Hello all. I haven't been by in a while.
I've written here and elsewhere in Usenet about the ultracapacitor bike. Unlike a battery, the state
of charge of a capacitor can be known to great accuracy.
The energy stored in a capacitor is 1/2 * Capacitance * Voltage^2. The energy stored in you and the
bike in motion is 1/2 * Mass * Speed^2. The voltage output of any brush-commutated PM DC motor is
proportional to speed directly. No square.
So by coupling the motor directly to the bike, we find that given time, the system will come to a
capacitor energy E which is proportional to the kinetic energy KE. The proportionality constant
can be made to be one, but not exactly unless by coincidence. Capacitors are only offered in
certain sizes.
It's useful to store even more energy in the cap than in kinetic energy. Since you have
proportionality of voltage to speed and of energy to energy, the system acts like a flywheel on a
fluid clutch. A very big flywheel.
For its mass the system is more effective at storing energy than a flywheel driven by the rear
wheel. For a small proportionality constant, an actual flywheel in the center of the frame diamond
would be more effective and also nearly optimally efficient. I may make one as a toy. The rotor of
the motor stores some energy. Not much.
There are only two other energy variables of scale near these two, relating bike and rider: One,
blood glucose or I think it is called liver glycogen, requiring a needle tap, so I am not
considering this, and two, the potential energy gained or lost on hills or slopes.
Well this PE is Mass * Gravity * Height, and it's really HUGE relative to your forward motion.
So there is a problem of scale. But that's not the only problem, it's just the main one.
Multiply by X, sure.
And there's my question:
Can you design a 320 x 240 Pocket PC display screen and interfaces that will show me my
instantaneous PE, KE, and E while I ride the ultracapacitor bicycle?
I can write the code.
Can you design a display screen that will show me these variables over time, showing the interchange
of one for another?
Sure, a strip chart. You can do better than that.
How about a little airplane that flies PE above the terrain or PE below the mountain peak, exploring
the area around "home" while KE and E vary from 0 to as much as humanly possible along the north and
west axes?
Now think about power, that is the rate of energy change.
Power in and out of a cap is just instantaneous voltage times terminal current. It is not the time
derivative of voltage. Power changing your kinetic energy is trickier. It's the time derivative of
instantaneous energy or so, speed. Acceleration. Gee Force. The power descending a hill, to be
measured accurately, would require an inclinometer, so it is trickiest of all. Timing an altimeter
would do it.
Is there any way to show the power? There should be. Just display the instantaneous value of PE, KE,
and E in a bar graph, and make the width of the bar, or the position of another bar.
Oh, one more thing. For someone to really enjoy the ultracapacitor bike, would a rider power output
be useful, or would that break the symmetry of three interconvertible energy readings with their
time derivatives?
Please don't hit me with numbers in a display. I want scaled gages that tell me what they can at a
glance, and more if I decide to read them. I don't believe anything else is safe.
Yours,
Doug Goncz (at aol dot com) Replikon Research, Seven Corners, VA
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