My FB project, Question on MOSFETs

**mx270a** · 04-12-2008, 08:44 PM

Well guys, today was the maiden voyage for the project I've been working on - steering a tractor via GPS. I'm using a fusion brain to read steering angle position, and triggering two outputs that control relays that drive an electro-hydraulic valve that steers the tractor. I was letting the software drive the tractor, which stayed within a range of about one foot of the line.

Can I use a MOSFET instead of a relay? Would the FB outputs be alright with that? The clicky clicky of the relays was a bit louder than I prefer. I could move them somewhere else for testing, but just checking out other options? The solenoids I'm driving are 12vDC at ~3.5 amps.

-Lance

More info (added by greenman100)
Here's a new video:
http://www.youtube.com/watch?v=YFqfTlqF2NY

The machine is a Case IH 2588 combine (~300HP) that is harvesting soybeans at 4 MPH. I'm using the FB to read a steering angle position sensor, a yaw sensor, and a tilt sensor. That is added to a GPS position to drive the machine in a straight line, with each pass parallel and at a consistent distance from the last pass. The fusion brain outputs steering commands, which go to a couple relays, which send power to solenoids on a hydraulic valve that is connected in parallel to the steering wheel orbital.

The header (thing on the front) is 25 feet wide. As you can see in the video, the yaw sensor makes the vehicle control very smooth. It still likes to drift off the line, then slowly come back to it (it can get up to about 8" away from the line.) I'm still working on revising the yaw sensor calibration algorithm, and the method used to calculate what angle the steer axle should be at. Yaw sensors are a royal pain due to their "zero" position changing as they warm up. As slow as the machine is moving, with subtle steering inputs, getting an accurate and precise yaw reading is a challenge.

-Lance

**2k1Toaster** · 04-13-2008, 12:44 AM

The output uses the ULN2003A which outputs 400mA to 500mA

**greenman100** · 04-13-2008, 01:27 AM

You could, of course.

I'm not sure exactly what your question is.

**mx270a** · 04-13-2008, 09:48 AM

My question was if I could use a FET in place of a relay. I'm relatively sure it will work, just thought I'd run it by you guys to confirm.

-Lance

**greenman100** · 04-13-2008, 09:56 AM

yes, it shouldn't be a problem

**greenman100** · 04-13-2008, 12:28 PM

Also: could you post a video/writeup on what you did? It sounds really cool.

**mx270a** · 05-06-2008, 12:51 AM

I'm working on putting together some details on what's going on here - will probably post it in the 'show off your project' section of the site. Still working on getting some video of the system in action.

Still haven't tried the mosfets. We found that it's actually preferable to use the relays while the system is in development, as it allows the operator to hear that the system is working, as well as how active it is. Here's a picture of what we're doing:

The computer is steering the tractor along a straight line, the operator turns around at the end, and the computer steers again. We end up with straight passes that are all equally spaced.

-Lance

**HiJackZX1** · 05-06-2008, 06:39 AM

Wow this is cool..... pretty soon Im sure someone will come up with a solution to drive a car on the streets on its own via GPS.

**h3rk** · 05-07-2008, 06:07 AM

Originally Posted by HiJackZX1

Wow this is cool..... pretty soon Im sure someone will come up with a solution to drive a car on the streets on its own via GPS.

What a scary thought.. At least this is way out in the open.

So, did you just happen to have a guide-a-tractor-by-gps program sitting around, waiting to be taken to the next step? That's the part that intrigues me the most. It's pretty impressive, what you did right thar.