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Turning an Old Phone’s Motherboard into an RC Plane Controller
Upcycling smartphones makes a lot of sense, especially since they contain so many components that remain useful long after their desirability as a smartphone has faded. In the case of [Mountain DS Lab], they opted to use an 8-year old Xiaomi Mi 8 phone to add long-range FPV video link and remote control functionality to an RC plane, using the phone’s LTE cellular connectivity.
The smartphone was bought used for $23, with the default Xiaomi ROM overwritten by LineageOS to get a more lightweight and up to date Android installation on it. From the video it’s clear that this phone has seen better days, with the glass back cracked and a few ugly lines running across the display. Fortunately all that is needed is the motherboard itself.
One gotcha here is that the OS checks for the display on boot and will time-out if it’s not present, potentially halting the process entirely. The workaround requires disabling the display in the device tree, which is done by modifying the boot.img file as explained in the video. Next a custom bracket for the motherboard was printed so that it could be fitted inside the target airplane.
To communicate with the avionics, a USB-to-UART adapter PCB was created with a CH340 IC on it. This was then connected together for an initial test, with the extended front camera being used as the FPV camera for the custom Android application. Using the controller via the remote LTE link worked with the flight controller, so next the airplane was assembled for initial testing.
From this point it’s all pretty standard RC airplane assembly and testing, just with the typical RF-based control and FPV link replaced with the LTE link. Unfortunately flying drones isn’t permitted in the immediate area where the creator lives, so only some taxiing was tried prior to its maiden flight at a local airstrip that will be featured in an upcoming video.
Naturally, this isn’t the first time that someone has tried this type of remote control, with the ongoing Russo-Ukraine war being a prime example of LTE-based remote control of drones. Although we do not advocate wiping out a third of a nation’s strategic bomber fleet with upcycled smartphones, ultimately this is the same technology and a good way to create an RC drone that can last more than the few kilometers eked out from a 2.4 GHz link or so. Just be prepared for the LTE link to add a few milliseconds of latency.
