Are all the 2.4GHz the same?

[Erfolg]

Personally I fly electrics, but this issue (if it is) may effect all.

When Timbo is discussing ESC he seems to suggest that the Spektrum receiver requires a higher than usual voltage (for 35MHz) to keep the receiver working properly.

Is this the same for all 2.4 receivers, or is it a Spektrum thing. Now that everyone has (or seems to have) a 2.4 set out.

If the Spektrum is a odd ball, what are the implications. In the past i have inadvertently run my batteries right down, yet my Sanwa (that is what I had then) kept on working. All be it slowly.

Regards

Erfolg

[260 Flyer]

Never had any problems with my 6EX. infact I hit the LVC flying on a duff pack yesterday, full control all the way back to the strip. 4 servos on a 2A ESC/BEC.

Rob

[Tim Mackey]

I am not sure I have actually ever suggested that Erfolg ? I know Scott Cupello has some real concerns about brown outs with some of his spekky stuff, but personally I have never suffered any. I do tend to ensure a more than ample supply for the radio, favouring either a good switching BEC or a standalone UBEC ( preferably set to 6V out )

The official line from Spekky is here...cant comment on Fuby stuff

"Spektrum’s receivers’ minimum operational voltage is 3.5 volts, it is highly recommended the system be tested per the guidelines below to a minimum acceptable voltage of 4.8 volts during ground testing. This will provide head room to compensate for battery discharging or if the actual flight loads are greater than the ground test loads.

Recommended power system guidelines:

1. When setting up large or complex aircraft with multiple high torque servos, it’s highly recommend a current and volt meter (Hangar 9 HAN172) be used. Plug the volt meter in an open channel port in the receiver and with the system on, load the control surfaces (apply pressure with your hand) while monitoring the voltage at the receiver. The voltage should remain above 4 volts even when all servos are heavily loaded.

2. With the current meter inline with the receiver battery lead, load the control surfaces (apply pressure with your hand) while monitoring the current. The maximum continuous recommended current for a single heavy duty servo/battery lead is three amps while short duration current spikes of up to five amps is acceptable. Consequently if your system draws more than three amps continuous or five amps for short durations, a single battery pack with a single switch harness plugged into the receiver for power will be inadequate.

 It will be necessary to use multiple packs with multiple switches and multiple leads plugged into the receiver.

3. If using a regulator it’s important the above tests be done for an extended period of 5 minutes. When current passes through a regulator heat is generated and this heat causes the regulator to increase resistance which in turn causes even more heat to build up (thermal runaway). While a regulator may provide adequate power for a short duration it’s important to test its ability over time as the regulator may not be able to maintain voltage at significant power levels.

4. For really large aircraft or complex models (35% and larger or jets) multiple battery packs with multiple switch harnesses are necessary or in many cases one of the commercially available power boxes/ busses is recommended. No matter what power systems you choose always carry out test #1 above making sure that the receiver is constantly provided with 4 volts or more under

[Tim Mackey]

" Spektrum’s receivers’ minimum operational voltage is 3.5 volts."

I am not speaking with absolute knowledge here...but...I would have thought that once you are down around 3.5V, you should be a bit concerned - to say the least.... with ANY radio system

Incidentally, the Eagle Tree logger unit has a servo current monitor sensor, and I have asked them about servo voltage monitoring ( which is really a better idea )...apparently its next off the drawing board real soon.

[Erfolg]

Timbo

I was not or am suggesting that you have implied that there is a problem with the Spektrum.

However I am left with the impression that it needs a higher voltage than my 35MGhz Futaba or any other gear I have used. Like many other modellers I have occasionally been rather cavalier (unintentionally) with my receiver battery. I have been fortunate with no real problems. I am left with the impression that I would have had a rebuilding project if i had had a Specktrum.

My question still is, is this only a Spektrum issue or are other 2,4GHz systems as demanding on the need for volts.

Reghards

Erfolg

[Tim Mackey]

I didn't take it that you were Erfolg ...merely answering your impression , quote -

"When Timbo is discussing ESC he seems to suggest that the Spektrum receiver requires a higher than usual voltage (for 35MHz) to keep the receiver working properly".

I just don't remember deliberately giving such a suggestion that's all

Of course until someone authorative actually states the receiver requirements ( as have, at least, Spektrum ) then we are all wondering the same question

[birdy]

Hi! My Futaba 2.4 as far as I know is safe as far as voltage is conserned, only the servos need it! I think Erfolg is refering to the artical about the recievers before the Qwick Connect thingy where if for a moment when the rx battery suddenly droped below 3.5v under load the rx might stop working for a few seconds. My answere to that is that they dont need more volts then usual. Its just you need to keep old, unupdated, spekky units above 3.5v. birdy

[Tim Mackey]

Yes I know what he is referring to, I simply stated that I did not make an assumption that spekky receivers required more than 35Mhz ones. Where does it say they do? As already laboured - the point is that without hard information from an authoritive source such as the radio manufacturer himself, we simply dont know what the minmum safe operating voltage of the 35mhz gear is.

What exactly is meant by the statement "My Futaba 2.4 as far as I know is safe as far as voltage is conserned" ?

Have you tested your Futaba 2.4 Ghz gear with a voltage below 3.5V ? - and while your at it, perhaps you could tell us what exactly happens after a brown out with the Fuby stuff ...is there along reboot delay or what ?

The fact that spekky receivers have been updated with quick connect makes no difference to their ability / inability to work at less than 3.5V - they will still brown out.... however with quick connect the re-boot is far quicker and in most cases should allow a safe recovery.

Quick connect is ABSOLUTELY NOT an excuse to use insufficient capacity for your radio power system, and just like anti lock brakes on a car is not a reason for complacency

Did you know that back in the 60 / 70s  certain Insurance companys increased its premiums for drivers of cars with the fancy new "ABS" - the reason cited was one of exactly that - complacency. Drivers were braking far later and harder in the belief that this new gizmo would prevent a problem, and in fact it increased the accident rate!

My company at the time were instructed to send all company vehicle drivers on a 6 hour course dedicated to this subject, or face higher premiums.

[Peter Christy]

Most integrated circuites used in consumer goods are only guaranteed down to 3.5 volts. That would include ALL radio gear, be it PCM, PPM or 2.4 GHz. Go below that at your peril. It may well continue to work - many Spektrum receivers do, but it is NOT GUARANTEED to work!

 Nicad manufacturers recommend that cells should not be discharged below 1.1 volts per cell, otherwise permanent damage may be caused.

If your volts are dropping below 4.4 volts, then either your Nicad is inadequate or knackered and needs replacing, or your switch harness is knackered and needs replacing!

If you are suffering brown outs it is because of POOR MAINTENANCE!

Having said all of that, should a brown out occur, the Spektrum receivers were rescanning the whole band to try and re-locate their "parent" transmitter, which could take some time. The quick connect feature makes it check the last channels in use first, where it should find its parent tranny immediately.

Quite what happens to a Futaba, which is hopping all over the place in a pseudo-random sequence, I don't know! But it too will have to relocate its parent transmitter somehow. This is unlikely to be instantaneous!

Brown outs are a symptom of a deeper problem, not the problem itself!

 --

Pete

[Erfolg]

I think I am begining to understand the issues.

With my 35MHz system, allow the receiver battery to run foolishly low, the servos tend to run a bit more sluggishly.

Do the same with 2,4, it seems that the receiver may loose its link to the transmitter. In the case of 35 it only had option, its set frequency.

Regards

Erfolg 

[birdy]

I just spent ten minutes writing a ridiculusly long and boring post... Anyway, to sum it up I didnt mean you could be complacent, and the fuby 2.4 closes the throtte (but gives you a chance to reopen it for a limited time) if the voltage gets to low, but having only flown five times I havent had a chance to experience this (thank god!). birdy...

[Tom Sharp]

What is a brown out?

Question asked in good faith.

[Former Member]

[This posting has been removed]

[Tom Sharp]

Thank you Eric.

[Tim Mackey]

Hi birdy...yeh I know what you mean about long posts - especially when they disappear into the ether after all that work

Are you sure the fuby closes the throttle on low supply battery voltage?   -This of course will happen on most electric models following LVC activation...but thats a different matter altogether. 

[Tim Mackey]

Actually its when the receiver momentarily shuts down due to low power.... loss of signal will not necessarily cause a brown out.

[Peter Christy]

The point is that ALL systems are at risk of "dropping out" if the volts drop as far as 3.5 volts, and that includes 35 MHz, be it PCM or PPM! The difference is the time it takes the system to recover when (and if!) the volts come back up.

I have to say I believe the problem has been seriously exaggerated! The only people I  have heard of suffering from it are extreme 3D helicopter pilots! A digital servo can draw a few amps under load. A typical 3D helicopter set up will have 5 digital servos plus a gyro. The instantaneous current draw could be as much as 10 amps - maybe more -  all going through a single little plug between the nicad and receiver!!!

 At that kind of current draw, it only takes a resistance of 0.1 ohm to reduce the voltage at the receiver by 1 volt!

Think about an old car starting in winter. Quite often it will refuse to crank or start, even though the battery is known to be good, because of corrosion where the earth lead connects to the chassis making a poor connection. It is exactly the same problem!

So for most fixed wing pilots - and even sport helicopters - it shouldn't be an issue at all.

But if you are into extreme 3D with helis, and insist on running a full house of digital servos, make sure your nicads and wiring harnesses are in tip-top condition - WHATEVER radio you use!

--

Pete

[YakMad]

The Futaba 2.4 Rx's do shut the throttle to warn you of impending low battery voltage you will only get about another minute of sufficent voltage after that at which point the rx will shut the throttle, and nothing will work, I persume it's in failsafe, at this point your 35 mhz would not be working either and the only thing you would have noticed up to this point was sluggish servos. I use both Futaba and Spectrum based systems (JR) so I am not biased either way, I think the Spectrum may have the edge as regards re-connect time as the Futaba does take a little longer. Having  said all this I have only had a Futaba rx shut the throttle to warn me of low voltage while I was setting up a model in the workshop. I have to agree with Peter that I the only person in our club who suffers low battery problems on a regular basis is one of the extreme 3D heli guys and he is still on 35 mhz and he uses lipos thru a UBEC to power his flight pack, if you apply enough load to any system you are going to run out of voltage.