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.