| >>3. How about some sort of foot pump like generator that you can pump the
| >>small lead battery back up, or possibly a lipo directly to save a few
| >>strokes, perhaps even while you are flying.
| >Not too sure if thats a serious suggestion? :-)
| Just tryin to think outside the box. I didn't know if the car was anywhere
| nearby or if you were hiking somewhere remote and wanted a more self
| sufficient solution. It might not take that many pumps to charge a battery,
| lessee if I can take a quick guess:
| Lets say your setup can make two pounds of thrust for 600 seconds (10
| minutes), or 1200 lb. seconds.
| Lets also say you weigh 200lbs.
| that means for you to make the same output, you would have to put all your
| weight on the pedal for 1200/200 seconds or 6 SECONDS!
Your understanding of the idea of work (in the physics sense) is very
Mere thrust (force) does not do work. Force * distance is what gives
you work (energy) -- you'd need to not only push on that pedal, but
actually move it. A long distance.
Assuming that you could push down on the pedal with 200 lbs of force,
if you moved it one foot that would produce 271 joules -- which would
give you one watt for 271 seconds or some combination thereof.
Assuming you had a 7Ah 12 volt battery (a popular size for field
boxes) and it was completely discharged, and you wanted to completely
charge it by pushing on your pedal with 200 lbs of force, you'd have
to push it 1116 feet. (This is assuming that everything is 100%
efficient, and that the voltage is exactly 12 volts and stays there,
of course -- assumptions that are not accurate. In the real world,
you'd have to push the pedal more to compensate for the losses and the
increase in voltage.)
That also means that this battery has enough power, fully charged, to
raise your body (if it weighs 200 lbs) 1116 feet in the air, assuming
all is 100% efficient.
It certainly is possible to charge batteries via muscle power, but a
lot more muscle is required than one might think.
I believe that a top athlete can produce about 1/2 horsepower (380
watts) for several minutes. Making the same (incorrect) assumptions
as before, this would mean that the athlete could charge that battery
in about 13 minutes, if the athlete could keep up that rate of work.
And this is just for a pretty small battery ...
To make this R/C related, your LiPo battery in your plane is probably
smaller than this field box battery. Perhaps 1/4th the size, So your
athlete could charge it in about three minutes, which is more
realistic, except that the battery couldn't tolerate that :)
Doug McLaren, firstname.lastname@example.org
When I die, I want to donate my body to science fiction.
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