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At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

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Old 08-01-2007, 02:48 PM
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iplayloud
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Default At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

I only fly a couple times every summer so I took my old Avistar out, inspected all the controls and went flying..
My radio is a basic Futaba 4-channel FM bought in 2000 (Skysport4 I think ?) and at certain RPMs the airplane kind of dances, and sometimes the ailerons turn 200% right and elevator 200% up during a split second. I think one of my servos or the receiver reacts to a certain vibration frequency. Anyone experienced something like this ?
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Old 08-01-2007, 02:57 PM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

I have a Voltwatch inside and the battery was good. I tried with another battery pack as well with exact same results. I agree my radio is a bit old but I tought radios lasted a while.. I has different brand servos so I tought maybe some incompatibility issue but now I changed all the servos to Futaba S3003, S3004 and old FP-S148.
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Old 08-01-2007, 03:06 PM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

Get to the reciever and remove and replace the crystal to make sure it's seated properly.
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Old 08-01-2007, 04:22 PM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..


ORIGINAL: iplayloud I only fly a couple times every summer so I took my old Avistar out, inspected all the controls and went flying.. My radio is a basic Futaba 4-channel FM bought in 2000 (Skysport4 I think ?) and at certain RPMs the airplane kind of dances, and sometimes the ailerons turn 200% right and elevator 200% up during a split second. I think one of my servos or the receiver reacts to a certain vibration frequency. Anyone experienced something like this ?
Further to suggestion of reseating crystal, do same for all other leads to refresh the connections, checking for any possible signs of blue or black corrosion on the connections and replace if any found. (you did remove the RX battery whilst it was not being used?). Make sure the receiver protection rubber has not perished and replace in need. Correct any metal to metal contacts e.g. Tailwheel tiller arm sliding in a metal bracket is a no no, insulate with a piece of fuel tubing slid down the arm then resecure bracket. Metal Pushrod Z bend or metal clevis is AOK with a nylon throttle arm but a no no for metal throttle arms - replace in need with a ball joint or plastic clevis.
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Old 08-02-2007, 01:43 AM
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Phil Heller
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

All of the above are valid suggestions. In addition you should look for any metal to metal connections that could resonate when your engine reaches certain RPM. I had a plane years ago that would do a snap roll occasionally for no apparent reason. A friend found the metal pushrod to the throttle would contact the crankcase at close to full throttle - slipped a piece of fuel tubing over it and the problem went away!


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Old 08-02-2007, 04:37 AM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

You might also try substituting another receiver, borrow one if necessary just for the test. A cold solder joint or cracked circuit board in the RX could present these symptoms. I'm assuming you have your receiver wrapped in foam rubber or otherwise isolated from the airframe.

Also, it sorta sounds like your prop is out of balance, the number one contributor to excessive airframe vibration. But that's only the proximate cause; you have another issue somewhere--could be metal-to-metal friction, could be corroded contacts, could be intermittent connection of another kind.
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Old 08-02-2007, 07:57 AM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

Dont forget the switch harness. The contacts could be vibrating at given harmonic.
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Old 08-02-2007, 11:43 AM
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Default RE: At a certain engine RPM my radio gear goes nuts ? Troubleshoot..

you can remove the batteries, receiver, and switch one at a time and hold in your hand while you run it up. Should be able to figure out which is causing the problem.. Bob
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