Today marks the second day of this blog, where I will be making D.I.Y drones seem like cooking microwave mac n' cheese. The first post was more of a background story and end goal of this blog, but today, I will dive right into the fine details of how I successfully built my own drone. If you've read the first post, I mentioned that the first drone I tried to build was a massive failure. The reason being was that I had motors with too high of a kv or kilo voltage. The kv of a motor is an essential part of building anything with a motor. In simple terms, KV show how fast a motor spins. A motor that has a higher kv will spin fast, but it will require more power than a motor with a low kv. You might be wondering how a motor with a low kv generates lift. The solution is larger propellers. These larger propellers have a larger surface area than smaller ones and thus generate more downward force or lift. The average quadcopter, such as the DJI Phantom, has motors that are 920kv. These motors are the sweet spot in the ratio of power draw to speed. Motors in the 800kv-1200kv range are mainly used for drones that want stable and efficient flight, ideal for shooting cinematic video. My first drone had 2300kv motors. These motors spun very fast, but had tiny props. High kv motors are primarily used for drone racing. The reason is that they don't necessarily have to last very long, but racing drones have to be able to make quick, sharp, and agile movements, things that your first quad shouldn't do. I thought that you would be able to hook the motors up to the flight control board directly. But sadly no, it's not that simple. Linking the motors to the battery and the flight control board are the electronic speed controllers, commonly referred to as ESCs. You can think of the ESC as firmware on a computer. Software is soft, hardware is hard, and firmware is right in the middle, allowing the two to talk to each other. ESCs actually do run the quadcopter's firmware. Speed controllers give commands to the motors, telling them when to spin, how fast to spin (distributing power), and then sending the output signal of the motors back to the flight control board. Now, you can't just grab any ESC, hook it up to your motor and expect it to work. You have to choose and ESC that has the correct amperage that corresponds to your motor. Just in case you didn't know, motors with a higher amperage will draws more power, or amps. So, for example, if you choose a 20A (Amp) motor and a 15A ESC, the ESC won't have the capability to drive the motor. On the flip side, if you choose and ESC that has a higher amperage than your motor, then the ESC might send too much power to your motor, resulting in fried motors. This was my mistake with my first drone. The heart of a drone, the battery, is a very important component. You want the battery to be light, so the aircraft doesn't have to work as hard, but you also want to fly for as long as possible. This is similar to the problem with having a higher powered engine in a car but getting really bad gas mileage, or having a Smart Car engine that is very weak, but gets good gas mileage. I looked on Hobbyking at the weights of the battery packs and I just chose the pack from the most trustworthy manufacturer that was the lightest. The reason I did this was because I didn't really know the measurement for the capacity of the batteries and how to value the capacity of a battery. Lets start with the unit for battery capacity, the milliamp per hour or mAH. You might have seen this unit used to show the capacity of a smartphone or laptop battery. The iPhone 6s has a battery around 2,000mAH, just for reference. My first drone had a 1,400mAh battery. In my mind, I reasoned that if an iPhone can barely last a day on a single charge, my drone should last about 20 minutes if I don't go too high. This is the worst way to calculate what type of battery you need. You need to factor in the of the kv of your motors and also the weight of your drone. As I said earlier, racing quads don't last too long. This is because they need a light battery for agility, but have high kv motors. I got around 5-6 minutes with my first quad, a little bit short even for a racing quad. Another thing to keep in mind when deciding on a battery is the discharge rate. Discharge rate can be symbolized by the letter c. So for example, a person might say that they have a 25-35C 2,200mAH battery. This means that their battery discharges 25-35 times its total capacity. In this case, the 2,200mAH battery could discharge between 55 and 77 amps. The reasoning behind this calculation is quite simple. 1000mAh = 1 Amp. This means that 2,200mAh = 2.2 Amps. Since the "c" rating means whatever the c rating is multiplied by a battery's capacity, it's 25*2.2, which equals 55 amps, and 35*2.2, which equals 77 amps. Keep in mind that 55 or a maximum of 77 amps is distributed across four or however many motors you have in your drone. If you divide 77 by 4, you get 19.25 amps and below per motor in the case of a quadcopter. So if you think that you can just say, "let me round the 19.25 to 20 amps, you're wrong. You don't want a battery to work full time all the time to drive your motors at the lowest required amperage. If you had a battery with these exact specifications (which I do), I would recommend getting 15 amp ESCs (which I have). If you thought that this whole calculus lecture was difficult, most parts on Hobbyking actually provide a recommended parts list. You shouldn't start with deciding on the motors first, because as you've seen, the motors are dependent on the ESCs, which are dependent on the battery. Start with the battery, calculate the amperage of the ESCs or look at the recommended list of components, then choose your ESCs based on this information, and then finally choose your motors based on what ESC you have chosen (the motor and the ESC should have the same amperage). The last necessary component for an electronic flying machine is some sort of controller, or the brain behind the whole operation. Flight controllers are one of the easiest parts to pick in a drone build. The reason why is because manufacturers have really perfected their flight controllers and separated them into three categories. At the bottom, you have the least advanced controllers, but they get the job done and are well suited for beginners. The next level up, you have the flight controllers for the consumers who have a sizeable budget and are usually not beginner pilots. The flight controllers in this level cater to people who want to add many accessories. At the very top, you have the Rolls-Royce style of flight controllers that include all the features and functions that anyone could want. One of the new features of these top-tier controllers is autonomous flight. Companies like DJI and 3DR, who are both non D.I.Y drone manufacturers, have actually developed flight controllers that are widely available to anyone wanting to spend a pretty penny. One of the best regarded flight controllers for beginners and for all is the Hobbyking manufactured KK2.1 board. There are many setup and tutorials online for this flight controller, and it is not only affordable, under $20, but is very reliable and easy to use. There are other entry level options, such as the Naze board, but the KK2.1 board is by far the flight controller I recommend. I actually have this controller in my quad right now, and it was the one thing I got right in my first quad. The KK2.1 is powered by 5 volts supplied from one of the ESCs that plug into the board (I will have another post dedicated to actually building the quad). It has an auto level feature that is very helpful for first time flyers or anybody who wants a stable drone. The board isn't like an iPhone either. It's completely customizable through the on-screen interface. The flight controller, ESCs, motors, and battery are all part of the necessary components to keep your drone from sitting in your room as a side project for a year. My next post will discuss the frame and transmitter + receiver you should use for your drone if you are a beginner. I understand that there might be more advanced topics that I haven't talked about, but like I said in my first blog post, I am committed to making D.I.Y drones easy to build and understand. All the info that comes off my keyboard is specifically intended for beginners, and beginners only.
Monday, August 1, 2016
Choosing a Battery, ESCs, Motors, and Flight Controller
Today marks the second day of this blog, where I will be making D.I.Y drones seem like cooking microwave mac n' cheese. The first post was more of a background story and end goal of this blog, but today, I will dive right into the fine details of how I successfully built my own drone. If you've read the first post, I mentioned that the first drone I tried to build was a massive failure. The reason being was that I had motors with too high of a kv or kilo voltage. The kv of a motor is an essential part of building anything with a motor. In simple terms, KV show how fast a motor spins. A motor that has a higher kv will spin fast, but it will require more power than a motor with a low kv. You might be wondering how a motor with a low kv generates lift. The solution is larger propellers. These larger propellers have a larger surface area than smaller ones and thus generate more downward force or lift. The average quadcopter, such as the DJI Phantom, has motors that are 920kv. These motors are the sweet spot in the ratio of power draw to speed. Motors in the 800kv-1200kv range are mainly used for drones that want stable and efficient flight, ideal for shooting cinematic video. My first drone had 2300kv motors. These motors spun very fast, but had tiny props. High kv motors are primarily used for drone racing. The reason is that they don't necessarily have to last very long, but racing drones have to be able to make quick, sharp, and agile movements, things that your first quad shouldn't do. I thought that you would be able to hook the motors up to the flight control board directly. But sadly no, it's not that simple. Linking the motors to the battery and the flight control board are the electronic speed controllers, commonly referred to as ESCs. You can think of the ESC as firmware on a computer. Software is soft, hardware is hard, and firmware is right in the middle, allowing the two to talk to each other. ESCs actually do run the quadcopter's firmware. Speed controllers give commands to the motors, telling them when to spin, how fast to spin (distributing power), and then sending the output signal of the motors back to the flight control board. Now, you can't just grab any ESC, hook it up to your motor and expect it to work. You have to choose and ESC that has the correct amperage that corresponds to your motor. Just in case you didn't know, motors with a higher amperage will draws more power, or amps. So, for example, if you choose a 20A (Amp) motor and a 15A ESC, the ESC won't have the capability to drive the motor. On the flip side, if you choose and ESC that has a higher amperage than your motor, then the ESC might send too much power to your motor, resulting in fried motors. This was my mistake with my first drone. The heart of a drone, the battery, is a very important component. You want the battery to be light, so the aircraft doesn't have to work as hard, but you also want to fly for as long as possible. This is similar to the problem with having a higher powered engine in a car but getting really bad gas mileage, or having a Smart Car engine that is very weak, but gets good gas mileage. I looked on Hobbyking at the weights of the battery packs and I just chose the pack from the most trustworthy manufacturer that was the lightest. The reason I did this was because I didn't really know the measurement for the capacity of the batteries and how to value the capacity of a battery. Lets start with the unit for battery capacity, the milliamp per hour or mAH. You might have seen this unit used to show the capacity of a smartphone or laptop battery. The iPhone 6s has a battery around 2,000mAH, just for reference. My first drone had a 1,400mAh battery. In my mind, I reasoned that if an iPhone can barely last a day on a single charge, my drone should last about 20 minutes if I don't go too high. This is the worst way to calculate what type of battery you need. You need to factor in the of the kv of your motors and also the weight of your drone. As I said earlier, racing quads don't last too long. This is because they need a light battery for agility, but have high kv motors. I got around 5-6 minutes with my first quad, a little bit short even for a racing quad. Another thing to keep in mind when deciding on a battery is the discharge rate. Discharge rate can be symbolized by the letter c. So for example, a person might say that they have a 25-35C 2,200mAH battery. This means that their battery discharges 25-35 times its total capacity. In this case, the 2,200mAH battery could discharge between 55 and 77 amps. The reasoning behind this calculation is quite simple. 1000mAh = 1 Amp. This means that 2,200mAh = 2.2 Amps. Since the "c" rating means whatever the c rating is multiplied by a battery's capacity, it's 25*2.2, which equals 55 amps, and 35*2.2, which equals 77 amps. Keep in mind that 55 or a maximum of 77 amps is distributed across four or however many motors you have in your drone. If you divide 77 by 4, you get 19.25 amps and below per motor in the case of a quadcopter. So if you think that you can just say, "let me round the 19.25 to 20 amps, you're wrong. You don't want a battery to work full time all the time to drive your motors at the lowest required amperage. If you had a battery with these exact specifications (which I do), I would recommend getting 15 amp ESCs (which I have). If you thought that this whole calculus lecture was difficult, most parts on Hobbyking actually provide a recommended parts list. You shouldn't start with deciding on the motors first, because as you've seen, the motors are dependent on the ESCs, which are dependent on the battery. Start with the battery, calculate the amperage of the ESCs or look at the recommended list of components, then choose your ESCs based on this information, and then finally choose your motors based on what ESC you have chosen (the motor and the ESC should have the same amperage). The last necessary component for an electronic flying machine is some sort of controller, or the brain behind the whole operation. Flight controllers are one of the easiest parts to pick in a drone build. The reason why is because manufacturers have really perfected their flight controllers and separated them into three categories. At the bottom, you have the least advanced controllers, but they get the job done and are well suited for beginners. The next level up, you have the flight controllers for the consumers who have a sizeable budget and are usually not beginner pilots. The flight controllers in this level cater to people who want to add many accessories. At the very top, you have the Rolls-Royce style of flight controllers that include all the features and functions that anyone could want. One of the new features of these top-tier controllers is autonomous flight. Companies like DJI and 3DR, who are both non D.I.Y drone manufacturers, have actually developed flight controllers that are widely available to anyone wanting to spend a pretty penny. One of the best regarded flight controllers for beginners and for all is the Hobbyking manufactured KK2.1 board. There are many setup and tutorials online for this flight controller, and it is not only affordable, under $20, but is very reliable and easy to use. There are other entry level options, such as the Naze board, but the KK2.1 board is by far the flight controller I recommend. I actually have this controller in my quad right now, and it was the one thing I got right in my first quad. The KK2.1 is powered by 5 volts supplied from one of the ESCs that plug into the board (I will have another post dedicated to actually building the quad). It has an auto level feature that is very helpful for first time flyers or anybody who wants a stable drone. The board isn't like an iPhone either. It's completely customizable through the on-screen interface. The flight controller, ESCs, motors, and battery are all part of the necessary components to keep your drone from sitting in your room as a side project for a year. My next post will discuss the frame and transmitter + receiver you should use for your drone if you are a beginner. I understand that there might be more advanced topics that I haven't talked about, but like I said in my first blog post, I am committed to making D.I.Y drones easy to build and understand. All the info that comes off my keyboard is specifically intended for beginners, and beginners only.
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