Can you get more channels off an FC? I'm confused on the Rx to FC Relationship.

[Ducky84]

I'm very new to RC and I'm trying to plan out my first fixed wing build.

I've done a ton of research, and watched a lot of youtube videos (Thank you Painless360) but the area I'm hung up on is the Rx, somewhat related the FC.

I'm wanting to pick up a Crossfire setup with a Radiomaster Tx16s using a Matek FC.

I'm wanting around 8 channels for what I hope to accomplish. I was looking at the TBS Crossfire 6ch PWM Nano RX. But it's a 6 channel receiver. Also their other Receivers minus the $100+ dollar one are all 6 Channel or less.

But in various Youtube videos I've seen, it almost seems like you can also hook up servos to your FC and gain additional channels. There's a communication mechanism such as SBUS or CSRF that I've heard about for connecting the FC to the Rx...But does this allow gain you additional channels?

I just don't know that I fully understand the FC and Rx relationship well enough to pick out a Crossfire Rx setup that works for what I want to accomplish. Just looking for some guidance.

 

[JasonK]

There is 2 different things here... the channel count from your TX to the RX -> Flight controller.
Then the channel count between the flight controller -> control surfaces/motors.

I happen to have spectrum stuff and my serial receiver can do as many channels as my TX can send at it. It looks like you picked out a receiver designed for when you don't have a flight controller. Don't use that one, get a serial receiver, which will let you get basically all your channels from your TX to the flight controller.

Then you have your output channels on your flight controller, which will be the limitation on how many things you can connect to it.

For example, one of the projects I am currently working on has the following output channels that I need: L/R Motor, L/R Motor pod tilt, L/R Flapperon, L/R V-tail, so I need 8 outputs, 2 of which are Dshot/ESC protocol and 6 which are PWM outputs for servos.

I then map 4 channels to throttle, roll, pitch, yaw in the FC, then a channel to arm (this can be shared), and I will be setting a channel to the flight mode (vertical, slow forward, forward flight). Then in the FC I will use the stabilized outputs + various mixing commands for the servos to drive the motors and mixers based on what I want it to do.

One thing in the firmware that I have includes the ability to add an airspeed sensor to the FC and it can even automatically deploy flaps when the speed drops/goes up, all without me flipping any switches on my TX (I don't have this setup, nor plan to use it, just an example of what the FC can do to help reduce pilot load). I suspect you could have it do the same thing with landing gear if you so choose.

 

[Ducky84]

Thank you for the feedback!

Don't use that one, get a serial receiver, which will let you get basically all your channels from your TX to the flight controller.

So a serial receiver being something like the Nano rx? If I look at the documentation here (Page 41) it specifies "Serial" allowing me to pass UART data, but which receiver port is that on the actual receiver? There's a lot of fancy acronyms in that docuentation, some of which I know, but I'm not sure which is used for "Serial"

Also, is there a limitation on how many UART ports I can pass over a single receiver connection? (Not sure if I'm using the terminology correctly)

For example the Matek F722-HD specifies 6 UARTS. Does that mean I could use say....2 channels on the Nano Rx, and 6 channels on the FC? (Sending those 6 channels through a single channel on the Rx)

Sorry if I'm getting any of this wrong.

 

[JasonK]

Thank you for the feedback!



So a serial receiver being something like the Nano rx? If I look at the documentation here (Page 41) it specifies "Serial" allowing me to pass UART data, but which receiver port is that on the actual receiver? There's a lot of fancy acronyms in that docuentation, some of which I know, but I'm not sure which is used for "Serial"

Also, is there a limitation on how many UART ports I can pass over a single receiver connection? (Not sure if I'm using the terminology correctly)

For example the Matek F722-HD specifies 6 UARTS. Does that mean I could use say....2 channels on the Nano Rx, and 6 channels on the FC? (Sending those 6 channels through a single channel on the Rx)

Sorry if I'm getting any of this wrong.

you only need 1 serial port to connect the receiver to the flight controller

 

[JasonK]

the flight controller your looking at has 10 outputs that can be used for either Dshot or PWM, typically they are set up in groups because of how the internal hardware of the MPU chip is setup, so for example, you might have to assign 2 ports together, so even if you only need 1 motor, you will have to assign 2 ports to motors, leaving only 8 other ports for PWM for servos.

 

[Merv]

But in various Youtube videos I've seen, it almost seems like you can also hook up servos to your FC and gain additional channels. There's a communication mechanism such as SBUS or CSRF that I've heard about for connecting the FC to the Rx...But does this allow gain you additional channels?

Yes, using a serial communication protocol CAN allow you access to more channels. The number of channels of a “servo” (PWM) receiver is limited to the number of servo pins it has. Using a serial protocol, removes this limit. Many Rx will not allow you to use both PWM & serial communication at the same time.

There is no way of knowing what your Rx is capable of, you need to consult the documentation from the manufacturer.

 

[Ducky84]

Got it, thank you guys for the help. I've got a bit more reading to do but this point me in the right direction.