• First Battery Com Capture

    Duane Degn • 03/28/2021 at 05:33 • 4 comments

    Based on my experience with the DJI RoboMaster S1's battery, I had assumed the FPV drone also communicated with the battery over I2C. I was wrong about this. The data transfer looks like CAN bus.

    My logic analyzer doesn't read CAN packets so I'll need to figure out a way of reading this data. I thought I'd share this information in case any of you are interested.

    Edit (April 1, 2021): Thanks to Andrew Young who informed me my logic analyzer was capable of decoding CAN. This is the exported text of the CAN data:

    Time [s],Packet,Type,Identifier,Control,Data,CRC,ACK
2.111320843750000,0,DATA,0x554,0xE,0xEF 0xEE 0x93 0xE9 0x7B 0xAE 0x8D 0xBF,,
2.114893812500000,1,DATA,0x138,0xF,,,
2.126467750000000,2,DATA,0x153EFBE9,0xE,0x67 0xFE 0xD6 0x15 0xE9,,
2.310771906250000,3,DATA,0x554,0xE,0xEF 0xEE 0x93 0xE9 0x7B 0xAE 0x8D 0xBF,,
2.314893750000000,4,DATA,0x138,0xF,,,
2.515036843750000,5,DATA,0x138,0xF,,,

  • The Controller Part 3

    Duane Degn • 03/25/2021 at 04:18 • 2 comments

    Here are some photos of the chips inside the controller. As I was cropping the photos I realized they weren't as clear as I had hoped. If anyone more better photos of any of the chips, let me know. I don't promise I'll get better photographs of the chips but a request will make such an event more likely.

    The heart of the controller has two large heatsinks. There's a black one near the back of the controller and bare metal one just behind the top of the controller. Between these heatsinks are two PCB with cans covering portions of the board.  Above you can see the top of the smaller square PCB with the can removed. The can also acts as a heat spreader. It was interesting to see the four similar rectangular chips are cooled from the opposite side of the PCB.

    Below you can see the backside of this PCB with the thermal paste cleaned away from the heatsink area of the PCB. The metal can is shaped to bring the metal in contact with portions of the board and some chips.
    I'm pretty sure the chip in the lower left of the photo above is a Winbond flash chip. Below shows the small square PCB next to the larger "L" shaped PCB. I also removed the lid of the metal can from this PCB. You can see the round speaker/buzzer in the photo below. The black heatsink has a circular cutout to accommodate this speaker.
    Below is a photo of the other side of the "L" shaped PCB. Again the lid of the metal can has been removed to provide a view of the chips inside.
    Below is a photo of the bottom side of the top heatsink and the two main PCBs with the lids back on the metal cans.
    Finally here are a few photos of the controller's enclosure. 
    I hadn't removed the button/gimbal wires which connect to the USB PCB in these last photos.

    While most of the buttons can be removed from the controller, the C1 and power buttons have plastic attachment points which have been melted to hold them captive.

    The two wire harnesses seen in this last photo are sandwiched between the copper tape inside the top of the controller and bare metal heatsink.

    I have plans to examine more of the components which come with this drone in the near future. 

  • The Controller Part 2

    Duane Degn • 03/24/2021 at 02:30 • 3 comments

    As mentioned in an earlier log, the gimbals use Hall Effect sensors. Below shows the magnet with the sensor PCB removed.

    The gimbal in the photo below has one sensor PCB in place and the other sensor PCB removed.

    Besides the two Hall Effect sensors, each gimbal has a small button. This small button is pressed when one of the adjustment screws is all the way in. I think this is so the firmware knows the controller has been configured for manual mode.

    The small button is on a flat flex cable. The cable connects to the USB board. The above photo has arrows pointing to the two connectors which are normally mated when assembled.

    Below is the left gimbal with the flax flex cable show at the bottom of the photo. The small switch is not in view in this photo.

    The small button and white plastic friction liner have been removed from the left joystick in the photo below. The two small buttons are circled.

    Below is a rubber light shroud to isolate the LED on the PDB with the USB connection.

    Below is the neck strap connector with another view of the light shroud.

    Above shows the USB PCB rotated 180 degrees. The charge state LEDs and two buttons are on the other side of the PCB. This PCB has connector to accept the flat flex cables with the small switches.

    Above is the connector for the left gimbal. Below shows the connector to the right gimbal.

    To be continued.

  • The Controller Part 1

    Duane Degn • 03/21/2021 at 20:15 • 2 comments

    I initially thought the controller was going to be really hard to open but I was pleasantly surprised to find four Philips screws at the bottom of holes under the back rubber grips. The red circles in the photo below show the location of these four screws.

    I was able to pry the shell open but starting where the rubber stick holders are sandwiched between the two halves. It wasn't easy to pry the controller open but it wasn't much worse than many game controllers.

    I took about the button and the potentiometer located in the top shell.

    The camera angle control dial has a cool return to center gizmo.

    I took mine apart so you don't have to. It's a bit of a trick to reassemble.  I've seen other return to center pots before but I think this mechanism is more involved than other gadgets I've taken apart.  The yellow shape near the center is a plastic tab which is likely used to make assembly easier and faster. 

    The lower section of the remote has a lot more going on inside.

    There are two 18650 Li-Ion cells inside. These cell each have a thermistor to monitor their temperature. I haven't figured out if the cells are in series or if they're parallel yet. My guess is they're wired in series.

    After removing the batteries, I removed the bottom heatsink. A good portion of the weight of this controller is from the heatsinks. There's a round cutout in the heatsink to allow the buzzer to pass through it.

    Above are the plastic buttons and the two leaf springs used to hold the vertical axes of the joysticks. 
    Above is the flat flex cable with connects the two main boards of the controller. The cable plugs into connectors seen just right of center in the photo below. The battery connection causes this cable to bend away from the PCBs. The bent cable can be seen next to the black heatsink in some of the earlier photos.

    The two main PCBs rest on the black heatsink above. The back of the top heatsink can be seen still in the shell in the photo above. The top heatsink has been removed from the shell in the photo below.

    Above is the PBC which has the USB connection, two buttons, and the power LEDs.Based on the wires, it's pretty clear this controller has two antennas. I was surprised to see the shape of these antenna.


    There's a wide 15mm x 30mm antenna in the base of the antenna and an 8mm x 30mm in the left side of the antenna. The right side of the antenna housing is empty.

    The backside of the unconnected PCBs have two traces. The traces are about 22mm long on both the PCBs but the traces on the narrow PCB are slightly farther apart than the traces on the wider PCB.  The traces are 6.8mm apart on the narrow PCB and 5.8mm apart on the wider PCB.

    The plastic spacer holds the unconnected PCBs 5mm from the wired PCBs.

    To be continued.

  • The Battery

    Duane Degn • 03/18/2021 at 16:50 • 1 comment

    DJI FPV uses a 6-cell 200mah LiPo battery. 

    Taking apart the battery is much easier than taking apart the battery in the DJI RoboMaster S1. The FPV battery is held together with two screws and liberal amounts of double sided tape.

    After removing the two hex screws the top panel needs to be pried away. I used a flat head screw driver but this did leave marks.

    Hopefully the following photos will allow anyone else to open their battery with less damage than done to mine.

    The rest of the battery enclosure is held on with double sided tape. I was able to carefully separate the various parts with a bit of prying.

    The white blob in the center of the battery pouches is a thermistor held in place with a bit of Silastic. The back side of the battery is sitting on the top cover to keep the double sided tape from sticking to my background paper. The smaller black rectangle on the left of the photo is the piece which would normally be connected to the back of the battery pack.

    The photos above and below show the battery management circuits.

    This last photo shows the plastic shell used to protect the battery.

    The battery has what looks like five connections. I see only four wires coming from the connector which are soldered to the PCB.

    I plan to investigate the communication between the battery and the quadcopter as well as the communication between the battery and the charger.