Random little discovery

[nardella]

You can make the screen light up immediately after turning the bot off. You do this by turning it off while something is displayed on the screen, immediately after you spin the motors.

The thing I found even more interesting is that when the bot is powered on bu not moving the wheels are harder to turn.

The first phenomenon is easily explained, most electric motors generate electricity when not powered but turning. This power ends up flowing through(among other things) the screen, lighting it.

But why would it be harder to turn the wheels when the bot is powered on but the wheels are not turning?

[senatorpenguin]

The OLED screen has a controller and memory, so that the last thing displayed will continue to show until it is changed. You are right, turning the wheels generates a voltage, and it backpowers the entire board through the motor drivers. This isn't ideal, as it can potentially damage parts that are turned off.
When the robot is on (and the motor drivers are also on), the motor terminals are shorted together. This is called "brake" mode, it makes them much more difficult to turn, and doing so pushes large amounts of current through the motor drivers.