5.3.7.18 Chair Stability Parameters
Parameter Possible Values Default Rev HHP Lite Std Adv
Speed x Turn for Grip 5 – 100 % 100 % C -
Accel Out Of A Turn For Grip 0 – 200 % 100 % C -
Accel Into A Turn For Grip 0 – 200 % 100 % C -
The Chair Stability Parameters can improve the safety, controllability and
performance of the powerchair, especially for mechanically unstable chairs like Front
Wheel Drive chairs or Mid Wheel Drive chairs. There is not much weight distribution
over the drive wheels of these chairs and therefore the wheels can slip easily.
For any chair design, there is a maximum combined value of Speed and Turn for
which the chair is stable. A chair may be stable turning slightly while moving at a high
speed forward, or it may be stable making a fast turn on the spot, but it may be
unstable and lose control when making a sharp turn at a high speed. Loss of control
means that the chair’s inertia and turn component are such that the tyres lose
traction and slide, rendering any action from the controller ineffective.
Traction is affected by many factors, such as
• the chair design
• the wheel base length and width
• the centre of gravity of the chair
• the state and inflation of the tyres
• the friction and slope of the driving surface
• the weight and the position of the user.
The Speed X Turn for Grip, Accel out of a Turn for Grip and Accel into a Turn for Grip
parameters together define the mechanical properties that affect the stability of the
chair and are set by the powerchair manufacturer for each particular chair design.
These parameters are NOT designed to be tuned for specific users.
Note:
The overall effect of the chair stability parameters is dependent on
the value of the
Grip parameter (5.3.7.15).
The Grip parameter can be adjusted by the dealer or therapist and
as such it must not be used by the powerchair manufacturer to
control the stability of the powerchair.
GBK60348
: Issue 1 – October 2007
74
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