FlyingGiants Exclusive! Introducing The Futaba 12FG, Modules & More!

[toprudder]

	Quote: Originally Posted by Julez
	I checked the time between the PPM pulse of channel one going to the module and coming out of the servo plug at the reciever. I doubt anyone can show us a system with less than 0,1ms of latency time.

That is only one, very small, part of the system contributing to latency.

The encoding process itself is a big part of the latency. In your example plot, what if the aileron stick moved just after the first pulse (aileron on a Futaba) left the system. It would take one whole frame of the PPM pulse train before that information would make it to the servo.

Bob R.

[OverTemp]

I don't think this was ever answered:

Can I use 2 RXs with the FASST system?

Facts only please, keep opinions in your head.

[peterschmidt]

	Quote: Originally Posted by OverTemp
	I don't think this was ever answered: Can I use 2 RXs with the FASST system? Facts only please, keep opinions in your head.

According to Futaba's QA it's possible,

6EXA 2.4GHz Radio System FAQ

I have gone to a 2-receiver setup for added insurance. Can this be done with the 2.4GHz system and how?
This is done very easily with this system. Simply use the linking process to bind both receivers to the same transmitter. When purchased as a transmitter receiver set, the receiver has already been linked to the transmitter at our factory. It will be necessary to use the Easy Link button to bind the second receiver.
To properly link the receiver follow these steps:

• Turn on the transmitter. Check the LED on the back of the transmitter to make sure that it is green. If so, proceed to step 2. If not, power down the transmitter and turn it on once again.
• Turn on the receiver.
• With the receiver on, press and hold the ID Set button (located between the two antenna exits) for more than one second. When the linking process has completed the receiver's LED will change to a solid green.

Home - 6EXA 2.4GHz FAQs - Main Futaba FAQ/Contact Info page

[Julez]

	Quote: Originally Posted by toprudder
	That is only one, very small, part of the system contributing to latency. The encoding process itself is a big part of the latency. In your example plot, what if the aileron stick moved just after the first pulse (aileron on a Futaba) left the system. It would take one whole frame of the PPM pulse train before that information would make it to the servo. Bob R.

This would also be the case with the PCM Pulse train.All stick positions are sampeled, then computed, then formed into a PPM or PCM pulse. When a stick moves after it was sampeled, its new position will not be known to the TX until the next sampling frame. The sampling framerate has nothing to do with the length of the output pulse trains, be it PPM or PCM.
I dont know if I still have the oscillogramme on my PC, but the PCM Pulse train is not shorter then the PPM pulse train. So, with PPM, the latency of an individual channel partly depends on its position in the pulse train. With PCM, ALL channels will be delayed until the last information of the PCM pulse train has been sent. Now the RX needs some time to decode the PCM, and it is unlikely that the TX can encode PCM faster than PPM, thus one will in every case have a higher latency with PCM than with PPM. Cheers, Julez

[MalaysianFlyer]

Julez, you need to go get Multiplex to give you a job designing their 2.4GHz system, you sound qualified enough!!!!

Or maybe not, as that would probably mean another product to make me drool and part with my meager income!!!

[juvaknin]

Well??? there suppose to be price for the Modules no??
the Toledo has started............
anyone? did futaba give any price of the Modules and RX for the 9C??

[RollingHarrier]

	Quote: Originally Posted by juvaknin
	Well??? there suppose to be price for the Modules no?? the Toledo has started............ anyone? did futaba give any price of the Modules and RX for the 9C??

They said in two weeks the prices will be up on the website.

[Julez]

	Quote: Originally Posted by MalaysianFlyer
	Julez, you need to go get Multiplex to give you a job designing their 2.4GHz system, you sound qualified enough!!!! Or maybe not, as that would probably mean another product to make me drool and part with my meager income!!!

Thanks!

Unfortunately, I'm not an engineer yet.
But I will do my best to test the XPS system with what I know about spread spectrum and radio technology so far.

I have made a little scheme about the various components that make up the latency. I have also posted it on RCG some time ago.

Sampling latency is always the same for an individual transmitter, regardless of PPM or PCM.

Processing latency is very likely to be higher with PCM, as it requires more computing power to produce a code than to output a PPM pulse train.

The RF Link Latency is also higher with PCM than it would be with PPM, as it requires some time to decode the digital PCM code, in contrast to the PPM pulses, which do not need to be decoded.

Some newer recievers use some signal postprocessing to prevent glitches. This can need some time, too.
While the RF Link Latency is less than 0.1ms with my 15 year old, fully analog reciever, it is 7ms with my newer Schulze micro reciever due to signal postprocessing.

So, when using a 2.4GHz module on a transmitter, it makes more sense to use a PPM signal than to use a PCM one.

XPS claims 2-5ms Latency for its system; this would be the RF Link Latency.

I will test this when I get my unit. I am excited how it will compare to Futabas modules.

Cheers,

Julez

[MalaysianFlyer]

Julez, please do post your testing results for the rest of us.

[paffy]

You can see a comprehensive Tx/Rx latency comparison here:

http://www.runryder.com/helicopter/t172571p1/

[RTK]

Paffy, I think some Rx's might have been missing in that data.

[MalaysianFlyer]

paffy, thanks for the link, its an eye opener!!!!