Arduino Micro Quadcopter

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This is Arduino based, 3D printed micro Quadcopter project for 8.5 mm diameter DC motors. However if you have some experience (or just have an hour of free time) you can adapt the design to fit to a different size motors.

I am doing this during my free time while I study in the university, thus I think it should take quite some time to finish (exams approaching!).

I decided to control the Quadcopter through Bluetooth using an Android phone/tablet. In the future I might redesign a bit to control it using Wifi or some radio communication. I will also write and publish an Android App for the control using bluetooth.

So lets get it started@!

P.S. The robot is dedicated for M.O.N.T.E. (Mobile Omnidirectional Neutralization and Termination Eradicator) killer robot from The Big Bang Theory 😀

Microcontroller

We need some small chip/microcontroller board for this Micro Quadcopter. A cheap option is to use Arduino Nano, which from China cost ~£1-2. Additionally, to lower the weight, alternatives could be Arduino Beetle or Arduino USB chip, which is a Chinese copy of original Beetle (Cheaper, works (tested) the same way and connectors are easier to solder). You could also follow this tutorial to program bare chips of ATMEL ATmega328/168, which you can get for free from ATMEL website (If you’re a student go to Atmel -> samples -> order a sample) or ebay otherwise. As for prototyping I will use Arduino Nano as it is easier to deal with. I think the next stage would be either use bare metal Atmel chip or look into Arduino Beetle BLE as you can also find them cheaply in some places, however they only have 2xPWM output, thus a register shifter might have to be used in addition. The weight of each chip varies depending on the microcontroller: Arduino Micro ~13g, Arduino Beetle ~5g, bare chip + crystal ~4-5g(?).

Motors

Jerry Boatman from AssunMotor.com says that coreless electric motors are a great option for quickly accelerating and decelerating. I myself used a little more expensive motors from here. They are supposed to be a lot faster than the original Hubsan X4 motors. I plan to use custom made hardware thus I need fast motors to lift the weight. If I was to buy a new motor set now, I would most likely buy them from the same shop, however the ones which say speed: insane. There are a few types of those as well, so choose the ones with the best reviews. The difference is quite significant with speed: insane as they can reach at max 3.2 A instead of 2.75 A with speed: fast (somehow still says that thrust is 40g/motor for both motor types). For those you can’t afford expensive motor, there is always an alternative from ebay or even cheaper from China. They, of course do not fly that fast, at least I assume that from performance curves. I haven’t tried myself, but max current is 1.85 A and thrust is 34g/motor, which is lower than on previous motors. (Total weight ~20g)

Bluetooth

For the project I used the usual HC-06 Bluetooth module. It works as a slave only, which is what we need if we want to control it using a smart phone. As you can see from the added picture, I bent the connectors and then shortened them. I might look into an option of adding a Bluetooth 4.0 module later, which has opposite connections so then you won’t need to do that. (Total weight ~5g)

MPU

For the project I used MPU6050 which I already had bought some long time ago. It has 3 axis Gyroscope and a 3 axis Accelerometer only. In later releases I might use some more expensive MPU, which would have Barometer and a Magnetometer. (Total weight ~1.4g)

Batteries

For the motors and electronics you will need two 1S 3.7V LiPo batteries. One is used to power up the motors and another only the electronics. Finding a battery for electronics is easy. Simply choose the smallest available battery on the market (e.g. 1s 3.7V 100mAh (3g)). You can also buy them from HobbyKing pretty cheaply.

Getting a battery for the motors is more tricky. There are a few important points to note when buying them, capacity (mAh), max allowed discharge (C) and average discharge rate (C). The larger the capacity, the longer the quadcopter will run on a single charge and the larger the discharge rate, the more power it will be able to provide for the motors (larger currents for constant and for peak times). There is often a rule of thumb that multiplication of both, the discharge rate and the capacity, will give the current that the batteries can supply. For example, you have a battery with 500 mAh and 10 C of average/constant discharge. 500 mAh * 10 C = 5 A. Thus on average such a battery can supply 5 A. Then add around 20 % safe margin and you should be good to go. Well, this might work in some cases, however we have extremely powerful motors, thus discharge rate MUST be a lot higher than that. I Previously tried Turnigy nano-tech 650mAh 1S 15c (13g) with absolutely no luck. They only managed to fully power a single motor and didn’t even turn up 4 motors a bit, which meant that the discharge rate was simply too small (capacity surely was enough). I then looked into Turnigy nano-tech 1s 260mAh 35-70C (14g) batteries. They managed to power up all 4 motors, however at the time when I bought them they cost half the price you see here. I suggest looking into HobbyKing for similar or alternative batteries e.g. Turnigy nano-tech 300mah 1S 45~90C (9g) or even Turnigy Graphene 600mAh 1S 65C (15g) which seem to be very promising. If you have a few $/£ extra, buy Graphene batteries as they are lighter when compared to alternative batteries with the same capacity and provide a lot higher discharge rates (at least on the paper). I didn’t try them myself but would be really interesting to see how they compare in reality as I think the currently provided 35C discharge rate is a bit smallish as well.

Let’s calculate how long the batteries will last. Lets say that apart from the motors the rest of electronics uses around 100 mA of current constantly. Total current = 2.75 * 4 + 0.1 = 11.1 A = 11.1 * 1000 = 11100 mAh. The batteries I bought have capacity of 260mAh, thus Time (min) = 260 * 60 / 11100 = 1.4 min. Doesn’t seem a lot at all does it? I tested when I attached the quadcopter with the threads to the ground and it seems like the numbers are reasonable, I really couldn’t hold the quadcopter in the air even 2min. Well, for longer flight rates you will have to either add bigger batteries, use cheaper Hubsan X4 motors or somehow lower the weight of the whole thing. (Total weight ~16 g)

Motor Connectors

The motors usually use mini JST type connectors, thus you would need to get some (4 pcs) from either Farnell or ebay to be able to connect the motors to the whole circuit. Make sure you buy the connectors as the ones in the image. There are very similar ones (e.g. micro JST), however they ARE different.

Battery Connectors

Many of the batteries from ebay and HobbyKing use micro JST connectors. The charger I used (given in later sections) has a slightly different JST connector (I know, a bit confusing as al of them have the same name), so I decided to order some of these from ebay and solder them on every battery instead. This also allowed later nicely connecting the battery to the PCB.

Propellers

Many of you might want to use Hubsan X4 propellers and you can do that if you want to, however I will use Walkera LadyBird props. They are a little pricey if you buy them in UK (around 5 times more when comparing with original Hubsan X4 props), however really cheap from China. If you yet do not have props, then I would recommend using them either – if I am correct, I read somewhere that they provide more thrust, thus giving our little beast more speed (Well, after all, Walkera LadyBird is known to be the best micro quadcopter up to date! I wonder who tested that but lets just trust them for now…) (A few grams in total ~3-5g)

Transistors

We need 4x MOSFET transistors and choosing one might be tricky. Firstly, they need to withstand the used power and current by the motors and secondly, the threshold voltage has to be quite low, otherwise Arduino won’t be able to turn them ON fully (in the case of N-type MOSFET). In my case the max current is 2.75 A with voltage of 3.7 V. This means I need a MOSFET, which would at least withstand around 4 – 5 A just in case (will also heat up less). I ordered some from Farnell (MOSFET Transistor, N Channel, 6 A, 20 V) but you are free to look into alternatives such as MOSFET Transistor, N Channel, 8 A, 20 V (these are actually identical to the previous ones but they have additional legs to be soldered to ground to work as a heat-sink. This isn’t needed as previous ones didn’t heat up at all). Both of them had threshold voltages of 600mV, which is good. If you are to look for alternatives, try not to go more than 1V, but also if you want to use the provided PCB, make sure the sizing is the same, plus the given transistors in here already have a free-wheeling diodes inside thus will save some space on the PCB. (Total weight <1g).

Resistors

For the project I needed a 6×10 kOhm and 2×56 kOhm resistors (to be decided, but this is not needed until the end), which you can find in any electronics shop. (Total weight <1g)

Capacitors

A single electrolytic capacitor will be used to smooth the voltage on the battery used for mottors of size 47uF, 50V. It can be bought at any electronics shop. (Total weight <1g)

Charger

You might already have a good chargers, however in case you don’t you can always get something like this. It uses JST type connectors, thus you will have to get the connectors mentioned before. Alternatively you could get a chip based charger module like this. This might be useful in later projects as the chip can become part of the circuit in that case.

Price

Probably many of you would like to know the price of the thingy. Well, lets just calculate that using some rough calculations as the price will depend on the supplier:
Expensive motors:

£2 (Arduino) + £3 (MPU6050) + £20 (Motors) + £3 (Motor Battery) + £2 (Electronics Battery) + £2 (Propellers) + £2 (MOSFETs) + £5 (HC-06) + £2 (The rest of electronics + plastic) + £1 (Connectors) + £3 (Charger) = £45 (adding only the used components, when they are bought in multiples)

Cheap Motors:

£45 – £15 = £30

Conclusions:

Overall price is not that big and if you have the connectors and the charger, it will decrease significantly! Using very fast motor implementation I managed to fit into £50 price range if all the parts had to be bought.

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Step 3: Weight Calculations
Expensive motors:

For our quadcopter to fly nicely there is a rule of thumb that 50 % of the max thrust of motors should be equal to the weight of the quadcopter itself. Thus meaning that the quadcopter will be in the constant height when giving 50% of its full power. The motors that I bought have 40g/motor of thrust. In total that adds up to 160g. 50% of that is 80g. Now lets add up all of the electronics + the frame:

15g (frame) + 20g (motors) + 23g (battery) + 5g (bluetooth module) + 5g (microcontroller) + 1.4g (MPU) + 2g (transistors) + 1g (diodes) + 1g (resistors) = 73.4g, which is more or less what we need! Of course there will be some additional weight from wires, etc. but they are small and at most it will increase the weight until 75g, which is still 6% lighter than what we could afford.

Cheap motors:

Total thrust from motors is 4 * 34g/motor = 136g. 50% of that is 68g. Total electronics will be more or less the same, just the battery will be 10g lighter, giving around 65g in total with everything, which is still lighter than 50% of the thrust! Actually, it will not fly as good as with faster motors, but oh well, you are using at least 4 times cheaper motors!

Conclusion:

The quadcopter should fly! With more expensive motors it will fly better/faster, but yet still both quadcopter should fly.

We will be happy to hear your thoughts

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