I woke up one morning a while ago feeling very restless. It was as if the daily routine of work, work and more work left me desperate and uneasy. Life was passing me by every day and I felt I did not accomplishing anything recently. I started scratching around and accidentally stumbled upon a drone kit advertised on Amazon. And I knew instantaneously what I had to do: I would be building another drone, and guide you into building your own drone with little or no previous experience.
Surprisingly, many different building kits are to be found on the Internet these days since my last build in 2016. The available kits were mostly smaller sized (less than 300mm) or Lego kits aimed at teaching youngsters.
For this project, I had something different in mind though. Firstly, I wanted to select the spare parts myself instead of merely buying a box filled with stuff that someone else thought would work well together. In addition, I wanted to use the opportunity to learn as much as I could from the project, and I doubt if stacking Lego blocks on each other would teach me much. I wanted the end product to become something useful- I have a head full of ideas and I needed a platform to do experiments on. And lastly, I didn’t want to break the bank- which is why I was initially more interested in a quad than a hexacopter.
After the necessary permissions were obtained from my good wife and Minister of Finances, the shopping started. It did not take me long to change my preference from a quadcopter to a hexacopter, which was only marginally more costly than the equivalent 4-arm design.
On that point, I started pondering the question about what the Maximum All Up Weight (MAUW) of my drone should be. Conceptually, the following equation describes the decision to be made:
Remember that batteries do not remain at full charge for the full duration of the flight, and the 25% effectively reduces as the flight progresses.
The calculation wasn’t as straightforward as it sounds. Starting the weight calculation involved some guess work initially. In principle, the total weight of the drone determines the motors that are needed, but, the selection of motors (and other components for that matter) determines the weight of the total system. So, it’s a chicken-egg situation and, as an initial guide, I inserted the component weights of a random hexacopter for sale into the formula. My initial calculation amounting to 497g lifting capability required per motor, would soon change as I progressed with selecting my components to eventually become 610g.
Some of the weights taken from the respective spec sheets included the packaging. I chose to ignore this inaccuracy as it represents a deviation to the “safe” side, and really would not be much. Also, I have a GoPro Hero 4 which would become the payload at a later stage, but had to be factored in at this stage already.
Finding a frame was not so difficult. There are only a few options available, and although their prices varied a lot, I quickly added the Hobbypower S550 F550 Hexacopter Frame kit (which I mentioned earlier) to my cart. It comes complete with a carbon fibre landing gear for $52.99.
“I did not know at the time that my selection of the frame would influence my downstream choices to a large extent. Very soon thereafter I would become unsure about the compatibility of the different components, and sticking to a particular brand would theoretically improve the chances that the different components will match up with each other.”
Next I sourced motors, ESC’s and propellers. The motors I liked were a six pack of Hobbypower 2212 920KV brushless motors for $48.99 (3 x clockwise and 3 x counter clockwise). As mentioned before, choosing Hobbypower again would minimise my chances of incompatibility between the frame and the motors.
I had to ensure first though, that these motors would be able to lift (my eventual calculation of) 610g each. The thrust produced by a motor is severely affected by the choice of the propeller. It was easy enough through a quick search to determine that most recommendations are for 10-4.5 propellers to be paired with 2212-920KV motors.
I located a number of Youtube videos showing tests with 2212-920KV motors. One of these had 9450 propellers fitted, and showed a lifting capacity of 621g maximum (just enough for my needs). In the other video, a 1045 propeller was fitted to the test bench, but the device was only able to reach a lifting capacity of 560g. This bothered me for a night or two because of my 610g target.
I eventually stuck with my original decision to use 2212-920KV motors and 10-4.5 propellers, simply because:
1. I provided abundantly for manoeuvring thrust in the calculation, and
2. I planned to only add the camera and gimbal after flight testing has been completed, and I could upgrade at that stage if needed.
Besides, it would be cheap and easy to experiment with 9450-size propellers if I wanted, which might potentially increase the thrust produced.
Once I learnt that a single ESC costs something like $15.99 and a 6-pack of Hobbypower SimonK 30A ESC Brushless 2A Speed Controllers sells for $38.95, it became an easy choice to add the 6-pack to my cart. The issue here is that an inadequate ESC would warm up at high RPM settings, and can potentially burn out. I made sure that most experienced drone bloggers would be happy with combining 30A ESC’s with my 2212-920’s.
Finally, I had to consider the flight controller and GPS, interfacing components that can be bought separate or as a combo. The newest technology on the market is costly and I was concerned about the final bill, so I settled for a combo APM2.8 Flight Controller/ NEO-7M GPS package at $82.99.
The autopilot included in the flight controller system has 6 degrees of freedom (DoF), able to control 3 gyro and 3 acceleration planes. Newer types have up to 10 DoF- but I figured I wouldn’t need as many. The Flight controller would need an upgrade later on if I get to a point to add data transmission (e.g. FPV video). A barometric sensor is built into the system.
The 7M GPS chip can operate with GPS, GLONASS, and QZSS (the American, Russian and Japanese networks respectively) and is advertised to consume less power than most competitors. I believed that the 7M would probably be sufficient as I fly in a very flat area with few shrubs and no trees, but might need an upgrade too if I fly my new contraption in an area that is remote or with many high trees.
Since I only planned to add the camera and telemetry plugin once my drone is airborne, I postponed the search for these items (including camera gimbal) for the moment.
During my research, I came across a handy “component calculator” at https://ecalc.ch/xcoptercalc.php. I didn’t use it much as it does not provide for the Hobbypower components which I selected. However, I keep the web address for future reference.
Just prior to sending through my order containing a bunch of components, I came across a building kit on the internet with many of the components that I so painstakingly chose. I considered that on the one hand, ordering a kit would be firmly against my initial intention of specifically picking the components myself. On the other, this Hobbypower S550 hexacopter kit costs $184.99 only, compared with about $272 for my own compilation. The cost consideration won and I gave in- I selected the kit and clicked “order now”.