budget transmitter ? Why won't my old jr work ?

S

spinzer

Member
I have searched high and low in my country for something that can work to no avail.

Can anyone tell me why a jr 9xII radio with a DJT frsky module with an RX8 frsky receiver will not work with my quad.

a local LHS is trying to set it up but they say it wont work.

I was told a few things but cannot get the exact answer ?

Is it because the JR radio is to slow to communicate with modern flight controllers ?

Is it the DJT module that is too aged (it can only connect in D8 mode, but that should not be a problem ?) But maybe there is something else with regards to the radio and DJT module combined that is causing a problem ?

The only TX i can afford is a used frsky QX7 but they are rare as hens teeth locally.
 
Try the jumper t8 or t12, they're fairly cheep and mine works great with the frsky d16 protocol but d8 is there too.
 
Dugdog47 said:
Try the jumper t8 or t12, they're fairly cheep and mine works great with the frsky d16 protocol but d8 is there too.
Click to expand...
Are you using the frsky DJT module ?
And this receiver in the picture attached.

Let me give you the background:

I dropped my jr 9XII radio with frsky DJT module off along with my quad at a local store. Asking them to put in the new strix flight controller for me.

They get back to me telling me that the frsky X8R receiver will not work with the DJT module in my Jr9XII radio. Now if i ask too many questions, i will sour the whole relationship so to speak, because it is quite clear that they don't want to try any further to make it work. On the other hand, maybe they know something i don't ???

They say the only way it will work is to get a Frsky QX7 transmitter.

Now i have mixed opinion about this that i do not share with them.
I have read people being able to connect the DJT module to the RX8 receiver. But not many, and some seem to be not getting it right.

And those that do get it connected, seemingly to make it work through ppm or sbus to communicate with a quad seems like a confusing task.

And finally the place i dropped the quad off gives me the impression that the DJT and JR 9XII radio is too old to communicate fast enough with the latest FC to control my quad.

And another thing about the D8 vs D16.
For some reason i am confused getting the idea that you need to get it to work in d16 mode or it will not work for a quad as you need to use the channels higher up, but the DJT only supports D8 mode.

Does any of what i say make sense, or do you think i'm confused and the people i dropped the quad off at is too lazy to set it up on my JR radio and DJT module because they are only used to FRSKY radios ?

Should i get my quad back and do it myself (but will it work ?)

The bottom line of the below paragraph is. Will the 8XR receiver work with my JR9XII radio and a Frsky DJT module, and will there be any issues for this combo to communicate with the latest fpv racing flight controllers.
 

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Digging in deeper into this rabbit hole i found another piece to the puzzle:
Frsky themselves gave me this answer:

You can put the DJT in D8 mode, bind the X8R in D8 mode (using the jumper, not the bind button) and it should all work for control using SBUS between receiver and FC.

You will get low refresh rate and high latency compared to modern solutions, whether that matters or not depends on how you fly.

Now this is the important part:

Will the low refresh rate and high latency affect the drone's response time between the flight controller and esc's ?

What i'm essentially asking is, will the drone be able to fly at it's full potential without any latent response time between the FC and flight controller (causing oscillations or vibrations)

Does the low latency and refresh rate affect the above or does it only affect the response time
of input between the drone and the transmitter (just being a little slower to respond to stick inputs ??)

I need to know if the low latency and refresh rate will cause the drone to oscillate, vibrate especially at high speed. (or is the oscillation/vibration issue solely related to the fc and esc's only ?)


Axefly is online now


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Last edited:
Digging in deeper into this rabbit hole i found another piece to the puzzle:
Frsky themselves gave me this answer:
You can put the DJT in D8 mode, bind the X8R in D8 mode (using the jumper, not the bind button) and it should all work for control using SBUS between receiver and FC.

You will get low refresh rate and high latency compared to modern solutions, whether that matters or not depends on how you fly.
Now this is the important part:
Will the low refresh rate and high latency affect the drone's response time between the flight controller and esc's ?
What i'm essentially asking is, will the drone be able to fly at it's full potential without any latent response time between the FC and flight controller (causing oscillations or vibrations)
Does the low latency and refresh rate affect the above or does it only affect the response time
of input between the drone and the transmitter (just being a little slower to respond to stick inputs ??)
I need to know if the low latency and refresh rate will cause the drone to oscillate, vibrate especially at high speed. (or is the oscillation/vibration issue solely related to the fc and esc's only ?)
 
Does this help or only making it more unclear ? I tried to put it into context in a text file.


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Am i on right path here ?

Will the latency and refresh rate of the DJT module and jr9x2 together with the R8XR frsky receiver be fast enough to run a racing drone ?

This is what i could find that influences Loop times (this is what i THINK will influence if the quad woblbles or not ? (see important part in bold letters)

Gyro Sensor Delay (caused by the built-in low-pass filter and limited sampling rate)
FC PID Looptime (what we’re discussing in this article)
ESC Protocol (the time it takes for data to be sent from FC, and read by ESC)
Motor refresh rate (how often ESC updates motor)
Motor/Propeller Physical Delay (aka, motor reaction time or, change of RPM)
Moment of inertia of a quadcopter (which is related to the weight distribution of the quad)
FPV system latency (caused by latency in FPV cameras, VTX, VRX, FPV Goggles and Displays)

Radio transmission delay (the time it takes the TX to send commands to the RX)
Receiver protocol delay (the time it takes the RX to send the command, and interpreted by the FC, for example SBUS is faster than PPM)

And what is the latency of the DJT module and RX8R receiver ?


Axefly is online now


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If you can get it to work I don't think you'll notice any latency unless you're racing.

I don't know anything about either the tx or rx you are referring to but latency is not really worth worrying about unless it's a "save it or lose it" situation lol.

Personally I recommend just buying the jumper tx but I also understand about using what you got. I also have some flysky ppm and afdhs 1 stuff that both work great.
 
Thank you Sir, i'm thinking about getting a frsky x7 i can get used. but might use what i have as it seems do-able from your responses, also received a response from frsky themselves which compliments your advice, so again thank you. I will update with the progress when i get started.


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from frsky: RC latency only affects stick response, nothing else. You'll have about 45Hz refresh rate and 30-60+ms latency (highly variable) with your old equipment while new one would give 110Hz refresh and about 15ms average latency with little variation.











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