here is a bit more info
Ok guys, Some comments and questions thus far. First, I should have mentioned that the tractors all have RTK GPS Autopilot systems so they steer themselves down the center of the rows very well. The sprayer however does not have any sort of GPS steering to it and would be economically unfeasible to do add that feature.
The tractor is not articulating in the middle like the big 4 wheel drives but rather steers similar to your car, with tie rods and each front wheel pivots left/right. This sprayer is pulled behind the tractor between 8-11mph. Terrain can be bumpy at times and we are on 30" row spacing. Our poor mans solution has been to mount a switch in the cab that controls a laterally mounted cylinder that moves the sprayer hitch left and right. When you hold the switch to the left, it puts power to the right solenoid and pushes the hitch to the right. When you hold the switch to the right, it puts power to the left solenoid and pushes the hitch to the right. You are correct, hydraulics are not lightning fast but have been sufficient to handle this task. I'm just looking for a more automated way to do this.
I could go the old school route and do this a variety of ways including dknguyens suggestion but this would be more fun!
dknguyen, I understand what your saying about using a yaw gyro to measure the angle between the tractor and sprayer at the pivot point where the two meet, however this would be very difficult and fairly inconsistent as that angle would change as the tractor tries to aim up hill to compensate for sliding down as well.
I'm getting the message that gyros have a certain amount of drift to them, meaning that while they sit perfectly still, the angle that they think they're measuring can actually increase or decrease? You'd have to zero it out periodically when you know your on a flat surface? That doesn't sound like any fun to deal with. I guess I don't understand how I could use accelerometers to measure the side hill slope that I'm on though? Can you explain please?