need math help, or sumtin

# Thread: need math help, or sumtin

1. ## need math help, or sumtin

i need to figure out power required to spin a flywheel

the flywheel will have about a 1.5-2" radius and will weigh about 1 pound
need to know power required to spin it to say, 10,000 rpm from a dead stop in say 5-10 seconds, and then maintain that speed.

i will power this with an electric motor, running dc current
any formulae or whatever you might know of would be great help, thanks.

2. 1+2=3? hope that helps

3. Energy in a spinning object is 1/2*moment_of_inertia*omega^2. The moment of inertia for a flywheel, assuming a radially even weight distribution, is 1/2*mass*radius^2. Omega would be 10000*2*pi/60 = 1047.2/s. So assuming 2" radius, and 5s spin-up time, average power would be 1/2*1/2*0.454*0.05^2*1047.2^2 / 5 = 62.2W. As for keeping it there, I have no idea how much friction you'd expect. The actual power drawn depends on your motor's efficiency. I'm sure someone more knowledgable (Teetee?) will post soon

4. cool thanks, thats a great help

5. Energy in a spinning object is 1/2*moment_of_inertia*omega^2. The moment of inertia for a flywheel, assuming a radially even weight distribution, is 1/2*mass*radius^2. Omega would be 10000*2*pi/60 = 1047.2/s. So assuming 2" radius, and 5s spin-up time, average power would be 1/2*1/2*0.454*0.05^2*1047.2^2 / 5 = 62.2W. As for keeping it there, I have no idea how much friction you'd expect. The actual power drawn depends on your motor's efficiency. I'm sure someone more knowledgable (Teetee?) will post soon
I got brain freeze just trying to read this!!

6. the only part i dont get is the /5 whats that for?

7. Originally Posted by ReelExterminato
Energy in a spinning object is 1/2*moment_of_inertia*omega^2. The moment of inertia for a flywheel, assuming a radially even weight distribution, is 1/2*mass*radius^2. Omega would be 10000*2*pi/60 = 1047.2/s. So assuming 2" radius, and 5s spin-up time, average power would be 1/2*1/2*0.454*0.05^2*1047.2^2 / 5 = 62.2W. As for keeping it there, I have no idea how much friction you'd expect. The actual power drawn depends on your motor's efficiency. I'm sure someone more knowledgable (Teetee?) will post soon
I actually thought you knew what you were talking about..

and the / 5 is divided by 5 ofcourse

8. Originally Posted by izad
and the / 5 is divided by 5 ofcourse
I'm pretty sure Jayson was asking what the logical reason is for dividing the product by 5, he's not completely stupid.

Originally Posted by ReelExterminato
So assuming 2" radius, and 5s spin-up time, average power would be 1/2*1/2*0.454*0.05^2*1047.2^2 / 5 = 62.2W.
If I read ReelExterminato's post correctly, it seems that the original equation of 1/2*moment_of_inertia*omega^2 is for total energy, so to get the average, he divided the total by the number of seconds that the wheel is in motion? Since omega is a measure of rpm*2pi, I suppose it would be necessary to determine how many rotations are completed within 5 seconds??

I dunno, it's been a while since first year physics.

9. urrr yeah thats ivy hah 'not completly stupid' :P yeah i gots it figured between you 2 and mr murphy. thanks! if i ever actually get off my ass and apply this, i will post pics, someone will be interested im sure.

10. /5 is the 5 seconds it takes to spin up, so it's the rate at which you need to supply energy. Eg. to get it to spin up in 10 seconds, you supply the energy at half the rate, but for twice the amount of time. What is it you're trying to make?

11. The power will be required to accelerate the flywheel. What doesthe flywheel look like?

Is it a solid wheel of uniform thickness?

12. For the record, Jayson is just a little bit stupid. But he has a nice bum.

13. 3 axis gyro

flywheel is not uniform thickness, they will look something like this

inside flywheel part will be aluminum outside will be lead. i just want to make strong gyro forces. and then maintain them for a while.

ps: ivy thanks :P

14. Originally Posted by Jayson
3 axis gyro

flywheel is not uniform thickness, they will look something like this

inside flywheel part will be aluminum outside will be lead. i just want to make strong gyro forces. and then maintain them for a while.

ps: ivy thanks :P
Would this be a camera mount for a motorcycle by any chance?

15. camera mount, yes, motorcycle, no. but really it could be used on anything up to a certain weight.

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