The octocopter

One of the first flights
One of the first flights

We recently built a brushless gimball for our Gopro but our quadcopter became too heavy to fligh safely, so it was time to get something bigger. We first thought about a nice hexa, but we couldn't resist to the appeal the octocopter. We wanted to get enough power to carry a lightweight DSLR such as my 550D, or simply all the FPV equipment we have, plus our Gopro on its brushless gimbal; all of this with a 10 minutes autonomy.

It all went so fast. Add to cart. Pay. Bam, it's delivered. We chose this time not to build the frame ourselves, just to put everything together, and have fun.

The Hobbyking X930 895mm glass fiber frame.

We bought this big and cheap octocopter frame from Hobbyking, the X930. The arms are in aluminum and the rest of the frame is made with pretty thick glass fiber.

[notice]THE MOTOR MOUNTS ARE VERY WEAK.[/notice]

If you look at the comments on Hobbyking's website for this frame, you will see that many people (including us) broke several of them while flying. So don't even try to fly with them, they will eventually break. We reproduced these motor mounts in aluminum with our CNC and mounted them under the original ones to get Β rock solid motor mounts.

Turnigy 3536 910kV
The Turnigy 3536 910kV motors mounted with 12x4.5 props. You can see the CNC milled aluminum motor mount under the original one.

The Turnigy 910kV motors provide plenty of power to lift anything you'll throw at the octocopter. They are controlled by 40A controllers (Turnigy Plush 40A), which are fed by an octocopter power board.We use two 3S 5000mAh batteries in parallel to reach our desired autonomy.

Our octocopter power stage
The power board and the 8 ESCs.

Be careful with this board, it is only certified to deliver 8x10A, which is really low (our motors can take up to 35A). We chose to add a lot of solder on the PCB in order to increase the amount of current it could deliver and it seems to be working fine so far.

We flashed our Ardupilot with the latest octocopter firmware and tried to find the best PID values for the octocopter. It does fly pretty well now but there is definitely room for improvement.

Our octocopter
The "command" part of the system.
Our octocopter
Ready to fly. (Yes, we broke one prop so we replaced it with a 9x4.7 :D)

We'll try to fly FPV with it as soon as we can with our new new brushless gimbal (article to come πŸ™‚ ) and we will obviously post videos of it here and on YouTube on our channel.Β 

We'll be back soon πŸ™‚

The Ardupilot Mega 2.5 : why it's awesome.

After a good run, we decided it was time for our homemade quadcopter controller board to go. Actually, it had to. It started to wobble in the air pretty violently for no reason while flying. We made no change to the program, nor touched the hardware, and since it was working fine before, we figured that it probably came from an electronic problem somewhere in the tons of wires and soldering we made. Pretty hard to "debug"...

So here we were, on 3D Robotics website, ready to click the famous "Add to cart" button. And we finally did click, after a long time of hesitation. It was not that long, in fact. It was a no-brainer. For 180$, you get a tiny assembled PCB with an accelerometer, gyroscope, magnetic sensor, pressure sensor, GPS, current sensor, with completely open-source software that will let you do basically anything you could want to do with any kind of RC model. Not only this works with quadcopters in + or X configurations, it's also made for RC cars, planes,hexacopters, Y6 copters, octocopters, tricopters, and even helicopters! 180$ seems pretty cheap now, doesn't it? πŸ˜‰

All the firmwares you can upload to the onboard Arduino mega
All the firmwares you can upload to the onboard Arduino mega
We don't regret having spent so much time on our controller board at all. It was a great experience, it worked pretty well and got us to understand pretty much everything about how these drones fly. We just couldn't make something so small and so well designed ourselves in our garage. Plus, the huge community working on the Ardupilot's software came to something close to perfection, with a dedicated windows program (APM mission planner) that can control every single parameter of the drone, communicate with it in flight via a telemetry module, prepare mission scripts with GPS waypoints and actions to take, read flights logs and export them into Google earth-friendly KML files (and more)!

What comes with the Ardupilot
What comes with the Ardupilot
We ordered the fully assembled APM 2.5 with a Mediatek GPS, and a current sensor. It also delivers with a USB to micro USB cable so you have everything you need to start playing πŸ™‚

The Mediatek GPS,  current sensor and APM2.5
The Mediatek GPS, current sensor and APM2.5
It turned out very easy to setup on our existing quadcopter frame. We followed the instructions given on the arducopter google code project and everything went smooth and fast! The steps are the following:

  1. Download mission planner and install it (it will also install the Arduino mega drivers on your computer)
  2. Plug-in your APM
  3. Start mission planner
  4. Choose from the drop-down list the COM port you APM has (check Windows Device manager to find which one)
  5. Go on the firmware tab, select the one you want to use, upload it!
  6. Press connect and you're ready to configure everything!

The default parameters should be fine for an average quadcopter frame (50cm wide, ~1200kv motors, 1kg). At least they are okay for flying. We lowered a bit the PIDs on ours because it was a bit too nervous but the first flight was still pretty good and the stability in the air was quite amazing, even with high winds!

A log from the the Ardupilot
A log from the the Ardupilot
You can assign any action you want on your radio extra switches and knobs. The most impressive one obviously being the "Auto" mode, where the quadcopter will follow a script of actions the user can write with the mission planer software. Just flick a switch, sit down and let the drone take off, fly to the waypoints you told him at the altitude you told him, and then land where you told him.

Casual flight around the Eiffel tower...
Flying has never been so easy! πŸ˜€ Also, it is really, really nice to have the return to launch (RTL) feature, which will bring back the drone where your armed the motors. It is a life saving feature, for those of us who put expensive cameras on their drones and don't want to crash them in case they lose the orientation or the video signal when doing FPV. It actually happened to us in one of our first flights. We were about to test the RTL feature when the drone was so far that we couldn't see its orientation anymore. We were already thinking about the "walk of shame" we would have to take with the broken pieces of our beloved quadcopter. But none of that happened. We flicked the RTL switch, and the drone came back home πŸ˜€ This feature really is a must-have! It's awesome and works great. We've only played with it last weekend, and even though it was a pretty windy weekend here, we managed to fly up to 80 meters with no problem whatsoever for the drone!

OMG, we see that the earth is round! No. It's the Gopro fisheye that does that. But everything seems pretty tiny at 80 meters of altitude.
"OMG, we see that the earth is round!" No. It's the Gopro fisheye that does that. But everything seems pretty tiny at 80 meters of altitude.
If there should be a conclusion to this article, it would be : buy the Ardupilot. It's great, works with everything, has a big developer community around it, and is actually not that expensive when you think about all the electronics it contains.
We just ordered the telemetry and OSD module so we can go all FPV on it πŸ˜‰ We are definitely going to play our quadcopter in the weeks to come, and will try to add a nice video to this article (or to a new one) to show you what you can do which such a powerful tool πŸ™‚