Several test flights later

Quadcopter
I’ve been doing a few test flights of my Arducopter-based quadcopter over the last couple of weeks, when it wasn’t snowing. The first flight test wasn’t so successful. Whilst it flew, I couldn’t get it much above about 1-2 metres off the ground even at full throttle. This turned out to be due to miscalibrated ESCs, which didn’t know what a full throttle signal from my transmitter looked like.

Once recalibrated, it flew pretty well but my inexperience led to a few crash landings and a few broken propellers (no major damage though). It also drifted around quite a bit, but I improved that by recalibrating the accelerometers much more carefully.

I tested out the “return to launch” (RTL) feature a few times too. The idea is that the quadcopter remembers the gps coordinates of the launch point, and when RTL mode is enabled, it flies home automatically. The exact behaviour involves it flying up to a safe altitude (above any possible trees and such), then flies home, holds it’s position there for 5 seconds and then lands.

The first time I tested this, it seemed to work but instead of holding its position, it flew off into a nearby tree. I tested it a couple more times and it worked once, but veered off again another time. I later discovered reported problems with gps accuracy with the Arducopter firmware version I was using (2.9.1). Upgrading to 2.9.1b seems to have improved the behaviour a lot, but RTL isn’t yet something I’m comfortable trusting.

I did discover that the arducopter firmware keeps quite detailed telemetry logs of its flights, along with gps coordinates and altitude. Very good for figuring out what went wrong afterwards.

Control-wise, a major breakthrough for me was realising I didn’t necessarily need to keep pointing the “front” of the aircraft where I wanted to fly. It can go in any direction at any time, you just need to keep track of where the front is pointing to know where roll and pitch will get you. This is admittedly a bit hard to keep track of, so I think I’ll paint the legs or something to help with that. When it’s up high, especially with the light behind it, it’s quite hard to tell whether it is turning towards or away from you. Need more practise.

I also had some problems with the legs sticking in the ground (or breaking) on heavy landings. I’m making some improvements and might blog about that later.

And I stuck an old plastic takeaway container on top to protect a bit from rain and snow. Which worked well until I crash landed it today and smashed it.

IMG_1977_cropped

And today, I strapped an old Android smartphone to it and recorded a first person view of a flight. It was an old cheap phone so the video quality is poor, but it’s still exciting. I’m researching what cameras I can get to record higher definition video atm – I’ll post about that later.

Overall, it’s been quite stable and much sturdier than I’d imagined. It’s a little stressful to fly but I’ve managed to resist the urge to panic and drop throttle any time I’m not certain what is going on. I’d definitely recommend doing your test flights in a large empty grassy field (not a hard road surface), well away from people and buying quite a few spare propellers (which I did).

I’ve gathered all my videos so far into this Youtube playlist.

Quadcopter build, aluminium frame

quadcopter frame take 1

I decided very early on that I wanted to build my own frame rather than buy a kit or anything. I wanted to learn some new skills, but I also expected to be crashing this thing quite a lot and didn’t want to have to keep waiting for new parts to be shipped out (or worse, find them out of stock!).

After some research, I decided to skip carbon fiber (for now?) and use aluminium. It’s strong, lightweight, cheap and pretty easy to work with. I asked around a few local fabrication companies but there apparently aren’t any aluminium stockists in Bradford any more. I gave up and bought online from aluminiumwarehouse.co.uk which worked out nicely, except for the £15 delivery charge.

I bought some square tubing of various sizes for the arms and a length of flat for some odd jobs (perhaps the landing legs). It’s pretty cheap (especially compared to buying from a diy store) so I bought about 10 metres in total. I could build a fleet of quadcopters with this.

I looked into getting the center plates laser cut by a local firm, but it turned out slightly too expensive. £5 each for up to 10 isn’t too bad really, but I wanted quite a few plates in case of crashes and I want a bit more flexibility with the layout as I develop the design. So instead I just got some blank square plates cut to size by aluminiumwarehouse at about 50p each (for 140mm x 140mm x 2mm) and am drilling them manually. I think the 2mm is a bit overkill, and each plate weighs in at 100 grams. I reckon I could have gotten away with 1mm even.

I’m using titanium-coated drill bits; a high rotational speed is recommended for aluminium, but I’ve done just fine with my battery powered drill which isn’t that fast.

And just a reminder to clamp your plates down firmly so the drill doesn’t catch them and fling them around like blunt alloy throwing stars.

I’ve started out with the 12.7mm x 12.7mm x 1.6mm tubing for now – it seems more than solid enough. Drilling the center plate has proven a little fiddlier than I’d hoped and one of my arms isn’t mounted as square as I need. But that’s why I bought lots of extra blank plates!

I cut the tubing using a hacksaw but it came out with uneven ends which makes it difficult to measure and align things. Next time I’ll use the mitre saw (for which I bought metal cutting blades just for this purpose, doh!).

The finished arms and plates (and screws) come in at 400 grams in total. I’m planning to cut some holes in the plates which might lighten it a bit, much not much.

Quadcopter build, first steps

After weeks of research, and then days of cultivating a Farnell
shopping basket, I finally handed over some cash for the first parts
for my quadcopter. Lots of nuts and bolts, cable ties, spacers and
other misc. Plus Amazon and Ebay purchases too: heat shrink stuff,
connectors, various tools and nice new variable power soldering iron
to replace my (admittedly very trusty) 25W Weller.

The frame stuff was in excess of the cost of a off-the-shelf
quadcopter frame kit, which did make me almost reconsider building my
own. A kit obviously gives you all the parts for one frame, and I have
enough parts here to rebuild my own frame 10 times over, for around
the same cost (though I’ve still to buy the aluminium, but that’s
quite cheap). From what I’ve read, frame breakage is to be expected,
especially if you’ve not flown anything before, so the idea is this
will pay for itself. It’s also going to be way more fun, and I’ve
already learned loads of new things about lots of diverse subjects!

I also ordered an Ardupilot APM 2.5+ flight controller, with the gps
addon. I went without the telemetry module for now – looking to
integrate it with my (to be chosen) transmitter’s built-in telemetry
display.

I’ve yet to choose transmitter, motors, escs, props or battery.

Plan is to get this flying and learn how to fly it before starting
down the first-person-view video setup.

I’ll try to keep up with blogging about it and file them all together here in the Quadcopter category.