Calculate Rotational Torque: 8700 kgm2 @ 18 RPMs

[CWatters]

I feel like we are losing our focus here. Regardless of what's making the driver rotate, I just need to know how to calculate the available torque at the axle at 18rpms.

Problem is you are asking a question that's impossible to answer based on the info provided. If it stops accelerating at 18rpm then there is NO torque available. It's all being used to overcome losses somewhere. You even explained that centrifugal force somehow stops or reduces the power to stop it accelerating further.

That's why I suggested using a lower rpm in the calculation above.

 

[Pinon1977]

Ok so if it takes say 3 seconds to go from zero to 18 rpm you can estimate the torque and power as follows...

Torque = MOI * Change in angular velocity/Time

18 rpm = 0.1 rads/s

= 8700 * 0.1/3
= 290 Nm

However if it has stopped accelerating at 18rpm you won't get that torque at 18rpm. Better use a lower value say 9rpm (0.05rads/s) for safety..

Then..

Power = Torque * angular velocity
= 290 * 0.05
= 14W

I have assumed your figure for the MOI is correct.

While I do not know exactly what the torque is at the axel, I do know it's more than 290Nm. I used a 4000 ftlbs prony brake last week and it maxed it out in less than 2 rotations. So the torque is at least 4000 ft lbs at 18rpms.

What's wrong with this calculation:
8700kgm2 * (18 RPMS/9.8) OR
8700kgm2 * 1.8 rad/sec = 15660Nm

 

[Pinon1977]

14 watts? Really? Common sense would tell you that a flywheel with a MOI of 8700 kgm2 spinning at 18 rpms is going to produce more than 14 watts of power. Right? I can generate 100 watts of power with my bicycle generator.

 

[Pinon1977]

This driver or (prime mover) I have designed is 10' in diameter with an overall weight of 3900lbs. The entire assembly creates a MOI of 8700kgm2. The driver is rotating at a constant speed of 18 rpms. That being said, you're telling me one can only expect 14 watts of power out of that beast?

 

[A.T.]

Common sense would tell you that a flywheel with a MOI of 8700 kgm2 spinning at 18 rpms is going to produce more than 14 watts of power. Right?

Depends for how long.

The driver is rotating at a constant speed of 18 rpms.

If it doesn't slow down, you will get out the power you put in, minus losses.

 

[sophiecentaur]

But it's still a state secret where the original Energy is coming from. As far as I'm concerned, the whole enterprise is suspect until that is known. Why should PF have any part of it? A machine that drives itself is just not in PF's terms, is it?

 

[CWatters]

What's wrong with this calculation:
8700kgm2 * (18 RPMS/9.8) OR
8700kgm2 * 1.8 rad/sec = 15660Nm

You are multiplying MOI * Angular Velocity. That gives you the angular momentum not the torque.

 

[sophiecentaur]

gravity was probably never perceived as a source for creating power. It's always been the enemy

What sort of a statement is that? How can gravity be an "enemy"? In any case. gravity is not the "source" of hydro power. The SUN is the source of the power because it causes evaporation which gives us rain etc. etc.. A long case clock 'uses' gravity as the weights fall but the guy who wound it up was the source of the energy.

 

[CWatters]

14 watts? Really? Common sense would tell you that a flywheel with a MOI of 8700 kgm2 spinning at 18 rpms is going to produce more than 14 watts of power. Right?

Wrong. Flywheels spinning at a constant rpm do not produce any power. Zero. None.

Perhaps you misunderstand what I calculated...

I calculated the torque required to accelerate your flywheel from rest to 18rpm in 3 seconds. That only takes a constant 290Nm. So all I can say is that your prime mover is capable of delivering at least that much torque.

If you say your prime mover is capable of generating more torque then that's fine but you will have to measure it. It cannot be calculated from the MOI and rpm alone.

 

[CWatters]

I used a 4000 ftlbs prony brake last week and it maxed it out in less than 2 rotations. So the torque is at least 4000 ft lbs at 18rpms.

All that shows is that the torque is at least 4000 ft lbs for 2 revolutions (about 6 seconds).

Leave it connected for 10 mins and measure the rpm after that time.

 

[fresh_42]

14 watts? Really? Common sense would tell you that a flywheel with a MOI of 8700 kgm2 spinning at 18 rpms is going to produce more than 14 watts of power. Right? I can generate 100 watts of power with my bicycle generator.

Yes, because you operate a generator in this example. It's not the wheel that produces the energy.

Wrong. Flywheels spinning at a constant rpm do not produce any power. Zero. None.

PMM are not possible, regardless how well hidden the mechanism or yield is. We do not discuss magical tricks on PF. The question has been answered in many ways. All use fundamental physics.

Thread closed.