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NICHOLAS VINEN gets to play! Parrot AR Drone 2 QuadCopter This impressive flying beast sports four rotors and two cameras. You can control it with an iPhone, iPad or Android device and capture 720p video of its exploits. It’s quite robust, easy to fly and has multiple control modes to suit different pilot experience levels. T here are plenty of build-ityourself kits out there now for quadcopters – but building your own isn’t for everyone. For those who want to have the fun without doing much work, the AR Drone 2 comes fully pre-assembled and it has many impressive features. Chief among these is the high definition wide-angle video camera with live streaming as well as recording to a USB flash drive. The main part of the drone houses the electronics and battery. Four carbon fibre tubular arms project from this with the rotors, motor drivers and motors at the end of each. You then slip one of the two expanded polypropylene “hulls” over the body, which protects it from damage in the event of a minor accident or collision. The “outdoor hull” only covers the electronics and battery, leaving the rotors exposed. This gives the best flying performance because it’s quite light. It 24  Silicon Chip also means that if you fly too low, you might end up mowing the lawn! The “indoor hull” is larger and surrounds the rotors entirely as well as providing more protection to the main body. This reduces the chance of major damage in the event you strike a wall or some furniture. We found the AR Drone 2 to be pretty robust, especially with the indoor hull in place. With it, it can shrug off minor impacts with obstacles; if you don’t hit them too hard, you can continue flying, often without any damage. This is of course great for beginners, who will probably have a few mishaps before they get the hang of controlling the Drone. It also has an an automatic motor cutout if the unit experiences an impact, tilts past a certain angle or detects the rotors hitting an object. The unit will normally survive the resulting fall without any serious damage as long as it isn’t too high and/or the ground below it is reasonably soft (eg, grass). We had this feature activate a few times with our demo unit and each time, it was still perfectly flight-worthy. This is thanks to its sturdy construction and energy-absorbing arm mounts; one arm usually takes the brunt of any impact. The hull, being made of a foam material, is the most likely part to break but if does split, it can simply be glued back together. They even give you some double-sided tape in the box for field repairs, should they be necessary. Stability and control The AR Drone 2 is self-stabilising. When you press the take-off button, it rises straight up from the ground to a height of about one metre and hovers in place until you are ready to take control. At any point, if you take your hands off the controls, it returns to a stable hover – this is great for beginners since if you lose control this is an easy way to recover. And if it’s being blown away siliconchip.com.au Here’s the more “decorative” version of the Parrot intended for outdoors flying where there’s less risk of damage to walls, furniture, etc. It also has better performance than the “indoor” version with its polypropylene “hull”. The colourful carapace also has an important outdoor benefit: it allows you to work out the PRA’s orientation at a distance. by wind or something like that, you can just press the “land” button and it will gracefully settle down onto the ground. If it flies out of range, it will hover and wait for you to get closer. The stated range is 50m in an open space but we were able to control the demo unit out to a range of about 100m. If the Drone’s battery runs out during flight, it lands itself but you get a warning beforehand so you can fly it to a safe location for landing. If you’re controlling it with a phone and somebody calls you, it will either hover or land, depending on whether you’ve set it to indoor or outdoor mode. There is a LED in each corner of the Drone, underneath the rotors. In flight, the two at the front turn green while the others are red, so you can see which way it is facing. Sometimes they can be obscured by other parts of the Drone and so it isn’t always clear which way the Drone is facing just by looking at it. If we owned one of these, we would think about fitting a bright blue LED under the camera to give a clear indication of which way it’s facing or perhaps paint the front a bright colour. With the outdoor hull in place, the front is a bit more obvious since it looks significantly less symmetrical than the indoor hull. siliconchip.com.au Performance We found the AR Drone 2 to be fairly agile. It certainly can spin fast and it can move in any direction parallel to the ground at up to about 18km/h. Its speed and manoeuvrability are impressive but having said that, we have seen some home-built quadcopters which are significantly more agile; this is mainly due to the fact that the AR Drone 2 uses surprisingly small 14.5W brushless motors while home-built drones tend to use more powerful units. Beginners and recreational flyers should be satisfied with the performance. People who really enjoy flying the AR Drone 2 may then decide to build their own and use larger motors, to get real acrobatic performance. Absolute and relative modes You have two main choices of control mode, called “relative” and “absolute”. Absolute control is rather clever and it’s what we prefer to use if you are flying the drone by looking at it, which is easier when flying indoors. In fact this is by far the easiest mode for beginners. When you enable absolute mode, the software takes advantage of a magnetometer (ie, 3-axis compass) in both the AR Drone 2 and your phone/tablet to work our how they are orientated relative to each other. Then if you tip the phone/tablet to your left (or in joypad mode, move your left-hand thumb to the left), the drone will move to your left, regardless of which way the drone itself is facing. In this mode, you don’t need to yaw the Drone at all, except if you want to aim the forward-facing camera in a particular direction. By comparison, in relative mode, the controls act depending on the direction the Drone is facing. This is the mode you need to control the Drone if you are looking at the camera feed, since your are then looking at whatever the Drone is facing. You can also use this mode without using the camera but this takes more concentration than absolute mode. If you’re going to be flying the drone out of direct line-of-sight then you will need to fly using the camera and hence will be using relative mode. Note that the camera update rate depends somewhat on the speed of the processor in your control device; we found it much easier to fly using the camera on a fast Android tablet than we did with an iPhone, where the video update rate was rather sluggish. Controls Once you have chosen absolute or August 2012  25 The Parrot can be controlled via an iPhone (as here), iPad or Android phone/ tablet (although we had problems with some Android tablets). Essentially the Parrot becomes a WiFi access point – the pic on screen is what the Parrot sees via its onboard camera! relative mode, you have some additional options. In “joypad” mode, the four main degrees of freedom are controlled with your thumbs placed on either side of the smart-phone or tablet screen, as if it’s a game controller. In this mode, your left thumb controls movement parallel to the ground, ie, moving forward and backward and “slipping” left and right. Your right thumb controls altitude (up/ down) and rotation left and right (ie, yawing). This can be swapped if you are left-handed. In the alternative mode, the right thumb control is identical but forward/ back/left/right movement is controlled by tipping the phone or tablet. The software detects the tipping using its built-in accelerometer. This is probably the easiest mode for beginners. But it’s impractical if you are going to be using the video feed to fly the Drone since you can’t really see the video while you are busy tipping the controller. This combination, where one hand controls altitude and yaw and the other movement in the horizontal plane is similar to what is commonly known as “mode two” for helicopter control. But we tend to prefer “mode one”, where one hand controls yaw and forward/ back movement and the other controls altitude and left/right movement. Unfortunately, the software does not seem to offer the ability to switch between these modes. This is a pity as it would not be difficult to do and many people will prefer mode one, which is commonly used in Australia. Our other main complaint about the controls is that since the control “sticks” are virtual, you don’t get any tactile feedback from them. With real “joystick” type controls, the centring springs let you know how far you have moved the stick from its neutral position without having to look at it. This is not the case when you are simply 26  Silicon Chip pressing your thumbs on the screen of a smart phone and so it’s easy to lose track of the control positions. It’s also quite easy to accidentally move your thumbs outside the control zones, in which case the phone will beep to let you know you’re not longer controlling the drone. This is why we tend to prefer using a proper remote control transmitter for this sort of job but then you would need a separate device to view the video feed from the Drone. When configuring the controls for the AR Drone 2, you can set various parameters which limit the rate at which it moves, turns, how high it will fly and so on. The initial settings are quite low and presumably are intended for beginners, so they won’t crash it too hard if they lose control. However we found it a bit easier to fly the Drone with the limits turned up as it’s then possible to make faster corrections to its flight path. The AR Drone 2 also has a “flip” mode where it does a somersault, which can be used when hovering or during flight. It seems to be primarily useful for showing off! This is activated by double-tapping the left control “stick” but can be disabled to prevent accidental activation if it isn’t being used. An accidental flip at low altitude could cause quite a nasty crash. Technology The electronics behind the AR Drone 2 are impressive. The main controller module is powered by a 1GHz ARM Cortex A8 32-bit processor with an 800MHz video DSP and 128Mbytes of memory. This runs Linux and has a Wi-Fi interface. It is effectively a flying Wi-Fi access point! To control the AR Drone 2, you first have to join its network. It is over this network that both control signals and video are sent. Each rotor is driven by a separate brushless motor which, as mentioned earlier, produces up to 14.5W and is about the size of half of a AA cell. The motors are mounted on PCBs, each with an 8-bit Atmel microcontroller which drives the windings in sequence, controlling speed. These are in turn controlled by the main board over a serial bus. For position and speed feedback, the controller effectively has what is known as a nine degree-of-freedom (“9DOF”) sensor comprising 3-axis MEMS accelerometer, 3-axis MEMS gyroscope and 3-axis magnetometer. This allows it to measure instantaneous acceleration, change in rotation and orientation and it is this information which allows it to automatically hold its position in a hover. The stabilisation system can compensate for wind and other factors although note that it could be overwhelmed by strong wind gusts. The stabilising system also becomes less effective once the drone is more than six metres or so above ground level although we found it was still pretty good. For more information on how the controller is able to stabilise and move the quadcopter through the air, see the accompanying feature article in this issue (page 21). For measuring height, the AR Drone 2 sports both a pair of ultrasonic sensors on the underside as well as a pressure sensor for measuring altitude (with <1m resolution). It can measure its altitude at take-off and compare it to the present altitude to implement its adjustable height limit (“ceiling”). At lower levels, the ultrasonic sensors give it more accurate feedback. The video quality from the main camera is good; the fast DSP allows it to do high-quality video compression in real time, which is necessary in order to get the video over the limited bandwidth of the wireless link. It also has a downward-facing camera (320x240 pixels) which can be used to check whether it’s safe to land the unit if you can’t see what’s immediately below it from your vantage point. A button on the screen switches the view between the two cameras. As well as allowing you to see what’s under the drone, the downward-facing camera is also used to estimate ground speed (in conjunction with the height measurement). This then lets you limit siliconchip.com.au The four motors are tiny – this shot from underneath shows one of the motors (circled) mounted on the arm which also houses the landing “foot”, along with the motor control electronics. You can see the massive gearing down of the motor from the size of the propellor shaft gear versus the just-visible motor shaft gear. the Drone’s horizontal speed. You can similarly limit its maximum angle of tilt (measured with the accelerometer) and rotation speed (via gyros). That’s a lot of different things to adjust. In fact there are several screens full of settings you can play with. Build quality We weren’t just impressed with the electronics in the Drone. Some clever mechanical and material engineering has also gone into the design. The rigid parts are, well, rigid while other parts are designed to have some “give” to reduce vibration and absorb impacts. For example, the battery is suspended on a flexible bed in order to prevent its weight from affecting stability. The motor, arm and rotor assemblies are designed and made with precision. Even the foam hulls are accurately moulded. One common problem with cameraequipped drones is image blurring due to vibration from the motors and rotors. We didn’t see any evidence of this from the AR Drone 2 and according to Parrot, this is due to carefully designed flexible joints between the arms and main body which prevent vibrations from being transmitted to the camera. It seems to work well. Software We found the software easy to install and set-up on an iPhone and we expect it will be just as easy on an iPad. We didn’t run into any problems with the iPhone software; it’s responsive, logical and easy to use. Ideally you would use a tablet since the iPhone screen is a little small to view the video, especially with controls and read-outs partially obscuring it. The iPhone also gave a slow video update rate. The Free Flight software is also siliconchip.com.au available for Android and is virtually identical to the iPhone/iPad application. It requires Android version 2.2 or later as well as a multi-touch screen and accelerometer. We expect most Android devices would meet these requirements but surprisingly, of the four we tried, it would only install on one. The version requirement is a bit of a problem since even some fairly new Android phones are only running on version 2.1; the Publisher has one and it’s only just over a year old. Two others we tried were running version 4.3 and appeared to meet the requirements but the software refused to install, in each case saying the device was not supported. On an Asus Transformer (Android), the software worked quite well with the exception that a couple of times we got stuck in piloting mode and had to “kill” the application to get out of it. It could have been worse; at least if you’re stuck in piloting mode, you retain control of the drone. The video quality and update rate were very good on the Transformer. If you have an Android phone or tablet and are interested in the AR Drone 2, your best strategy is to install the software first and check that it works before you buy the hardware. To do this, just follow the link to the free software from the Parrot website at http:// ardrone.parrot.com/parrot-ar-drone/ Hopefully, the compatibility problems and software glitches will be sorted out with a software update. Oh, and Parrot also provide firmware updates for the Drone itself, should this be necessary. Battery The AR Drone 2 comes with a 3-cell, 1Ah Lithium Polymer battery which is good for about 12 minutes of flight. The software has a battery meter in the corner of the screen so you can keep track of the charge state while flying. This battery clips into a plugpack-style balance charger and it charges reasonably quickly – up to about 90 minutes, but usually less than an hour unless you’ve run it right down. That’s pretty good but if you want to take the Drone out to a park for an extended flying session you will probably want to buy some spare batteries. Parrot insist that you only use their batteries but a little birdie told us that you can use other 3-cell Lithium Ion/ Polymer batteries if you make a suitable adaptor cable. Spare parts Most of the AR Drone parts are available as spares so that you can repair it if you have a prang. Having said that, careful pilots should not need to be replacing parts very often given its overall robustness. Mostly minor impacts just result in some scratches or maybe split the hull; as beginners we had a number of “oops” moments with our demo unit but only did relatively minor damage to the hull. Inevitably most owners will eventually end up breaking something that you can’t fix with tape. When you do, you can get replacements for most of the parts from their website (URL below). They also sell a range of accessories to customise your Drone or play games with it. Conclusion The AR Drone 2 itself is an impressive piece of gear, well-built and cleverly designed with a lot of excellent features. The story with the software is not quite as rosy although if you manage to get it installed, you shouldn’t run into many issues. We hope and expect that the Android application will receive some improvements in the near future. If you’re looking for a well-made pre-built drone that’s fun to fly and with lots of features, the AR Drone 2 is hard to beat. Price & availability The AR Drone 2 retails for $349 and is available for purchase at their website: http://ardrone.parrotshopping. com/au/p=ardrone=main.aspx It is also available from many elecSC tronics and hobby retailers. August 2012  27