Since my previous introductory post we've installed APM in ArduWot and racked up quite a bit of flight testing. In this post I'll give you guys some details on the setup of APM and the flight testing we've done so far.
I mentioned in my previous post that we'd famliarised ourselves with APM using a flying wing before purchasing the Wot 4, for completeness here's a photo of that setup.
The poor old flying wing has suffered a lot of abuse in the past but with APM strapped to it it performed remarkably well. However as you can see it isn't the neatest looking installation and it has a fairly big impact on the wings performance. With the weight of a larger than standard battery as well as the APM it flies pretty quickly which doesn't suit our small test area. So the next step was to find a more suitable airframe with a few key features:
- Easy to assemble - allows us to rapidly expand the fleet
- Robust - we conduct a lot more flights than your average RC hobbiest
- Internal space for APM - additional payload space not too important, but APM must be enclosed
- Slow flying - to afford us the best use of our test area
- Undercarriage - enabling take off and landing from grass
- Able to handle wind
The Wot 4 Foam-e seemed a good match to all these criteria and so ArduWot was born. The video below shows a flight test of the Wot 4 prior to the installation of APM. We have always conducted these sorts of familiarisation flights when using a new airframe as they allow us to identify any undesirable characterists, but the Wot 4 had none!
Shortly after that flight the installation of APM started, and shortly after that it was finished! Removal of some foam reinforcement created a space the perfect size for APM, it's almost like it was designed for it.
The APM was modified to include the magnetometer and a battery lead for voltage monitoring. A small cut out was made in the fuselage ahead of the wing to mount the GPS in. Quite a bit of fiddling was needed to get APM to sit neatly without getting servo wires trapped, but eventually it went in. There's even sufficient space on top of the APM for our relatively massive receiver.
At this point we went out for a few flights to test the basic fly-by-wire functions and we were very pleased with the results. The following day we tackled the installation of a pitot-static probe.
After deciding to go with a conventional wing mounted pitot-static we spent the best part of a day figuring out the least destructive way of installing it. Eventually we decided to feed the pipes through the hollow wing to the aileron servo mount with the aid of a metal rod and a small hole cut in the wing to guide it through a rib. From the aileron servo the pipes head forwards through a hole we made in the spar and leading edge structure where they were attached to the probe. Finally a slot was cut in the leading edge to push the probe into and it was epoxied in place. The pressure sensor itself is mounted to the wing in a position that puts it directly above the APM when installed.
With the exception of a permanently installed XBee module (which is currently crammed in the battery bay), the ArduWot is complete!
Our preliminary flight tests have focused on determining the parameters for stabilisation and navigation. So far everything is going well with the APM surpassing our expectations. Before we can start using the ArduWot as a research tool we will need to create a MAVLink interface for MATLAB/Simulink and we have just started work on this. In the meantime we will continue testing what APM can do as standard (auto take off and landing look like fun!). We are also planning to contribute to Arduplane (and Arducopter with our ArduRex project), we will be implementing features such as initialisation offsets for taildragger aircraft (like ArduWot) once we are familiar with the code.
I hope this has been an interesting insight into our exploits with APM!