What is Regeneration?

Let me see, I think I've heard that it occurs during gravitational operations.

Sometimes gravitational operations is called regeneration operations.
Look at the illustration below. In Figure B, it is moving downward, so it's called a gravitational operation.
The reason why gravitational operations are called regeneration operations is because regenerative power is generated during gravitational operations.

Regenerative power?

The reason regenerative power is generated during gravitational operations is because of the motor structure. Do you know what the structure of a brushless motor is like, Vex?

I thought the rotor had permanent magnets built into it, and the stator was an electromagnet that rotated the rotor by reversing the north and south poles.

That's right. In other words, the brushless motor tries to maintain the setting speed by reversing the polarity of the electromagnets in the stator one after another. That's why stable speed control is possible even in gravitational operation. However, the shaft of the motor will be pulled by gravity and rotated somewhat during gravitational operation. Then the permanent magnets in the rotor turn into a generator, and the motor generates reverse voltage to the driver. The power generated at this time is called "regenerative power," and if the driver is not capable of absorbing this power, it will be damaged during gravitational operation.

I see! Even if stable speed control is possible, it is useless if the driver is corrupted.

Yes! That's why you need regeneration resistors.
By connecting a regeneration resistor to the driver, it dissipates the regenerative power that the driver can't absorb as thermal energy.
There is a limit to the amount of power that can be dissipated, though, so you need to calculate* how much regenerative power will be generated based on torque, rotation speed, operating time, operating cycle, and other factors.

Oh, I see. Whether you use a regeneration resistor or not depends on the operating conditions of customers! Then, I will try to explain! Thank you very much!