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The steering of the psix is arranged to allow the machine to turn with the centre of the machine as the point of rotation. The front wheels are capable to 270 degrees of turn and the rear bogie is capable of 200 degrees. Although the machine is undoubtedly large this allows it to turn back on itself. Control is electronic by wire from the cab; we have a wide range of track widths and the rear is independent from the front so the difference in angle of the front wheels (the ackermann angle) varies, computers allow us to keep everything pointing the right way.
Think of the machine as an articulated lorry traveling backwards. The rear bogie sits under a slew ring bearing which is free to rotate; the four wheels on the bogie steer together like a telescopic loader. The bogie could theoretically fully rotate but is electronically prevented from doing so.
That slew ring is bolted to a cylindrical column on the top of which is another slew bearing which takes the hopper - it rotates, see bunker for details - the column is therefore the main load bearing structure, the chassis connects everything else to it
This is a substantial structure as can be seen from the picture opposite showing the prototype chassis with a Discovery parked underneath, the rear bogie behind. The photographer is standing on the front cross beam
The front steering is via motorised slew ring, a hydraulic motor driving a worm which turns the wheel. The wheel can turn almost all the way around in a complete circle, Each of the front wheels is moved indepenently, the compter keeping them in the correct alignment, this is due to the range of track widths, see front axle for more on that.
Of course with this level of turn and control the machine is capable of a programmed about face at the end of the row with the operator contolling the forward motion and the computer controlling the steering. A field could be worked from one side to the other rather than opening up and working out in lands which is for more efficent.
Of course that is only possible with the ability to unload both sides. See bunker for details
Updated 23rd November
