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Radio - Servo - Gyro - Gov - Batt > TX/RX eCCPM Latency Test Results
 
 
noahb
Senior Heliman
Location: Carlasbad, NM

latency

Any info on the 9303 system?
05-21-2005 Over year old.
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

> Any info on the 9303 system?

Nothing yet. A friend has offered his 9303 and another friend his 10x for testing purposes. Just got to get them and then have time to do the testing.

- John
05-22-2005 Over year old.
 
 
noahb
Senior Heliman
Location: Carlasbad, NM

Thanks John. I know I speak for most if not all here, that we really appreciate this information.

Keep us posted.
05-23-2005 Over year old.
 
 
THX1138
Elite Veteran
Location: Plainfield, IN

I am interested to see how the JR systems compare among it s competitors.

Lou

Back off man, I'm a scientist.
06-17-2005 Over year old.
 
 
Dr_Crash
Veteran
Location: Keller, TX

I'm interested also, especially being a 9C owner. It really makes me think about other TX's.

Thanks for you research.
06-25-2005 Over year old.
HOMEPAGE  
 
 
tadawson
Key Veteran
Location: Lewisville, TX

Love to see a test of the Multiplex Evos as well, if you find the time and motivation . . . .

- Tim
06-27-2005 Over year old.
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

Tim,
Hmm, I don't know of anyone local to me with a Multiplex Evo. It is pretty much an "unkown" brand in my area. Anyone care to loan me one for a few tests?

I am fully willing to test any radio I can get my hands on!!! Yes, I am still trying to get a 9303 and 10X from friends to test.

- John
06-27-2005 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

Hi JKos,

Very nice measurements, I was searching for latency as (as usual..) Futaba has been silent about it. Also nice to finally see the airtronics measurements that I never could find.

Sorry to ring in so late, I did not notice that this was going on here.

You already found my preliminary report about PCM latency measurements.
What you did not notice is that there we also did a full dissemination of the format. It is on the same webpage,

http://graphics.tudelft.nl/~wouter/...s/pasman04b.pdf

In fact the whole reverse engineering took place via this forum:
http://runryder.com/helicopter/t710...everse+engineer


We reverse engineered every single bit in the code. Every latency aspect on every channel. The delta codes. etc

For this, we have written special reverse-engineering software. I strongly suspect that the same code and approach will work with the 14Z
06-30-2005 Over year old.
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

BTW I still can not find the sequel to that reverse engineering project, where I also introduce the reverse engineering software.
The thread was named "1024PCM PART II" and it seems to be gone Please let me know if you need it, I think I still have it somewhere in my own archives
06-30-2005 Over year old.
HOMEPAGE  
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

w.pasman,
Thanks for chiming in! I knew you had done more work but had been unable to find it. Have you done anything with decoding JR's or Airtronic's PCM?

- John
06-30-2005 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

I remember vaguely that there was mentioning of JR decoding during our work on the PCM1024 format. We never dived into it, we focused on the PCM1024 because we want a full reverse engineering. I was after an exact understanding of the latency, as I had found unexplicable things with the straightforward measurements (like you did). If I understand it right you are mainly after the latencies

At least I was also interested in the airtronics stuff. But I could not find one to borrow. It's here that I find the airtronics data that I was looking for then


So it seems I really need to get one of those airtronics, the max latency is even lower than a 14MZ! And for me max latency is what really counts.

BTW how is your average calculated? Is it based on a large number of latency measurements or just the average of the numbers you found (and if so, how does that relate then to the 'real' average?)

Furthermore I am amazed about the HUGE latency you find for the 9Z, 110ms!!. The highest I found was 74.4 and I already found that really excessive. This must be purely the 9Z computer as the format is the same?
06-30-2005 Over year old.
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

I just checked further on what I asked about airtronix at that time (2003) and found this

http://runryder.com/helicopter/t659...ight=stylus+pcm

Actually you were discussing with us in that very same thread

BTW Did you measure the Hitec Eclipse 7 already? It was a serious competitor for the airtronix at that time
06-30-2005 Over year old.
HOMEPAGE  
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

w.pasman,
> BTW how is your average calculated?

The average in the chart is simply the average of the " Minimum latency to last change at receivers output" and the " Maximum latency to last change at receivers output". Is it the right average? I don't know and it can certainily be calculated in different ways.

> how does that relate then to the 'real' average?

Well, in the case of the 14MZ I think it does work since the all three channels change at the same time and fully. Since the user's input is uncorellated with the system's timing, I think it is fair to argue that in the case of the14MZ, the average latency the user gets is the average as I calculated it.

In the case of more complicated encoding, Futaba PCM1024 in particular, stating an "average" is much more difficult.

> Furthermore I am amazed about the HUGE latency you find for the
> 9Z, 110ms!!.

Please note that I tested the 9C, not the 9Z. The high latency numbers for the 9C stem from two things: 1) It took several frames (3 to be exact) before ANY change occured in the receivers output. And, 2) it took four to five frames for the full change on all three channels to occur.

> BTW Did you measure the Hitec Eclipse 7 already?

I almost forgot about that radio!

I should be testing a JR 9303 and a Futaba 9C Super this weekend. I'll see if I can get my hands on and Eclipse 7 as well.



- John
06-30-2005 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

BTW in that thread MarkF announced that he was going to measure the airtronics latencies. I can't remember that he posted the results but he puts so many posts that I probably missed it
06-30-2005 Over year old.
HOMEPAGE  
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

> MarkF announced that he was going to measure the airtronics
> latencies.

I don't remember seeing them either. Searches don't seem to turn anything up either.

- John
06-30-2005 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

Quote 
I don't remember seeing them either. Searches don't seem to turn anything up either.


Well that does not say too much, I cant even find some of my own old threads Maybe they were removed, or a harddisk crashed?
07-01-2005 Over year old.
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

Quote 
I'm not sure how to measure this one since it takes 4 to 5 frames to transition from one collective setting to another. Any ideas? To be fair to the two combinations tested thus far, it would need to be to the end of the transition. That will automatically put it in the 60+ ms range. This would also then be true of the 14MZ when used with a PCM1024 rx.


Latency is always measured from the moment the stick moves to the moment the transition is complete. PCM1024 has a way to make 'half a move' in the first frame, followed by the final move in the next frame. Just as with servos, it does NOT count when it STARTS to move, it counts when it ARRIVES. And yes, this is BAD for the max latency but it's just as bad when you try to control your machine.
And BTW I think that a large spread on the latency is also not good, it would give a jittery, unreliable feel to the controls.


Quote 
I found it more difficult to test this setup due to the odd nature of how the channels change so I only went for the minimums. In theory you would add one frame time to get the maximums.

and
Quote 
So perhaps if we can assume the 14MZ starts sending the change "immediately", then we can subtract about 39 ms (3 frames)from the 9C numbers and use those as the 14MZ + PCM1024 receiver numbers.


Please report the raw findings, and leave such 'corrections' for a discussion. I would not try to use such educated guesses. As you can see in my reports, they can think of pretty nasty update schemes, combined with many other factors resulting in very weird (usually high) max latencies. For the 9C guess, I think that my latency report already proved that your suggested 1-frame difference is not what is found in reality.
07-01-2005 Over year old.
HOMEPAGE  
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

> And BTW I think that a large spread on the latency is also not good, it
> would give a jittery, unreliable feel to the controls.

I agree. It would seem that such a system would give the controls a somewhat "squishy"/uncertain feel. We as humans are very good at predicting and compensating for time delays in controls. However, when that time delay varies widely, we can't do as well.

> For the 9C guess, I think that my latency report already proved that
> your suggested 1-frame difference is not what is found in reality.

I believe my assumption in this case is correct. I simply meant that if your stick input missed "this frame" it would be picked up one frame later. In other words, if you input is 1 microsecond late for the "next available frame", it will be picked up one additional frame later. This has held correct in all tests of all the setups thus far.

- John
07-01-2005 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

Quote 
I simply meant that if your stick input missed "this frame" it would be picked up one frame later.


Let me give an example of how your reasoning goes wrong on PCM1024, let's say that frame 1 is just missed. The signal will go through frame 2. However frame 2 is differentially coded and the signal will completely go through only on frame 3. Thus we have an extra latency of TWO frames instead of 1.
07-01-2005 Over year old.
HOMEPAGE  
 
 
JKos
Elite Veteran
Location: Town of California in the state of Maryland

FINALLY! I just added the results of my 9303 latency tests to the table in the first post of this thread.

A few word about why MLL and MaxLL are the same for this setup... It seems that when you are on the edge of the MLF, it takes three frames for all the channels to change. Step just over MLF into MaxLF, and it only takes two frames for full change of all three channels. Therefore, MLL and MaxLL appear to be the same.

I know plenty of folks have been waiting for these numbers.

Futaba 9C Super and 7C are next.

- John
07-04-2005 Over year old.
 
 
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