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[tobyker]

I've been thinking about the location of the hardware in the Perkasa. The simplest place to put the Rx would be on a tray about 1.5 -2" above the motors - probably electrically a bad place. Would it help if I lined the tray with aluminium foil to shield the Rx? The  aerial will be coiled in the tray and about 1' of it go up inside a hollow wooden or lattice mast. The motors are speed 600s which I am told are internally suppressed.

[wombat]

Hi Tobyker,

My view is that this is not the best place for the reciever - though in my next model (or next but one) I may be forced to get them pretty close  >:( :(

If you are going to use a metal plate to shield the reciever, I would suggest that you use a steel plate rather than aluminium as this will help to suppress the magnetic fileds from the motors.

The motor supression will help, but it really will only deal with the cable bourne interference not the radiated interference.

Tim the Wombat

[Doc]

tobyker,
The 'Wombat' is right, in the middle of electrical fields isn't all that desirable if it can be helped.  Then again, it it can't be helped, then put it where you have to.  Shielding for the receiver can be almost any metal, even aluminum.  Sheilding works best if it surrounds the thing producing the unwanted fields, as in the motors, not the receiver.  There's a "but" in that too.  While wrapping the motors may be electrically good, mechanically it's gonna introduce some other problems (heat retention), besides, motors with metal 'cans' already have shielding.  So, a metal tray might be of some help, try it and see.  The one thing you suggested that I would disagree with is coiling the antenna in that metal tray, for two reasons.  First, coiling any antenna is not good, about the same as cutting off how ever much wire you've got in a coil.  And second, electrically shielding any antenna prevents it from doing what it's supposed to do, pick up electrical 'fields'.  Receivers 'deal' in electrical fields.  Shielding is to prevent them from being over loaded by those fields before they can 'deal' with the one field it want's to see.
 - 'Doc

"I thought it was a simple question."
"It was, just not real simple."
"So why doesn't he make up his mind about what to do?"
"He's got a simple mind..."

[ambernblu]

tobyker,

Doc's spot on about coiling the antenna - not a good idea! For simplicity, is there anyway you can run it from your Rx tray around the inside of the model's hull (I've held mine in place with lumps of blue tack - crude I agree, but it works fine!) before running the final section up your mast?

[ukengineman]

The best way of shielding the radiated interference from motors is to bond the metal motor case to the prop shaft. This effectively earths the motor case to the water. I have used this with considerable success on a number of boats including one where the Rx was next to a Speed 700 BB Turbo. This is not a substitute for the usual suppressor capacitors which are still required. I add these even if the motor is supposed to have them internally.
Alan

[Doc]

Alan,
Not criticizing what you said, but there are exceptions to the 'earthing' to a prop shaft thingy.  The first that comes to mind is when using two motors, one counter rotating.  If that motor that runs in the 'wrong' direction wasn't specifically built to do so, then the voltages applied to the two motors are not the same.  The case of one motor would be (+) and the case of the other would be (-).  Or, a short circuit.  Not good, lets smoke out of electronic stuff, no smoke inside, no work.
Another thing that comes to mind is that water is non-conductive unless it's 'dirty' or has salt in it.  Being non-conductive, there's no place for the interference energy to go except back into the system, it isn't 'drained' away to the bottom of the pond (or does interference float?).  ...then again, very few places I've ever floated a boat had 'clean' water.
The most common 'place' that interference gets 'dumped' is in the battery.  Batteries 'like' the taste of interference and unless there are huge amounts of it, no problem.  Sort of a 'filter', kind of.  What happens if there is a huge amount?  The battery sort of gets 'fat', swells up.  That's the sealed ones, the vented batteries just need to be checked fairly often, they may need a 'drink' (ever had to add water to a car battery?).  Is that the truth? ... :)  No, but it makes for a good story line, doesn't it?
 - 'Doc

[ukengineman]

Hi Doc,
Most of the motors we use do not have a direct connection between either power terminal and the case. I am not suggesting you add such a direct connection. The usual arrangement is a delta arrangement of suppression capacitors (preferably ceramic), one across the power terminals and one from each power terminal to the case. This arrangemnet has a limitation in that the capacitors to the case direct some of the RF brush noise to the case which can re-radiate it. The armature also radiates some of the brush noise which again is re-radiated by the case. The bonding of the case to the prop shaft provides a path to dump this source of interference. Normal lake water is more than conductive enough to achieve this. Of course motor generated noise is only one source, although probably the most common. RF interference is also generated by the fast switching edges of modern speed controllers and this can be tricky to deal with, layout and cable lengths being important factors. The source of interference must be established and dealt with by the appropriate means. The one I mentioned for motor noise is one which has proved itself on several occasions with myself and club friends.
Alan

[tobyker]

Thanks, chaps - plenty of food for thought there. I have seen aerials "coiled" round a flat piece of plasticard or whatever to absorb the surplus length, but perhaps I will try stringing it round the inside of the hull, well away from motors and power wires, before it goes up the mast. I like the idea of earthing everything - since my motors will both be turning the same way I guess it will be safe to bond the cases, shaft tubes and maybe even the rudders.

I do quite like the idea of putting the shielding over the motors. Do I just need to block the line of sight between the motors and Rx+aerial, or does this interference stuff creep round corners? And should I earth the shielding too? Sorry to ask more but there is plainly more to be said. I wish I'd paid more attention in Physics at School but they never explained what it was for, in those days.

[Shipmate60]

Why do you have to put receiver there?
There is plenty of room in a Perkassa hull.

Bob

[dougal99]

Thanks, chaps - plenty of food for thought there. I have seen aerials "coiled" round a flat piece of plasticard or whatever to absorb the surplus length, but perhaps I will try stringing it round the inside of the hull, well away from motors and power wires, before it goes up the mast.

In my experience 'coiled' aerials give nothing but trouble. Best vertical or as much as you can sensibly achieve.

Doug

[OneBladeMissing]

As shipmate60 asked, why do you have to put it there? Above the motors would be the worst place to put a receiver, there's no logic in that at all. Measure how long the aerial wire is, and how much will be up the mast. Then use the length of the aerial inside the hull to get the receiver as far away from the potential source of interference as possible.

[tobyker]

I don't have to put it there - it would just be the simplest place to put it. Based on the replies and advice so kindly given, it seems that the disadvantages in terms of interference would outweigh the convenience. That's why I asked the question. Now I'll go and have another look at motor, battery, ESC and  rudder servo locations, and think again. Thank you all for your advice.

[Shipmate60]

I only asked the question in case there was an overriding reason that made you put the reciever there and we could have discussed ways of getting over that.

Bob

[tobyker]

Thank'ee Shipmate. My reasoning was that I'd like the ESC near the motors and with the battery aft of them , the ESC could go forward of them. To save extending both the ESC to Rx and the Rudder servo to Rx wiring, The Rx could be located above the motors, which would also get it off the floor and possibly protected from the oggin and spray and any sloshing around the bottom of the boat. But I will ponder further. Maybe the best place would be right aft, away from all the power wiring. I could then string the aerial on a strut as high as possible within the superstructure, forward to and up inside the mast.

Next question; are servo wires subject to interference from power wires and motor radiation? Since people sell 12" extensions for aileron servos I guess length won't be a problem.

[Shipmate60]

Tobyker,
Inside the hull there are usually only 2 components that will be "Fixed".
The Main Battery (for ballast) and the motors.
If you7 get these positions set the rest does usually become clear.
The speed controller(s) between battery and Motor(s).
Yes the Main Power cabling should be as far away as practical from the Radio Wiring, especially for higher power consumption motors.
If its any help, I usually connect the Main Power wiring up first and run it down one side of the hull. Then I put the receiver in the electrically clearest part of the hull .
Yes you can get extensions for the receiver connections up to 2 metres long.
I usually use one of these for the rudder servo (length to suit).
I prefer not to use these on the speed controllers unless it is crucial, but have done in the past without problems.

Bob

[FullLeatherJacket]

Tobyker

Model aircraft wings don't generally contain power wiring to electric motors (although some clever dick is bound to pick me up about twin-engined ones....). The only problem you might encounter with long extention leads in an aircraft wing is a voltage drop which could cause the servos to operate erratically. Been there; seen it; done it; got the tee shirt etc.

Like Bob says, it's best to route the wiring between the receiver and its servos (incl ESC) as far away from the power wiring as you can. Your idea of keeping the ESCs close to the motors is sound and should also help reduce radiated interference.

If I were you I'd try the receiver exactly where you planned for a start - without any screening etc - just to see what happens. You could then "add" the screening and extra suppressors progressively, although I'll bet you find your last idea to be the best of all. As long as you aren't intending to use BEC then you could use a 5-cell (6 volt) battery pack for the receiver and its servos.

I'll go along 100% with all that's been said about coiling up the antenna wire. I'd personally use a non-scale whip aerial right at the stern which you can unplug for transporting and displaying the Perky. If you use 16 or 18 gauge piano wire you'll hardly notice it when the model is travelling. Works fine on my Swordsman! PM me if you want any further details.

Suit yourself

[John W E]

Hi there Tobyker

I totally agree with the above statements, especially Shipmates60 & FullLeatherJacket's (FLJ) comments - Ive got a funny feeling FLJ has built a good few models than the rest of us on this Forum so I am sure he knows what he is talking about.  However, there is only one thing I would (not disagree but) at least experiment with and that is coiling the aerial wire around a Former.  Ive done this myself several times - once on a type-42 warship which I coiled the aerial round a sewing bobbin and then covered it with the radar dome and then on an world war 2 MTB, where I coiled the aerial wire around the inside of a life raft - the life raft size was approx 2" x 1.5" - and doing this, I never had any interference because they were placed up on the deck of the vessel.  I still had full range of radio equipment.  The only problem with this method is you have to put a plug in your RX aerial - you can then detach the superstructure.

Hope this is of some help.

All the best,

Aye
John E
BLUEBIRD