I've been working on this a few weeks, so the design is already quite advanced. Here's what I've got so far:

The mechanism is quite different: a nut is driven along a straight, linear leadscrew which in turn opens the two halves via a linkage. Since the opening angle must increase at a constant rate, but the position of the nut along the screw is not proportional to the angle, the screw cannot be driven at a constant rate. Instead a microcontroller (Arduino Nano) is used to calculate the precise moment to step the motor each time (20-30 times per second) in order to compensate for the changing relationship between nut position and opening angle.