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HomeRC & PowerAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › TX/RX Latency Test Results
02-06-2008 06:18 PM  10 years agoPost 681
hootowl

rrProfessor

Garnet Valley, Pa.

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I think this "squeeking" John is referring to is just the plastic sliding against plastic at the base of the sticks.

Wolves don't lose sleep over the opinions of sheep

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02-06-2008 08:09 PM  10 years agoPost 682
RCHelicopterGuy

rrVeteran

Michigan

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Their actual words were "summer" but you could be right
The Vibe 50 was supposed to be here by Christmas.

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02-06-2008 08:34 PM  10 years agoPost 683
Shoo

rrApprentice

Eastern MA

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9c squeak
A little servo grease and the squeak goes away. I had it happen to mine.

Shawn

BTW, JKos, thanks.

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02-07-2008 08:46 PM  10 years agoPost 684
Chuckie

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Crofton Maryland

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I have a theory as to why the FASST 12z TM14/R6014FS is not perceived as slower than the 12/14mz/R5115DPS by pilots who have flown both. Or why the latency characterizes of Futaba’s FASST is not an issue in real flight tests. No I don’t work for Futaba and yes I was surprised to see such high average and max latency numbers from John’s TM14 tests.

A few years back I read posts about Curtis Youngblood or his Dad making a real time glitch counter using his JR radio (I don’t remember what model the radio was). They modified the receiver and used the rx decoder chip which had an output that triggers when incoming data cannot be decoded. They built a counter and LED circuit to display max percentage of data loss, over an interval of one second. Curtis’ circuit is unlike aftermarket glitch counters that only detect when the rx goes into fail safe; as they are plugged into the rx like a servo and can only read the rx servo signal. I also read that the Futaba PCM1024 rx also has in the decoder chip an output that goes low every time the decoder cannot decode the signal due to RF interference, blockage, exceeding max range, etc.

What Curtis discovered was the RF link in the heli application is very susceptible to data drop outs due to RF interference or noise. The percentages seen by the glitch counter were higher than what Curtis expected, however, he didn’t report actual percentages. If I remember correct some people suspect average values around 20 to 50 percent per second.

I can image that no one can detect when the percentage is in the 10 to 20 range due to the nature of the how the servos and model react (flybar stability), range to the aircraft, what maneuver is being flow, when the pilot gives an input, and other factors. What is even more possible is that at 50 percent data loss where every other servo signal is old data (or the last good servo position is sent) the pilot would probably not detect a problem. The pilot might not feel anything was wrong but the response of the heli would be out of sync or slower. The data latency could be twice as high or in the 40 to 60ms range and you might not detect a problem. Now if the RF link gets blocked for half a second the pilot will probably detect this as a glitch because the heli stopped responding for long period of time, assuming the pilots is giving an input at the time.

The PCM receiver decoder is designed to send the last good servo position if a RF drop out occurs and after a second or more later if data cannot be decoded the decoder will go into fail safe. Once in fail safe the decoder sends the servos to the preprogrammed position, if set. PPM rx’s don’t do any of this. I believe the G3 rx decoder functions the same way as PCM1024 but it processes a higher resolution and faster RF data rate signal (correct me if I’m wrong). The G3 rx is just as susceptible to RF drop out as the older PCM rx’s and because it’s running at a higher rates there is more data to loose over the same period of time.

The RF drop outs are caused by RF noise or interference from the heli itself (for example bearings, belts drives in booms, and metal to metal contact) and electronic equipment (such as voltage regulators, gyros, servos, governors, bad switches, wiring layout, etc). A change in signal to noise ratio occurs with distance and rx antenna orientation. So as the heli rotor is spooled up and is flown around the RF noise level or signal to noise ratio at the rx is constantly changing. With FASST or SS all of these RF issues are eliminated. Like everyone else I appreciate all of John’s work but his tests don’t factor in the varying RF signal link or the affects of drop outs in the signal link.

To wrap this up, even though the FASST TM14 appears to have a higher latency the percentage of data that can be decoded is closer to 100 due to the use of 2.4GHz frequency, constant channel shifting, and dual antenna diversity. I believe the pilot flying the 12z TM14 FASST would actually perceive to have the same link speed than someone flying the G3 FM RF link with 30-50 percent data loss.

Charles

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02-07-2008 08:55 PM  10 years agoPost 685
JKos

rrProfessor

Redondo Beach, CA

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Charles,
> A few years back I read posts about Curtis Youngblood or his Dad
> making a real time glitch counter using his JR radio

Finally, someone else who has heard about this.

I've mentioned previously exactly what you just wrote up as an elusive aspect of latency with zero hard data available on actual data loss for PCM and G3 systems. And, yes, may just explain some of the "lack of difference in flight" between certain systems.

- John

RR rules!

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02-07-2008 09:26 PM  10 years agoPost 686
hootowl

rrProfessor

Garnet Valley, Pa.

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So let's see...

G3 is so good that even after factoring possible in-flight, real time signal dropouts, it performs the same as the cleaner but more latent FASST TM-14/6014.

Make sense?

Or

The FASST TM-14/6014 combination with higher latency is so clean it performs as good as the G3/5114 with much less latency but more in-flight signal dropouts.

Another big plus for 2.4 if this theory holds true.

Personally I have experience a phenomenal performance/connection gain.

Wolves don't lose sleep over the opinions of sheep

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02-07-2008 09:58 PM  10 years agoPost 687
TMoore

rrMaster

Cookeville, TN

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Dave Youngblood did the original system that I saw on the early 1024 PCM RX's. Airtronics had the same thing on the ATCP 1024 system that the old Infinity radios used starting in 1989.

I remeber Dave telling me about instances where they wouldn't even fly because the hit ratios were simply too high and hence unsafe to even go out and try it. That didn't stop other folks with different PCM Rx's from trying and sometimes crashing. The thing is that most folks think that PCM is safer.

TM

Delayed Response Operator Not Engaged
AMA SECTION 336 = Good
Drones = EVIL

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02-07-2008 10:59 PM  10 years agoPost 688
Four Stroker

rrElite Veteran

Atlanta

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The RF link is the exact opposite end of the argument to John's tests. The probability of a bit error is inversely proportional to the bit time width. The data frames all have a bit error check such as a 32 bit CRC. The bit errors are essentially never decoded and the frame is tossed. For any RF environment, there is an optimal data rate (translates to latency). Any manufacturer could produce a 10 ms average latency system in an ideal RF environment. They all compromise to reduce the bit error rate and therefore the actual observed latency.

Two guys from NZ are going to attempt to analyze the 2.4 GHz RF links of the available systems. This is an order of magnitude harder problem than measuring latency since you have to model the RF environment. We'll see how this goes.

Futaba made the PCM 1024 extremely conservative - and slow. The PCM 2048 was made very quick in the same bandwidth. The net result is an equivalent ~4.4 dB drop in signal to noise ratio. Lots of complaints from poor (antenna) installations. You could not do what you got away with on the 1024. The FASST protocol is also a design compromise. I am sure that the latency observed is a very deliberate attempt to balance bit error rate and latency in a real world RF environment.

John also measures CCPM servo synchronization and sort of implicitly the CCPM calculations thenselves. This is really important and is relatively independent of the latency.

The bottom line is that the lowest latency system may not be the best in real world flying. If you fly in a corn field in the outback, then get the lowest latency. If you plan to fly in a congested urban area near military/industrial sites, that's probably not the best choice.

For about $400 you can get a WiSpy spectrum analyzer and check you field out. Laptop not included.

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02-07-2008 11:42 PM  10 years agoPost 689
Ace Dude

rrProfessor

USA

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> A few years back I read posts about Curtis Youngblood or his Dad
> making a real time glitch counter using his JR radio

Finally, someone else who has heard about this.
I recall hearing about this also, but I don't recall hearing about the results of his findings from the glitch counter. I have to dig up my old issues of MHT because as that's where I recall hearing about his home made glitch counter.

Seems like it might be fairly simple to build something to using a micro-controller to count glitches. Guess this would only work with PCM as there is not checksum on an analog (PPM) signal.

  

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02-08-2008 02:36 AM  10 years agoPost 690
tchavei

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Portugal

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I have a helitron device that shows exactly this on ppm recievers. It will count the glitches even before they appear visible to the pilot. On pcm recievers it will only count true fail safe situations though as it can't scan undecoded incoming data.

Its a nice gadget. I used it to log voltage fluctuations during flight and chart them LONG before the eagletree system appeared in the market.

Tony


--------------------
"Perfection and patience usually walk side by side..."

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02-08-2008 02:54 AM  10 years agoPost 691
Ace Dude

rrProfessor

USA

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I have a helitron device that shows exactly this on ppm recievers. It will count the glitches even before they appear visible to the pilot. On pcm recievers it will only count true fail safe situations though as it can't scan undecoded incoming data.
I assume you're talking about a device that monitors servo signal output from the RX. Not sure what algorithm they use on the PPM signal to determine an error (perhaps just a PPM signal outside of the nominal 1-2ms range). The BC-6 also did this to count glitches.

  

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02-08-2008 03:04 AM  10 years agoPost 692
tchavei

rrProfessor

Portugal

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Yes. I believe it uses something similar. I can't remember the range but over 150 hits was considered bad and between 10 to 50 was considered ok during a flight.

Tony


--------------------
"Perfection and patience usually walk side by side..."

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02-08-2008 03:07 AM  10 years agoPost 693
Ace Dude

rrProfessor

USA

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Yes, but there's a big difference between a 5 minute flight and a 15 minute flight.

  

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02-08-2008 10:45 AM  10 years agoPost 694
Harris

rrApprentice

Cyprus

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To wrap this up, even though the FASST TM14 appears to have a higher latency the percentage of data that can be decoded is closer to 100 due to the use of 2.4GHz frequency, constant channel shifting, and dual antenna diversity. I believe the pilot flying the 12z TM14 FASST would actually perceive to have the same link speed than someone flying the G3 FM RF link with 30-50 percent data loss.
Or, perhaps, humans just cannot perceive such small differences!

What we need to do is a scientific double blind study, where both the pilot and the observers are blinded to the type of radio link used. Then we will really know if there is any difference between the two technologies or if it's all in one's mind...

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02-08-2008 10:54 PM  10 years agoPost 695
da20driver

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Midland, TX

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02-08-2008 10:56 PM  10 years agoPost 696
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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Linky no worky.

Is this the one you're referring to?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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02-09-2008 12:40 AM  10 years agoPost 697
akschu

rrNovice

Big Lake, AK

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That looks great and all, but will it perform, and even if it does, will they ship small/lite/cheap receivers?

schu

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02-09-2008 04:57 AM  10 years agoPost 698
MEDFLIGHT

rrVeteran

South Webster, Ohio

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will they ship small/lite/cheap receivers?
Futaba doesn't know what cheap is (as far as price goes). I used to think they were the best but lately I've been doing some research and I'm starting to change my mind. I'm starting to think the performance you get for the price they demand isn't worth it.

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02-11-2008 04:14 PM  10 years agoPost 699
Chuckie

rrKey Veteran

Crofton Maryland

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Finally, someone else who has heard about this.

I've mentioned previously exactly what you just wrote up as an elusive aspect of latency with zero hard data available on actual data loss for PCM and G3 systems. And, yes, may just explain some of the "lack of difference in flight" between certain systems.

- John
I tried to find the old link and searched the web over the weekend to no avail. I remember seeing pictures of the heli and modified rx. We'll never get any official data so maybe others who have built or own true counters would post their findings. Auger and a few others were working on building counters a few years back. See my link below.
If you fly in a corn field in the outback, then get the lowest latency. If you plan to fly in a congested urban area near military/industrial sites, that's probably not the best choice.
Four Stroker, your post is right on but flying in an open corn field does not guarantee low latency. The interference I’ve experienced is with the G3 picking up rf noise from the heli and electronics onboard the heli. This interference would be constant throughout the entire flight. When flying in an environment with a lot of noise the error rate would be worse.
Seems like it might be fairly simple to build something to using a micro-controller to count glitches.
Check out this old post where Auger discussed building a PCM Bad frame counter, http://runryder.com/t17135p1/

*******************
Well after testing out an N9 this weekend where my friend went from G3 rx to TM-14 I’ll have to update my conclusions.

To wrap this up, even though the FASST TM14 appears to have a higher latency the percentage of data that can be decoded is closer to 100 due to the use of 2.4GHz frequency, constant channel shifting, and dual antenna diversity. From my experience a pilot flying the 14z TM14 FASST would perceive to have the same or faster link speed than someone flying a G3 FM RF link. Faster link - especially when the G3 Rx is being hit with interference (40-60 percent data loss - best guess) but it is not apparent to the pilot that the G3 is having any interference issues, lost data, or lockouts. The affect of the FASST over the G3 link with interference is faster cyclic controls off center (like expo is set lower), faster collective response, more precise control when hovering in 10 to 15 knot winds, higher sense of control during high speed flight where small corrections have a greater affect over a long period, and more control during autos especially at the landing when winds are 10 to 15 knots. I felt a much better connection which to me was not a minor improvement.

Charles

Please stand by for faster service!

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02-11-2008 04:37 PM  10 years agoPost 700
BisonFlyer

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Winter Garden, FL

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hey charles, thanks for sharing your impressions. i too felt like the fasst setup was every bit as good, if not better, than my g3 setup. there def must be a missing link somewhere between the latency testing and in-flight performance, and it seems logical that the dropped frames with pcm/g3 could account for the difference.

Art Hughes
SAB Heli Division~Byron Fuels~Mikado V-Team~Scorpion~Pulse~Xpert Servo~Kontronik Drives

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 77 pages [ <<    <     33      34     ( 35 )     36      37     NEXT    >> ] 336054 views POST REPLY
HomeRC & PowerAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › TX/RX Latency Test Results
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