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Tx Latency Question - 8/7/2012 3:33 AM   
SeamusG



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Status: offline 		I've been told (and I read it on the internet so it must be so) that latency is that time it takes for the Tx to react to a change in one of its controls and respond with some action like send a message to the Rx to move the throttle servo arm to position x. So, a Tx with latency of 11 ms responds twice as fast as a Tx with a latency of 22 ms.

Let's say that I'm taking off and I smoothly move the throttle stick from idle to full throttle in 3 seconds. The Tx would take 11 ms to react to the inital movement of the throttle and send a message to the Rx. My throttle stick is still moving. How long will it take the Tx to send the 2nd, 3rd, 4th, etc. messages to the Rx to smoothly progress the throttle from initial state of "idle" to a final state of WOT?

Finally, what is this frequency of sending continuous messages called?

Hope this makes sense - it did to me when I had my aluminum foil hat on ...


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RE: Tx Latency Question - 8/7/2012 4:03 AM   
Charlie P.



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Status: offline 		If you have 11ms at the initial movement it's not cummulative.  The topping out of the three second throttle movement will be enacted by the receiver at 3.011 seconds.

What is the frequency of sending continuous messages?  Continuous-time dynamic proportional signals, maybe? 

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RE: Tx Latency Question - 8/7/2012 4:26 AM   
SeamusG



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Status: offline 		How many steps between the initial servo pulse message and the final servo pulse message? Will there be a pulse message sent every 11 ms to reflect the new throttle positions?


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RE: Tx Latency Question - 8/7/2012 4:38 AM   
dirtybird


 

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Status: online 		In the 72mhz equipment the frame rate is about 50cps. A new pulse is transmitted in each frame. On the 2.4 ghz equipment the frame rate is the designers choice.
I think you are wondering about things that matter little if you are not a circuit designer.
Go fly your airplane and be happy.

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RE: Tx Latency Question - 8/7/2012 2:35 PM   
SeamusG



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RE: Tx Latency Question - 8/7/2012 2:58 PM   
Four Stroker


 

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Status: offline 		Oddly enough, the ancient AM/FM digital proportional had an average latency of 8~12 ms. This is why old guys kept it long into the PCM era. Early PCM had latencies of 100 ms or more.

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RE: Tx Latency Question - 8/7/2012 2:58 PM   
BarracudaHockey



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Status: offline 		Very few gifted pilots can tell the difference in response between the two. Even then its on high end helis with 8v systems and .10 speed servos.

If you want to learn more, here you go...
http://rc.runryder.com/helicopter/t172571p1/

Don't read it before operating heavy machinery

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RE: Tx Latency Question - 8/7/2012 3:02 PM   
Bax


 

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Status: offline 		When "latency" is measured, it's measured from initial movement of the stick until the servo actually moves. Latency for most systems is 11-30 mS. More channels in your transmitter, plus more processing, extend the latency period. Newer systems are faster than older ones because their newer hardware is just faster.

If you are a world-class flyer, especially with eCCPM helis, then you may be able to notice differing latencies. However, it's mostly a "I guess it's something to know" for most people, and maybe a source of bragging rights, but it really isn't something noticed by the vast, vast majority of RC users. Manufacturers try to make their top-level systems so that top-level modelers are happy with the results. They're not so concerned with the lower-level, entry systems, other than to make sure reliability and controllability are not compromised.

< Message edited by Bax -- 8/7/2012 8:50 PM >

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RE: Tx Latency Question - 8/7/2012 3:07 PM   
Four Stroker


 

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Status: offline 		Latency was blamed for (and partically contributed to) the poor CCPM performance of many radios - Futaba 9C, 9Z. Modern radios have channel grouping and such to get around latency issues that actually effect control. The rest is a mind game. You get used to what you fly.

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RE: Tx Latency Question - 8/7/2012 3:36 PM   
dirtybird


 

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quote:

ORIGINAL: SeamusG

DB - the more you know the better it gets.



If you really want to know go get yourself an education in electronics. This is a poor place to get that kind of information.

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RE: Tx Latency Question - 8/7/2012 3:41 PM   
BarracudaHockey



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quote:

ORIGINAL: dirtybird


quote:

ORIGINAL: SeamusG

DB - the more you know the better it gets.



If you really want to know go get yourself an education in electronics. This is a poor place to get that kind of information.

Depends on who is answering the question

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RE: Tx Latency Question - 8/7/2012 4:42 PM   
SeamusG



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Geez dude - why not just skip the thread and keep your "fingers" quiet?


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RE: Tx Latency Question - 8/7/2012 7:02 PM   
dirtybird


 

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RE: Tx Latency Question - 8/7/2012 7:05 PM   
dirtybird


 

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RE: Tx Latency Question - 8/7/2012 7:23 PM   
SeamusG



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Status: offline 		BH - please close this thread. Thx


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RE: Tx Latency Question - 8/7/2012 11:14 PM   
eddieC



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Status: offline 		I've talked to many world-class pattern pilots, and 3-D and heli fliers whose names you'd recognize. Only the heli guys say it's perceptible, and then only during rapid maneuvers. We've tried comparisons at the field, couldn't tell.  But then again, we're all hacks !  

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RE: Tx Latency Question - 8/8/2012 1:24 AM   
SeamusG



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Status: offline 		That is really insightful and technically accurate ...


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RE: Tx Latency Question - 8/8/2012 3:27 AM   
oliveDrab



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