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bobcat32
10-25-2011, 10:43 PM
I am working on the brake team and I am trying to figure out the size of the rotor. I need help doing the heat transfer calculations to figure this out. One method that I am thinking of using is the lumped capacitance method, to find the surface of the temperature. Another method that I was thinking of using was the finite difference method. Does anyone have any suggestions?

Nathan Doornenbal
UC Merced

Nathan Doornenbal
UC Merced SAE International

mech5107
10-26-2011, 01:28 AM
Why starting with heat calculations? Just estimate/find a friction coefficient and your maximum traction and you can find the needed size.

Or just see what the others do...sometimes calculations aren't realistic...

Buckingham
10-26-2011, 11:50 AM
While the heat transfer characteristics of the braking system can be important, most thermodynamic or fluid engineering problems are extremely difficult to model/calculate without experimental data.

The equation you need is

Energy Rate In = Energy Rate Stored + Energy Rate Out

Trying constructing a few different designs, instrument your vehicle, and design tests to measure each of the variables in the above equation.

Hint: It's possible that you will observe that as your test approaches steady state, energy rate stored approaches zero. (At which point Rotor Temp is no longer a function of rotor mass).

Der Krug
10-26-2011, 12:34 PM
If you want to justify your rotor mass, you need to do thermal and stiffness calculations.

It's basic physics. Grab your old entry level engineering physics course equation sheet and start figuring out your static and quasi-static conditions.

bobcat32
10-31-2011, 02:10 AM
Thank you for your input. I was thinking of using the lumped capacitance method to evaluate the thermal method: q=mc(t2-t1). For the stiffness calculations are you referring to the thermal stress and seeing how much the rotor will warp?


Originally posted by Der Krug:
If you want to justify your rotor mass, you need to do thermal and stiffness calculations.

It's basic physics. Grab your old entry level engineering physics course equation sheet and start figuring out your static and quasi-static conditions.

Der Krug
10-31-2011, 10:24 PM
Stiffness requirements, AKA Finite Element Analysis (FEA). Solidworks has FEA simulation available in the student edition.

Q=MCAT works and is a good start.

The metal will not warp physically upon gaining thermal energy in this application. Braking temps should not generally exceed 1000F if you are using steel/iron. If they do, your pads will not like it and you will see significant brake fade.