Quote from: mpsaju on October 16, 2009, 09:41:37 AM
Please note that most TTL based IC technology use 5v as a standard. The 4.8v spec given is the lowest value the ICs can tolerate. The higher value of 6v provided is just to provide a sort of protection from wrong polarity by way of a diode in series with the Rx main circuit. The forward bias drop of a silicon based diode is 0.7v. So if that is subtracted from 6v, we arrive bang on the std TTL voltage upper tolerance of 5.3v. Therefore providing 6v is a non-issue.

Nobody uses TTL components these days. If it was TTL, the receivers would not have worked reliably at lower voltages from 4 cell NiMH battery pack. Without knowing the exactly what fails in the Futaba rx, I see merit in Gaurav's hypothesis. In general the power dissipated in electronic devices does increase with voltage. The nominal working voltage of devices I have worked on developing have  been going down over the years for this very reason - reducing power dissipation. Current devices work at a nominal voltage of 1V.

It is true that TTL is not widely used nowadays... however, with the old foundries being scrapped to asian countries you wouldn't know what the chinese component manufactures have inside their products. I am a 'victim' of a chinese manufacturer who claimed good things in his component datasheet.. it worked fine in samples but in production it burnt my fingers.. on close examination its found to be out of specification!! Well, I do not mean that you may have a component like that in your radio systems. Its just my experience with electronic components...

At 2.4GHz signalling rate, it would be wise to use a 1.0V - 1.8V for power supply to conserver power and to maintain the requried slew rates. My guess would be the RF back end would be using a lower voltage (1V - 1.8V) while the Digital Front end system would be using higher voltage (3.0V - 6.0V)... So, the system to work the supply voltage should be >= 3.0V.
(Again, note that the voltage figures are just arbitary values)

-Ismail

Quote from: RotorZone on October 16, 2009, 11:27:57 AM
Without knowing the exactly what fails in the Futaba rx, I see merit in Gaurav's hypothesis. In general the power dissipated in electronic devices does increase with voltage.

While this is true, there is a different issue to consider.

If Gaurav is trying to be cautious, which I thought was the intention, then there is a choice to make.  One possibility is a low voltage reset, and the other possibility is receiver overheating.  Between these, low voltage reset is more prevalent, hence my recommendation that a 6V setup would be more resilient.

I didn't see where the 6V was suggested, I was responding to Gaurav's post about Futaba. I guess somewhere the spektrum low voltage reset issue and futaba overheating has got mixed up.

His question, I believe, was "is 6V riskier than 4.8V because of heat issue".  I believe heat is a lesser risk than the risk of running a lower voltage on the receiver.  6V is within the rating of the receiver, and the small increase in voltage and possible additional heat generated due to that is less of a concern than the risk of receiver power going low.  The number of 6V setups people use on Futaba FASST especially on larger planes seems to confirm this.

Which component overheats in Futaba ? Is it the processor or regulator ?

Quote from: anwar on October 16, 2009, 12:16:19 AM
Gaurav -

Like anything in life, do not do anything that you have second thoughts about.  But try to do your research first, so that you can draw your own meaningful conclusions. If you feel uncomfortable even after that, do NOT do it.

Ever since I became aware of the heat issue, I was looking at how people are dealing with it, and if this is affecting people's confidence in deploying this.  To my surprise, I found that more people who are flying the bigger models (especially gassers) were going for Futaba FASST as compared to any other radio !

Well, I agree that people are using FASST for gassers and other big airplanes, but there have been incidents worldwide. Not that i do not trust 2.4G, the technology is the future, but the FASST implementation is not 100% there yet. All these heat and voltage issues never existed in the 72Mhz, and these issues cropping up after their product release surely proves that Futaba went wrong somewhere.

Quote from: anwar on October 16, 2009, 12:16:19 AM

Newer receivers are coming to the market from Futaba, and I did not do much research on how much they have fixed the heat issue in those.  May be with the newer receivers, this whole issue is a non-issue ! After all, it is only the receivers that are affected.

Agree to this. But we live in the present and we cannot ignore this issue. The importance of this issue is realized only once you crash your model and have no explanations what caused it. We just cannot take it lightly.

Quote from: anwar on October 16, 2009, 12:16:19 AM
To directly answer you, the number of gasser flyers who use Futaba 2.4 is a good indication that you are safe. 

and also remember that there have been a number of un-explained crashes.

This is why I said, go with what makes "you" comfortable.  Yes, these heat issues were not discovered in India, it has affected people worldwide.  But worldwide, Futaba FASST seems to be a top choice when it comes to flying large planes.  You make the pick, that suits you

Futaba implementation erred on the heat tolerance of a receiver chip. It is known, and acknowledged. I am not sure why it needs to be "proved".  For common use with precautions, people still seem to prefer it.  Does not mean that you or me should follow suit.

Unexplained crashes have happened with every radio technology.  If you feel the share of Futaba FASST is particularly significant, do NOT go for it.  Let the people who are trusting it now, have their trust shaken when they hit the dirt   Just remember that it is a tiny minority though (as compared to the total number of people using it) !  If you want 100% guarantee (which I am not sure is achievable), you should make decisions towards that end. 

Futaba is only one of the choices, after all.

Receiver voltage is an issue everywhere, including 72Mhz.  Newer 2.4 implementations have drastically improved the reconnect times.  Heat is a Futaba FASST specific issue, not a 2.4Ghz wide issue.

Gaurav and all

The processor used in the Futaba Tx and Rx is the same : ML 2724 from Micro linear. This is a fully integrated 1.5Mbps frequency shift keyed (FSK) transceiver that operates in the unlicensed 2.4GHz ISM frequency band.

I am attaching the max ratings specified for your benefit. This data sheet specifies that the processor can operate even as low as 2.7v but subject to other components on the rx operating at that voltage. This is the processor which has the unfortunate bad habit of heating especially in the rx mode. This chip is used extensively in cordless phones. It has an upper tolerance of 5.5v for its VDD. Futaba certainly has other components interspersed to see that the voltage at this chips VDD does not exceed specs. So you can rest assured about the use of 6v.

As I said before, one has to take ones options cautiously, knowing the risks involved.

Saju

Yep, this is the one with the 60C temperature limit. 

Futaba should have made a better choice, not giving Spektrum guys a chance to come up with advertisements like these 

http://www.spektrumrc.com/content/images/products/challenge_AD_3.pdf

Here is an interesting video on low voltage impact on both Futaba and Spektrum/JR 2.4Ghz systems.



At 3.0V, I can't see how regular (72) Mhz links can fare any better either.

QuoteAt 3.0V, I can't see how regular (72) Mhz links can fare any better either.

at this voltage the servo will be going there own thing beside one can notice non responsiveness of the plane or glitching well before 3volts !

PS: the above experience was with Futaba AM 4ch RX and e-sky servos 9 grammar's

Sponsored by Spektrum    Still quite a bit of good information.

http://www.spektrumrc.com/Content/Images/Products/calOrrSPMarticle.pdf

My all time favorite thread 

The latest news is that Futaba seems to have slipped in a new set of receivers which are much more head tolerant. 

[1] The newer batches of the original "FS" series receivers have small dot (either white or gold) under the antenna. People on other forums who have tested these for heat tolerance have reported that they cannot reproduce the heat-triggering-failsafe issue on these.

[2] The new "HS" and "FF" series receivers have also been tested to be free from the heat issue. They also seem to have a gold dot.

So if you are in the market for a Futaba 2.4Ghz (FASST) receiver, please note this.

What is sad is that Futaba seems to have never acknowledged any change to the heat tolerance with these newer receivers (still the same 60C), which seems to be a business decision driven by the worry of heightening the concern for existing FS series receivers in the market. 

NOTE to Saju bhai:  As this is bad customer service, the marriage has been called off (although we continue to be friends) 

NOTE: If someone is reading this for the first time, please be aware that the Futaba heat issue is not a concern for routine flying and tens of thousands are using them without issues, with the appropriate best practices applied.

This thread has a picture of the white dot.

http://www.rcuniverse.com/forum/m_8859612/anchors_8859612/mpage_1/key_/anchor/tm.htm#8859612

And here is a oven test, on an FS series receiver with the dot !

Anwar Bhai

"NOTE to Saju bhai:  As this is bad customer service, the marriage has been called off (although we continue to be friends)  "

Noted... Now will be the next in line ? and when will the blessed event take place ?

Saju

Quoteplease be aware that the Futaba heat issue is not a concern for routine flying

What is the kind of flying where it could/would be a concern?

I have a feeling you know the answer already, but here goes again 

The issue is not the type of flying, rather the place and modus operandi that matters.

It is an issue in severely hot places, combined with keeping the receiver exposed in the sun through the canopy (causing the inside of the fuselage to get really hot). It has also been reportedly triggered by the receiver being kept next to sources of heat inside the aircraft itself.

A large majority of people who have noticed this issue have experienced this on the ground, as the plane was on the ground exposed to the sun, and when it is time to take off, they see the led on the receiver in red as failsafe has already kicked in.  Most people move the plane to the shade for less than 5 minutes, and take off after the receiver led turns green.

The 148 page thread on Flying giants is a pretty good bed time reading, and if nothing else, you end up with some respect for the Airtronics SD-10G

With fans like in the attached picture (which I just noticed on Facebook), I guess Futaba can get away with a lot 

did some one say Airtronics SD-10G   (mine is on its way)

what is the operating temperature of 2.4GHZ receivers sold by futaba,JR,spectrum radios ?? i know that Airtronics stuff operates upto 50C !

QuoteWith fans like in the attached picture (which I just noticed on Facebook), I guess Futaba can get away with a lot  Roll Eyes

Quote from: sahilkit on January 18, 2010, 09:55:36 AM
what is the operating temperature of 2.4GHZ receivers sold by futaba,JR,spectrum radios ?? i know that Airtronics stuff operates upto 50C !

This has been discussed to death here   Just search !

Note that newer Futaba receivers have higher temperature tolerance, but not officially acknowledged.

BTW, 50C for Airtronics does not sound right.  Futaba had listed tolerance of 60C, and people had issues when such receivers were exposed inside canopies.

okay will do  

QuoteThe 148 page thread on Flying giants is a pretty good bed time reading

link please

QuoteBTW, 50C for Airtronics does not sound right.  Futaba had listed tolerance of 60C, and people had issues when such receivers were exposed inside canopies.

hmm....summer season is on its way so lets wait n see if i have anything bad to report !