I had several objectives during field testing:
- Get the rover tuned properly, and see if there is any strange autonomous behavior like weaving, jerking, etc.
- Familiarize myself with planning autonomous missions in Mission Planner. I was specifically interested in seeing how to autogenerate waypoints.
- See how well the GPS blending reports position. I was interested in both absolute and relative accuracy, but really just wanted to get a feel for things at this point.
To start, I took the rover V2 out in my backyard and got it to run autonomously, but my backyard isn’t very big. I have lots of tall trees in my neighborhood, too, so GPS signal reception wasn’t great either.
I would estimate position accuracy relative to the satellite map data was +/-3m. Not horrible, but not great, either. Throughout the afternoon position would drift slightly, I would estimate +/-1m.
I had the rover run an autonomous mission of 20 waypoints positioned in a circle several times to test repeatability. I did this close to 10 times over the course of an hour, and each time the rover took a slightly different path, as evidenced by the track marks in the grass. Sometimes the rover would go on the left side of my sprinkler well, other times to the right. Not very repeatable, but this was a somewhat challenging GPS environment.
So knowing that things were at least configured somewhat correctly I decided to take the rover V2 out to a large parking lot with a good view of the sky. In Kansas, those aren’t too hard to find. I chose a parking lot way out of town, with newly painted stripes that showed up on the satellite imagery so that I could have a good measure of relative accuracy.
The rover weighs something close to 100lb, so I had to take the batteries off of the chassis and remove both of the control boxes. I brought my tool box with me to help reassemble the rover and I also made sure my laptop was charged, but I forgot to bring a few things. If you’re ever out field testing, a checklist is a really good idea. Here’s mine for the next time I go out:
- Cell phone with cellular data
- AA batteries for the RC transmitter
- Make sure rover batteries are sufficiently charged
- The toolbox with hex wrenches, adjustable wrench, and screwdrivers
- Laptop with a good battery charge
- Telemetry radio for the laptop
- SD card, installed in the Pixhawk
I asked my very supportive wife to go with me, thinking she would bring her phone and that I could use it as a wireless hotspot to download Mission Planner map data. I forgot to explicitly ask her to bring it, which was a huge mistake because this was the one time she decided to leave her phone at home. And I’m too cheap to have a data plan, so I was depending on her. We had a good laugh about it when we realized she’d left it at home.
So while I was able to do some autonomous missions, I was unable to compare the position data to the parking stripes on the satellite map. I could zoom in, but the ~300 car parking lot was reduced to 6 pixels in Mission Planner.
So without any good imagery, I took the rover manually around the parking lot perimeter to demarcate the edges and then planned some missions. The first ones were circular, and then I did some square ones, and some random ones.
Overall, I felt like the rover was tuned perfectly. I had a few odd shimmies here and there, but I didn’t spend too much time trying to find the cause. They weren’t debilitating, just noticeable. Seeing the rover run autonomously without toilet bowling was very satisfying given my rover V1 experience.
So field testing was only a partial success. I felt like the rover was tuned really well with just the default settings, so that was a win. But I wasn’t able to get a good feel for GPS positioning accuracy or repeatability. I did get to spend some time familiarizing myself with Mission Planner.
An observation about field testing that may be specific to Kansas: Wind stinks. The laptop almost blew off the hood of my car while I was in the parking lot. I set up shop in the trunk of my car where I was sheltered from the wind a little, but I noticed this affected my radio range somewhat. I had the rover more than 500ft from my car at some points, and much past that things got spotty. In the future I’ll choose a calmer day for field testing.
Another observation: Kansas is flat. Very flat. When the rover got more than 200ft or so away from me distance to obstacles becomes very difficult to judge (especially with no satellite map). I hopped a few curbs in manual mode, but the rover V2 handled it like a champ.
Overall I’d say it was a 1.5 out of 3. We’ll bring a good cell phone and choose a calmer day next time.