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Spektrum DX7 dropout problem

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Old 02-03-2008, 03:08 PM
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dilled
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Default Spektrum DX7 dropout problem

I’ve just finished building a Hanger 9 B-25. I’m using the Spektrum DX7 and an AR7000 rec. I have eleven servo’s on a seven channel radio and 4200 ma battery, heavy wiring and switch.

Now all I read about is how the AR7000 drops out and takes different times to reset depending on the firmware the unit is running. Can anyone tell me what the real problem is with this system and how can you deal with it. Is it that the voltage is dropping off? Can you cure it with two batteries? Do you have to use two batteries and a power bus, one for the rec. and one for the servo’s? Maybe the bus in the rec. is to small.

If anyone has any insight into this problem I would like to hear about it. I can always go back to old PCM.
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Old 02-03-2008, 04:45 PM
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Default RE: Spektrum DX7 dropout problem

The problem is a voltage issue. If the voltage at the receiver drops below 3.5 volt, the receiver shuts off. When/if the voltage raises above 3.5 volt the receiver will turn back on. If it is running the older firmware, it goes through a process of discovery to find the two channels its bonded transmitter is transmitting on. That process takes from 1 to 3 seconds or so. If the receivers (main plus remote) have the newest firmware, they try to connect to the required transmitter on the last two channels previously used. If the transmitter is there, it reconnects and gives you back control of the model very quickly.

There a host of methods one can take to insure the voltage to the receiver never dips below 3.5v. The best method to do this will vary with the particuliar installation. In your case you have a lot of servos but you didn't say if they are digital or not. Digitals of course can end up with a serious current draw in the right circumstances, that may cause voltage to drop below the critical level for a split second and cause a problem.

You could have a seperate battery pack that powers the receiver only and not the servos, using another power source for the servers. Or you could provide two A123 receiver packs with 6v regulators and different switchs plugged into 2 channels on the receiver, to name a couple of ways. The bus in the receiver doesn't seem to be the problem. Two 5 cell, large ma. packs might be enough depending on servo load.

For an airplane as big and expensive as yours, I would be using the AR9000 receiver with two remotes attached instead of the AR7000, but I'm sure others might report no problems with the AR7000, just my 2 cents.

I personally don't believe any Spektrum receiver should be used without the new "quick connect" firmware, now that it is available.
Nor would I use anything less than a 5 cell receiver pack.

If you take steps to control the voltage to the receiver, the Spektrum system seems to be a very reliable/dependable system.
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Old 02-03-2008, 08:25 PM
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Default RE: Spektrum DX7 dropout problem

Only two of the servo's are digital
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Old 02-03-2008, 08:49 PM
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Default RE: Spektrum DX7 dropout problem

You might check out the thread that's pretty much on this same subject.

http://www.rcuniverse.com/forum/m_6985963/tm.htm
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Old 02-04-2008, 09:30 AM
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Default RE: Spektrum DX7 dropout problem

jimhlt has pretty much nailed things down for you except that should you choose to go with the A123 batteries, you don't need regulators unless it's for one of the particular brand electronic ignitions used on some two stroke gasser engines.

You need to pay attention to what your required amperage is for all the servos, not necessarily what the mah rating of the battery is. In the past guys have gone to higher mah ratings to get a higher continuous amperage capability, not because they needed more mah. One of the places you can get seriously burnt is if you have a battery pack with high impedence (resistance) cells. Those will not be able to provide as much amperage.

The other issue is that the small connectors used in our models on the servo leads, extensions and most switches will only carry about 3.5 to 4 amps continous with spike capability somewhere around 1.5 to 2 times that amount. So having one battery and power input to your rx on a model with 11 servos could prove to be a serious bottleneck to the electrical current. Long servo extensions can also be a bottle neck which can be mostly cured by using at least 20 AWG wire for your stuff. HD wiring is a bit of a misnomer as some manufacturers call 24 AWG a HD, most use 22 AWG and there are a few out there who actually use the 20 AWG wire, it would behoove you to use the bigger wire.

IMHO, this setup at the very least needs dual power inputs to the rx and probably separate power supply to the matchboxes. If you're using Y-harnesses especially the reversing type, that's not a good idea either. Using the 9 channel rx is also worth considering not only for it's dual satellite rx's, but you can use the data logger on it when range testing to identify any possible problems with antenna locations. You can also run some tests on the ground using a meter to see what kind of current draw you're getting, but that will be a bit on the low side as there are no air loads being place on the control surfaces, or say the landing gear when it extends. You've got a chunk of money and time in this thing, do some more research on your power setup and it'll be well worth your time....[8D]
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Old 02-04-2008, 10:50 AM
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Default RE: Spektrum DX7 dropout problem

I agree 100%. Thanks for the assist.

Jim
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Old 02-04-2008, 11:32 AM
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Default RE: Spektrum DX7 dropout problem

Thanks for the assist. I have one problem that makes for some real issues. I'm also using a Futaba PA-2 Pilot Assist Link Auto Pilot to help coverup my poor flying skills. The PA is setup to use only 4 cell batteries. I'm looking at using a EGR-111 Pow'r Bus Pro. I can isolated and amplifed control signal to servo's by using the EGR-111. I will be able to run the rec. on 6 volts and the servo's and PA on 4.8 volts. All of the other power bus units start out with 6 volts.

Pat
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Old 02-04-2008, 11:37 AM
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Default RE: Spektrum DX7 dropout problem

You know I started out with nice new PCM rec. setup and then changed to the AR7000.

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Old 02-04-2008, 12:32 PM
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Default RE: Spektrum DX7 dropout problem

Just send your reciever to Horizon and have them udate it to include the "quick connect" feature. I just got all of mine back and they are all quick connect enabled now.


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