Just a little something for those of you with a mechanics-related inclination ;-)
Take, for example, a Catherine wheel-type firework, as in diagram 1. The 4 motors positioned at the tips of the wheel in the diagram each produce thrust in the direction of the blue arrows, thus causing the wheel to rotate in the opposite direction. Fair enough so far.
Now, connect the Catherine wheel to a drive wheel on some sort of buggy of the same diameter, as in diagram 2. As the Catherine wheel spins, torque (T) is transferred along the shaft to the wheel. Since the wheel converts rotational torque into linear motion along the ground (The brown lines), force R, then this seems to infer that the individual contribution of the thrust from each of the 4 motors to the torque output, and thus the motion of the buggy is always constant and even…
Now here’s the
other way of looking at it. Since the Catherine wheel is of the same physical size as the driven wheel and the drive shaft is simply serving as a connecting medium, then the driven wheel can therefore be replaced by the Catherine wheel (neglecting thrust interactions to the buggy, etc), as shown in diagram 3. In diagram 3A, the motor thrust at the top of the wheel acts on the wheel in the form of a second class lever, with the fulcrum point (F) at the ground and the force output forcing the axle of the buggy forwards (Force R).
In diagrams 3B and 3C, a similar scenario is present compared to 3A, except the theoretical levers are bent at 90 degrees.
However, in diagram 3D, the motor thrust is acting
at the fulcrum point, and as a result, presumably this motor produces no forwards force on the buggy.
Hence, why does there appear to be a mechanical difference between these two viewpoints, and if there really is a difference, could the motors passing nearest to the ground be shut off in order to improve fuel efficiency?
(Why am I asking this? For those of you who have seen Dad's Army, can you remember the rolling, rocket-propelled mine type contraption? What’s their proper name?)
Hodgkinson.
