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Old 02-15-2013, 03:43 AM   #1
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Default Power requirements / voltage drop

Hi there,

does anyone know if we have already reached a critical area in terms of power requirement? Is the voltage still stable enough to prevent any brown-outs of the receiver?

Reason why I'm asking is because I have had issues every know and then with failsafe activiation or control loss of my 1/8th car with Futaba 2.4Ghz and can not figure out why. I hate changing rx tx, power leads and never find the root cause of the issue.

I am also into RC helicopters and preventing voltage drops which could get the receiver to reboot is a big thing over there. Everyone is now using capacitors to dampen the current peaks and avoid voltage drops.

You can only measure voltage into the rx with a scope because every kind of telemetry or voltmeter is way to slow in detecting voltage undershoots that last only for miliseconds. I dont have a scope, but maybe someone else has already or could measure voltage on a typical car system with 2.4Ghz receiver, two strong digital servos a transponder and our old 6v NimH receiver packs.

The helicopter guys found that reversing the digital servos quickly creates the biggest effect.. They draw more then 10 amps each when stopping from full speed in one direction and going to full speed in the other direction...

Any thoughts are appreciated...
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Old 02-15-2013, 04:46 AM   #2
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My thoughts would be to get rid of the NiMh receiver pack.

Where are you still getting them. They have all but diappeared.
Lipo or Life voltage is much more consistent over the discharge cycle.

We had a top racer here who got driven nuts by glitches with his Futaba, pretty much what you described.
He changed TX ans RX and the problem was gone
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Old 02-15-2013, 04:46 AM   #3
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Quote:
Originally Posted by fulcrum2 View Post
Reason why I'm asking is because I have had issues every know and then with failsafe activiation or control loss of my 1/8th car
Do you have the possibility to connect 2 receiver packs in parralel, as a test?
If you the still have this problem, it lies somewhere else....
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Old 02-15-2013, 05:28 AM   #4
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For the upcoming season I've already ordered Life packs because of the higher voltage and better discharge curve. So we will see...
However, it would be interesting to measure how much the voltage drops and if it gets close to the minimum of the rx...

Having this said, we get more and more complaints about brown-out's amongst the drivers in our series. There is always pit talk going on about this conspiracy-theory where people think it is the radio link that is disturbed by wifi-routers, cheap radios or whatever.
But it could also be voltage drop. Servos getting faster and stronger all the time...

Last edited by fulcrum2; 02-15-2013 at 05:40 AM.
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Old 02-15-2013, 07:34 AM   #5
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While a scope is certainly nice for checking volt drops, I think a good DMM with Min/Max function should be more than capable of catching this kind of stuff too. If it has graphing capability more the better.
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Old 02-15-2013, 07:52 AM   #6
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Another thing to aware of is binding or dead ending in linkage or steering. Current state digital servos are very capable of visually masking any linkage binding yet this will crowbar the hell out of the battery and cause a voltage drop. I have on occasion done current draw test on my cars looking for this kind of stuff.
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Old 02-15-2013, 08:55 AM   #7
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Ive had my Futaba 3pks for 5 years and I ve never had any glitches what so ever. If my bateries were charge there were no problems. You're problem is somewhere else in the system.
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Old 02-15-2013, 12:54 PM   #8
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I have seen early 2.4GHz from Futaba suffer because of high temperatures. However that is not the case with all of them. That problem was addressed as far as I know. Linkage binding is on posible culprit since lock rotor currents are 4 or even more times the nominal current in any motor. EPA is supper important to prevent this as well. Like P2gee said linkage can cause all sorts of trouble. Make sure everything is super smooth during the whole movement of the linkages. Capacitor banks can help smooth out the current spikes and will help a lot. Also even though I use LIPO or LIFE batteries I always use a little rubber band in my carburator. No matter what failsafe one has a throtle return spring or rubber band works. Imagine if the battery gets disconnected? No failsafe will work in that situation. Better be safe than sorry.
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Old 02-15-2013, 02:24 PM   #9
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this has been a problem for me too. This was what i did.

I read the specs from differant receivers and the Sanwa receivers had a working voltage of approx 2,5 Volts. All others had about 3,5 volts. I used life with 6,6 volts and i had occasional brownouts mostly when braking. But also on full throttle

I had no binding on the links.

Sold the spektrum and bought the Sanwa after a whole year trying glitch busters and nimh batts.

Sanwa did it , no glitching what so ever. I do believe it has to do with the minimum voltage on wich they still operate.

wish you all luck. resolving this.
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Old 02-15-2013, 03:13 PM   #10
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Using Spektrum and NiMh batteries and never had a problem. Once I have seen a same problem and finally after swapping several components it was the AMB transponder to blame. People do forget the transponder is also a transmitter and so it is not wise to mount it near the receiver.
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Old 02-15-2013, 03:28 PM   #11
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Which servo brand are you using?. If it's Savox get rid of them and get some Futaba, Sanwa or Kopropo servos.
Savox servos use a ridiculous amount of current because of their inferieur software and hardware.
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Old 02-15-2013, 05:31 PM   #12
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Quote:
Originally Posted by DS Motorsport View Post
Which servo brand are you using?. If it's Savox get rid of them and get some Futaba, Sanwa or Kopropo servos.
Savox servos use a ridiculous amount of current because of their inferieur software and hardware.
Sorry to hear of such servo difficulties but I found my 'magic' with the Savox servos. I run Futaba 3PMX/ NimH and have enjoyed the performance once I learned to 'secure' my battery connector against 'G-Force...disengagement'.

Not all servos will allow a 'return-spring' to pull the servo for a throttle closure but the Savox moves freely so that the 'last-command-before-power-loss' doesn't need to mean "ABSOLUTE" curb contact.

....

I've had failures w/Airtronics and Hitec in GT8 and would only use Futaba in my aircraft and boats.
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Old 02-15-2013, 07:39 PM   #13
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I run the same servos is my 2 GT cars and in my 1/8th buggy and truggy.... Savox 1256tg & 1257tg all 4 cars run nimh receiver packs on my "cheap" Futaba 2pl 2.4 system.

The only runaway I ever had was when the 3 year old on/off switch on my truggy went bad....since then I replace my switches very regularly and have never had a glitch, I race all summer here in Utah with 95-100 degree temps as normal, heat has never affected my Futaba system.
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Old 02-16-2013, 01:55 AM   #14
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Thank you very much for all the feedback, as I already said it is much appreciated.

I run Fuaba servos. BLS451 steering 9452 throttle brake. When I hold both servo arms with my hand (full stall condition) the receiver will not brown out or activate the failsafe. This tells me that some binding in any linkage (which I do not have) should not cause the issue.
It happens very rarely which makes it difficult to find the cause (on the bench I can not replicate at all). I have switched RX and TX as well but my set-up is still not 100% reliable. I know that Futaba is considered to be the best and some of my friends have zero issues but I had too many problems over the years so I consider switching the brand as well. I do also use some of the equipment (Two different TX and some of my receivers) with virtual rc on the computer and I never had a loss off signal there. OK, power requirements, range and vibrations are different there...
It is a shame that there is no data logging or at least LED blinking signals in case something goes wrong. For example if the receiver would blink after a power loss, I could see this when it is back in the pits.
But when my car glitches, the mechanic puts it back on track and it willl run like normal again without touching anything. However, if it happens I stop the race or qualifier because I dont want to risk the car and and dont want to run into other drivers. Focus and concentration go straight out of the window anyway when it happens...
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Old 02-16-2013, 02:23 AM   #15
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I've had similar problems and it was the switch. I don't run switches anymore for that reason.
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