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The Building of the BebBit

BebBit bit by bit

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Big Bandit02/05/2011 07:23:51
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Nice job BEB,
 
The servo mounting reminds me of the type of mounting on the Eflight Taylorcraft, very effective. Far too gusty down here today so it's back in the shed, try to finish the Webbittneezzer for the Mayfly meeting at Old Warden next weekend.
 
Cheers,
 
Chris.
Biggles' Elder Brother - Moderator07/05/2011 22:00:49
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OK another little departure from the standard WebBit script.
 
As I said earlier I'm not a big fan of wing bands so I'm modifying the BebBit to have bolt-on wings. As such the mod itself is very straightforward, just a couple of extra formers - one with two 4mm captive nuts fitted, two dowels in the leading edge and two bolt holes in the trailing edge, but there is one little problem - the WebBit has a very narrow fuselage for the size of its wing. This means the dowels and the fixing bolts are narrowly spaced and don't offer much resistance to axial twist. Which in turn means I will have to bolt the wings on pretty tight. Now the problem with that is the bolt holes are in the balsa trailing edge - if I start regularly tightening up the bolts I will gradually crush the balsa
 
Solution - I need to let a ply plate into the trailing edge.
 
First step mark where the rebate for the plate is going to be...
 

I'm going to use 1/8th ply, so obviously the rebate will have to be 1/8th deep. To start I took my balsa stripper and set the scalpel blade so that it was 3/16th below the plate of the stripper. With this I then cut round the perimeter of the rebate.
 
Next I reset my balsa stripper blade so that it was 1/8th below the plate and scored a series of horizontal and vertical cuts inside the boundary of the rebate...
 

All you have to do now is take a scalpel and use the point to "flick" the little squares out. The balsa wont split outside the boundary because the cuts between the squares are 1/8th and those around the boundary are slightly deeper at 3/16. Clever eh?
 
So, your left with a pretty neat 1/8 deep rebate. Any remaining bits here and there can be trimmed out with a sharp scalpel blade....
 

As you can see we have the ply plate ready. Just glue it in and drill the holes through from the back and hey presto instant reinforcing...
 

So, with the wing on - from the back....
 

And from the front....
 

Since these photos were taken earlier today I have added the wing tips. So just finish fitting the lower sheeting and a light rub down and she's ready for the basic covering. Still haven't decided on the colour, I'll have to have a rumage among the old ends of film and see what I have enough of - it'll probably be white and something...
 
BEB
Chris Bott - Moderator07/05/2011 22:13:01
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Coming on nicely BEB
Big Bandit07/05/2011 22:27:05
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Looking good BEB, I've left blocks in mine in case I fancy changing to bolts.
 
Cheers,
 
 
Chris.
Biggles' Elder Brother - Moderator20/05/2011 11:19:41
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Last night I had a little time so I made up the undercart - I was very careful to make it just the size on the plan, but I think the trailing arm is too long. As it is it positions the undercart much to far forward at an extreme angle? Looks like I'm going to have to desolder it, trim the trailing arm and reassemble
 
Anyone else had this problem?
 
BEB
Big Bandit20/05/2011 13:18:41
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Hi BEB,
 
Mine was a bit that way but not too extreme, as I made another due to "lumpy" soldering I adjusted it then.
 
Cheers,
 
Chris.
Biggles' Elder Brother - Moderator20/05/2011 18:45:04
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Well, I've unsoldered the undercart (which was a pain having to unwind the soldered bindings!). I put the trailing arm up against the drawing for bending the wire and its spot on. Then checked it in the side elevation of the fuselage and its about 1/2" too long! Chopped a bit off, rebent the ends and soldered it all up again - much better. Now the wheel are in a sensible place - it looked like it had "buck teeth" before!
 
BEB
Biggles' Elder Brother - Moderator24/05/2011 21:14:22
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OK, the power train is installed. This is the first time I've "gone it alone" on an electric set up, previously I've always just bought the "recommended" set up. I've just invested in a wattmeter so this was "make or break" time!
 
I was aiming for about 300W - and got 310W at full chat - not at all bad! I'm pleased with that. It drew 28Amps, and the ESC is rated for 40Amps continuous, so that should be fine as well.
 
I'd better be careful, I just might be getting the hang of this electrickery stuff, and think what that would do to my "oily hand" image - I'd never be able to hold my head up in the bar of the "Flyin' Piston" again
 
BEB
Chris Bott - Moderator24/05/2011 21:28:59
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BEB do you remember fixing a playing card to your pushbike frame so that the end was flicked by the wheel spokes to make a motorbike noise?
 
I recon if you tape one to the nose of the BEBbit, that pokes out into the prop, then your reputation would stay intact
Tom Wright 224/05/2011 21:36:53
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Posted by Biggles' Elder Brother - Moderator on 24/05/2011 21:14:22:
 
I'd better be careful, I just might be getting the hang of this electrickery stuff, and think what that would do to my "oily hand" image - I'd never be able to hold my head up in the bar of the "Flyin' Piston" again
 
BEB
Don't worry about it ,can get you in at the ,The switch mode arms.
Congrats on you first independent choice of elec-tricery bits.
Tom.
 
Richard Harris24/05/2011 22:31:05
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BEB,
Your power train is reading roughly the same as mine so you should have more than enough power. Mine is showing 300 watts, pulling 30Amps steady on a 3s Lipo swinging a 10 x 5 prop.
I remember my first 'guess' at an electric power train, only lasted a few flights, good old Watt meters, worth their weight in gold!
Looking forward to some photos, nice 'top notch' build so far!
 
Rich
Big Bandit25/05/2011 18:10:47
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BEB,
 
As it's quiet you can indulge in some urban guerrilla flying, sneak in under the radar a few aeros, back in the car and away before the victims wake up..
 
Chris.
Biggles' Elder Brother - Moderator25/05/2011 19:54:22
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But I haven't got an urban gorilla to fly Chris!
 
Do you think that Webbies do them?
 
BEB
Biggles' Elder Brother - Moderator30/05/2011 21:18:29
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OK just a quick update. I got some time in the workshop today so; rx fitted and everything except the ailerons tested and set up. All seems well.
 
I've decided to fit her out with closed loop to the both the rudder and the elevator. I'll post some piccies on that when I get a chance to take some as some folks might be interested in how a full set closed loop is installed and set up.
 
I've started the covering, covered the rudder, elevator and the wing so far, so just the fuselage tailplane/fin and ailerons to go.
 
BEB
Chris Bott - Moderator30/05/2011 21:33:27
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Sounds like you're getting on well BEB. Will be great to see some pics.
 
Closed loop on both sounds interesting. I think it's the best, lightest system, but only when set up properly. On small models I've used kevlar fishing thread which has worked well.
David Gilder30/05/2011 23:16:42
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Looking good BEB
 
I managed to Maiden mine today at last and all went well.. Have just put in some down thrust on the motor tonight. I see quite a few people have had to do this so it might be something to bear in mind!!
 
Hoping to get out for another few flights soon to re-trim but at least it has maidened now ready for Greenacres!!!
 
Got a parcel from A.R. the other day with some banners, balloons, stickers and t-shirts!!
 
What colour scheme are you going with then? I like the thought of close loop systems on the rudder and elevator!!! Will be interested to see that!!
 
Keep it going... It will fly a dream!!
 
Dave
 
Biggles' Elder Brother - Moderator31/05/2011 11:03:41
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It better hadn't need downthrust Dave as the motor is not that accessable! If it does I'll have to change the wing incidence instead - much easier
 
Chris. presumably you get the kevlar thread from fishing tackle shops? I've not tried that, I usually just use the standard stuff from Dubro or the like basically plastic sheathed steel wire.
 
I too am a great fan of closed loop, correctly installed its very light and positive in action with no slop. Some folks say they find it a pain to install and set up - but to be honest I find its less work than a snake or push rod - maybe I'm just rubbish with snakes and pushrods!
 
Often closed loop on evevator tends to use separate elevator halves - but I wasn't thinking and have joined my halves as per design - but it shouldn't make much difference it just means I have three wires exiting one side and only one on the other!
 
As I say I'll try and take some photos, but the problem is the set up is very small and my camera is very rubbish - not good at making small detail visible. But I'll have a go.
 
BEB
 
PS Oh I forgot - Dave, the colour scheme is white with metallic red upper surfaces and black trim - its what I had "in stock" - but only just enough red I suspect, mustn't make any mistakes or I'll be redesigning the colour scheme! 

Edited By Biggles' Elder Brother - Moderator on 31/05/2011 11:06:22

Biggles' Elder Brother - Moderator31/05/2011 23:08:15
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Hi, as promised some attempts at pictures of the closed loop installation.
 
This will be an "elevator in one piece" version so there will be two elevator connections on one side (top and bottom) and one rudder connection on each side (left and right). This means three outlets on on side and one on the another. A bit different, but it should be alright.
 
For a model this size the exits need to be about 31/2" forward of the hinge points and more or less on a line between where the control horn will be and the servo horn. This means the upper elevator cable will have to pass through the top decking - which is only 1/16th balsa and so not really strong enough to support this. So, a small 1/8th thick balsa strip has been glued inside the fuselage at the exit points as a bit of local reinforcement.
 
The holes were first drilled 1mm, and then opened out to an elongated shape in the direction of the cable run, at a very shallow angle to the fuselage side, using a miniture round file. The holes are now about 2mm diameter lying on a angle between the control horns and the servo horns.
 
We then take 10mm length of small bore, approx 1mm, plastic tube and rough the outer surface up a bit to give it a key. This is then epoxied into each of the exit holes. These tubes will act as bearing surfaces for the cables runing through the exit holes.
 
This picture shows the down-elevator and rudder cable exit holes, with the tube epoxied in place, on the port side....


Next we see the up-elevator cable exit on the rear top decking....(This one looks a bit long - I might trim it a bit!)


Finally we can see the rudder cable-exit on the starboard side...
 

I'm currently covering the fuselage. Once that is done I get back and deal with running the cables themselves and finally connecting everything up.

BEB
Chris Bott - Moderator01/06/2011 08:01:48
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Posted by Biggles' Elder Brother - Moderator on 31/05/2011 11:03:41:

Chris. presumably you get the kevlar thread from fishing tackle shops? I've not tried that, I usually just use the standard stuff from Dubro or the like basically plastic sheathed steel wire.

As far as I can remember BEB, the thread was from ebay, came on a 25m roll I think so will last for some time. Sorry I can't be more specific.

Yors is coming along nicely
 
 
Biggles' Elder Brother - Moderator08/06/2011 22:34:47
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OK, I said I would detail how the full closed loop system is installed and adjusted. This is really by way of being for anyone who has not done a closed loop system and wants to see how it is done. I'm not claiming this is the only way - or even the best way - but it works for me
 
First we fix the control horns on. One either side of the rudder and one top and bottom of one side of the elevator. As I said above its more common to have a split elevator with closed loop with elevator control horns top and bottom on both sides - but hey, this is WebBit, we do things different here
 
So here are the control horns - need to trim those bolts!
 

And another view...
 

The rudder control horns are just a mite further back than I would like. really the holes should line up with the hinge line (as in any control system) but the stern of the fuselage is just a little too wide to permit full rudder movement if I do that. Its only a couple of millimetres so no problem. Closed loop is also very tolerant of this sort of thing because the wires can pivot really easily in the control horn holes and move sideways so they don't starin the hinges like say a control rod or a snake would do on a horn that was out of line with the hinge line.
 
Next we thread the wire through the horn - here we are doing this on the rudder...
 

(Sorry about the focus - or lack of it - I'm a rubbish photographer!) Prior to threading the wire through the horn a small ferrule is threaded onto the wire. The wire is then taken through the hole and back through the ferrule. Pull it snug and crimp the ferrule. We then thread the wire through the plastic tube bearings we epoxied into the fuselage prior to covering. This is shown in the photo below...
 

Now for the servo end. You need special clevis fittings for closed loop. I use the Dubro ones but there are many available...
 

A really blurred photo of the clevises. They have a short threaded rod inserted with a small hole for the wire in the free end. The threaded section provides us with adjustability. I always fit a nut to this threaded section as a locking mechanism.
 
Now we pick up the wires that have been passed through the fuselage and attach them to the clevis rods. We get it about right before we crimp the wire at this end, and then fine adust with the thread...
 

Here we are with everything connected. Adjust the wires with the control surfaces taped in the neutral position and tighten the wires just until the slack is eliminated. They do not have to be really tight - just not slack.
 
So here's the finished job, Top view...
 

Bottom view....
 

And side view...
 

Just have to trim the loose ends of the wire pulled through the crimps and also the bolts and its all done. There is absolutely no slop in the system and its working fine. I did try to take a video - but failed, I'll have another go!
 
Anyway, there you go. Closed loop in a nutshell. I my view the simplest, easiest and lightest control system. And second only to short control rods with ball links for precission.
 
BEB

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