Last time we looked at why I chose to build a small UAV/RPAS from foam board. In this article I commit the design to foam, start building, throw it in the bin, and start building again…
MicroWing UAV Recap…
The MicroWing UAV is a small, fully autonomous aircraft designed and constructed using foam board building techniques. Born from a combination of the VersaDrone and MicroWing projects, the aim was to build a low-cost platform that was able to perform tasks similar to commercially available RPAS costing tens of thousands of dollars.
Getting it all in
The biggest challenge I faced during the early part of the build was how to fit commercially available flight electronics, a large(ish) battery pack AND a downward facing stills camera into the tiny airframe.
With the plans printed I spent a good few evenings laying things out and drawing cutouts on the wing to try somehow to make it all fit without destroying either the inherent strength of the foam board or the aerodynamic performance of the KFm7 section. In the original MicroWing I had simply cut down through the top layer and taped everything on top of the wing. That just wasn’t going to work here, where a professional appearance was going to be almost as important as performance – everything had to go inside the wing.
I had originally intended to use a GoPro as the flight camera but soon changed my mind. The GoPro is awesome at video and takes some nice still shots as well. The problem is the fisheye lens makes still shots useless for photo-mapping. Yes you can remove the fisheye in software such as Lightroom and Photoshop but the results are never perfect. I had to find a stills camera.
Eventually I bought a cheap Canon Ixus 70 camera from eBay. The beauty of these small compact Canon cameras is you can load them up with the Canon Hacker Development Kit (CHDK) and run scripts such as taking photos automatically at set intervals. With this new bit of kit I just about managed to fit everything on the plan and was ready to start cutting.
Cutting the small channels for wires and equipment bays was a little time consuming but I still had all the parts cut within a couple of hours work. Sadly the MicroWing UAV was no longer a 1 sheet airframe but I only needed a little more than 1 sheet and it still worked out at around $12 of material – even using expensive Australian foam board.
As saving weight was of importance I didn’t want to use hot glue for this build and looked to some different methods. The first I tried was a spreadable “Gorilla” glue. The expanding foam adhesive was messy to work with but achieved a good result. The only problem I found was when it leaked into equipment bays it created small bulges that got in the way where space was tight.
I HAD BUILT THE WING UPSIDE DOWN!
It is becoming something of a common thing for me to build things upside down, inside out, back-to-front, two left wings etc. etc. but this was beyond a joke.
It didn’t matter how I spun it, I just couldn’t get the gear to fit with the bays reversed so I threw the whole lot on the shelf and sulked…
A week later I came back to the plans and took another look. Eager to learn something from my first attempt I wanted to make some changes and improve the design.
The most obvious problem I was facing was the space available in the center section for the flight controller, ESC, battery and camera. I took another look at the problem and did some thinking – finally I had an idea…
It dawned on me as I lay in bed thinking about the camera problem one night.
“My smartphone has a 20 megapixel camera on it,” I thought. “I could mount the phone on the outside of an airframe easily. It’s thin, relatively lightweight and user friendly.” My mind raced. “Surely there must be an app that will allow me to take photos at set intervals”…
The next day I began my search and discovered that, at least as far as Android is concerned, there is NO app that will allow you to take photos at set intervals with your smartphone.
So, I contracted a developer on Elance and had one built for me!
- Allows the user to select a resolution based on the native device defaults.
- Allows the user to set the desired shooting interval in 1 second increments.
- Saves photos to a dedicated folder so download and transfer is simple.
- Tags photos with GPS coordinates to aid in the mapping process.
- A future development will be to have photos upload to the cloud in real-time so shots can be reviewed whilst the RPAS is still in flight.
Watch this space, I will probably make the RPAS Camera available for download in the near future…
The Build – Again…
I expanded and combined the central bays to form one larger bay. This gave me plenty of room for the electronics and I quickly had the MicroWing UAV together. Because of the nature of the design I had to build some of the gear into the wing but this was remarkably easy and everything fit together nicely. This time I opted for spray adhesive and after some trial and error I was getting a good fast bond.
The central top and bottom plates were cut from 3mm corflute plastic to add some protection for the electronics in rough landing spots. The top hatch was hinged at the front and locks at the back using a small wire clip.
TOP TIP! Using magnets to secure hatches is a no-no if you have an APM with onboard compass. The magnetic field interferes with the compass and you’ll never be able to navigate properly.
Not only does the MicroWing UAV have to perform, it also has to look the part.
Foam board is not known for its weatherproofing abilities so I gave the entire model a spray coat of black enamel paint and then a final layer of clear polyurethane. This finish was easy to apply and seems to have added an extra dimension of strength to the skin of the wing with very little extra weight gained.
I wrapped the leading edge in cloth tape and also covered the open GPS bay. The red stripe not only looks good, it also aids orientation on an otherwise “stealth” airframe!
With everything hooked up and including flight battery, but not camera, the final weight was 530g. Although heavier than the original MicroWing (350g), this is still considerably lighter than other commercial platforms of the same size so I was hopeful of a good performance in the air.
I finally head out to the airfield for a maiden flight. Tune in to find out why the OrangeRX isn’t the ideal transmitter for an autonomous vehicle.
We’ll even have some flight video to look at…