Its Baaack... The servo twitch curse.

The Ugly Stik had this aileron twitch I could not get rid of... it eventually lead to the loss of the Stik. I guess I haven't fired up the Ultra Stik with the wing on, because I would have noticed this twitch curse has come to the new plane. I had her out at the field and set her up, excited to maiden her, even drove her around to range test her, but I noticed that at idle and WOT the twitch showed up, curiously not in midrange. The video doesn't capture the worst of it, it would occasionally go full deflection. The only parts that are the same are the Hitec HS-485HB servos, except for the elevator which is new. Odd, the left aileron is again affected, and the elevator! The connections are all solid but will get a second look. These are usually voltage issues.

Needless to say, I grounded her, "fool me once" sorta thing. I am thinking about the facts: only the servos are the same. I ave no idea why its the left aileron again... The elevator is a brand new servo; the old one locked up and failed without the engine on. I am thinking these discontinued Hitec HS-485HB are the problem, but possibly fixable. The other clue is that with the engine off they are perfect, no twitch, rock solid, function perfectly. This suggests the ignition is somehow involved. Now the ignition is in perfect condition, and this is a different engine, the EVO 10cc and its CDI. Its a different battery from the old Stik. This aircraft has a simple RCexl opto remote kill switch, not sure if it was on the Sbach or the Stik... 

So here's my plan. I can't afford to change out the aileron and elevator servos to higher end digital metal gear servos at about $35+ a pop (I would need 4), so I am working up the food chain.

1. A capacitor.  The theory here is that the twitch is from voltage spikes and drops, and the milliamps stored in the capacitor acts to buffer this letting those variations come from the capacitor per se, and not the reciever. This plugs into a spare port on the reciever. I am not sure they work, and people seem to find them controversial as to their effectiveness or need for that matter. This one from Amazon for $8 delivered (had a coupon, cost me $3).

2. Tech-Aero Ultra IBEC. This is what I prefer to the simple RCexl remote opto switch. The optical switch is supposed to isolate the electrical noise from the ignition and keep it out of the reciever by using a optical interrupt (the electrical signal gets turned into an optical (photon) signal, back to electrical, with that light isolating the two sides from on another, or something like that). It runs about $17. The Ultra IBEC instead filters the signal 4 times through various capacitors and then stabilizes the power to remove any noise. I honestly don't know if these have any functional differences otherwise. They both could be replaced from a noise cleanup standpoint, by using a ignition only battery. Clearly if this is an ignition noise issue the RCexel switch is not stopping it. Since I think it would, if the IBEC instead works, then its a voltage stabilizing issue that the capacitor could not solve.

3. Change the servos.  People knock "budget" servos, but honestly the only difference I have seen is initial quality. If they work out of the bag/box, they work fine, but yeah there are some junk brands out there so you have to know what you are buying. Reviews show these to be very reliable and I get 4 metal gear digital servos for a great price, $18 for 4. I have never had one that failed, even out of the bag. Someday when I can drop $150 on 4 name brand servos I may change them, but right now, this is the way to go.

I will probably end up doing all these things, leaving the Hitecs on the flaps, but one at a time to see what fixes the twitch. Something has to work...