Thats and awesome project! Lots of great shots too - good job man!

Impressive project!

I've done a marine autopilot based on Arduino (using GPS, Gyro and Compass for course keeping) and it would be interesting to know how you achieve an average cross track error of less than 2 inches?

To get the cross track error down to this level took some time. Part of it has to do with having a proportional hydraulic valve to get smooth slow steering when needed, and fast response when needed. Part of it has to do with how to get accurate heading data - couple the yaw sensor to the GPS data with a Kalman filter. A steering angle sensor helps, and the steering algorithms were critical to being able to keep the machine smooth. While a 2 inch average cross track error is sweet, my goal is to get that down to the 1/2 inch range.

There are several failsafes built in. The system will not engage or operate at speeds above 6 MPH, the system disengages if the steering wheel is moved, the arduino will close the valve if it doesn't receive any data from the computer for 200ms, and worst case, there is a power switch in the cab to kill the circuit that drives the solenoids on the hydraulic valve.

At the speeds we normally travel at, nothing serious will happen if the system freaks out. At 5 MPH you can stop, shut the system off, back up, and keep going. The critical part is when we're on the road at 20 MPH. While that isn't fast in a car, these machines with rear steering aren't very stable at 20 MPH. When on the road, we flip the lockout switch in the cab so the valve can't possibly open.

-Lance

nice application! there are commercial things like this, but making it with a arduino is a lot smoother  

Is that a touchscreen monitor hooked to the computer or do you have a keyboard in mouse that you use?  I am looking for a good touchscreen solution for some automotive projects.

Hows the project coming along?

What kind of accuracy are you seeing? Im considering doing something like this for my parents, but I need some pretty extreme accuracy (accurate to 2" at the VERY WORST, preferably 1"). John Deere sells a system that can do this, using DGPS and a portable base station, but the setup is around $40,000. Have you looked into using DGPS at all?

We've got a JD 9550 that we use for corn, beans, and wheat, so I know alllllllllllllll about driving slow I was looking at using some sort of DGPS system to auto-steer a plastic-laying tractor in a straight line; thats all it needs to do. Im not interested in it turning around or doing much, it would just involve the operator lowering the implement, enabling the system, and putting it in gear, and having the auto-steer system keep it in a straight line.

Do you have any insight to share about RTK?