FLYWHEELS

What is a flywheel?

Its just a heavy wheel, very heavy wheel. To be more precise, its a rotating device with a large Moment of Inertia. 

So what does it do?

It does wonders.

Ideally speaking, you can punch a hole through a 10mm steel plate using a regular 9 Volt 250 RPM motor if you only knew how to include a flywheel in the power transmission circuit. We will get to it later. Lets first get  the bottom line right.

Flywheel stores Rotational Kinetic Energy. How? By rotating. 

Just assume that the gear on the shaft of your motor meshes with a flywheel mounted on another parallel shaft. Now you turn on the motor. What happens? Does your 250 RPM motor attains 250 RPM immediately? NO. When you turn on the motor, it has huge load associated with it in the form of flywheel ( that meshes with the gear on its shaft). But the motor supplies a constant torque. We know that Torque=MOI*Angular Acceleration, and this gives a constant but small angular acceleration (=Torque/MOI, bigger the MOI, smaller the angular acceleration) to the flywheel. So our flywheel starts from zero angular velocity and keeps on accelerating till....?? Till the motor (which too was obviously accelerating during this time) reaches the rated RPM. Hence now, the motor, the gear and the flywheel, all are at 250 RPM. 

So flywheel some Rotational Kinetic Energy(=1/2 MOI*angular Velocity^2) now. It accumulated it during its acceleration and is now at its capacity. 

So how to use this stored energy??

1. By Discharging the stored energy.

2. By Not Discharging the stored energy. . . . . . .  :-P 

( No, I did not go full retard. Continue reading)

1. The Discharging-

Just attach a piston/ connecting rod assembly to another gear that meshes with the flywheel. Constrain the piston to move in a straight line and there we have it!! The ultimate Ram.

Let flywheel attain the maximum angular velocity, the piston will be moving in a straight line with proportional speed. Now bring a metal plate in-front of the piston just before its lowermost point( i.e. where its velocity is maximum) and if everything is right, the piston shall punch a hole in the plate and lose all its momentum. But the motor keeps supplying torque and so the flywheel will again accelerate to the rated RPM and piston is again ready for another strike. 

So we turned your regular motor that could have hardly punched a hole through a cardboard into a ram that can nail metals!! 

2. The Not Discharging-

The thing about having a large MOI is that, they don't lose their velocity easily. So if you cant supply torque continuously, but still want a fairly constant speed, flywheel is the way to go. How? Lets take the example of an IC Engine.

In an IC engine, the fuel combustion in the combustion chamber pushes the piston downwards which in turn rotates something called a Crank. This rotation is ultimately carried to the wheels. But the problem is, the fuel combustion occurs only once in two cycles in a four stroke engine. And even then, the force on the piston and hence the angular velocity of crank is not constant. This means a highly fluctuating torque would get transferred to the wheels leading to total loss of speed control over the vehicle and VERY jerky performance too.

Flywheel to the rescue--- Now we attach a flywheel to the crank. Just because it has a large MOI, it can keep rotating with almost constant angular velocity even when due to no fuel combustion no torque is being supplied to the crank. Also the variation in torque during the power stroke (when fuel combustion pushes the piston down) are minimized in an attempt to change the angular velocity of a high MOI body. Thus, flywheel ensures a fairly constant supply of torque to the wheels.

A formula handy to handle speed fluctuations is-

Max. fluctuation in Energy=MOI*(avg angular velocity)^2*K

where K is the tolerable fluctuation in speed. (if you can tolerate a 2% speed fluctuation, K=0.02)

So, that's all about the flywheels in theory. You can always refer wikipedia for the mathematics. Adios!! :)

How taking loan can be beneficial!!!

Here is my first post. I once asked my father when I was a child , why do people take loan to buy things even if they already have sufficient money to buy it. He said something which i did not understand at that time. But the reason is pretty simple. The reason is that loans are available at different interest rates from different places. If the interest rate which the bank pays, of which you are an account holder, is greater than the interest rate charged on taking a loan(from same bank, different bank, company, individual or anybody else) then clearly we get benefit. e.g. I wish to buy a bike worth Rs. 50,000 and say, Rs. 50,000 are deposited in my bank account (assume zero balance is possible) at an interest rate of 10% per annum. But I do not use this money. Instead I take a loan from some place at say 9%  per annum for an year. At the end of the year I will pay back Rs. 54,500. It seems I had loss of Rs. 4500 as bike's actual cost is only Rs. 50000. But hey, bank payed me interest of 10% over Rs. 50000 that I kept deposited( i.e. Rs. 5000 return in an year) which I would have not got had I spent the money from bank a/c. So actually I got a benefit of Rs. (5000-4500) = Rs. 500.
So I guess, taking loan is not always a burden. :-P   :-)

hey