So I finally managed to get a better video recorded...
The original set up used a Wii Nunchuck + arduino to radio control the 4 motors, mixing channels as required to control the hoverbot. Today we didn't have all that running so we just had an RC transmitter making the already difficult control even harder. The design is unstable and our intention is to add a 6DOF gyro/accelerometer stabiliser circuit, but for now it spins off rapidly. The last part of the movie we tethered it to stop it spinning off and it hovers stabley:
As you can see in the tethered part of the video, the left blue rotor isn't floating as high. Its motor is slower for some reason (supposed to be the same but cheap motors...). We are running the black rotors at part throttle to compensate so could go higher if they all worked properly. Also we only filled half the rotor magnet holes, so we need to fit more and see how much better it is.
Next step is definitely gyro stability though:)