Adjusting the properties

For dealers of The Skipper, a special wireless programming interface is available. This interface comprises a USB dongle for a laptop or PC and a programmer box to be installed between The Skipper and the wheelchair. The dongle and the programmer are linked via built-in radio modules.

The adjustment program

With a special Windows program, various settings of the Skipper can be adjusted while the user is free to drive around. Because the dealer gets instant feedback from the user about the effect of an adjustment, the optimal values can be found quickly and easily. The maximum working distance between the laptop and the wheelchair is at least 25 meters and usually more. If the radio link fails, the wheelchair stops automatically.  If anything goes wrong, the dealer can stop the wheelchair immediately.

Linear or exponential output

In most wheelchair controllers, the relationship between input force and wheelchair speed is linear. This means that if the input force is half the maximum, the speed is also half the maximum. With the Skipper, the relationship between force and speed can be adjusted to be non-linear. In that case, half the maximum force gives less than half the maximum speed but the maximum force still gives the maximum speed.

The Skipper has this feature because a users’ perception of a particular change in speed depends on the current speed. A speed increase from 0% to 10% is highly noticeable but an increase from 90% to 100% hardly is.  The effect of a particular change of the input force at low speed is much more noticeable than the same input change at high speed.

To the user, linear control feels more sensitive at low speed and less sensitive at high speed. With non-linear control the sensitivities at low speed and high speed feel more equal. Precise steering at low speed gets easier and the control feels more responsive at high speed.

If the Skipper is set to linear output, the wheelchair speed at half the maximum input is half the maximum speed. If you draw the relation between input force and wheelchair speed, you get a straight line, as shown in the figure. Notice that the line does not start at zero force but at some threshold value. All wheelchair controllers have this feature. It prevents the motors from reacting to unavoidable small deviations from zero output at zero input because of manufacturing tolerances, temperature effects, aging, etc.

If the Skipper is set to non-linear output, the speed at half the maximum input is less than half the maximum speed.  If you draw the relation between input force and wheelchair speed, you get a curved line. The curvature can be continuously adjusted between linear and exponential. In the last case, every extra gram of force multiplies the speed with a constant factor.

The amount of curvature has a number from 0 (linear) to 20 (pure exponential) on the laptop.  A value of 5 to 10 may be optimal for the average user. This can only be determined in practice. Experienced wheelchair users, who are used to linear control, will probably have to get used to non-linear control. For them, linear control always remains an option with the Skipper.