P47 - Electric Conversion.

[davegrennan]

I hooked up the electrics over the weekend and yes there is quite a spark but its not as scary I as I thought. Just a flash and pop, certainly nothing that I'd be worried about. However when you look close at the connectors up real close, you can see little pits where the little arcs struck.  I guess given enough time these little pits would add up to degradation of the connector. I will try adding the parallel resistor trick later and see if that stops the sparks.

[Happy Days]

Hey dave,

You’ll find that closing the circuit by connecting the resistor first will greatly reduce the sparking, although at 10 ohms it might not completely stop it.

I’ve been flying my 6S Li-Po pack for a total 43 hours (flight time). I’m not too sure exactly how many individual flights that equates to, but a good many. The bullet connector I use to close the circuit still works perfectly. The arcing only occurs from the tip of the male plug and the rim of the female ’socket’ as the two parts are bought close together. The bulk of the contact area (the parts that will pass the current when the motor is run up) should remain fine.  

As I implied to you before, with practice, whichever method of connecting the battery to the speed controller you use you’ll soon get used to it as it becomes second nature.

L. Keith

[Fred]

I'm not a pro, but I believe that the sparks issue, is more to do with the ESC taking the heat each time you plug the battery, and can prematurely break the ESC.

[Happy Days]

It’s actually all to do with things called Capacitors. (They were called condensers in my day,……..About the time of Aristotle :roll: ) (Anyone with a vintage car or motor cycle would remember that ‘condensers’ were used in parallel with the ignition contact points, but I’m digressing….)  Capacitors behave rather like rechargeable batteries in that they charge up, store, and then discharge electric current. Unlike batteries however, they charge up and discharge instantly. (Well,….‘instantly’ from a human perspective anyway)

All brushless speed controllers use capacitors of some size or another. As soon as you connect a battery to the ESC the capacitors draw a charge ( or surge) of current. In other words, they ‘charge up‘. So if they’re big’ish capacitors in the ESC they will draw a large charge,…and there will likely be a spark at the point that connects the ESC to the battery or “switches on” the ESC circuit.

Actually, almost every time any electric circuit is turned on there is a spark, visible or not, which is why you must never operate any electrical appliance in a room that is full of gas, but I’m digressing again!!! :oops:

As for damaging the ESC’s. Most reputable manufactures over-engineer their circuits because they know of the potential risks caused by these surge currents. So provided the ESC that you are using is being operated within its specification, and is not some cheap crap, these sparks are not likely to cause any probs to the ESC. Although they can be rather alarming for the operator! :shock:
The ESC that burnt figures when I connected the battery to it is still in use today!

Here endith the Lecture, sorry for prattling on………… :wink: .

L. Keith

[davegrennan]

Hi Guys,

I've been a busy boy this week installing everything.

First up was the front side electrics and motor mounting.  

..and a close up of the mounting.

I machined the standoffs from 10mm brass bar.  None of this is permanently fixed yet.  I don't have any 4mm anti-vibration nuts, so I need to get some.  What you don't see here is an aluminium plate (1.5mm thick 20grams added weight) at the rear which ensures that the bolts can't tear through the firewall.

I'm a bit concerned by the rudder setup.  I used a pull/pull setup.

, but I'm not happy the way the wire just rubs along the slot in the side of the fuse;


I think some nylon tubing will be used here to prevent the wire rubbing and snagging.

Here's how the rudder and elevator controls terminate at the servos.


Here's the starboard side aileron servo;


BTW I got the servos used 3xS3001 and 2xS3003 for 25quid on e-bay.  They all seem good.
None of these are glued yet so everything can be moved/changed.  Spot anything you wouldn't do or any better idea's for the rudder?

[Happy Days]

Any progress on the P47 yet Dave?

L. Keith

[davegrennan]

Hi LK,

Did you see the progress in my post from May 22nd?  I'd be very interested in your opinion on some of the issues I raised in that post.  Been a busy bot in work since then.  Hopefully more progress later in the week.

Cheers...
Dave.

[Happy Days]

Hi Dave,
it all looks pretty good to me. The only “points of difference” that I can think of are………..

On the firewall:……… the ESC seems to be held in place by a single oversized washer. I’d probably remove the screw, drill a hole on the opposite side of the ESC and secure the ESC with a strong cable tie. (Don’t want the ESC shaking loose after a heavy landing )
And while talking about that area of the plane,….I suggest you’ll need another ‘airflow’ hole in the firewall to allow a good volume of cooling air to exhaust from the cowling into the fuse. The cooling air will likely need somewhere to exit from the fuselage as well. :wink:

Now you may already know this, in which case please forgive me mentioning it, but the firewall will have been built not at 90 degrees to the fuselage. This is done to produce a Thrust Angle. (Normally a few degrees towards the right hand side of the fuse, hence it’s called the Right Thrust angle.  It’s important therefore that your motor stand off rods are all  exactly  the same length to enable the motor shaft to be at the correct axial angle to the fuse. But like I say, you may already know this.

In terms of the rudder pull - pull system. Whenever I’ve found such cables rubbing I’ve used the little plastic ink tube found inside cheap ball point pens to run the cables through. These ink tubes are just the right size and are made of quite tough plastic. Bit messy flushing the ink out of them though!

Like I said Dave these points are not criticisms, just points of difference. “Horses for Courses” sort of thing.

Good Luck with the rest of the build :clap:
L.Keith

[davegrennan]

Hi Keith,

Thanks for the feedback.  Yes the washer on the ESC is only temporary, a couple of cable ties will be employed.  Good point re airflow, I'll make some more holes.

Regarding the right thrust, the odd thing is it doesn't look like there is any by default.  The standoffs were machined up on my lathe and are all the same to 1/100mm.  I might need to knock a small bit off two of them if there is no right thrust by default. I'll have to get  the t-square out to check.

Thanks for the idea re the sleeve for the pushrods, sounds like a champion idea.

Hopefully some more progress this weekend.  In fact I don't see why I can't finish it.  I do plan to do a bit of airbrushing.  At some point I might even redo the covering as it's a little bit tatty.  That's another day's work.

Cheers.....
Dave.

[Happy Days]

Hmmm,…regarding the Right Thrust Dave, :?: …..

If the firewall is at 90 degrees to the longitudinal axis of the fuse then I’d say there is a fair bet that this particular model doesn’t need any Right thrust. (Not every model does)

I think if I were in your shoes, and the motor mounts are to within 1/100mm (pretty tight tolerance that :clap:  ) then I’d finish the model ‘as is’ and see how it flys.
 Normally any lack of Right Thrust, (or down thrust, left thrust, or up thrust) becomes apparent when power is increases or decreased from level trimmed flight.

L. Keith