Steering

No matter what type of design I decide to follow steering will be a vital element.This is an overview of the steering systens used on skateboard designs. Currently I am leaning towards a two wheeled design similar to the dirt surfer because I prefer the aesthetics and there are functional benefits such as having a reduced weight.

Casters are the steering system used on castor boards and a modified version is found in the dirt surfer. Swivel castors as found on the Ripstick are able to rotate 360degrees because they are mounted on ball bearings, this makes them extremely agile. Because of the distance between the axel and the swivel joint casters always follows the direction of travel and tend to maintain the direction they have been moved in. Caster boards use a tilting platform on which the casters are mounted to force a change in the swivel angle that is proportional to the angle of tilt; this is done by transferring pressure to one side of the castor by lowering one side of the platform. The major problems with castors are that they are prone to an uncontrollable flutter at speed, though this can be reduced by increasing the distance from the swivel joint to the axel. They are also prone to being pushed by or caught in raises or ruts on the surface of travel because they swivel freely.

The dirt surfer uses a similar system to a caster, though it reduces these problems by using a pivot point rather than swivel, the degree the wheel can move is also reduced to about 30degrees and the distance between the axel and pivot is increased. The large diameter of the wheels means that they provide gyroscopic force proportional to the speed of rotation, this stops them being pushed by or caught on an uneven surface and provides proportional dampening to the steering making it impossible to over steer

Truck style steering as found on most skateboards works by causing the wheels on the lower side of the board to pull towards each other, this happens because the kingpin, which is the pivot point of the axel, is set at an angle that is less than 90degrees to the board so when one side becomes lower the axels are forced into a position that means they are no longer parallel. The board then turns around the point where imaginary lines drawn through the axels intersect. Depending on the angle of the king pin trucks are prone to speed wobble.

The foot steering used by the wheelman uses the angle of the rider’s foot to change that of the wheel, this gives precise proportional steering that is effective at low and high speeds. I am aware that hitting an obstacle would transfer the force to the rider’s ankle and potentially cause injury. However as long as the wheels range of movement is within the tolerance of the ankle it would most likely be ok although I doubt it would be suitable for off road use because even small consistent shocks would quickly tyre the muscles required to maintain control. This style of steering caused me to wonder if it would be possible to use with a non-spokeless wheel, I am confident that a method could be devised, such as having a swivelling footstrap connected to the wheel by a rod.

I am familiar with servos as a steering system. They could be wirelessly controlled to change the angle of the wheel with a high degree of accuracy at high and low speeds and would not risk injury to the rider through shock transfer. The wheel would also be able to ride through uneven terrain without being caught in ruts or pushed by high spots because the servo would not allow the wheel to deviate from its set course.

Information derived from previous posts, http://en.wikipedia.org/wiki/Caster and http://en.wikipedia.org/wiki/Skateboard