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I would like to build a system to carry out a fatigue test of a damper. I am not able to understand the role of the fly-wheel in such a system. The base idea is a crank-shaft mechanism which has a constant angular velocity and moves the damper along a sinusoidal. The required torque is sinusoidal as well, it oscillates between 0 and a maximum value. When I try to imagine the process, I think the fly-wheel can't help since we just need more work to keep the energy of the fly-wheel constant. The parameters: $$ Force: F_{max}=13000N\\ Angular\ velocity:\omega=10\ s^{-1}\\ Amplitude:A=0.01\ m\\ fly-wheel\ moment\ of\ inertia: Θ=2 $$ From the force and the velocity I calculated a damping constant: $b=130000\frac{Ns}{m}$.The next idea was to check how does the system work without any input, after a certain starting angular velocity. I made the following equation, and checked how the system slows down in time. $$\frac{d\omega (t)}{dt}=\frac{-b\ A^2\ \omega (t)\ sin^2(\omega (t) t)}{Θ}$$ I can see, a bigger fly-wheel can store more energy, and let the system work longer without any input torque. But when I would like to maintain the angular velocity (or the energy) of the constant, I do not see, how can a fly-wheel help the work of the motor which inputs the required torque into the system. Can you give me an intuition to understand the role of the fly-wheel in such a system?

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2 Answers 2

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The flywheel is used to help the crank turn when the angle is either 0 or 180 degrees ie the force is applied in line with the crank.

Once there is an offset then the force is applied at an angle ie a lever.

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  • $\begingroup$ Now, I think I should focous on the case, when my motor can produce constant torque. Since the required torque is sinusoidal, the output angular velocity is not going to be constant. This fluctuation can be made smaller with the help of the fly-wheel. But to maintain the required angular velocity, I do still need near the maximum of the required torque. If I start the motor from 0, the size of the fly-wheel affects the time I need to obtain the required angular velocity, and the value of the angular velocity fluctuation. Is it correct thought? $\endgroup$ Nov 8, 2022 at 14:11
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As you said, the torque required to turn the crank is sinusoidal. If you add a flywheel, then lets say and peak torque (90deg) the motor would slow down somewhat. The flywheel would fight this and reduce the reduction. Likewise, the motor may want to speed up at 0 and 180deg, where the torque required is 0. The flywheel will reduce this increase in speed.

I think your confusion comes from the assumption "the angular velocity is constant". If that's actually true, the motor will not "feel" the flywheel at all, except during startup and shutdown (which you noted).

In reality, the motor probably does not have a square torque curve. In that case the flywheel would have some effect.

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