Latency from Tx module PPM input to Nano Rx PPM output - RC Groups
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Nov 18, 2017, 08:34 AM
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FlyingW's Avatar
Question

Latency from Tx module PPM input to Nano Rx PPM output


Jim,

Can you please estimate how much time passes from when:

Servo position information in a PPM frame output from a transmitter to the XPS Tx module comes out of a Nano Rx's PPM output.

I'm thinking some microseconds?

Thanks,

Paul




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Nov 18, 2017, 03:38 PM
It takes up 14ms to collect the data from the PPM stream before it can be sent via the transmitter. Sending the data over air takes under 1ms with 8 channels. The Nano decodes the packet after it arrives, so another 1ms before the servo positions are changed - which occurs in less than 2ms.

The longest delay in the entire process is the transmitter's frame rate.
Nov 19, 2017, 01:27 PM
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Interesting, about 17ms, with the majority of the time spent waiting for the complete frame to accumulate out of the transmitter. Thanks Jim, Paul.
Jan 07, 2018, 12:32 AM
John Hendry

CRSF with Frsky X7 issue


Quote:
Originally Posted by FlyingW
Interesting, about 17ms, with the majority of the time spent waiting for the complete frame to accumulate out of the transmitter. Thanks Jim, Paul.
That's on the low end with Crossfire on a HORUS10 @ 19.5ms one test showed, and a lower line Spektrum TX at 41.5ms. Crossfire reduces latency on HORUS10 using CRSF (not PPM) almost in half due to its faster processing. But be aware current Frsky X7's have an issue that requires a hardware and software mod to get telemetry with CRSF working correctly. There is a software alone fix but it "works" by slowing down the data flow to 25% according to one site. Really have to do your homework as half of what is said is often half true half of the time. The dream of an amazing $200 radio with fast reflexes and long legs has been put on hold it seems until the next revision of the X7. Issues like this is where a manufacture needs to post information online to control the fallout and keep facts straight as for a lot of people this will be a non issue, but some will scream about it.
Jan 07, 2018, 12:49 AM
This thread is about a PPM data stream, which has nothing to do with FrSky transmitters.


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