I have a 360° steering control question!

[sgkoether]

I am designing a self propelled piece of tillage equipment. I want the tires to face one direction in the field and be able to steer like a self propelled trencher, ie regular steering, crab steering, and opposite direction steering to make tight circles. Then in transport mode I want the tires to turn 90° and have regular steering in a sideways direction. I think I have the physical design figured out but I don't know how to drive each individual wheel spindle left/right and then 90° and left/right again. After I know how to drive them each direction I need to have a control system to tell them which direction to go when the wheel is turned. I need the spindle to know where it is as far as a 360° compass angle is concerned and have it be able to calibrate it to the same degrees on two tires at a time. Anyone have any suggestions where to start? I think it could be broken into three parts. 1)Drive system to control spindles approximately 300° rotation. 2) System to control that drive system when the steering wheel is turned. 3) method for the control system to understand the spindle direction in space in that 300° rotation and match two or 4 tire in the same direction. I am looking into hydraulic or electric drive to move the machine so one of these methods might be best to steer as well but I will certainly consider anything. Thanks

 

[CWB1]

1. Google "driven casters." There are many variations, but all have a motor (electric or hydraulic) driving a caster's axle/wheel, with or without a gearbox or chain drive.
2. A gear/chain drive connecting the spindles of two casters locks the rotation/orientation together to help with steering. It also allows you to have one steering motor and for two casters, and one electronic encoder providing rotational position of those two casters.

Many combines and choppers have a hydraulic motor driving each fixed front wheel and casters out back. I'd use a similar concept - two casters up front chained/geared together rotationally with an encoder and steer motor; and another two casters out back chained/geared together with a second encoder and steer motor (to allow crab and four-wheel steer). The second set could be undriven to save cost or also driven if max traction is needed.

I dont recall where, but I've seen the exact setup I described in use commercially.