Repurpose partly fried fpv drone receiver for car?

So a while ago I got myself a BetaFPV Cetus X in ELRS flavour, and after climbing the steepest part of the learning curve it was fun for a while, until one motor channel got fried from an immobilised rotor…

Got a new receiver board (which includes the motor controllers), painstakingly soldered connectors onto it, and took it for a handful of flights before promptly frying that board in the same manner.

Given this hazard, not to mention the huge adrenaline spikes when I lose control of the thing, I’m thinking I’m better off on the ground.

It strikes me that it should be possible to adapt the guts to run a car, assuming it’s possible to reconfigure the board with Betaflight to suit… although my initial attempts to search for such a thing a drawing are blank…

I’m guessing that if it’s doable, it would involve sort of demoting the receiver/ESC to just a receiver, by altering the firmware to output the sort of signals intended to operate servos? (I’m assuming modern RC car ESCs are backwards compatible with ancient ones designed to replace a servo operating a resistor switch.)

Obviously this is way too tall an order for a noob, but if somebody with skillz has done it and documented the process, I could follow along okay I reckon.

TL;DR: anyone aware of a quad-to-car firmware mod?


Hi Kimmo,

Really neat project! I havent seen any guides around for this kind of conversion due to the complexity.

I imagine the PCB on the quad is quite proprietary and optimised for weight.
While you could reflash the mainboard you’ll probably hit some roadblocks with finding the right pins to tap in from the microcontroller. (you’ll have to get to the signal before the ESC).

Another solution might be to use a seperate RX and TX for the car and use the mainboards FPV attached with a regulator.


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There’s a lot to learn before I can come up with the best search terms, but from what I’ve dug up so far, it might be possible to get PWM out of the motor outputs on the flight controller through something called channel forwarding, or maybe it’s more feasible if it’s possible to reflash the FC with something called INAV, which “runs on the most popular F4, F7 and H7 flight controllers”… whatever that means; chipset I guess.

Looks like the Cetus X FC is F4, which I gather might be a bit marginal for memory…?

A car application won’t use much of the hardware on the board, so maybe I can flash a cut-down version of the firmware if necessary…

Hey Liam, I can’t figure out what you’re saying here…

Maybe it’d help if I clarified the situation. The flight controller (FC) is the RX, sensors and brain, along with ESCs. It also provides power and OSD info for a separate video module incorporating its TX…

I had a thought - it should be possible to come up with a basic little circuit to filter the motor drive signals from the FC into something an Arduino can read, and then getting a couple of PWM signals is easy.

Then the hard part would be a lot easier; rather than trying to re-jig the firmware to make a couple of the ESCs output PWM, it would just be a matter of making a couple of motor outputs proportional to a couple of channels of the input signal, ditching all that ‘reference the sensors and do magic to make the quadcopter move in a sensible way’ business. I reckon that should be doable…

Anyone have any thoughts on how to make a circuit to filter brushless motor power into a readable signal? I’m guessing it wouldn’t be much more complicated than a rectifier?

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Do you have specifications for the motors? That would tell you what the power signals look like, and from that you could work out what’s needed to use the power as a control signal. An oscilloscope would also provide useful information about how those motors are being driven. You mention that the motors are driven by an ESC. Have you confirmed that - for instance, do the motors have three wires? If so then a simple rectifier would not work. If they are two-wire motors then you could determine whether the power is DC or digital PWM using a logic analyzer. If it appears to be digital then you can buffer the motor power and get an idea of the signaling by using the Arduino as a simple logic analyzer. See:
If the input to the ESCs is accessible that would be more directly usable as a digital signal for analyzing.

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The motors are brushless (three wires), 11000kv, 3.7-7.4V. But I’d be running it off 5V.

This flight controller is tiny. There’s no way I’m tapping into the guts; I was flat out soldering the motor connectors onto my replacement board.

I wasn’t imagining a simple rectifier would work (not sure what help that would be with a DC motor drive); but surely there’s a circuit to turn 3-phase AC into DC?

If not, I could attach a DC motor onto the end of the brushless motor as a generator, lol.

Although… those four pairs of pads on the motor connector side are very interesting…

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