R/C and FPV frequencies

MalcB

MalcB

Member
Hi folks
Total newbie to Quad flying but it seems the more I read, the more confused I get.
I'm currently trying to modify/tweak a TBS Discovery for long flight photography, and would like decent range as well.
Can anyone please tell me if TBS Crossfire is superior enough to ezUHF 433MHz R/c (with SRH177 antenna) to justify switching, or better just to stick with the latter ?
Cheers
MalcB
 
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To introduce a third option I'm moving my stuff to ELRS or ExpressLRS which is an open source RX/TX option that is just rolling out and boasts better performance/range than TBS crossfire and is more affordable to boot. The downside is it's still very early days of active development in terms of hardware released, so have to do some hunting around to find modules or get the components and piece it together (also not all that easy to find the radio modules themselves).

github.com

GitHub - ExpressLRS/ExpressLRS: ESP32/ESP8285-based High-Performance Radio Link for RC applications

ESP32/ESP8285-based High-Performance Radio Link for RC applications - ExpressLRS/ExpressLRS
github.com github.com

github.com

GitHub - ExpressLRS/ExpressLRS-Configurator: Cross platform configuration & build tool for the ExpressLRS radio link

Cross platform configuration & build tool for the ExpressLRS radio link - ExpressLRS/ExpressLRS-Configurator
github.com github.com

There is a company called "HappyModel" that has put out a few preflashed bits of hardware that you can just buy off the shelf and get hooked up, but you need to do some extra configuration on the OpenTX side of things (load up a LUA script onto the SD card and run it from the OpenTX menus) and basically requires some digging to get configured, but once setup it works very well in my limited experience so far and from some other user testing it can work amazingly well (they also have different options for the actual radio/antennas being used and show some high level comparison charts on the github page)
 
One thing to be aware of is the ELRS modules use the crossfire wire protocol (send stuff from receiver to FC in the same way) the over the air protocol is different but they do overlap in that way and it means any FC hooked up to an ELRS module will be able to understand crossfire protocol on the wire (any OpenTX controller has this baked in). I've been tinkering the last few days on getting an ESP32 to act as a bridge between a receiver and a RC car (basically reads in Crossfire protocol on the wire from an ELRS receiver and converts to PWM signals so can drive ESC and servo signal)

Eventually I imagine there will be ELRS receivers that output PWM signals too but for now just making due with a ESP32 acting as adapter/translator and "motor controller" sending out the PWM signals.
 
o_O Many thanks wafflejock for an extremely detailed reply. Unfortunately you rather lost me just after the word 'introduce' !
As an absolute thicko when it comes to radio, it's components and terminology , I can just about grasp frequency, modulation and harmonics but anything deeper especially all the acronyms (PWM, etc.) are pure Martian !

Unfortunately this leaves me having to rely on already fully developed 'plug and play' systems.
I have almost Zero experience with Quads, having only flown a Hubsan Q4 indoors, :rolleyes: so going 'supersize' is going to be a gigantic learning curve as things stand.
To explain (as I should have done earlier): I bought the Discovery online. It came without props or R/c aerials.
I am informed it ran 9" props and as it has an ezUHF receiver I am buying two 'Sander' aerials and have already bought an ezUHF JR module with an SRH771 aerial.
Just trying to get the bloody thing in the air to hover initially, but seeing how without care it's potentially dangerous, OH! the bloody hoops I'm having to jump through !
Still have to sort out the correct Lipos for Quad and Turnigy 9x and sort out goggles and/or a base station.
(Never had this with the Hubsan :D)
Could really do with someone like yourself as a near neighbour.

Cheers
MalcB
 
Haha yah the expresslrs/elrs stuff is a bit in the deep end but sounds like you have a fairly good understanding on the radio side of things.

PWM is pulse width modulation, it's not too complicated really just a "square wave" signal (looks like a square on a scope with sharp increase in voltage followed by a sharp drop). The time the voltage is high or on for a given "window" is called the "duty cycle". For servos used in model airplanes a lot or for escs used for controlling throttle on brushless motors for quads you can use a PWM signal from a flight controller or receiver to control the position of the servo or the amount of throttle (usually the range is 1ms to 2ms corresponding to 0-100% throttle for an esc or 0-180 degrees for throttle)

Modern ESCs that control motors and the flight controller (FCs) that talk to them will usually use some higher speed and less susceptible to noise or interference protocol than PWM for sending signals but in pretty much all cases the will still work with simpler PWM signals (shorter or wider pulses).

To sum up most servos or escs just require power to be hooked up, some GND/common to be shared with the flight controller sending them signals, and finally a single signal line to be hooked up to a flight controller or receiver that sends out pwm signals.


GreatScott or Electronoobs are also great channels for filling little gaps of knowledge on electronics.
 
An Arduino or for our common flight controllers a stm32 arm chip with internal timers can generate at least a few pwm signals without much issue (libraries make it as easy as import the servo lib and make a function call)
 
MalcB said:
o_O Many thanks wafflejock for an extremely detailed reply. Unfortunately you rather lost me just after the word 'introduce' !
As an absolute thicko when it comes to radio, it's components and terminology , I can just about grasp frequency, modulation and harmonics but anything deeper especially all the acronyms (PWM, etc.) are pure Martian !

Unfortunately this leaves me having to rely on already fully developed 'plug and play' systems.
I have almost Zero experience with Quads, having only flown a Hubsan Q4 indoors, :rolleyes: so going 'supersize' is going to be a gigantic learning curve as things stand.
To explain (as I should have done earlier): I bought the Discovery online. It came without props or R/c aerials.
I am informed it ran 9" props and as it has an ezUHF receiver I am buying two 'Sander' aerials and have already bought an ezUHF JR module with an SRH771 aerial.
Just trying to get the bloody thing in the air to hover initially, but seeing how without care it's potentially dangerous, OH! the bloody hoops I'm having to jump through !
Still have to sort out the correct Lipos for Quad and Turnigy 9x and sort out goggles and/or a base station.
(Never had this with the Hubsan :D)
Could really do with someone like yourself as a near neighbour.

Cheers
MalcB
Click to expand...
I'll see if I can give more helpful answer later specific to your problem but figured at least pwm I can explain off hand :D it is a steep curve for all of us for sure.
 
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