Not many people know but we have an piece of open source software for controlling an Antenna Tracker. It's been built by Tridge (Arduplane lead developer) for use in the outback challenge.
Sadly we have no documentation and, as far as I know, nobody except Tridge has used it. Still given Tridge's track record on building great software I suspect it works well and if it doesn't, I'm sure we can fix it. So to not let this piece of code go to waste, I'd like some help from people who are interested to give it a try and help me figure out how it works.
Here's the little that I know:
- It runs on any of our supported board (APM1, APM2, PX4, Pixhawk, Flymaple and perhaps VRBrain)
- For APM1/APM2 users building the code is as easy as opening our hacked ArduinoIDE and selecting File > SketchBook > Tools > AntennaTracker and then building in the normal way. For PX4/Pixhawk, our autobuilder doesn't automatically build a binary but I can provide one if people are interested.
- It can control a Pan and Tilt gimbal like this or this found on servocity.com.
- It may or may not require a GPS
- It must somehow receive vehicle position updates from the ground station which has the telemetry radio that is connected to the vehicle. Maybe through a USB cable. Tridge probably uses the python ground station, MAVProxy, to passthrough the vehicle position data to the AT but perhaps we can get MichaelO to build out a similar feature in Mission Planner.
- I imagine this antenna tracker could also be used to keep a camera focused on the vehicle which might be good for easing the burden on creating videos of our vehicles.
So if you want to give it a try please do and stick any findings, questions or issues below. Alternatively Issues can go into the issues list.
I'll start sticking things into the wiki as they become clear.
Replies
I had similar results. AT doesn't use INS features and relys only on GPS. I implemented GPS averaging to get rid of that and it works nice (assuming the tracker is not mounted on a moving vehicle). I use 5% of new location and 95% of the old one.
This effect is only visible and relevant with short distances between AT and MRC. At such distances good antenna alignment is usually not critical. The longer the distance the better alignment we get. It should start working reliably with distances greater than 30-50 meters (when sum of GPS errors on both ends is small in relation to distance between objects).
You can either wait for my fix (I will make it available via parameters in an upcoming version - I am collecting "features" for AT 1.0) or you can disconnect your GPS and set starting location via parameters. You can also disconnect your gps during operation and AT will use last known location.
That sounds great.
Can you do something on the latency?
I flew about 500m away, left and right and the Traker takes long time to follow, 2-5 sec. In that time there is no video connection because the antenna not pointing to the Copter. Also the accuracy is sometimes very bad and not pointing to the Copter.
Andre,
If you are not using a Pixhawk with buzzer, you may not notice if the telemetry link is intermittent. I am not sure if there is an audible on APM 2.x setups. Also, at 500m distance, are you using an RFD900 module?
no I´m using the 3DR radio 433Mhz with 100mW, I've a dipole Antenna, the range is about 2 KM.
I didn't experience such problems and I will have to take a look at this. AT firmware is trying to "estimate" MAV position by taking it's ground course and speed and it may not work well with copter. I am currently in Germany and I don't have my tracker with me so I am unable to test it. I will work on that next week. Perhaps "MAVLink loop problem" has something to do with it.
Jakub,
While I wait for your new firmware, I will try your version of 0.7.2 for Pixhawk today since I have an opportunity to fly. Next week, I may switch my AT to APM v2.5.2 board and see how that goes.
Thanks for the information and firmware updates!
Hi Greg,
Unfortunately I´ve the same behavior, also the bang-angle (in the HUD) is always to the left.
Today was the first time the AT works, not very good but works in Yaw and Pitch, I´ve still to adjust the PIDs. It looks like the Tracker has a high latency to follow the UAV.
Hi Andre,
Yes, the latency is significant. I expect that for planes farther out it may work better. My experience has been that the HUD works fine for pitch and yaw, and, eventually settles in on the roll. I am not sure why the roll isn't immediately locked to the Pixhawk or APM acc position on the AT.
This is one of the reasons why my version of firmware uses special INITIALIZING mode - when AT is powered-on it needs time to figure out it's exact orientation. With CR servos it could result in erratic behavior, so I deliberately wait 5 seconds after setting pitch to +45 degrees to make sure, that it is at least below +90 degees. It usually takes less than 10 seconds to establish a good orientation (within +- 20 derees) and another 10-15 seconds to reduce it to +- 1 or 2 degrees.
Hi Jakub and Randy,
It was my fault. I probably have done some stupid thing during AT pixhawk setup.
I re installed 0.72 firmware and tested in the field today. IT WORKS !!! PITCH AND YAW
Thanks a lot for the hard work.
Now I have a very good AT. Next step is to test it with an airplane.
Many thanks...
The only thing still to be investigated is related to loss of telemetry once in a while (similar on what Greg mentioned few pages back).
Cheers,
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