Radio intereference again!

[FCM]

I really hope that somebody can provide me with a fix for my gasser radio interference problem that I have on my Bezine based cameraship.

Last month I thought I had sorted everything out after installing a suppressed plug cap, NGK CMR7H plug, shielding the HT lead with Coax braid earthed to the engine and installing a Deans whip antenna facing to the rear due to Rx position on the heli.

I tested it on ground and after repositioning the antenna 3 times, with everything switched on (2.4 GHZ downlink, Heli and camera TX) and the engine running unloaded (no blades fitted) at a fast speed with my Tx facing the heli (antenna collapsed) at 4 different aspects with these results:

Facing tail - 110 paces
Facing left side - 78 paces
Facing nose - 63 paces
Facing right side - 58 paces.

I am running JR PCM S with the throttle fail safe set to 'cut' to determine the range with the engine running.

I think most people would agree that these figures are okay.

The heli was innactive for approx. 1 month until yesterday when during a normal pre-flight range check (eng. off) I noticed the range was poor with the TX facing the left side of the heli. I did not record the exact range but after this I did a engine running check and the results were bad enough for me to not fly.

After this I decided to revert to an original JR antenna due to the problems I had experienced with positioning the Deans whip due to the construction of the heli I suppose.

This morning I did an engine running test and these were the results:

Nose - 46 paces
Left side - 85 paces
Tail - 97 paces
Right side 40 paces.

I did an engine off test at the nose position and got 79 paces which looks like engine induced interference to me.

I also re- did the right side with engine running and got a fail -safe at 4 paces - yes four!

At this I decided again not to fly (who would with a range of 4 paces?!) and consult the experts.

Any advice will be considered!

Paul.

[bigrcr]

I would definitely check out the receiver and radio system (battery and connections, etc.). You may have a bad filter in the receiver caused from vibration at a prior time. Then make sure the plug is good, just replace it and gap it to 20 thousandths, any more and you can induce RF from the ignition system. A broken down plug (or one with too much gap) can cause havoc with the radio.

Hope this helps!

[FCM]

John,

Thanks you for responding. I have now sorted it all out but you will probably laugh when I tell you that a lot of the interference was down to a loose drive gear pin that eventually shook itself right out loosing all of my drive to the rotor! Luckily the heli was on ground when this happened!

It had been doing this for some time as I had been doing lots of blade off ground running to position my Deans antenna. Running without load sure does shake the heli!

I have now reverted to the original JR antenna but repositioned and am getting really good range checks so I will stick with this for now. The flight testing has also been very good.

The problem with the Deans whip is that its position is pretty critical and it is vulnerable to damage due to its location on my camcopter. I still have the Deans mounted and may try connecting it up again in the future.

One last thing, I have found when using the NGK plug that I have to use an NGK suppressed plug cap covered in foil and co-ax braid with the whole lot earthed to the engine. As soon as you disconnect the earth the engine - on range drops to around 4 paces! With it all connected up it works great (70 to 90+ paces). I never realised just how important the shielding of the HT lead and cap was. When done properly it really makes a difference.

Regards,

Paul.

[bigrcr]

Glad you found the issue! I have not had a lot of success with the Dean's personally, they break far too easy and are very location sensitive. Use what works!

On the NGK, I am assuming that it is a resistor plug. The gap makes a big difference since the wider the gap, the more power is being put out by the coil. This additional energy can bleed around the plug end connection and anywhere that it can and the increased gap on the plug just creates more RF energy as well. Some machines just need extra shielding, I don't know why? :dontknow

Later,

[FCM]

John, the interference has started again :!:

It started playing up again when we were flying/filming on Tuesday. As the heli comes around from side on to nose on it locks out, engine revs drop and the Rx recovers. This is happening at around 10 feet altitude and 30 feet away from me with the heli cruising in forward flight. Last week we had flown a lot including fast forward flight at long range without a hint of trouble.

Yesterday I changed the engine as I was sure it must be mechanical noise due to the HT set up I am now running. The removed engine has got a shot bearing on the flywheel side (top in the Benzine) giving radial play.

The replacement engine was fitted with a new NGK plug and suppressed cap together with co-ax braiding earthed to the engine.

This morning the engine ran nice and smooth (it helps if you have two good main bearings I guess) but as soon as I moved out of the hover and repeated the flight position where the lock-outs occured before, it locked out! I tried an engine on range check with blades on and Tx antenna collapsed but while standing about 4 paces away from the nose of the heli, as soon as I try to raise the RPM off idle, it locks out and actually killed the engine this time as I had the fail safe set for engine cut. Not good as I'm sure you will agree.

I am now considering replacing the ignition coil although I am using a different coil due to the engine change. I wonder what the chances are of getting duff coils in two different engines?

I am also looking at loose items especially around the camera mount (front mounted) that may be inducing the lock-out. So far the only thing I have found is a loose fairing screw. The fairing is GRP and is in place of a normal heli canopy. It seems a bit unlikely that this could be responsible for the lock-outs.

Your help and suggestions would as always, be much appreciated.

Paul.

[bigrcr]

Paul,
If you have not done so, replace the antenna if you are using a whip, it may be breaking down or have a broken coil. I would think about sending in the receiver for a check up as from your description it could possibly have a cracked or bad Rf filter. If the lockout starts when you raise the RPM off of idle it could well be that the vibration is exciting the receiver board and causing this. For that matter, a bad bearing or a cracked muffler could also be the culprit from creating Rf that is overpowering the antenna(signal).

It is possible that the coil could be causing the problem, but not very probable at all.

Hope this helps, and good luck!!

[FCM]

Hi John,

I have this problem posted on RR and somebody else suggested the Rx. I did change the antenna on the Rx and I guess I may have damaged it when I soldered.

I have a good replacement Rx and crystal that I will be trying out hopefully tomorrow.

I think that all of my bearings are good as I addressed this before by changing them all.

I am also going over the front section of the heli again to check or anything loose or un-earthed but so far apart from what I mentioned before, I have found nothing.

Thanks for your help John,

Paul.

[bigrcr]

Keep me posted. I am interested in the outcome!!

Later,

[FCM]

Turns out I was on the right track when I said I would check out the front of the heli again.

The problem was a worn, improperly earthed bearing that I had installed on the pan axis of the camera mount. Changed the bearing and ensured it was properly earthed and it checked out fine earlier today.

This was the one thing that I had changed follwing the original 'fix' - I should have suspected it straight away :arggg:

Never mind, the looking on the bright side, due to this happening, I found out about the bad main bearing on the old engine and now I have a nice smooth running engine giving me good video images :D

I have also totally changed my engine running regime and will be updating the post that relates to this straight away in case anybody is misled by it! Please have a look at it John and see if I'm doing it right at last :roll:

Paul.