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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 10-25-2010, 09:22 AM   #1
nevio p
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Default Powering the AR7000 Receiver in a large scale airplane

I have just purchased an 88 inch Yak54 and will use a 6000W electric motor for power.
The motor will have its own Opto ESC and 12s battery.
The Spektrum AR7000 receiver and 5 Power HD, HD9110MG (10,5 Kg at 6v) will be powered through a separate dual UBEC (8A per Ubec) with two 3s Lipos.
The question is: Can the AR7000 take all that current flowing directly through it?
The HD servos each have a stall current at locked of 1700 mA
I have no idea what the Tx uses but that cannot be too much.
The Spektrum manual that comes with the radio makes no mention of max current for the AR7000 receiver nor can I find this info in the frequently asked questions on the Spektrum web page.
Many thanks for any advice.
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Old 10-25-2010, 12:20 PM   #2
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AR7000 voltage range is 3.5 to 9.6 volts
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Old 10-25-2010, 01:04 PM   #3
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At a minimum, run a 6 volt receiver battery. You can use the 4.8, actually that is what comes with the spektrum radios, but why take the chance of a low voltage issue.

I run 6v batts in all my big stuff like that.

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Old 10-25-2010, 04:46 PM   #4
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Originally Posted by nevio p View Post
I have just purchased an 88 inch Yak54 and will use a 6000W electric motor for power.
The motor will have its own Opto ESC and 12s battery.
The Spektrum AR7000 receiver and 5 Power HD, HD9110MG (10,5 Kg at 6v) will be powered through a separate dual UBEC (8A per Ubec) with two 3s Lipos.
The question is: Can the AR7000 take all that current flowing directly through it?
The HD servos each have a stall current at locked of 1700 mA
I have no idea what the Tx uses but that cannot be too much.
The Spektrum manual that comes with the radio makes no mention of max current for the AR7000 receiver nor can I find this info in the frequently asked questions on the Spektrum web page.
Many thanks for any advice.
I've had my AR7000 receiver apart tracing down a bad solder joint three years ago. The AR7000 servo connector buss copper foil should be able to handle more than a few amperes.

Still best to check with JR though.

As for primary backup batteries, take a look:

http://www.wattflyer.com/forums/showthread.php?t=58310
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Old 10-25-2010, 05:04 PM   #5
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Except for ignition batteries, I won't even allow a 4.8V battery near any of my planes anymore. Learned my lesson on the 1/4 scale PA-18

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Old 10-25-2010, 05:08 PM   #6
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Originally Posted by Old Fart View Post
Except for ignition batteries, I won't even allow a 4.8V battery near any of my planes anymore. Learned my lesson on the 1/4 scale PA-18
100% Agree!
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Old 10-26-2010, 09:48 AM   #7
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Originally Posted by firemanbill View Post
At a minimum, run a 6 volt receiver battery. You can use the 4.8, actually that is what comes with the spektrum radios, but why take the chance of a low voltage issue.

I run 6v batts in all my big stuff like that.
Sorry that I forgot to mention that the Dual Ubec and Controler are supplied by two 2s Lipos and that the Ubecs then output 6 volts to the receiver.
From what I read there should be no problem with the AR7000 circuits running the kind of load I am expecting
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Old 10-26-2010, 04:03 PM   #8
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Originally Posted by nevio p View Post
Sorry that I forgot to mention that the Dual Ubec and Controler are supplied by two 2s Lipos and that the Ubecs then output 6 volts to the receiver.
From what I read there should be no problem with the AR7000 circuits running the kind of load I am expecting
Uh Oh.

Be certain to check with the manufacturer of your uBEC's that your uBEC's will work OK in a parallel output setup. Running the outputs of two different switching power supply uBEC's is usually not a good idea.

Perhaps running the uBEC's to a commercial dual battery system would be OK, don't know.

At the very least, put a high current schottky diode in series with the positive output of each uBEC might work. (Putting diodes in series with the positive output prevents a shorted "bad" uBEC output from short circuiting the "good uBEC".) It might also prevent "hunting" on the output of two paralleled uBEC's.

These Schottky diodes are now available in currents exceding 15 amperes. (They have a lower voltage drop than silicon diodes. Example, www.digikey.com has some 15,000 DIFFERENT types of diodes.

Check out their part number http://search.digikey.com/scripts/Dk...=12TQ040PBF-ND. This 15 Ampere diode has a voltage drop on the order of 0.5 volts DC at 10 amperes.)

Digikey is a near billion dollar business that will sell parts to anyone with a credit card. I've purchased a LOT of stuff from them, both at work before retiring, and at home. Good company to work with.
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Old 10-26-2010, 06:07 PM   #9
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Default Thanks kyleservicetech

Thanks for your suggestion but that puts me way out of my depth when it comes to electronics/electrics.
I will actually use something that has recently hit the market. Its a Turnigy redundant dual 8A UBEC Rx power system. It is a plug and play thing which will suit my scarce electronics understanding.
My fear was weather or not my AR7000 could take all the current drawn by the 5,10.5 kilo digital servos I will be using.
Spektrum does not specify in its instruction manual just how much current you can put through the AR7000 Rx. What if instead I was using say 10, 30Kg digital servos, would the Rx be damaged?
Spektrum market Rx's, the AR9100 and AR9200, which they define as "Powersafe"
"AR9100 DSM2 9-Channel PowerSafe Receiver
The AR9100 is designed for models using multiple servos that draw excess current or multiple high-torque servos, such as giant-scale airplanes and jet models. It features a robust power bus designed to manage high-current loads, as well as dual 16AWG battery input leads with EC3 connectors for use with larger battery packs. This makes it possible to support high-current systems straight through the AR9100 without the need for a separate power system"

The above has been copied directly from the Spektrum web site.
Now what exactly do they mean by "servos that draw excess current or multiple high-torque servos". Where do you draw the line? Where do I stop using my AR7000 and buy an AR9100.
How many of my 1700 Ma servos can I use before I do damage to my receiver.
To me this sounds like pretty crucial stuff which should always be included in instruction manuals.
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Old 10-26-2010, 07:25 PM   #10
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Originally Posted by nevio p View Post
Spektrum market Rx's, the AR9100 and AR9200, which they define as "Powersafe"
"AR9100 DSM2 9-Channel PowerSafe Receiver
The AR9100 is designed for models using multiple servos that draw excess current or multiple high-torque servos, such as giant-scale airplanes and jet models. It features a robust power bus designed to manage high-current loads, as well as dual 16AWG battery input leads with EC3 connectors for use with larger battery packs. This makes it possible to support high-current systems straight through the AR9100 without the need for a separate power system"

The above has been copied directly from the Spektrum web site.
Now what exactly do they mean by "servos that draw excess current or multiple high-torque servos". Where do you draw the line? Where do I stop using my AR7000 and buy an AR9100.
How many of my 1700 Ma servos can I use before I do damage to my receiver.
To me this sounds like pretty crucial stuff which should always be included in instruction manuals.
As one of my club members pointed out, using the Spektrum AR7000 or similar receivers in giant scale has a "Single Point Failure", where the battery power is connected to only one DC input to the receiver. So, even if you have dual battery sources, those two dual sources still connect to one point in the receiver, its battery input. And, worse, you are running all of the current pulled by your servos through that single point, using the standard battery plug used by the AR7000 and similar type receivers.

One big advantage of the top of the line Spektrum 9100 receivers, is their battery inputs are separate cables. I do not know if these separate cables are actually isolated from each other, that would have to be checked by contacting Horizon Hobby.

The Turnigy units mentioned, one response is a question as to their Quality Control, something to be aware of in a Giant Scale model.
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Old 10-26-2010, 08:44 PM   #11
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You can plug a second (or a third, etc) battery source into any open port in a Spektrum RX. Tha advantage to the AR9100 (or the JR equal) is the larger wire guage, and that it doesn't take up a port. I have my 50cc Ultimate set up this way with an AR9000. (Have seen that RX w/o the case)

The cables on a 9100 go to the same bus IIRC, but they soft switch to a "fail to power available" mode. I have that RX on my 36% Katana (but haven't ever taken the case off the RX)

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Old 10-26-2010, 10:35 PM   #12
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Originally Posted by Old Fart View Post
You can plug a second (or a third, etc) battery source into any open port in a Spektrum RX. Tha advantage to the AR9100 (or the JR equal) is the larger wire guage, and that it doesn't take up a port. I have my 50cc Ultimate set up this way with an AR9000. (Have seen that RX w/o the case)

The cables on a 9100 go to the same bus IIRC, but they soft switch to a "fail to power available" mode. I have that RX on my 36% Katana (but haven't ever taken the case off the RX)
Agreed, that's what I'm doing with my A123 backup system for next year's giant scale 2 KW model:

http://www.wattflyer.com/forums/showthread.php?t=58310
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Old 10-26-2010, 11:09 PM   #13
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Originally Posted by Old Fart View Post
Except for ignition batteries, I won't even allow a 4.8V battery near any of my planes anymore. Learned my lesson on the 1/4 scale PA-18
I am just finishing up a Pilot 1 Piper PA-12 1/4 scale & installing the electronics. Can I ask what happened to the PA-18 with the 4.8 battery?

Reason for asking is I have a 4.8/4500mah but have been looking at some 7.4 volt Lipos.

Kevin
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Old 10-26-2010, 11:28 PM   #14
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Originally Posted by BEAR-AvHistory View Post
I am just finishing up a Pilot 1 Piper PA-12 1/4 scale & installing the electronics. Can I ask what happened to the PA-18 with the 4.8 battery?

Reason for asking is I have a 4.8/4500mah but have been looking at some 7.4 volt Lipos.
I've got six AR7000 Spektrum receivers, all work well. When this "undervoltage" phenomenon first became news, I tested all of mine at reduced voltage with a variable power supply. These receivers "reboot" at 3.2 Volts DC, plus or minus a few percent.

So, if your receiver voltage drops below 3.2 volts, even for a very small fraction of a second, your receiver will reboot its little microcontroller (a version of microprocessor). And, it used to take a second or three for the receiver to start working again.

The latest Spektrum receiver software now reboots in a fraction of a second, resolving most of the issues. I had all of my Spektrum receivers updated by Horizon Hobby at no charge several years ago.

Problem is, with 4800 Milliampere Hour batteries, if they are Nicads, or Nickel Hydride "Sub C" types of cells, getting 4800 Mah out of them requires very thin internal plates, causing their internal resistance to increase. Trying to pull lots of current out of them could result in a voltage sag low enough for a 4.8 volt battery pack to sag below the critical 3.2 Volts DC.

Using the five cell battery packs gives you an extra volt or so of "headroom" reducing the possibility of the receiver "rebooting".

I've put together a thread on the A123 2300 milliampere hour battery packs that might be of interest. Take a look:
http://www.wattflyer.com/forums/showthread.php?t=58600 This thread shows tests of the A123 cells both at 75 degrees, and 31 degrees F. Some of the Nih and Lipo batteries do not work well at 31 degrees F.

Lipos will require a voltage regulator. Regulators are usually pretty reliable, but is something else that could fail. This thread shows that a two cell 2300 Mah A123 battery pack is a direct equivalent of a five cell 2000 Mah Nicad pack, voltage and current values. Using four A123 cells in a two series, two parallel setup will match your 4800 Mah pack, and will weigh in at about 10 ounces.

That thread above shows that you can pull 15 amperes out of these A123 cells, even at 31 degrees F, and still have over 5.5 volts DC available. That would be 30 amperes for a 2S2P A123 pack. I regularly pull 60 amperes out of my three battery flight packs of 6S2P A123 cells, they still have the same exact performance as when brand new, three years ago.
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Old 10-27-2010, 12:35 AM   #15
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Originally Posted by BEAR-AvHistory View Post
I am just finishing up a Pilot 1 Piper PA-12 1/4 scale & installing the electronics. Can I ask what happened to the PA-18 with the 4.8 battery?

Reason for asking is I have a 4.8/4500mah but have been looking at some 7.4 volt Lipos.
No problem. I had the -18 up several hundred feet, turning into a strong headwind at almost full throttle (Zenoah G26), when (I think) I lost one cell on the 4.8V NiMH. Lost ALL control function - and never recovered in the "reboot time" (ran out of altitude) - essentially went into the ground at full power.

What went up:




Came down


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