Have you ever wondered where the power ends up when you slam the brakes on an RC car or use a drag brake on an RC airplane? Energy can not be destroyed once it has been built up in a high speed RC Car. This kinetic energy is converted to other energy forms. The big question is what is the new energy form? Let’s start by looking in simplistic terms how an ESC slows down our RC car.
How does the ESC slow or apply brakes on an RC Car
Electric brakes are controlled by the ESC using the motor. Rotational kinetic energy built up in the motor creates a voltage known as back EMF that the ESC is able to read. When brakes are applied via the transmitter, the ESC uses the FETs within the ESC as a switch to short out the motor leads. This action allows the ESC to bring your RC car to a halt.
If you are even more curious as to how this works, grab a brushless motor kicking around. Take all of the leads coming out of the motor and short them out using wire terminated with alligator clips. Now try and rotate the motor with the leads shorted out. What you will notice is that there is resistance to the rotation of the motor shaft. Also, the faster that you try and spin up the motor, the stronger the resistance to motion will be. Lastly, if you remove the leads shorting out the leads exiting the motor, the added resistance to motion disappears.
A lot of energy Ends up in Heat
During the test, ran in the video above, a lot of heat is built up in the motor and ESC. During the test the motor and ESC rise in temperature quite significantly. It is estimated that about 65-85% of the energy dissipated when braking exists the system as heat. The question is, where else does this energy go? Also, how are we able to estimate 65 to 85 percent of the energy is converted in to heat?
Braking Energy Converted in to Chemical Energy
The answer to the question in the last paragraph is that the remaining bunch of power has been demonstrated to be converted in to chemicals energy. Take a look at the regenerative braking page for more information.
Conclusion
It is very interesting to be able to demonstrate where the energy ends up as we use the brakes in our RC Car. Although a large percentage of power ends up being converted to heat, a smaller percentage of energy is converted to chemicals energy.
Does this represent all forms of energy that is converted upon brake input? Simple answer is no, but the large majority consists of these 2 items. For example, sound energy is also created as brakes are applied, however, the total amount of energy would be very small making its value negligible. Knowing where the energy ends up can change the way we think about our RC setup.