Suggested topic: Robotics, PID controllers etc...

Generally, a series on robotics-related topics would be interesting.
You could develop a PID controller and demo it graphically by modelling a temperature sensor and heater with some delay as the volume of the 'room' heats up.
More relevant to robotics you'd need some simple physics to model, say, a springy arm driven by a servo motor and drive it to set points without overshoot.

Have some bonus points for each additional degree of freedom in your robot model :)