Mr Thant wrote:
snip

Rear-engined bendy buses are a modern invention - there's some
ridiculously complicated hydraulics and computer control in the hinge
to stop them jacknifing constantly.

snip

Actually you couldn't be further from the truth. The articulated joint
(manufactured by Hubner) is very simple comprising of a large centre
rotating bearing and two self contained hydraulic rams to passively
counteract the jacknife effect.

Link here http://ischmelzer.com/HNG19_5.html

The same unit is fitted to both the Scania and Volvo bendies.
The computer control is to let the front half know where the back half
is going so the engine and ABS systems can apply power and brake in the
right proportion.

Bob