Under The Hood – DJI Phantom 4 – Part 1
The DJI Phantom 4 is one of the most advanced consumer drones to hit the market to date. DJI has been a leader in this technology for close to 10 years. They continue to push the boundaries of innovation. One of the most talked about innovations of the P4 is the inclusion of optical sensors. Using a separate VPU (Vision Processing Unit) along with computer vision software, sense and avoid capabilities are now a reality. In this series I’ll dissect the P4 piece by piece and give an in depth analysis of the various systems.
First a disclaimer. If you chose to disassemble your drone you do so on you own will. You will be voiding the manufacturer’s warranty. You also realize your drone may never fly the same again. But if you do find a defect (cold solder joint), you probably just saved your drone. I only do this because I’m an Engineer and I’m curious. I have accepted these risks and only do this to educate others who want to know how things work. I recommend working on a ESD surface and be careful what you touch. You do not want to introduce a latent ESD event. There are many ribbon cables that can easily be torn. Many small screws to track. Be organized, take lots of pictures, and you should be okay. Now, let’s see what is “Under The Hood”.
When doing such projects, I like to use my 54 bit driver kit by iFixit. It comes with a wide range of bits: pentalobe, flathead, phillips, JIS, torx, torx security, and hex. Pretty much every fastener you will encounter, iFitit has a bit for. This is very important as you don’t want to strip any of the fastener heads. The right tool always makes the job easier.
The hardest part of the whole disassembly was the removal of the top and bottom housings. It took me hours to get these apart. DJI obviously does not want you to get these apart. This is not a DIY modularized system where you are able to easily upgrade components. When doing this be mindful of trying to force things apart. If it’s not coming apart easily, it’s probably not meant to be. If it has a fastener, then it comes apart. If something is glued or welded I do not proceed any further.
Removing the top and bottom housings
1. We begin by removing the (4) 2mm hex screws from each arm. These are the screws furthest out on the arms next to the LED covers. These do not contain loctite and just screw into plastic threaded holes. Be careful when reinstalling you don’t strip the holes by over tightening.
2. The landing gear does not need to be removed and can stay in place. If you need to remove the landing gear there is a small plastic access hatch that can be pried off with a flat head screwdriver. Each leg has (2) 1.5mm hex screws. These do have loctite on them. Each leg will have an antenna running down them. Two antenna are for the video and two for the control. In addition the front two legs will each have a compass sensor. None of these are interesting and were not removed.
3. There are (4) more 2mm hex screws that need to be removed from the bottom. These are located on the inside of the landing gear legs. The screws are deeply countersunk and you’ll need a longer allen key to reach these. Like the screws from step #1, these also screw into plastic holes.
After this you may think you can just remove the top cover, and you will try mightily for hours, like I did. But before you break something it’s best to remain calm and collect yourself. There must be some hidden screws, but where? How about underneath those LED covers.
4. Using a flathead screwdriver pry off the LED cover to one of the motors. There you will find a cardboard cover. This has a little adhesive on it, but is easily removed. Underneath you will find (3) 2mm hex screws. You know what to do with these. Take them out. Now repeat this procedure for the other three motors.
5. Now the covers just fall apart. WRONG!!! At this point you just want to take a Dremel tool to it and resolve the situation once and for all. But then you realize at some point you purchased this to actually fly and have fun. Okay now what to do.
6. At this point the only thing left to attack is this cool looking magnesium alloy gimbal cover. This is a new material introduced to the drone by DJI. I will speak more about the material later. Remove the (8) 1.5mm hex screws that secure the gimbal plate to the body.
7. When lifting up the gimbal plate there are two cables attached to the main board. A 4 pin cable and a ribbon cable. Be very very careful with these ribbon cables. They will tear easily and you will be screwed. They are not readily available on Amazon, and good luck trying to fix them yourself. The 4 pin cable is simple to unplug. To remove the ribbon cable requires more disassembly. On top of the ribbon cable is a metal retaining bar. There are (2) phillips head screws holding it. Remove them and then the ribbon cable can be simply slid off. Set aside the gimbal assembly for later.
So, here we are, at our holy grail, and the ark opens!!! But once again you are setting yourself up to be disappointed. They still do not come apart.
8. See those two white tabs on either side of the body? They are part of the bottom half housing. There are (2) phillips head screws, remove them. Now the two halves will pull apart. Do it cautiously as there are some plastic tabs. But it should snap apart without incident.
9. You will need to disconnect a few cables and antennas first to completely separate the housings. Unplug the two compass cables.
The antenna connections can be removed by taking off the retaining bracket.I made note of which antennas were connected to their pads.
Pad 1: white
Pad 2: light gray
Pad 3: dark gray
Pad 4: black
10. Your prize is now unrestricted access to most everything. In Part 2 I will continue the series with more insight into the hardware components.
As you will see the outer gimbal housing and the internal structure as advertised by DJI are made from a magnesium alloy. Most of these alloys consist of 90% magnesium, 9% aluminum, and 1% zinc. This is one of the lightest structural metals in the world. It’s 34% lighter by volume than aluminum and 50% lighter than titanium. It offers excellent fatigue, denting, and buckling resistance. It has a very high damping capacity. It’s twice the hardness of ABS plastics but weighs ⅓ as much. It’s a popular choice for ultra-thin or small size laptop shells and camera bodies. You can see why DJI used this material. It adds structural rigidity and is very light. Join me soon as we continue in Part 2 of the series with an in depth look at the CCAs themselves. What is all this talk of computer vision and how does it work? I will elaborate on that topic as well.