How-To Tutorials - IoT and Hardware

In this article by Ty Audronis, the author of Building Multicopter Video Drone, the process and thought process required to choose a few of the components required to build your multicopter will be discussed. (For more resources related to this topic, see here.) Let's dive into the process of choosing components for your multicopter. There are a ton of choices, permutations, and combinations available. In fact, there are so many choices out there that it's highly unlikely that two do it yourself (DIY) multicopters are configured alike. It's very important to note before we start this article that this is just one example. This is only an example of the thought process involved. This configuration may not be right for your particular needs, but the thought process applies to any multicopter you may build. With all these disclaimers in mind … let's get started! What kind of drone should I build? It sounds obvious, but believe it or not, a lot of people venture into a project like this with one thing in mind: "big!". This is completely the wrong approach to building a multicopter. Big is expensive, big is also less stable, and moreover, when something goes wrong, big causes more damage and is harder to repair. Ask yourself what your purpose is. Is it for photography? Videography? Fun and hobby interest? What will it carry? How many rotors should it have? There are many configurations, but three of these rotor counts are the most common: four, six, and eight (quad, hexa, and octo-copters). The knee-jerk response of most people is again "big". It's about balancing stability and battery life. Although eight rotors do offer more stability, it also decreases flight time because it increases the strain on batteries. In fact, the number of rotors in relation to flight time is exponential and not linear. Having a big platform is completely useless if the batteries only last two or three minutes. Redundancy versus stability Once you get into hexacopter and octocopters, there are two basic configurations of the rotors: redundant and independent. In an independent (or flat) configuration, the rotors are arranged in a circular pattern, equidistant from the center of the platform with each rotor (as you go around) turning in an opposite direction from the one before it. These look a lot like a pie with many slices. In a redundant configuration, the number of spars (poles from the center of the platform) is cut in half, and each has a rotor on the top as well as underneath. Usually, all the rotors on the top spin in one direction, and all rotors at the bottom spin in the opposite direction. The following image shows a redundant hexacopter (left) and an independent hexacopter (right): The advantage of redundancy is apparent. If a rotor should break or fail, the motor underneath it can spin up to keep the craft in the air. However, with less points of lift, stress on the airframe is greater, and stability is not quite as good. If you use the right guidance system, a flat configuration can overcome a failed rotor as well. For this reason (and for battery efficiency), we're going with a flat-six (independent hexacopter) configuration over the redundant, or octocopter configurations. The calculations you'll need There is an exorbitant amount of math involved in calculating just how you're going to make your multicopter fly. An entire book can be written on these calculations alone. However, the work has been done for you! There is a calculator available online at eCalc (http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en) to calculate how well your multicopter will function and for how long, based on the components you choose. The following screenshot shows the eCalc interface: Choosing your airframe Although we've decided to go with a flat-six airframe, the exact airframe is yet to be decided. The materials, brand, and price can vary incredibly. Let's take a quick look at some specifications you should consider. Carbon fiber versus aluminum Carbon fiber looks cool, sounds even cooler, but what is it? It's exactly what it sounds like. It's basically a woven fabric of carbon strands encased in an epoxy resin. It's extremely easy to form, very strong, and very light. Carbon fiber is the material they make super cars, racing motorcycles, and yes, aircraft from. However, it's very expensive and can be brittle if it's compromised. It can also be welded using nothing more than a superglue-like substance known as C.A. glue (cyanoacrylate or Superglue). Aluminum is also light and strong. However, it's bendable and more flexible. It's less expensive, readily available, and can make an effective airframe. It is also used in cars, racing motorcycles, and aircraft. It cannot be welded easily and requires very special equipment to form it and machine it. Also, aluminum can be easier to drill, while drilling carbon fiber can cause cracks and compromise the strength of the airframe. What we care about in a DIY multicopter is strength, weight, and yes … expense. There is nothing wrong with carbon fiber (in fact, in many ways, it is superior to aluminum), but we're going with an aluminum frame as our starting point. We'll need a fairly large frame (to keep the large rotors, which we'll probably need, from hitting each other while rotating). What we really want to look at is all the stress points on the airframe. If you really think about it, the motor mounts, and where each arm attaches to the hub of the airframe are the areas we need to examine carefully. A metal plate is a must for the motor mounts. If a carbon fiber motor mount is used, a metal backplate is a must. Many a multicopter has been lost because of screws popping right through the motor mounts. The following image shows a motor mount (left) where just such a thing happened. The fix (right) is to use a backplate when encountering carbon fiber motor mounts. This distributes the stress to the whole plate (rather than a small point the size of a screwhead). Washers are usually not enough. Similarly, because we've decided to use an airframe with long arms, leverage must be taken into account on the points where the arms attach to the hub. It's very important to have a sturdy hub that cradles the spars in a way that distributes the stress as much as possible. If a spar is merely sandwiched between two plates with a couple of bolts holding it … that may not be enough to hold the spars firmly. The following image shows a properly cradled spar: In the preceding image, you'll notice that the spars are cradled so that stress in any direction is distributed across a lot of surface area. Furthermore, you'll notice 45 degree angles in the cradles. As the cradle is tightened down, it cinches the aluminum spar and deforms it along these angles. This also prevents the spars from rolling. Between this cradling and the aluminum motor mounts (predrilled for many motor types), we're going to use the Turnigy H.A.L. (Heavy Aerial Lift) hexacopter frame. It carries a 775 mm motor span (plenty of room for up to 14-inch rotors) and has a protective cover for our electronics. Best of all, this frame retails for under 70 USD at http://www.hobbyking.com/hobbyking/store/uh_viewitem. asp?idproduct=25698&aff=492101. Now that we've chosen our airframe, we know it weighs 983 grams (based on the specifications mentioned on the previous link). Let's plug this information into our calculator (refer to the following screenshot). You can see that we've set our copter to 6 rotors, our weight to 983 grams, and specified that this weight is a without Drive system (not including our motors, props, ESCs, or batteries). You can leave all of the other entries alone. These specify the environment you'd be flying in. Air density can affect the efficiency of your rotors, and temperature can affect your motors. These default settings are at your typical temperature and elevation. Unless you're flying in the desert, high elevations, or in the cold, you can leave these alone. We're after what your typical performance will be. Choosing your propellers Let's skip down to the propellers. These will usually dictate what motors you choose, and the motors dictate the ESCs, and the ESCs and motors combined will determine your battery. So, let's take a look at the drive system in that order. This is another huge point of stress. If you consider it, every bit of weight is supported by the props in the air. So, here it's very important to have strong props that cut the air well, with as little flex as possible, and are very light. Flex can produce bounce, which can actually produce harmonic vibration between the guidance system and the flexing of the props (sending your drone into uncontrolled tumbles). Does one of the materials that we've already discussed sound strong, light, and very stiff? If you're thinking carbon fiber, you're right on the money. We're going to have a lot of weight here, so we'll go with pretty large props because they'll move a whole lot more air and carbon fiber because they're strong. The larger the props, the stronger they need to be, and consequently the more powerful the motor, ESC, and battery. Before we start shopping around for parts, let's plug in stats and see what we come up with. When we look at props, there are two stats we need to look at. These are diameter and pitch. The diameter is simple enough. It's just how big the props are. The pitch is another story. The pitch is how much of pitch the blade has. The tips of a propeller are more flat in relation to the rotation. In other words, they twist. Your typical blade would have something more like a 4.7-inch pitch at 10 inches. Why? Believe it or not, these motors encounter a ton of resistance. The resistance comes from the wind, and a fully-pitched blade may sound nice, but believe it or not, propulsion is really more of a game of efficiency than raw power. It's all about the balance. There's no doubt that we'll have to adjust our power system later, so for now let's start big. We'll go with a 14-inch propeller (because it's the biggest that can possibly fit on that frame without the props touching), with a typical (for that size) 8-inch pitch. The following screenshot shows these entries in our calculator: You can see we've entered 14 for Diameter and 8 for Pitch. Our propellers will be typical two-blade props. Three- and four-blade props can provide more lift, but also have more resistance and consequently will kill our batteries faster. The PConst (or power constraint) indicates how much power is absorbed by the props. The value of 1.3 is a typical value. Each brand and size of prop may be slightly different, and unless the specific prop you choose has those statistics available … leave this alone. A value of 1.0 is a perfectly efficient propeller. This is an unattainable value. The gear ratio is 1:1 because we're using a prop directly attached to a motor. If we were using a gear box, we'd change this value accordingly. Don't hit calculate yet. We don't have enough fields filled out. It should be said that most likely these propellers will be too large. We'll probably have to go down to a 12- or even 11-inch propeller (or change our pitch) for maximum efficiency. However … this is a good place to start. Summary In this article, we discussed what are the points to keep in mind when planning to build a multicopter, such as the type of multicopter, number of rotors, and various parameters to consider when choosing the airframe and propellers. Resources for Article:   Further resources on this subject: 3D Websites [article] Managing Adobe Connect Meeting Room [article] Getting Started with Adobe Premiere Pro CS6 Hotshot [article]

(For more resources related to this topic, see here.) The following is an image of a finished project: Even though you've made your robot mobile by adding wheels or tracks, this mobile platform will only work well on smooth, flat surfaces. Often, you'll want your robot to work in environments where the path is not smooth or flat; perhaps you'll even want your robot to go up stairs or around curbs. In this article, you'll learn how to attach your board, both mechanically and electrically, to a platform with legs so that your projects can be mobile in many more environments. Robots that can walk! What could be more amazing than that? In this article, we will cover the following topics: Connecting Raspberry Pi to a two-legged mobile platform using a servo motor controller Creating a program in Linux so that you can control the movement of the two-legged mobile platform Making your robot truly mobile by adding voice control Gathering the hardware In this article, you'll need to add a legged platform to make your project mobile. For a legged robot, there are a lot of choices for hardware. Some are completely assembled, others require some assembly, and you may even choose to buy the components and construct your own custom mobile platform. Also I'm going to assume that you don't want to do any soldering or mechanical machining yourself, so let's look at several choices of hardware that are available completely assembled or can be assembled using simple tools (a screwdriver and/or pliers). One of the simplest legged mobile platforms is one that has two legs and four servo motors. The following is an image of this type of platform: We'll use this legged mobile platform in this article because it is the simplest to program and the least expensive, requiring only four servos. To construct this platform, you must purchase the parts and then assemble them yourself. Find the instructions and parts list at http://www.lynxmotion.com/images/html/build112.htm. Another easy way to get all the mechanical parts (except servos) is by purchasing a biped robot kit with six DOF (degrees of freedom). This will contain the parts needed to construct your four-servo biped. These six DOF bipeds can be purchased on eBay or at http://www.robotshop.com/2-wheeled-development-platforms-1.html. You'll also need to purchase the servo motors. Servo motors are designed to move at specific angles based on the control signals that you send. For this type of robot, you can use standard-sized servos. I like the Hitec HS-311 or HS-322 for this robot. They are inexpensive but powerful enough in operations. You can get them on Amazon or eBay. The following is an image of an HS-311 servo: You'll need a mobile power supply for Raspberry Pi. I personally like the 5V cell phone rechargeable batteries that are available at almost any place that supplies cell phones. Choose one that comes with two USB connectors; you can use the second port to power your servo controller. The mobile power supply shown in the following image mounts well on the biped hardware platform: You'll also need a USB cable to connect your battery to Raspberry Pi. You should already have one of those. Now that you have the mechanical parts for your legged mobile platform, you'll need some hardware that will turn the control signals from your Raspberry Pi into voltage levels that can control the servo motors. Servo motors are controlled using a signal called PWM. For a good overview of this type of control, see http://pcbheaven.com/wikipages/How_RC_Servos_Works/ or https://www.ghielectronics.com/docs/18/pwm. You can find tutorials that show you how to control servos directly using Raspberry Pi's GPIO (General Purpose Input/Output) pins, for example, those at http://learn.adafruit.com/adafruit-16-channel-servo-driver-with-raspberry-pi/ and http://www.youtube.com/watch?v=ddlDgUymbxc. For ease of use, I've chosen to purchase a servo controller that can talk over a USB and control the servo motor. These controllers protect my board and make controlling many servos easy. My personal favorite for this application is a simple servo motor controller utilizing a USB from Pololu that can control six servo motors—the Micro Maestro 6-Channel USB Servo Controller (Assembled). The following is an image of the unit: Make sure you order the assembled version. This piece of hardware will turn USB commands into voltage levels that control your servo motors. Pololu makes a number of different versions of this controller, each able to control a certain number of servos. Once you've chosen your legged platform, simply count the number of servos you need to control and choose a controller that can control that many servos. In this article, we will use a two-legged, four-servo robot, so I will illustrate the robot using the six-servo version. Since you are going to connect this controller to Raspberry Pi via USB, you'll also need a USB A to mini-B cable. You'll also need a power cable running from the battery to your servo controller. You'll want to purchase a USB to FTDI cable adapter that has female connectors, for example, the PL2303HX USB to TTL to UART RS232 COM cable available on amazon.com. The TTL to UART RS232 cable isn't particularly important, other than that the cable itself provides individual connectors to each of the four wires in a  USB cable. The following is an image of the cable: Now that you have all the hardware, let's walk through a quick tutorial of how a two-legged system with servos works and then some step-by-step instructions to make your project walk. Connecting Raspberry Pi to the mobile platform using a servo controller Now that you have a legged platform and a servo motor controller, you are ready to make your project walk! Before you begin, you'll need some background on servo motors. Servo motors are somewhat similar to DC motors. However, there is an important difference: while DC motors are generally designed to move in a continuous way, rotating 360 degrees at a given speed, servo motors are generally designed to move at angles within a limited set. In other words, in the DC motor world, you generally want your motors to spin at a continuous rotation speed that you control. In the servo world, you want to control the movement of your motor to a specific position. For more information on how servos work, visit http://www.seattlerobotics.org/guide/servos.html or http://www.societyofrobots.com/actuators_servos.shtml. Connecting the hardware To make your project walk, you first need to connect the servo motor controller to the servos. There are two connections you need to make: the first is to the servo motors and the second is to the battery holder. In this section, you'll connect your servo controller to your PC or Linux machine to check to see whether or not everything is working. The steps for that are as follows: Connect the servos to the controller. The following is an image of your two-legged robot and the four different servo connections: In order to be consistent, let's connect your four servos to the connections marked 0 through 3 on the controller using the following configurations: 0: Left foot 1: Left hip 2: Right foot 3: Right hip The following is an image of the back of the controller; it will show you where to connect your servos: Connect these servos to the servo motor controller as follows: The left foot to the 0 to the top connector, the black cable to the outside (-) The left hip to the 1 connector, the black cable out The right foot to the 2 connector, the black cable out The right hip to the 3 connector, the black cable out See the following image indicating how to connect servos to the controller: Now you need to connect the servo motor controller to your battery. You'll use the USB to FTDI UART cable; plug the red and black cables into the power connector on the servo controller, as shown in the following image: Configuring the software Now you can connect the motor controller to your PC or Linux machine to see whether or not you can talk to it. Once the hardware is connected, you can use some of the software provided by Polulu to control the servos. It is easiest to do this using your personal computer or Linux machine. The steps to do so are as follows: Download the Polulu software from http://www.pololu.com/docs/0J40/3.a and install it based on the instructions on the website. Once it is installed, run the software; you should see the window shown in the following screenshot: You will first need to change the Serial mode configuration in Serial Settings, so select the Serial Settings tab; you should see the window shown in the following screenshot: Make sure that USB Chained is selected; this will allow you to connect to and control the motor controller over the USB. Now go back to the main screen by selecting the Status tab; now you can turn on the four servos. The screen should look as shown in the following screenshot: Now you can use the sliders to control the servos. Enable the four servos and make sure that the servo 0 moves the left foot, 1 the left hip, 2 the right foot, and 3 the right hip. You've checked the motor controllers and the servos and you'll now connect the motor controller to Raspberry Pi to control the servos from there. Remove the USB cable from the PC and connect it to Raspberry Pi. The entire system will look as shown in the following image: Let's now talk to the motor controller by downloading the Linux code from Pololu at http://www.pololu.com/docs/0J40/3.b. Perhaps the best way to do this is by logging on to Raspberry Pi using vncserver and opening a VNC Viewer window on your PC. To do this, log in to your Raspberry Pi using PuTTY and then type vncserver at the prompt to make sure vncserver is running. Then, perform the following steps: On your PC, open the VNC Viewer application, enter your IP address, and then click on Connect. Then, enter the password that you created for the vncserver; you should see the Raspberry Pi viewer screen, which should look as shown in the following screenshot: Open a Firefox browser window and go to http://www.pololu.com/docs/0J40/3.b. Click on the Maestro Servo Controller Linux Software link. You will need to download the file maestro_linux_100507.tar.gz to the Download directory. You can also use wget to get this software by typing wget http://www.pololu.com/file/download/maestro-linux-100507.tar.gz?file_id=0J315 in a terminal window. Go to your Download directory, move it to your home directory by typing mv maestro_linux_100507.tar.gz .. and then you can go back to your home directory. Unpack the file by typing tar –xzfv maestro_linux_011507.tar.gz. This will create a directory called maestro_linux. Go to that directory by typing cd maestro_linux and then type ls. You should see the output as shown in the following screenshot: The document README.txt will give you explicit instructions on how to install the software. Unfortunately, you can't run MaestroControlCenter on your Raspberry Pi. Our version of windowing doesn't support the graphics, but you can control your servos using the UscCmd command-line application. First, type ./UscCmd --list and you should see the following screenshot: The unit sees your servo controller. If you just type ./UscCmd, you can see all the commands you could send to your controller. When you run this command, you can see the result as shown in the following screenshot: Notice that you can send a servo a specific target angle, although if the target angle is not within range, it makes it a bit difficult to know where you are sending your servo. Try typing ./UscCmd --servo 0, 10. The servo will most likely move to its full angle position. Type ./UscCmd – servo 0, 0 and it will stop the servo from trying to move. If you haven't run the Maestro Controller tool and set the Serial Settings setting to USB Chained, your motor controller may not respond.