Spectrum RX issue

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Big Dog
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Spectrum RX issue

Post by Big Dog »

I started using AR6200 Rx in some open b planes with a 6v 370Nmih battery. on 72MHZ I did not have an issue with battery power but for some reason I am getting lock outs on the Spectrums.

I was told that when these Rx see a voltage drop they go into fail safe. The problem is that they take several second to come back out of fail safe. It has not been pretty and caused one crash.

Has any one else had or heard of similar problems? Is there a fix? How much can 3 servos draw to cause enough drop in voltage in a good pack?
Pathous
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Post by Pathous »

Big Dog this is true that the spectrum receiver will reset at 3.5 volts. You can send your RX back to horizon and they can update them for a quick reconnect this will eliminate the long lock out time. I ran Spectrum all last year with AR7000's and 6volt 350mah batteries and had no trouble. If you don't want to send them in my only suggestion is try a 500 or 750mah battery pack.
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boiler
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Post by boiler »

I had a transmitter that had a voltage fluctuation issue. Flying the Berg receivers, it went into fail safe when the tx signal was lost for a moment. With an electric I had to close the throttle stick and then open after the glitch to re-engage the motor. I have retired that transmitter.
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Big Dog
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Post by Big Dog »

Is there a bulletin out on the reset mod by Horizion? I also found that there is a capacitor that you can buy that plugs into a servo port. I bought 3 but dont know if it works yet I have not tried it yet
crash_out
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Post by crash_out »

In theory the capacitor should work. It stores energy so that when there is a sortage, it can supply a little extra power.

I've got a buddy that flies strictly Spektrum, in some pretty large planes at that. Most of them have some high drain digital servos. I've never seen or heard about one of his "browning out." It sounds more to me like there's an issue somewhere in the system, whether there is binding in the linkage causing excessive current draw, or perhaps the batteries not being able to hold their voltage. I personally avoid NiMH for this and several other reasons. Everything I fly now is on either NiCD or LiPo or LiFe.

Maybe you could switch to nicads or even the new 1100 A123 cells. Both hold their voltage a lot better compared to nickel-metals. If nothing else, I'd get a whattmeter/amp meter and try to determine how much current your servos are drawing.
Vapor52
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Post by Vapor52 »

I fly XPS in a Futaba 9C and every battery I own is NiMH, I have heard there is a brown out issue with all the SS systems but I have had no issues, only complete sucess-------------rick
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Big Dog
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Post by Big Dog »

I checked the factory support section of Flying giants for JR/ Spektrum. It appears I am not alone. Brown outs are common. The patch is to send the TX and all rx to Horizion for an upgrade that reconnects faster (about 1/2 second as opposed to 2 to 5 seconds). Though I dont understand Crash outs statement about NiMh's do they have a lower abilty to supply current (c rating?) a Lipo and regulator is not a good option for open B. Were can I find info on the current draw for servos?
Pathous
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Post by Pathous »

Big Dog many nimh cells have a high internal resistance which limits the batteries ability to supply large amp loads. I use nimh's all the time without any problem. I would suggest looking for some sort of linkage binding or better batteries. What servos are you using?
crash_out
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Post by crash_out »

NiMH do not hold their voltage as well as Nicd or lithium under load. In power system packs for electric flight, it was common practice to put an extra cell in the pack to compensate for the voltage sag.

A123/lithium iron cells don't require a regulator when used as a 2 cell flight pack. That's a primary reason me a couple of the people I fly with have switched to them. They roughly equivilent to a 6v nickel chemistry pack.
Vapor52
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Post by Vapor52 »

Nick, how do your servos react to the voltage? I see a lot of servos are starting to be rated at 7.4V now--------rick
crash_out
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Post by crash_out »

Lithium iron cells are rated at a lower voltage than the traditional lithium polymer. This makes the voltage of a two cell pack match a traditional NiCd or miMH pack very closely. They are in a metal can, and look very much like nickel chemistry cells.

As long as the servos are rated for use at 6 volts, they seem to be fine. I've got some older JR DS811's that are only rated at 4.8 volts, and when I hooked them up to one of the packs, they went utterly berserk. I probably shouldn't have done that...On the new DS821's and some Hitec 425HB's, as well as various mini/micro servos, they all seemed to react as they would with a standard 6v pack. Some of them will "chatter" until the voltage drops to nominal, but they did with good quality 6v packs as well.

The LiFe cells level off to around 6.4 volts under load very quickly, and hold that voltage for a long time. A fully charged 5 cell receiver pack peaks around 7.2 volts, which is about what 2 LiFe cells peak at. So there isn't a lot of difference voltage wise.

With polymer cells, you would have to employ a regulator of some type. Unless the servos are rated to handle 7.4-8.4 volts.
mark s
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Post by mark s »

To get a 6 volt pack to draw down to 3.5 volts, you would have to draw a ton of current. Hook a current meter into the + side of the battery (you have to open the + of the battery to inset the current meter). Operate the radio system and look for spikes in current draw. Chances are that you have a servo in a bind or a shorted spot on one of your servo motors. Also, with this type of problem your battery charge won't last very long.

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Vapor52
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Post by Vapor52 »

It was explained to me long ago that NiCads discharge curve was very uniform whereas a NiMh holds voltage better & longer till the end of the cycle where it drops off quickly, it is at this point that it may pull below the 3.5V for an instant-----rick
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Big Dog
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Post by Big Dog »

Well I have not replied to this forum in a while but I have got an eductaion and will share what I have learned about Spectrum and my setups.

1)The low voltage is part my fault I fly avengers and set the the aileron throw as far as it will go and then a little more to get the best roll possible. It works but there is a current draw penalty. (the servos are Hitec 645MG)I also use 6V batteries for the extra speed and torque but this may have added to the low voltage drop.

2)The update from Horizion ony requires the RX and the Satlite antennas to be sent back ( not the TX) The turn around was good and all my RX reconnect in about .5 seconds.

3)The capacitor is usually a surface radio accessory but it does work. Though I have gone to a slightly larger 700Mah NiMh. This handles my set up better, at a very small weight penalty.

With a little thought and the update from Horizion all my spectrum planes are perfoming flawless. I think the better reseloution and lower latency time makes them feel better than on 72 MHz
Pinecone
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Post by Pinecone »

I did the calcs on the capacitor and it works out to be about 0.01 seconds of power with a nominal load of 1 amp. And some digital servos can draw 2 amps without being bound up.
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