What sensor can control a farm equipment's turns based on distance?

[sganesh88]

We're going to build a prototype of an autonomous farm equipment. It tills the land going from one side to the other, reaches the end, takes a 180 degree turn clockwise, reaches the other end and takes a 180 degree turn anti-clockwise and so on. (I hope i have made it clear. )
The basic idea is that the vehicle should take a turn when it comes to a particular distance from a board(which represents the end of the land on one side). What sensor can we use to do this job?

P.S: Maybe this question doesn't belong here. But "homework and coursework" doesn't seem to fit either. :-)

 

[Danger]

It seems to me that the easiest way would be to run a perimeter wire around the property. When the implement gets to within a certain distance of it, it hooks a Uey. The last corner of the property could have a secondary transmitter with a 'stop' signal. The implement would have to be programmed only to alternate turn directions on each pass.
Come to think of it, that alternation of direction could be transmitted independently by the wires at each end of the field.

 

[Dale]

I would use GPS. Do a search for "precision agriculture" or "farming by the foot". A lot of farm equipment now uses GPS to determine its precise location and vary the amount of fertilizer or seed or insecticide as needed for that precise location.

 

[Danger]

Good point, Dale. I don't tend to think so 'high-tech'.

 

[Redbelly98]

There's also the electronic detectors for keeping pet's within a certain area. I don't know details of how they work, but it might be useful here.

 

[sganesh88]

GPS would prove too costly for our project. (and ya. The autonomous tractors these days use GPS.). We're planning to use an ultrasonic sensor to find the distance from the boards(The kind they use in "cruise controlled" vehicles). The tractor alternately takes clockwise and anticlockwise turns. When the number of turns reaches a predetermined value and when the tractor reaches a particular distance from the final board, it will stop.
Any suggestions or comments is welcomed.

 

[LURCH]

What are you using to keep the tractor running a straight furrow? It would be most efficient if you could use that same guide to teel it when to turn 'round.