Starting Out

Intro

My name is Jake, and this is my post all about my path to try and build my own drone. To give you a little bit of background, I’m an engineering student at Utah State University pursuing my bachelor’s degree in mechanical and aerospace engineering with a minor in computer science. I love the idea of creating things, of taking a bunch of useless parts and putting them together in a way that takes advantage of principles of engineering, physics, and chemistry and gets it to carry out a useful task, giving my creation “life” so to speak.

I have worked on cars for many years and have also been studying engineering for a while now which has allowed me to work on and study the physical side of things, what I like to think of as the body of a creation. However, I recently discovered coding which opened a whole new world to me. If mechanical engineering is the creation of the body of an invention then coding and computer science is the creation of the mind. It amazes me as a sit at my computer and type in code that I’m teaching my creation how to think. The commands that I type in are the logic that it will live by and it will carry out what I want it to do without fail (ok, actually it fails to do what I want it to quite a bit, but after enough debugging everything complies in the end… hopefully).

Anyways, that’s just to give you a little history on me and why I feel the way I do about this stuff. I originally started college with the goal of going to med school (I kind of feel like everyone did that though) so I was doing pre med but by a happy accident I was majoring in mechanical engineering and after the first semester I was hooked. I realized nothing else as a career would make me as happy or leave me feeling as fulfilled as engineering had managed to do after only a few months. It gets me excited just thinking about it. I wish other people could understand what I do about this process of creation. I feel like they would be just as excited about making things as I am if they did.

How I Ended Up Here

 Several engineering friends and I have always thrown ideas around about projects we want to try to build. Usually everything is just hypothetical because of the money and time restraints of being a student, however over the summer break of 2017 my friend Caleb and I decided we would try to go through with one of our projects. The ideas we’ve played with have ranged from building things like a tank to a rail gun. I think it’s the inner child in us that wants to build something cool and destructive. However, for this summer we decided to build our own drone. Studying the flight mechanics and optimal design of a drone will help us in our future studies in aerospace engineering and if I’m being honest this was one of the cheaper projects we could have gone through with.

In order to get as much as possible out of this project we wanted to build the drone completely from scratch. Looking up how individual pieces worked, such as an Arduino function or an accelerometer calculation, were acceptable. The idea, however, was to avoid following a cookie cutter recipe that we found online. We aren’t doing this so much to have a drone to fly (if we wanted to do that we could have bought one for much cheaper). We’re trying to learn the ins and outs of how all the different parts come together and work (I even have the goal to figure out how all the parts of an Arduino work, but that might be a little out of the scope of this project). After mentioning the project to a neighbor he suggested that I write my process down in a blog to have a record of it, so here it goes.

Anyways, enough background, let me tell you about our process.

Methods

               The first thing we needed to do was create our parts list. The first thing that came to mind was motors. I looked around online for some options but just left more confused than anything, so we went to a local hobby shop that specialized in remote control flight parts. They had several motors available but we ended up just going with the cheapest ones. Eventually I would like to build a drone that has some real power but for right now I just want one that can get off the ground, keep its balance, and hopefully not run into anything.

               I bought one Suppo M2204 2350Kv brushless motor. I wanted to just get one and make sure I could get it to work before I spent sixty dollars on an entire set. The motors are servos so they require an electronic speed controller, or ESC for short. These basically allow you to adjust the speed of the motors, which is essential since the voltage for a digital logic circuit only allows for one speed which would make for a pretty boring drone. The guys at the hobby shop said they didn’t sell any ESC’s that they would recommend using (I really appreciated their honesty), so I got online to try looking again. This time I got lucky and found a good ESC for a cheap price. I bought a hobbymate 15 amp BLHeli ESC, just getting one to test with before going all out. Caleb and I also bought a 2250 mAh 3S LiPo battery from the hobby shop.

               The next step was the brain of the drone. At first we thought we’d use a raspberry pi 3 because it has built in Bluetooth and WIFI which we thought would be a good way to control the drone. I had this crazy idea that I was going to develop an android app with a controller interface to run the drone through Bluetooth. It makes me laugh thinking back about that. Besides the fact that Bluetooth has an extremely short range, I barely know a thing about android development and the one tutorial I followed on how to make a ‘hello world’ app left me more confused than enlightened. So I’m sure that would’ve been a disaster.

               I had an Arduino Uno microcontroller board that I decided to use for the initial tests with the motor and ESC (I’ll tell you about that in a minute). After running a few tests with the Arduino I realized that we would be able to run the entire program on the microcontroller. I feel like it was a good decision since Caleb and I know how to code best in C++ which is what Arduino runs on. Buying a raspberry pi would have required learning a whole new system, and we already had enough new things to learn.
              So now that I had a motor, ESC, and a battery I wanted to test how it worked. I didn't know what kind of signal an ESC needed to receive so I did have to google that, but it turned out to be pretty simple.

Set up of the motor, ESC, and arduino

              The ESC has three wires running out from it that connect with the three wires coming out of the servo motor. The order that you connect them in determines whether it spins clockwise or counterclockwise. However, because the three wires coming out of the motor and ESC were all black I'm not really sure how they need to be connected to get it to spin in a certain direction. My solution in the end was to just test it by trail and error until I got the connections right.

              On the other end of the ESC there are four wires. There is a red and black wire on the sides that connect to the lipo battery (not shown in picture) and a black and white wire in the middle that will go to the arduino. The white is the signal wire and the black is the ground (it's important to note that this ground wire needs to be grounded to the arduino or wherever the signal is coming from, not the lipo battery).

              Initially I wasn't sure what kind of signal the ESC needed to receive so I had to search around. 

http://www.instructables.com/id/ESC-Programming-on-Arduino-Hobbyking-ESC/

              This website explained it pretty well. First you need to download the servo library for Arduino. Once you have that you can create servo objects that you simply send a number to, either through the serial monitor or a radio controller.
             

              I hooked the ESC signal pin into the arduino and loaded up the sketch so that I would be able to send numbers to the ESC through the serial monitor. I wasn't sure what number to send at first. The website that I referenced earlier said the HobbyKing ESC ranges from 700 to 2000, so I tried that. Sending 700 didn't do anything, I later found out that was below range, but at the time I thought I might have done something wrong. Just to check I decided to send 2000. Unfortunately, I didn't have a very good grip on the motor (I was just barely holding onto the bottom in my hand) and 2000 turned out to be max velocity for this ESC. So as soon as the ESC recieved the signal the motor flew right out of my hand, the nut came off of the motor (I had the propeller spinning the wrong way for the threads), and the propeller shot across the room. It all happened in a second, the motor got all wound up in it's wires and the propeller almost took my eye out. So if you try this make sure you're careful.
              I needed to find the minimum and maximum numbers that could be sent to the ESC.  But since I just learned these can vary by ESC some experimenting had to be done here. In the end I figured out that the upper limit was 2000 and the lower limit was around 1100.