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Hitec servos and Spektrum

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Old 01-22-2011, 02:14 PM
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jim52519
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Default Hitec servos and Spektrum

I am setting up the radio gear in a 106" Hurley Extra I built. I am using a Spektrum DX7 TX and an AR7000 RX. I am using Hitec HS-7955TG servos.I am using 2 elevator servos. I used an Elevator to Aux2 mix so I could use 2 servos. When I test the setup the servos move very spastically. It could never be flown like this. I went through the radio programming about 3 times. Always the same result. I then plugged 2 JR servos in place of the Hitecs and the JR's worked flawlessly. Are Hitec servos not compatible with a Spektrum radio????? Am I doing something wrong? Has anyone else had this problem?
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Jim
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Old 01-22-2011, 02:21 PM
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Default RE: Hitec servos and Spektrum

Jim, i had that problem, but only on certain channels, in a futaba receiver. It turned out to be the signal voltage on some channels is lower than required for the 7955 servos. Newer servos can operate at lower signal voltages. Try plugging the servos into channel 1 and see if the problem goes away.
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Old 01-22-2011, 04:25 PM
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Default RE: Hitec servos and Spektrum

The only thing I can think of that you did not mention is weather or not you used mix 5 or 6? reason being that these are the only 2 mixes that have the trim working both the master and slave channel. The other mixes may be getting weird with 100% mix value not having the combined trim feature. Other then that a phone call to both Horizon and Hitec would be my next move.
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Old 01-23-2011, 09:54 AM
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Default RE: Hitec servos and Spektrum

I use 7955s on both elevator halves, ailerons and rudder using a JR9 channel receiver with no problem. I'm fairly certain I've used several different Hitec servos (including 7955s) off of my Spektrum 7 channel reciever in the past with no problems either. My first thought would be perhaps either one of the 7955s is bad/has a bad connection?? Have you tried individually swapping the two servos for the JRs to see if the problem only shows up when you put a particular servo in the circuit?? How about battery levels? What type of battery are you using and is it charged fully? You didn't specify your exact wiring configuration so don't know if there are extensions involved that might be introducing issues as well? Perhaps a bad connection that you "fixed" when you plugged in the JR servos? Look at the connectors on the 7955s and make sure a pin is not backing out... that kind of thing.

The signal issue the previous post refers to I have never heard of being a problem OTHER than with Futaba who has posted a bulletin to that effect so it shouldn't be an issue here. That's a particularly Futaba problem from everything I've heard.
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Old 01-23-2011, 06:12 PM
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jim52519
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Default RE: Hitec servos and Spektrum

I think I solved my problem. I tried the same servos with a Futaba RX and TX and had the same poor result. I was starting to think the servos were bad but then I tried a 5 cell battery pack and the problem disappeared! I think there must be something wrong with the 4 cell pack. It is an old pack I was just using for set up. It measures ok on an ESV but must not deliver the necessary voltage under load. With the 5 cell pack everything works great! I guess do not assume a pack is good even if it measures ok on an ESV. Lesson learned.
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Jim
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Old 01-24-2011, 09:20 AM
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Default RE: Hitec servos and Spektrum

I was going to say, I have that configuration in 2 50cc planes (7955's with an AR7000) and they work just fine.
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