Ok – Christmas is over and I’m back to work. I’m leaving the program for now and moving on to the physical quadcopter: once I have a finished and connected product it will be significantly easier to complete the code and test it.
The first step is to work out everything that will need to go into the quadcopter. Here’s a shortlist:
- The 4-motor ESC. I’ve acquired a central speed controller that contains the circuitry for powering all four motors, negating the need to have a seperate ESC on each arm.
- The PCB. As I don’t at the moment have access to a CNC mill to make a custom PCB, I will just be using a soldered breadboard for this purpose. It’s basically a PCB with tracks in the configuration of a standard breadboard. On the breadboard I’ll have a few electronics connections and the gyro/accelerometer, as well as a buzzer probably.
- The Arduino. This is the flight controller, and is self-explanatory.
- The battery. I’ll be using a 3-cell LiPo (lithium polymer) battery connected via XT-60 connectors to the electronics.
- Motors. Four brushless motors, one for each arm.
- Propellers. A 10-inch black nylon propeller for each motor. (pictured above)
There are also some specifications I would like to stick to regarding the design and position of the components:
- The battery should be able to slide in and out of its compartment, which should be at the bottom of the casing. As it’s the heaviest component, this will lower the centre of gravity and make the quadcopter more stable in flight.
- The ESC should be mounted using double-sided foam mounting tape to the bottom of the inside of the casing. It’s the securest way of attachment (from my experience) and as it is quite heavy this will also help stabilise the quad.
- The PCB and Arduino should be mounted via their screw-holes to the inside of the casing. This will require some clever CAD-ding but will make the internal components very secure.
- The XT-60 connector (between the battery and the components) should be clearly visible and easy to plug in and unplug. This is a safety requirement more than anything, so that power can be removed as quickly as possible, but will also make it easier to use.
- The motors should be equidistant from each other and far enough apart to allow 10-inch propellers. This means that the motors need to form a square with sides of over 10 inches. I know that this is a good propeller size, and being equidistant will make sure that the quad behaves the same way in all directions of flight.
- The casing should have a hard cover to protect the internal components. If possible it should also be waterproof.
- The arms should screw into the main body securely. This ensures that the quad is stable and secure in flight.
Having set these out, I’m now starting to look at the physical design of the centre of the body. Although not strictly necessary, I connected (most of) the electronic components to get an idea of how much space they’d take up:
As you can see, the wires actually take up quite a bit of space – I should bear this in mind when making the main design.
I’m focusing on the central body, containing the main electronics, first – I’ll do the arms afterwards. Both the PCB and the Arduino have mounting holes on them, which will work with my fairly large range of M3 bolts and nuts left over from previous projects. I downloaded the schematic files from SparkFun (the retailer) and measured out the dimensions of the boards and distances between the holes:
With this info in hand, I am now thinking about how it’s all going to fit together within the casing. Right now I’m considering only the internal component space, I’ll add connections to the arms later.
The longest component, the breadboard/PCB/whatever-you-want-to-call-it, has a length of 3.7″ which is just under 95mm, I’ll need a width of 80mm or so to accommodate the ESC at the bottom. However, I also need some space for wires and connections between the different boards, so I’m extending the length by 20mm for this: rounding up, that means I have internal space of 80x120mm. Now for the height: the ESC is about 15mm high, the PCB (with connections) about 30mm and the Arduino (also with connections) also about 30mm. That makes for a total height, allowing a bit extra for room to work with, of 80mm.
This means I have a nice internal space to deal with of 80x100x80mm.
Now the ESC will be in a little inset in the bottom, secured with double sided foam mounting tape, but the other two need to be positioned above, on ledges with screwholes to mount them to. Because this is going to be 3D-printed, and it’s hard to print overhangs, that means that the Arduino goes above the ESC, with the PCB above both of them, as the PCB’s mounting holes are much further apart so can be supported outside the Arduino’s footprint.
I’ll start working on the CAD shortly. The next question is how to attach the arms to the body, and the overall shape of the body.