DJI digital FPV is pretty new on the scene and new products such as flight controllers, quad frames and antennas that are designed to work with the system are becoming available. The air unit has a pretty high current draw that cannot be handled by BECs (battery eliminator circuit) voltage regulators on all old-style flight controllers. The one big differentiator for flight controllers specifically designed for the system is beefier BEC and a socket that would make the flight controller plug and play with the air unit.
The specific application I was looking for was using single arm-mounted ESCs on a quad with a DJI air unit. This meant that I needed a AOI flight controller, where ESCs get soldered to the flight controller and flight controller is directly connected to the battery. The only available option that would meet that requirement was Holybro Kakute F7 HDV AIO flight controller. The controller was priced at a reasonable $41.99 and is available from multiple vendors in the US.
List of features of the flight controller:
- MPU6000 gyro
- Integrated BMP280 barometer and SCL/SDA for use with external GPS/magnetometer units
- 2 oz. copper PCB allows up to 120A maximum continuous current
- Input voltage 7v to 42v.
- 2 On-board regulators output 5V and 8V. 5V output up to 1.5A to power peripherals such as receiver, FPV camera, or LED strip. 8V output up to 2A to DJI air unit
- USB VCP Driver (all UARTs usable simultaneously; USB does not take up a UART)
- 6 hardware UARTS (UART1,2,3,4,6,7)
- All UARTS support hardware inversion.
- TF card for Blackbox logging
- Dimensions: 45x37mm
- Mounting Holes: Standard 30.5mm square to center of holes
- Weight: 10g
Included in the package:
- FC board
- M3 Damping Ball*4
- JST GHR 8pin to JST GHR 6pin 80mm cable*1
The flight controller’s geometry and pad orientation is a bit weird. The flight controller is asymmetrical, it is longer that it is wider (if mounted the suggested way). The ESC pads are arranged in a rather odd way – they are placed on the front and back of the board, instead of usual placement in the corners on the sides, which reduces clearance for routing ESC wires. Not a big fan of this kind of design.
When mating the flight controller with the air unit I came across an annoying problem: the cable that connects the flight controller with the air unit included with the package was way too short. It would only reach the air unit if the FC is mounted with the air unit cable plug facing backwards (FC mounted sideways). To make things worse, the flight controller had a connector but no breakout pads for the pins within this connector. Thus, I could not just solder on the cable that was included with the air unit. I had two choices – mount the flight controller sideways, so the cable can reach or splice the DJI cable with the included JST GHR cable. I chose to splice the two cables together. This resulted in a really long cable that I will have to tuck above the air unit (not a big deal). The placement of the plug on the back of the air unit is kind of a bad design choice from DJI as well. I wish the air unit had the plug on the side where the camera cables go in (front) rather than where the antennas attach (back). Maybe it would work better in a different frame.
Holybro, if you are hearing this, please include a longer GHR cable with your flight controller or at least include breakout pads so that the DJI cable can be used.
Full evaluation is coming up once I get the whole thing running. So far the air unit works (transmits and receives signal) and the FC connects to betaflight fine and appears to function. I don’t expect anything crazy here, as flight controllers all perform very well these days.
Honestly, I think the design of the controller is not very well thought through. It appears that they just took the Kakute AIO F7 controller, added a GHR plug, deleted the gyro damping, added a bigger BEC and called it a day. The dimensions of the controller and direction of heavy-gauge wires make it kind of difficult to fit in frames where so much space is already taken up by the air unit. If mounted sideways, I think too much of the controller is sticking out of the sides of the frame unprotected. Regardless of the fit issues, the flight controller does what it supposed to do and is integrated with the DJI air unit system.
For the price, the accessories included with the controller are kind of sparse. The competitors usually include a low ESR capacitor, a battery pigtail and some mounting hardware, as well as spare cables.
And there is just no excuse for the GHR connector that is too short. It looks to me like they just took the same connector from the non-AIO version (where the plug is located in the rear of the controller and reaches the air unit just fine) and included it with the AIO version where the plug is on the side (much farther away). Whoever included this thing clearly did not measure the distance.
Correct BEC (2A @ 8V) to run DJI air unit
All in one design – allows for discrete single ESCs
Flight controller functions correctly
Stable MPU6000 gyro
Well suited for use with GPS
Design makes it difficult to fit in tight space
Included GHR cable that connects the FC to the DJI air unit is way too short
Heavy gauge cable pads all are in awkward places making it hard to run cables
Gyro not soft mounted like on other kakute models