- #1
Heros
- 9
- 0
Hi, i didnt know where to put this question cos its kind of multitopic, here is why...
I am working on a better way to take mechanical energy from muscles, i made a teste bench for pedalling in very different ways, including traditional(circular) pedalling, the thing is. I am measuring the power of the athletes with a big dc motor(working as dynamo) attached with a lot of possible connections of incandescent car bulbs, and so, i tested diferents speeds and number/setup of light bulbs to produce different "brake" powers.
The thing is that after a lot of experiments to determine the torque vs speed function for every light bulbs setup and i discovered nothing surprising, the torque function is like this Torque=k*speed+RestingFriction being k of course the constant i was looking for.
I made a curve fit and got a very good precision(r^2=1 on excel) for every experiment, and found that of course, the more bulbs connected in parallel the higher K but not in a linear fashion, but that's not the problem...
The mistery begun when my girlfriend(she helps me a lot in my research) asked me why i didnt shortcircuited the motor and then we tried, at first the results were a K a little bit bigger than 8 bulbs in parallel( of course because that's a very low resistance arrangement) and when speeds got faster, the data begun to increase in a non linear fashion, so non linear, that with a linear fit i got a r^2=0.9456, then tried parabolic and got a beautifull r^2=1...?
So...why is bulb resistance linear and short ciruit not? I suspected about filament temperature, but it would just make it a negative concavity curve, i think...
Excuse my english...thanks a lot :)
I am working on a better way to take mechanical energy from muscles, i made a teste bench for pedalling in very different ways, including traditional(circular) pedalling, the thing is. I am measuring the power of the athletes with a big dc motor(working as dynamo) attached with a lot of possible connections of incandescent car bulbs, and so, i tested diferents speeds and number/setup of light bulbs to produce different "brake" powers.
The thing is that after a lot of experiments to determine the torque vs speed function for every light bulbs setup and i discovered nothing surprising, the torque function is like this Torque=k*speed+RestingFriction being k of course the constant i was looking for.
I made a curve fit and got a very good precision(r^2=1 on excel) for every experiment, and found that of course, the more bulbs connected in parallel the higher K but not in a linear fashion, but that's not the problem...
The mistery begun when my girlfriend(she helps me a lot in my research) asked me why i didnt shortcircuited the motor and then we tried, at first the results were a K a little bit bigger than 8 bulbs in parallel( of course because that's a very low resistance arrangement) and when speeds got faster, the data begun to increase in a non linear fashion, so non linear, that with a linear fit i got a r^2=0.9456, then tried parabolic and got a beautifull r^2=1...?
So...why is bulb resistance linear and short ciruit not? I suspected about filament temperature, but it would just make it a negative concavity curve, i think...
Excuse my english...thanks a lot :)