Bring on the drones

-June 02, 2014

The holidays always bring out the kid in me – which gives me good reason to buy a toy for myself. Sometimes I rationalize it and tell the family it is for all of us. In the latest example, I bought a quad-copter with integrated HD camera. I would have written about it earlier but I really wanted to get more flight time. And the weather and my travel schedule just interfered too much. However, I finally accumulated 25+ hours of flight time over the last 5 months.


The particular model I purchased is a DJI Phantom 2 Vision. It has an amazing number of sensors to help make flying simple. Beyond the 14 megapixel camera, there is a GPS, compass, barometric sensor, and inertial sensor. I was surprised at how easy it is to fly. As a comparison, I have crashed several RC planes and a few cars – but I have not crashed this unit “yet.”

The device uses three different batteries. The main battery is a 5200 mAH Lithium-polymer battery. This is rated for 25 minutes of flying time. In one test where it just hovered, the battery warning went off after about 22 minutes. The alarm sounds from the Wi-Fi® connected device and sounds like the dive sound from a submarine movie. The alarm is supposed to indicate that there is 30% battery remaining. Actually 25 minutes is a long time, if you are watching the device fly around with head turned to the sky. In my experience the recharge time for this battery is about 2 hours, which also is a long time.


One of the other batteries is integrated into the Wi-Fi range extender and is rechargeable through a micro USB connector. This also seems to take several hours to recharge, again a long time.


The last battery type is 4 AA located in the flight controller. These batteries seem to last a long time, more than 10 hours. In actuality there is yet another battery. It’s the one in the smartphone or tablet that is communicating with the quad-copter and is used to show real-time video from the onboard camera. I used a tablet for my connected device. The biggest issue is screen visibility on a sunny day. A sun shade helped, but moving your eyes from sky to screen and back was not a treat for my eyes.


So my flying experience has been interesting. I have lost sight of the quad-copter more than once. This is a problem when flying on a cloudy day and the device seems to integrate into the cloud pattern. Fortunately the device learns where it took off from and will try to get back to this position, if it loses communication.


Another interesting observation is that cows and buzzards are not afraid of the quad-copter. I flew it over some cows and they did not seem to notice it, even though it is not that quiet. It sounds a little like a weed trimmer. I also flew it up to some circling buzzards and they seem to just ignore it. Maybe they were more focused on something on the ground.


To determine flight time versus battery capacity, I needed to do more research. Table 1 shows four different models and the associated battery capacity. There are a couple figures of merit (FOM). One is simply the battery capacity per flight time. The second is weight times the flight time divided by the battery capacity.


Both FOMs include the energy used for thrust as well as operating the electronics, so they should not be considered a rigorous analysis. FOM 1 indicates the number of mAH used per minute of flight. It is no surprise that the lightest quad-copter uses the least mAH per minute. FOM 2 relates the payload minutes per mAH. In this case the DJI may produce the most thrust minutes per mAH, or maybe it has a more efficient use of energy for the electronics.



Table 1. Quad-copter comparisons between drone models.


There are concerns about the use of these devices by the general public. Some are the dangers that they present to other aircraft, or damage incurred if they crash into other objects. There are also bigger privacy concerns given the onboard camera. Last October was the first conference held that covered broad topics of drones: Drones & Aerial Robotics Conference.1 The conference was held at NYU. This conference included leaders from companies that made some of the quad-copters in Table 1. Outside the technical challenges in making low-cost aerial robotics the conference also covered legal, regulation, privacy and surveillance issues.


Whether it is a quad-copter, drone, or aerial robot, these devices are quite an opportunity to manage energy. Everything from motor control to Wi-Fi needs to be managed so that flight time can be optimized. There is also a need to improve the recharge time of the onboard batteries.


Let me know what you think of these devices and the challenges you see. I do not think our neighborhoods will be saturated by aerial robots anytime soon, but it is a fun recreational device. I told my wife that I could use it for roof inspection after a hail storm, or an inspection of the work done on our roof. She seemed to think that this would help offset the cost of my new toy. If I could come up with a way to use it to keep the rabbits out of my backyard, then I could probably buy a few more.

Editor’s note: Image courtesy of DJI


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