Jason Arnold

Hi Guy's,

My MVVS 58 is causing my radio to do the funky chicken i.e. servos jittering and IPD(MPX Rx) lock out.

The motor and radio have worked fine before and I have since made some changes to the CG by moving the throttle and choke servo aft and also moving the ignition about 20mm further aft. I have reversed all changes with exception to the servos but it still does the funky chicken. I'm using an emcotec remote control switch for the ignition cut and will try connecting the ignition direct to the battery and see if I still get problems. The pug cap seems to be fitting firmly and the plug is a CM-6 which came with the engine.

Any help would be greatly appreciated.

Cheers
Jason.

pe reivers

You may have some metal to metal bouncing contact some place, or the ignition high tension cable shielding is damaged.
How is the distance between ignition system and radio system? should be 10" or more.

janch

Hi,

Do you have connected ground connection betwen ignition and engine ?
/ wire/

Jason Arnold

Hi Guy's,

Firstly, thanks for your help.

The ignition is about two feet from the receiver but I have mounted the ignition battery about six inches from the receiver for CG reasons (this motor is heavy). I tried moving the battery so it was about twelve inches from the receiver but there was no change.

Yes I do have the HT earth cable connected. I have tried it connected to an engine mounting bolt and to the MVVS soft mount. The Engine has had less than two gallons of fuel through it. Still using the MVVS supplied oil at 30:1.

On inspection of the plug I can see some abrasion near the hex part of the plug i.e. where the plug spanner engages. It looks like it's caused by the metal plug cap. Perhaps it's moving a bit more than normal due to the soft mount?

Cheers
Jason.

pe reivers

One test you may still do, is to activate battery test of the ignition. Then check for servo jitter when the ignition is switched on. (the ignition checks battery under ignition firing condition)
If no servo jitter occurs, it it not the ignition that causes this, and you need to look for metal to metal contacts in your airframe, faulty switches faulty wiring etc. Especially broken electrical wires can drive one crazy, and a sound portion of luck is needed to find them.

Jason Arnold

I think my funky chicken has been located!

I have just run the engine again and found that the plug cap rotates with engine vibration so it's obviously loose when vibrated. I have re-tensioned the spring clip on the plug cap but this didn't seem to help. The problem appears to be related to my ignition installation and the fact I'm using a MVVS soft mount. The ignition is mounted to the engine box and not the soft mount. I didn't purchase the MVVS ignition soft mount plate. I might try making a slightly stronger spring clip for the plug cap out of piano wire and tie the HT lead to the soft mount.

What are your thoughts Pe?

Cheers
Jason.

pe reivers

With capped ignitions I used to fix the cap to the plug with a small hose clamp so it could not move.
A rubber mounted engine is harder on the ignition and carb components, so that could well be the culprit.
Do take care to tie all leads to the engine, and have a free loop to absorb the movement towards the frame fixed components. Also take care that the cable entries into the ignition potting are fixed, so the cable cores do not break at that point.

Jason Arnold

G'day Pe,

I'm now pulling my hair out with this issue....

I thought I was onto something with the ignition cable plug cap but that was a false lead... If I bypass the Emcotec RCS by plugging the 2S LiPo directly into the ignition, all my problems disappear. It seems that ignition noise is getting into the receiver via the Emcotec RCS. I even purchased a second RCS thinking my original one had developed a fault but it does the same thing.

It makes me wonder if there could be a problem with my ignition. Having said that, the Emcotec is supposed to be optically isolated from the ignition via two opto couplers. Obviously it doesn't work too well. Maybe I need some sort of capacitive filter on the ignition side of the RCS?

What ignition switch do you guys normally use?

Regards
Jason.

BaldEagel

You have already proved its not the ignition, by the bypass, its the Emcotec whatever that is, I just use an ordinary HD switch and set up the engine so that at low throttle trim the engine cuts, if you need an on board ignition cut due to local rules, then put a servo on a manual switch, gets rid of extra electronics that can and in your case did go wrong. All of this is only my opinion and will be dissagreed with by all those who use opto isolators.

Mike

pe reivers

an optical coupler only blocks the wire bound interference. It not necessarily blocks the airborne RF radiation onto the cable leads, that is why the 10" distance is advocated by all ignition manufacturers.
RTK did some nice tests, where the resistorless plugs radiated all over the place and caused problems, whilst the R-type plugs were quite safe in modern ignitions. If using the CM6 plug, which does not have a resistor, a resistor type HT cable could be used. I am not sure if this is the case with the ICU ignitions that MVVS now uses.

Jason Arnold

G'day Pe,

The Funky Chicken has left the building..... Finally!

I replaced the Emcotec RCS with a Smart-Fly optical ignition switch and the Funky Chicken was exterminated.

Finally got to fly my Extreme Flight 88" Yak 54 yesterday and it was a blast! The MVVS 58 on a KS pipe really honks. It seems to come onto the pipe at about 1/3 to 1/2 throttle which is quite good. I'm using a Mejlik 24 x 10TH prop and it does about 6300 rpm.

I'm a happy chappy now...

Cheers
Jason.

pe reivers

Good to hear that.
Enjoy your season. You solved the problem just in time.
I got 6600 rpm with the MTW TP2 and 3W 24x10 wood prop, at header length of 400mm. Your tune may still be a bit off.

Jason Arnold

Hi Pe,

Yes my engine is still running on the 30:1 run-in oil supplied with the engine and I'm also yet to start tweaking the low and high needles. The engine is running very well so I'll wait until all the 30:1 fuel is used before tuning.[8D]

BTW we can fly all year round down here which is great! I feel for you guys up north that can't fly in winter.[] I'd go nuts but would get a lot of building projects done...

Thanks for your support mate.

Cheers
Jason.

pe reivers

tune right away, and reduce oil later (if at all).
I did not read your location, and thought about Melbourne. Sydney is quite a ways up north.. Down-under is a nice place to be.