Since getting my Phantom 2 Vision last year I have enjoyed some great fun learning how to fly it. I was originally dissatisfied with the cameras image quality and hoped to be able to attach a much better camera but found that even a small increase in weight, of about one pound (about 450 grams) of my Nikon 1, it was a bit unstable and had some flight characteristics that were undesirable, at least for carrying around an expensive camera.
I was planning from the start simply to evaluate the Phantom with the idea that the Phantom was simply an entry level point with my sights set on a larger model but I became very hesitant. This was due to there being a lot of chatter that the FAA may outlaw these drones sometime in the near future, thankfully with the recent FAA Notice of Proposed Rule Making this does not seem to be the case. Search for “Drone NPRM” if you wish to read the proposal. Last year the Minnesota Legislature was actually testing the legal waters by floating a knee jerk bill that would have outlawed all RC aircraft. Thankfully there was enough resistance that they tabled the ridiculous piece of legislation, at least for the time being.
So I recently started to re-explore the idea of putting together another more powerful drone. Yes, I would like to get my hands on one of those very pricey ten-grand drones but I can’t see spending a fortune on equipment that cant even handle a Nikon camera. For some unknown reason to me nobody in this hobby seems to have any interest in supporting Nikon products, at least at the consumer end of the spectrum.
So how do I take my Phantom and provide it with the additional power that could carry something like my Nikon D800? Simple, make a new frame that is capable of carrying larger motors with larger propellers. Unfortunately the Phantom uses a proprietary Flight Controller that can only be minimally configured compared to other controllers. The only configuration available is a Quad V and in order to carry a large camera it needed to have a recommended take off weight of somewhere around five to eight pounds (2-4 kg).
Thankfully DJI has a new motor and controller that can provide a quad with exactly that specification, The E800 Tuned Propulsion System consisting of 3510/350kv BLDC motors and the new 620S Electronic Speed Controller (ESC) using 13.5 inch propellers. The same setup used on DJI’s new Inspire 1 quadracopter. The very interesting thing about this new controller is that DJI supposedly (testing will follow) introduced something that I wanted to do with the original Phantom, that is create a motor controller that commutates the BLDC motor sinusoidally rather than using the square or trapezoidal commutation found in most every other RC controller. Sinusoidal commutation should provide much more efficiency and should reduce vibrations considerably. (I’m wondering whether DJI engineers read my suggestions from my previous blog posts)
The E800 Tuned Propulsion system was placed on order, I then needed an airframe, buy a DIY ready made frame or build one myself. The quickest and cheapest route was to simply make one myself. I could have made one from aluminum sheet metal stock or even tubing made from aluminum or even carbon fiber but this would have been much costlier that a ready made frame. I opted to use wood for this prototype since I should have an excess of power and with the new motors weight became much less of a factor. To my surprise my frame (less landing gear) weighs only five ounces more than the plastic DJI Phantom frame. For those of you laughing at my red neck approach of using wooden sticks let me tell you that wood is an ideal material for aircraft, it absorbs vibrations a hell of a lot better than carbon fiber and it can take a hell of a lot more abuse than any carbon fiber airframe. For reasons that will come later I crashed this thing very hard four times on my initial flight testing and it came away unscathed, six plastic props were destroyed, however.
If you are interested in using wood for aircraft structures here is a very good source that can get you started, it is from the FAA publication: FAA-H-8083-31 Aviation Technician Airframe Handbook Vol. One, Chapter six. Note that there are only a few species of wood suitable for use in aircraft structures, Spruce is the preferred species but luckily Home Depot sells furniture grade Poplar 1×2’s so the total cost of the airframe was under $10 US dollars!
Aviation Technician Airframe Handbook
I simply created my X-frame with a glued-and-screwed half-lap joint with 1/8 inch balsa wood gussets glued to the center providing some additional strength and platforms to mount the hardware and electronics. To mount the GPS and its antennae I created a platform up on a wooden dowel rod with a section of unetched circuit board material to provide some shielding from the electrically noisy electronics and motors, the Phantom uses a copper sheet embedded in foam tape to isolate the GPS. I simply used a aluminum sheet stock to mount the Phantom camera. I resurrected the extended landing gear that I built for my Phantom with my roll axis gimbal platform. I also temporarily mounted the magnetic flux sensor way up on top of the wooden dowel until I find the best magnetically quiet place to mount it.
I still had one dilemma, and that was powering this Frankenstein drone. The Phantom is powered with a 3S 11.1V battery and the recommended voltage source for the motors is a 6S 22.2V battery. Since I have no idea if the Phantom main board can handle or regulate the 22.2V 6S battery I powered it from one Phantom battery, I then powered the motors and controllers with an additional Phantom battery wired in series with the first battery. The biggest problem is that the Phantom battery connectors wont lock without being installed in the Phantom frame. Additionally the Phantom main board relies on information supplied by two spring loaded contacts just below the power connectors. I used some Velcro and a chunk of plastic to hold the connectors in place, not ideal but this is only a prototype – after all. The second problem relating to the batteries is that the Phantom will not allow the motors to arm without a genuine Phantom battery with a secure data connection to it, there are NO other choices for powering the Phantom. (I may look into this more closely for a possible future hack.)
One other problem with the Phantom’s “Intelligent” battery is that if there is no current draw it will shut itself off within five minutes, potentially a very serious problem if the battery decides to shut itself off in flight! So far in my initial testing the battery won’t shut itself off as long as the motors are drawing sufficient current. This is something that definitely needs to be addressed.
One last item needed to be dealt with, and that was the LED indication lights used to communicate the Phantom’s flight modes and status. They are located on the Phantom’s ESC, since I couldn’t find a normal Naza USB/LED for sale anywhere I simply de-soldered the motor from one of the Phantom’s ESC and tied the ESC to the dowel rod supporting the GPS with the LED’s facing towards the rear.
After installing the new motors and ESC’s I did some initial testing of the motors, everything seemed to work flawlessly the motors all turned in the right directions and acted properly to elevator, aileron, rudder, and throttle controls. Time to take this beast out and flight test it, I used initial gain settings 50% greater than the Phantom’s default settings.
Initial take off was uneventful, it rose to about two feet off of the ground and hovered in place wondering around fifteen to twenty feet from its take-off point in GPS mode. I gave it some control inputs to bring it back to its take-off point and it started to loose altitude so I gave it some more throttle and all hell broke loose! It took off on its own, I tried to counter the beast and was able to slow it down somewhat but unfortunately it was already loosing altitude fast and heading for some trees so I chopped the motors off. I had to watch the thing pile into the ground. There goes two props just like that. Needless to say I was disappointed, I thought that the Attitude gain setting may have been too high and the basic settings too low due to the wondering in hover mode.
To make this story short I tried several different gain settings and while the characteristics did change noticeably as expected, every time I gave it some more throttle the damn thing would haul ass in some indeterminate direction followed by an uncontrollable crash into terra firrma. After six of eight of the propellers were trashed I was done flying. So I ran the thing on my bench without the props to see if I could isolate the problem which soon became obvious. Every time I started the motors everything seemed just fine, again all of the motors spun up normally and responded correctly to the radio controller inputs, and good grief! Suddenly everything that was wrong became obvious! After applying full throttle and allowing the motors to spin up one of the motors became uncontrollable at full throttle. I could shut the other motors off normally with the radio but the only way to shut off the renegade motor was to kill the battery power. OH WHAT A RELIEF! IT’S NOT MY FAULT!
After doing some basic trouble shooting and swapping ESC’s, motors around and connecting the ESC’s to varying positions on the Inertial Management Unit (IMU) the problem was obviously with the new 620S ESC. Now will Atlanta Hobby, the place where I bought it, replace the ESC and the six broken props? The answer was no, they referred me to DJI, awe crap, from what I have read all over the internet DJI customer service was supposedly nonexistent. In reality I am in the middle of my dealing with DJI and I found the customer service to have been extremely polite and responsive, They requested I send the ESC back to them and they will replace it and the broken props under warranty, will they actually come through? We’ll see since I just sent it back to them today.
To be honest I have been considering some serious issues with DJI and lately have been exploring other avenues and found that there are basically two camps of drone fliers, DJI fans and those that despise DJI. The biggest advantage with DJI is that they have some very good well tested and very reliable, but expensive, platforms that work very well right out of the box. The major problem is that they are basically closed source so tinkering or modifying any DJI product becomes very difficult, if not impossible with any level of success. They also have some disturbing practices, mainly with maintaining absolute control over the use or usability of their products.
I updated my Phantom iPhone app but did not use it for a week and when I did it would not allow me to enter my registration info and locked me out of the program displaying a irritating message that program registration timed out, the only way to get it running was to delete the app and re-download it, and of course register it right away. Luckily, I was home and had the registration info handy, if I had been on the road or away from cell coverage I would have been totally screwed. Additionally I saw a YouTube video review of their new Inspire 1 platform and the reviewer noticed that his drone would not arm until he updated his firmware. So DJI maintains the capability to disable their products at will! Another area is in flashing their products, it must be done with an internet connection and with only the firmware update that they choose, the last update does not appear to be retained on the local computer, again if there is no active internet connection you are screwed!
Additionally I found that when scanning my Windoze partition from my dual boot macbook using ClamXav anti-virus program it flagged and quarantined all of the DJI software on the Windoze partition as spyware. I’m not sure if it was a false warning, but you have to wonder…
Alas, I’m actually seriously looking at some open source alternatives that are very popular and well supported, like the PixHawk flight controller, which is much much more tunable and is at least as reliable and robust as any of DJI’s product line. A lot depends on my customer service outcome with DJI. DJI does have one advantage with their very expensive A2 controller in that it can make a hex or an octo-rotor easily controllable with a motor failure. But with the open source PixHawk writing control algorithms are easily possible, if an accurate state space model can be successfully created for it, sounds like a challenge to me;-)
So I’m stuck waiting for another ESC, I will report back if I find that my Frankendrone becomes a reliable flier.