# Controlling torque output from a flywheel

1. Aug 13, 2013

### MichelKS

Question
Is there a component that controls the torque output from a flywheel so that its output is constant?

Context:
Parts:

1) An engage/disengage switch
2) A cable reel
3) A flywheel
4) A mechanism to control the torque output from the flywheel.

Process
When the switch is engaged, the flywheel transfers a constant amount of torque to the reel and the reel winds the cable.
When the switch is disengaged, the flywheel spins freely and no torque is transferred to the reel.

2. Aug 13, 2013

### Staff: Mentor

Welcome to the PF.

What is the context of the question? Is it for schoolwork? There is indeed such a mechanism...

3. Aug 13, 2013

### MichelKS

No, not for school work. Just a tool I want to build.

4. Aug 13, 2013

### Staff: Mentor

Okay, fair enough. What mechanism is used to transfer power from a car's engine (which contains a flywheel) to the drive wheels?

5. Aug 13, 2013

### MichelKS

The transmission?

I suppose the clutch would decouple the flywheel from the reel?

6. Aug 13, 2013

### Staff: Mentor

Yes, the clutch is what I was asking for. The only tricky part of your question is to control the clutch so that the output torque is constant. You will need some way to measure the output torque, and use feedback to control the clutch pressure to maintain the target torque.

If you know the moment of inertia of the output that you are driving, you can use this equation:

$$\tau = I * \alpha$$

Are you familiar with that equation about angular acceleration?

What is the thing you are driving with this? Will it be turning at a constant speed when the output torque is constant? Or will it be accelerating for some period of time?

7. Aug 13, 2013

### MichelKS

It will be a constant speed.

8. Aug 13, 2013

### Staff: Mentor

So you just servo the clutch to maintain that constant speed. Done!

9. Aug 13, 2013

### Staff: Mentor

BTW, is your flywheel getting energy input from an engine, so that it will maintain a constant speed too? If so, you could just put a continuously-variable transmission (CVT) between the flywheel/motor and the thing you want to drive at a constant speed. Or even a fixed gear ratio if the relative speeds will be known ahead of time...

10. Aug 13, 2013

### MichelKS

Perfect =) Thanks for helping.

11. Aug 14, 2013

### marellasunny

berkeman: what does the phrase 'servo the clutch' mean? Are you referring to clutches commonly referred to as 'torque converters' with a turbine and pump mechanism OR to the usual friction clutch? And if so, what did you mean by that phrase in your context of the clutch?
The torque curves are usually parabolic shaped w.r.t engine speed in IC engines, peaking at a certain engine speed.So, How would the clutch make the torque output constant?

12. Aug 14, 2013

### 256bits

A clutch commonly used in a vehicle where there are 2 foot peddles - one for the brake and one for the clutch ( a third is the accelerator ).
The clutch operates by friction. By engaging the clutch so that it slips less or more one can control the torque applied to the drivetrain down the line.
A fully engaged clutch would transmit the engine torque curve.

Torque is force multiplied by the radius, so a controlled variable friction force between the clutch plates can control the torque.

13. Aug 14, 2013

### MichelKS

I may have been wrong about it turning at a constant speed. The force output needs to remain constant, so if the load decreases then the reel would need to accelerate, correct?

The system might be built like this

Manual crank (energy in) -> Flywheel -> clutch? -> reel -> cable/rope/etc -> load

In use it would proceed like this:
1.The user will crank the flywheel
2.The user sets the amount of torque he wants from the system
3.He waits for an event outside the system
4.When that event occurs, the user engages the flywheel with the reel
5.The reel then pulls on the load
6.The user waits for another event, then disengages the flywheel from the wheel.
7.Repeats steps 3-6 until flywheel is out of energy or user stops process.

The load may change during operation, but the cable must always apply the amount of force set by the user.

Last edited: Aug 14, 2013
14. Aug 14, 2013

### Staff: Mentor

I just meant use feedback to control the clutch pressure to get the output torque characteristic that is desired.