First published in the Science and Engineering forum of the For Freedom Forums
Posted: Thursday 5th August 2010 02:52 am
Here is an idea. If you need to, please review this diagram of a steering mechanism from Wikipedia on Steering.
OK my idea is you replace parts of the steering rod with pneumatic pistons, either side of the connection to the steering column as follows.
There is an air tank topped up by an air pump which when its valve is turned on inflates the pneumatic pistons now integral to the steering rod. (This should only ever be done while the vehicle is at rest and the driver has selected clockwise or anti-clockwise gear - some kind of safety cut out.)
The air pressure quickly rises (that is why you use air, not hydraulics, it is so much faster if you supply from an air pressure reservoir - there is not a need for huge force, just speed, so pneumatics is the driver of choice I think) and when the air pressure exceeds a critical amount, retaining catches, which normally hold the pistons firmly closed against all manner of road bumps, suddenly break open and the pressurised air forces the pistons open against a spring and the steering rod lengthens to a maximum and the wheels are turned inwards to their respective stops - hard right hand turn for the left hand wheel and hard left hand turn for the right hand wheel, ready for rotation.
It is clear to me that the 45-50 degrees or so maximum turning angle normally is limited by the steering rod at full stretch - not by the wheel bumping into the axle - so 75 degrees in this diagram looks easy.
When you want to revert to normal steering, the system simply releases the air pressure in the pistons and the pistons close with the spring and the pistons snap shut into their retaining catches ready for normal steering.
As you can see this is for rotation about a point mid-way between the rear axle. It is only when I add on my trailer to my armoured personnel carrier that the vehicle does zero turning radius, strictly speaking.
Hence I have always called it "rotation around a spot".
So do you think that would work? I would doubt that is the way that lawnmowers do zero turning radius.