The main mechanism of the machine consists of two heavy wheels, between 30 and 50 cm in diameter, fitted with solid or pneumatic rubber tyres, each driven by its own electric motor.
The whole assembly is mounted on a sturdy tripod or other frame so that the plane of the wheels is roughly at the height that a typical bowler would release the ball.
This is achieved by setting both wheels to the same speed, as fast as the batsman is able to deal with, although the machine itself would have to be tipped horizontally.
This means the ball will spin about an axis perpendicular to the ground, causing it to swing due to the Magnus effect.
However, by the law of averages, a ball will occasionally come out with its seam at the correct angle, and bounce unpredictably as a result.
To get balls that bounce unnaturally high or low, the plane of the machine must be set so that it is vertical.
Not all machines can do this, simply because their ball joint doesn't give the required range of movement.
To get balls that bounce higher than normal, the lower wheel should spin slightly faster than the upper.
Deliveries that bounce much lower than normal are less common and are usually the result of the ball striking a broken-up patch of ground.
When the pressure is so great that the restrictor can no longer hold it, the ball bursts through, out of the main body of the machine and into an external tube, which guides it upwards and releases it at the height of a bowler's arm.
A system exists that allows air to escape from the barrel shortly after it has passed the restrictor.
[3] Crucially, the machine was claimed to be able to emulate Shane Warne's leg breaks, and although he is dismissive of its usefulness,[4] the England batsmen disagree, and consider their ability to play spin bowling significantly improved.
Loughborough University demonstrated visual feedback by showing a representation of the bowler projected onto a screen in 2006.
[7] In the winter of 2009/10 the ECB acquired 20 of the "Merlyn" machines, one for each county and two for the performance centre at Loughborough.