P47 - Electric Conversion.

[davegrennan]

Hi I'm Dave and I'm in Raheny.  Delighted to find an Irish RC forum.  I thought I was going to be forever tagging along on the UK sites hoping they don't mind too much.  To be fair, they're nice guys. Might as well start with a bit of an intro.

My primary interest is fixed wing.  I've only being doing this a few months but I've learned loads and broken lots of stuff. No not really, I've been fairly lucky.  I did manage to break my Ultra Micro Spitfire once but a bit of foam safe CA fixed it all up good as new.  I'm not in a club yet but intend to go along and introduce myself to the guys in the Phoenix Park at the next available opportunity.  I just love building stuff and know that I will end up building most of my own stuff as I get a great kick out of that.

My first major project will be to complete and convert a 57" span balsa P47 given to me by a friend a few years ago.  I got it mostly planned out where everything is to go and put in a nice order to hobbyking over the weekend for all the bits.  It's going to run on a .60 equivilent outrunner. Off a 6S lipo and an 85A ESC.

Here it is laid out on the kitchen floor.



There's a whole lot of hardware with it too, some useful some not so useful.  Those brass hinges are nasty.  They stick and just seem to be poor quailty.  I've ordered some CA hinge sheet to replace these.





So the build begins.  I decided to make the battery hatch on the top side of the nose section.  The battery will go behind the firewall. There is plenty of space in there.  



The ESC will probably be on the front of the firewall with the outrunner so it gets plenty of air.  I imaging I will have to make some more holes in the firewall to let air through to keep the lipo cool too.  This is how I envisage it will be, however there is also the option of installing a chute so the lipo will go in diagonally.



Here it is marked out ready for cutting.



...and after cutting.  It seems my balsa warbird is a hybrid foamie!!



I made a dummy battery from ply to test fit.  As you can see it rides a bit high however there is a few inches of foam at the bottom so I plan to make a recess in that just big enough to capture the bottom of the lipo and also so it sits down further.  I will wait right to the end to do this when I have a better idea where the COG will be.



Well all the gear has shipped from hobbyking.  I bought some used Futaba S3001s on ebay.  So more when all that arrives.

[Fred]

Hi Dave,

Welcome to the forum  
And I have to say, an honour to have you with us!

For the ones who have interest in Astronomy, Dave website: http://www.webtreatz.com/

Anyway, back in topic
Nice job on the P47, a favourite of mine.

What outrunner from HK did you picked?  :?:

[davegrennan]

Thanks for the welcome Fred.  As my late mum used to say, 'One man's carpenter is some plumbers customer'.  We all have out areas of expertise. I build a lot of the astronomy gear myself so this is a big help with building RC stuff as I have ended up with quite a well equipped workshop and have at least got some experience of engineering.

I went with the Turnigy G60/500.  It is advertised as 500Kv 1500W and is sold as a direct swap for a .60 glow engine.  I sort of figured that the 120W per pound would work here and I have roughly calulated the final weight around 10lb including battery so 1500W will give be a little more to play with and if it proves too much, I can just derate the throttle a bit anyway.

I haven't settled on a prop yet.  I would like to find a suitable 4 blade (for scale).  But props are cheap so its something I can afford to experiment with a bit.

Regards,

Dave.

[Happy Days]

Hi Dave and welcome aboard. :clap:

P47 er?……you’re obviously one of the scale enthusiasts yea’? Glad to see you haven’t gone for the proverbial Spitfire. (They’re so common)

As for cooling your Li-Po……….I assume you got a 5amp battery to accommodate long duration flight times. If you are going to fly this model ‘in scale’ a 5amp 6S Li-Po rated at 30C is going to be barely “ticking over“. I doubt if it would even get warm to the touch. Even if you spent five minutes beating-up-the-sky I shouldn’t think it would get much above room temperature.

Anyway, like I said, glad you’ve joined our happy little forum.

Little Keith.
(As distinct from Big Keith, who normally just signs himself as Keith because he’s too bloody lazy to sign as ‘Big’ Keith. Not that I would tell him that to his face you understand,,….He’s much bigger than me :shock: !)

[dg]

Hi Dave, I agree with ditching those hinges. Furry mylar hinges held in with CA glue should be fine for that type of model. Also, the LiPo cooling isn't really essential as your unlikely to be pulling huge Amps from it.
ps. I just sent you a PM.
Dermo

[davegrennan]

Thanks little Keith :-)

Actually I didn't choose the plane, it was given to me by a friend who started to assemble it and never finished it. But if I were to choose a jug would be well up the list anyway. I just love old warbirds, sure I married one:-) (she better not read this)

Yes I got 2x30C 5Ah 6S's. I was looking at the 8Ah ones but they were nearly double the price of the 5Ah ones. Batteries start to get pricy when you go up that end. I made some more progress this evening. Got all the control surfaces hinged up and the tail section installed.  Next trick to install the control rods and wires. The wire that came with the plane look a little flimsy, a can hear the mid air 'ping' followed by expletives so I'll get stronger rudder wire. I also need to get hold of some T connectors as the batteries came with bullet connectors.

I heard that putting a low value power resistor in series can help avoid sparking on these big lipos. Is it necessary?

Cheers
Dave.

[Happy Days]

I heard that putting a low value power resistor in series can help avoid sparking on these big lipos. Is it necessary?

Cheers
Dave.

Interesting point Dave.

Firstly let’s clear up a matter of ambiguity. When you refer to ‘T’ connectors I assume you mean these type of connectors.




These are actually called Deans connectors, I use them on all my Li-Po’s including my 6S packs. And yes, they can produce some quite substantial sparks, particularly when you’re trying to connect then together with cold “pingies“. I once received a rather painful burn (all-be-it from a very dramatic spark) whilst connecting my 6S pack.

The second aspect;……..


You may already know this Dave, coming from a technical background, (The angle of incidence equals the angle of outsidence. :oops:  Oopss sorry ,…the angle of refraction.) but it would not be a good idea to leave anything in series with the circuit. It would reduce the circuit voltage and would likely get rather warm unless it’s of extremely low resistance in which case it won’t reduce the sparking anyway.  ( anything that gets warm/hot wastes battery power. :evil: )

It occurs to me that you may have heard of temporarily using a Thermistor, just while connecting the two parts of a connector together. However I couldn’t think of a way of arranging a temporary way of connecting a Thermristor when using my set up of Deans connectors. :!:  So this is how I do it........



It’s a male Deans connector (The female part of the connector should be connected to the battery leads* )

On one of the leads coming from the Deans I’ve fitted a bullet connector (the positive lead in this case although it wouldn’t matter which lead was used) . I’ve fitted some heat shrink insulating covering around the female bullet connector. The insulation is slightly longer than the female connector. The reason being that the male connector has to go inside the insulating sleeve first, so any spark that may occur is shielded by the insulating sleeve. In other words it can't do any damage.
So the procedure is to first make sure that the bullet connectors are ‘open‘. Then, connect the battery Deans, and secondly connect the bullet connector. With practice, if I insert the two parts of the bullet connector quickly, there often isn’t a spark anyway.

There, that wasn’t too painfull was it? Hope it’s been of use.

L.K.

* Don’t try to shorten the battery leads from a Li-Po. Some of the multi core leads supplied have an insulating covering on each of the individual strands of the lead and render them extremely difficult to properly solder new connectors to. (Ask me how I know!)

[Fred]

Ok, first, I have to say that I have a very limited knowledge on this electric magic things (it's magic right?  :?: )

But here is an article (translated from the French) about this sparking problem (discussed with the author while doing some researches to electrify my P47... One day!  :roll: )

http://www.microsofttranslator.com/bv.aspx?from=&to=en&a=http%3a%2f%2fjivaro-models.org%2fspark%2fpage_spark.html

[davegrennan]

Hey Guys, I found where I saw the resistor thing.

http://youtu.be/CJQoUcm7okc

This makes good sense. Watch the vid, its all explained in there.  The trick is to put the resistor in parallel with the negative terminals and then disconnect the wire with the resistor installed when you're powered up. I have so big 7watt 10ohm resistors so I think I'll give this a go. I just dont like the idea of the sparks. I suppose a simpler trick is to wear a pair of rubber gloves to avoid getting burned but that doesn't stop your connectors getting carbonised.

[Happy Days]

Good man Dave, go for what feels good!

This matter actually epitomises one of the difficulties with aeromodeling. If you ask six pilots the same question, you’ll get six different answers! :lol:

Years ago I met a guy who was responsible for building Atlas rockets. I’ll always remember he told me that, “Precision engineering, is a question of compromise.” :shock:

Keep us up to date with the rest of the build Dave

L.Keith

[Fred]

Oh wait, let's just start a topic about "which radio is best"  :lol:  :lol:

[selleri]

JR!

Now that we've settled that lets move on to computer operating systems!   :lol:


Looking good on the Jug front Dave!   :clap:

[Fred]

Was JR/Graupner for years! Untill I had a MPX3030 to replace my MC18...

Ok, ok, off topic  :oops:

[Happy Days]

Settle down children, …………. (Futaba is the best actually,……ooops, that slipped out, sorry :oops: )


LK

[EI1638]

Here is what the current F2B World Champion is using to arrest sparks during plug in on his championship winning model. If I recall correctly he is running 5S, but don't quote me on that.

Very very simple, but not really suitable for Deans connectors.