GliderIreland - Ireland RC Forum - Flying Model forum in Ireland
Planes => Scale => Topic started by: davegrennan on May 12, 2014, 22:50:21 PM
-
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.
(http://www.webtreatz.com/images/Jug1.jpg)
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.
(http://www.webtreatz.com/images/P47/Img_0879.jpg)
(http://www.webtreatz.com/images/P47/Img_0880.jpg)
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.
(http://www.webtreatz.com/images/P47/Img_0903.jpg)
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.
(http://www.webtreatz.com/images/P47/front.jpg)
Here it is marked out ready for cutting.
(http://www.webtreatz.com/images/P47/Img_0921.jpg)
...and after cutting. It seems my balsa warbird is a hybrid foamie!!
(http://www.webtreatz.com/images/P47/Img_0923.jpg)
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.
(http://www.webtreatz.com/images/P47/IMG_0925.JPG)
Well all the gear has shipped from hobbyking. I bought some used Futaba S3001s on ebay. So more when all that arrives.
-
Hi Dave,
Welcome to the forum :D
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? :?:
-
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.
-
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: !)
-
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
-
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.
-
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. :D
Firstly let’s clear up a matter of ambiguity. When you refer to ‘T’ connectors I assume you mean these type of connectors.
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/deans%202.jpg)
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........
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Connectors.jpg)
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!)
-
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
-
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.
-
Good man Dave, go for what feels good! :D
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
-
Oh wait, let's just start a topic about "which radio is best" :lol: :lol:
-
JR!
Now that we've settled that lets move on to computer operating systems! :lol:
Looking good on the Jug front Dave! :clap:
-
Was JR/Graupner for years! Untill I had a MPX3030 to replace my MC18...
Ok, ok, off topic :oops:
-
Settle down children, …………. (Futaba is the best actually,……ooops, that slipped out, sorry :oops: )
LK
-
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.(http://www.gliderireland.net/forum/images/uploads/EI1638/SparkEliminator.png)
-
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.
-
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. :D
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
-
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.
-
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
-
Hi Guys,
I've been a busy boy this week installing everything.
First up was the front side electrics and motor mounting.
(http://www.webtreatz.com/images/P47/front_electrics.jpg)
..and a close up of the mounting.
(http://www.webtreatz.com/images/P47/motor.jpg)
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.
(http://www.webtreatz.com/images/P47/tail.jpg)
, but I'm not happy the way the wire just rubs along the slot in the side of the fuse;
(http://www.webtreatz.com/images/P47/slots.jpg)
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.
(http://www.webtreatz.com/images/P47/ruddr_elev_servos.jpg)
Here's the starboard side aileron servo;
(http://www.webtreatz.com/images/P47/elev_servo.jpg)
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?
-
Any progress on the P47 yet Dave?
L. Keith
-
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.
-
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. :D
Good Luck with the rest of the build :clap:
L.Keith
-
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.
-
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