed forward until the rear wheels are on the
pavement. It can also be an unpleasant experience, perhaps most for those with weak
trunk and neck muscles, or for those suffering with pain exacerbated by movement. It
is important to note that a kerb climber can also get in the way of standing transfers, as
many manufacturers do not have the option to easily remove the kerb climber; some,
however, provide a ‘park’ position, which tucks the climber foot back out of the way.

Mid-Wheel Drive
Mid-wheel drive chairs generally (Fig. 9-4) offer a greater degree of manoeuvrability than
their rear wheel drive counterparts. They can be particularly effective where a wheelchair
is to be used in an indoor environment where space is more limited.
While they will turn 180 degrees about their own centre point, some can be very long
end to end due to having three sets of wheels. In some instances a compact rear wheel
drive chair may actually be shorter; this highlights the importance of extensive trialling in
whatever environment is intended.
The three axles will articulate over rough ground, but this is sometimes felt as a rocking
motion, which can be unpleasant for the occupant. The chair can end up ‘beaching’ when
driving onto vehicle access ramps, as mentioned previously, particularly if the ramp is steep.
The additional length can be too great to allow access to some of the smaller through-floor lifts.
The overall weight of some of the larger mid-wheel drive chairs can be considerable,
which can cause problems where lifts, ramps and vehicle tie-down systems are not weight
rated with sufficient capacity. There do not tend to be any problems with excess loading of
castor wheels, as opposed to the situation with rear wheel drive chairs.
Dependent upon the design of the chair, when the seat frame is adjusted for minimum
depth (as is commonly the case for children), the backrest can end up in front of the drive