Design and evaluation of a sit-snowboard for advanced users, focusing on comfort and control

Abstract

A sit-snowboard is a weight supporting mechanism that allows
people with lower extremity impairments to perform the sport of snowboarding.
Comfort and control of the Twinrider (the only sit-snowboard on the market) are
insufficient for advanced riders who reach higher speeds and ride more bumpy
slopes. The goal of this study is to design a sit-snowboarding mechanism that
provides sufficient comfort and control for advanced users.

In the new mechanism design (Snowcruiser), vertical
suspension is added between the seat and the board using two mountain bike
forks. Independent compression of the forks, nose/tail translation of the seat
and board flex are allowed. These alterations prevent control interference, visional
and vibrational discomfort due to seat tilt, vibrations or shocks on the seat.
A continuous interaction of the snowboard with the surface though board flexion
and less vibrations on the board also improves control.

With a quantitative test the performance of the new design
is evaluated by a straight descent from a bumpy, artificial slope. The
prototype carried a dummy weight and the descent is guided by a skier. Using
four accelerometers of which two were placed on the board and two on the seat,
accelerations were measured. To assess the severity of these vibrations and
shocks the standard BS 6841 is used. Vibration Dose Values (VDVs) for the board
and the seat are determined after weighting the accelerations to the frequency
and direction as described in the standard. Seat tilt and contactless distance
were determined using data from high speed cameras. Setting each combination of
maximum and minimum height, compression and rebound speed resulted in eight
Snowcruiser models. With analysis of the variables, speed dependency is checked
and an insight is gained on the behavior of the different combinations of
settings. Also a qualitative test is performed in which two riders actually sit
in the prototype and slide over hills while turns are made.

The measurements show that the VDVs on the seat are lower
for all Snowcruiser models than for the Twinrider, indicating less discomfort.
The riders of the qualitative test confirmed this by experiencing a smooth run:
No shock is felt when landing after a hill. The Seat Effective Amplitude
Transmissibility (S.E.A.T.) is not lower for the Snowcruiser than for the
Twinrider, so vibration isolation is not more efficient for the Snowcruiser.
However, the Snowcruiser shows reduced accelerations on the board. The
Snowcruiser is able to keep the seat horizontal for small inclines. The
qualitative test shows that more board flexion is possible. The variable of
contactless distance is strongly depending on riding speed, and therefore not a
useful variable in this study.

Both tests show that comfort and control are improved for
the Snowcruiser and that the goal is achieved. A height of 500mm, maximum
compression and fast rebound form the most promising combination of settings.
The measurement method presented in this study is a valid method for
performance evaluation of comfort and control for a sit-snowboard, using the
variables VDV and seat tilt.