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Geoff's Wot4 Mk2 electrification

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Geoff Sleath11/10/2018 21:37:07
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I know that there are already some threads on this topic but the newest ARTF Wot4 is more directed at electric conversion than formerly in that one of the trickiest parts is already done - ie a battery hatch with a spring-loaded catch right at the front and on top where it's easily accessible.

I thought I'd separate my efforts from the general chat with specific reference to the power train. The actual build isn't too taxing.

I'm using components I already have to hand and incidentally finding some are less suitable than others

I received my kit yesterday morning from KIngs Lynn models within 40 hours of placing the order on-line.

This was my first attempt at motor installation.

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I've had this motor for some time and according to the spec supplied when I bought it from BRC it should have been ideal but once I did a few tests it didn't score very highly.

I tried it with an 11x6 prop and it drew well over 60 amps on 4S when it should have been nearer 35! I can only assume its kv is a lot higher than the 919 specified.

I eventually ended up with an 11x4 (a cut down 13x4) which still drew 46 amps delivering 640 watts at around 11,500 rpm. The motor was warm even after the brief runs to get the figures. I think it might be Ok on 3S but not really suitable.

So I took this Foxy C4020/10 out of another model. Unfortunately the cruciform mount is too big for the sheet backplate and I don't have any other material to make another. The I realised I didn't need the mount as there is access to the back of the motor so I drilled out the 3mm aluminium sheet to fix the motor directly to it. Like this:

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It's a lot bigger and beefy than the Himodel at 800 watts with a kv of 755 and a maximum current rating of 50 amps for 30 seconds.

A previous test with a 12x6 prop draws 46 amps about 600 watts and 9,000 rpm which I think will suffice. I'll use it with a Foxy 65 amp esc so there shouldn't be any issues.

So that's nearly 2 days work and all I've done is get a motor fitted! Am I the only person who takes 2 days to do a job which should take 2 hours?

For a bit of light relief I opened up the slots for the tail plane and checked the alignment. It's not absolutely perfect but very close and I'm happy it will be fine when glued in. I slice down then centre of the slot then fold back the 3mm/side surplus so it can be ironed onto the fin and tailplane joints to hide them.

I found the closed loop rudder slots OK but the elevator push rod exit is on the left (port) rather than the right (starboard) side as described in the instructions.

Geoff

Biggles' Elder Brother - Moderator11/10/2018 22:02:44
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Posted by Geoff Sleath on 11/10/2018 21:37:07

So that's nearly 2 days work and all I've done is get a motor fitted! Am I the only person who takes 2 days to do a job which should take 2 hours?

Most emphatically not Geoff - I'm a member of that club too! I start with what should be something simple and then it all just magnifies beyond my control! Think back to my WOT4XL thread - that was supposed to be just tidying up a winter hack! Three weeks it took!

Anyway interesting thread, I will be following.

BEB

Nigel R11/10/2018 23:15:39
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2 days sounds positively rapid to me.
Jonathan M12/10/2018 07:22:04
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Lightening fast Geoff!

I'll also be following this thread due to a particular vested interest... although the bits that will eventually make up my own versionl are still dotted around various warehouses.

As you've started to discover, take nothing for granted and make no assumptions about things being manufactured on the money. My IC Acro Wot from the same Foss/Ripmax balsa ARTF stable initially had to be trimmed out with a lot of up elevator even with CG spot on. Just before the hole I was scratching in my head came through the other side, I checked the wing-seating in the fuselage sides... which had nearly 2 degrees of negative-incidence.

Jon

Geoff Sleath12/10/2018 11:47:40
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Despite construction looking very good with triangular stock reinforcing the usually vulnerable places (firewall, u/c plate) I added some WEST epoxy to the interior as a precaution. WEST is very slow curing but it was fine over night.

A test of the Foxy motor looks really promising.

12x6 APCe prop; 46 amps; 700 watts; 10,000 rpm

Well inside the motor current limit of 50 amps (especially as full throttle will not be continuous) and esc limit of 65 amps. There's even a bit extra if needed but 100 watts/lb should be adequate for a pilot with insufficient talent to be a real hooligan.

So now on with the battery tray.

Geoff

Nigel R12/10/2018 12:16:36
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Numbers look good Geoff - should provide plenty of welly!

Geoff Sleath13/10/2018 11:21:16
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A little more progress - this is supposed to be quick but I always find it surprising how long the few ARTFs I've assembled take me. The RTF foamies are very quick, of course. I thought I was just having a look at my Riot and 30 minutes later all I had to do was plug the servo/esc leads into my receiver, install a battery and fly! This is taking longer.

I'm using Kpower MO200 mini servos mainly because I have enough new ones in stock. They're quite a bit lighter than Futaba 148sized servos but are metal geared, have ball races rather than bushes and have the same torque (3kg cm). I've used them successfully in the past. They just need a little modification to the servo slots.

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I've made and fitted the battery tray from 3mm birch ply with cooling/lightening holes. The battery will be retained with a Velcro strap and sticky-back foam on the tray itself to stop slipping. For others making a tray, the width is 55mm for a snug fit in the former. I cut the wood slightly over size and sanded back (or perhaps Permagritted) to get it just so.

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Plenty of room for a 4 AH 4S LiPo and the standard top hatch make access ridiculously easy. That hatch was a big factor in my choice of this airframe. It makes life so easy.

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The covering is a bit wrinkled but a bit of time with an iron cured that. I tried feeding the elevator push rod through and it's quite easy. I fed a length of snake inner through from the back then screwed the push rod into it and simply pulled it through. I'll do the closed loop rudder wires in a similar way except I'll use snake outer and thread the wire through. Actually feeding things through fuselages is all I use snakes for!

The instructions tell you to remove any film overlap on the wing root ribs. Easier said than done as the overlap is only a couple of mm and on mine it's well stuck down. I've removed as much as I can but I wonder about the need. I've put the wings together as a trial fit with the dihedral brace (actually there's no dihedral!) and with 2 bolts as well as the root rib tongues acting as a wing location dowel at the front I'm sure it could be flown without glueing the wings together at all. I certainly will be glueing the wing; I just wonder if anyone has tried flying without?

Geoff

Ron Gray13/10/2018 11:32:23
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286 photos

Nice work Geoff. I built my battery tray very similar to yours and had it positioned just like yours but in the end I've had to move it back so that the front of my 5S battery is in line with the front former. That was the only way I could get the C of G to the correct location. Fortunately I hadn't stuck my tray in, it is a screw fixing.

Bob Cotsford13/10/2018 11:41:53
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I don't worry about a mm or two of film in the glue joint, if anything it helps to stop the film lifting at the edge. The bulk of the load should be going through the hardwood joiner with the root ribs providing additional support.

I don't think I'd like to fly with unglued wing halves simply because I wouldn't trust that liteply tongue on the leading edge. It's not the strongest of location methods even with a good layer of epoxy joining the two sides. I would groove the front of the root rib faces so that you can embed some carbon rods into that leading edge tongue which is what I've done on my WotsWot. Alternately, on my Bf-108 which uses a similar LE tongue I've added a couple of 1/4" dowels to provide some extra strength. It's not unknown for the tongues to break away, or at least it has been reported to do so on WotsWots lower wings and larger Wot 4s.

Biggles' Elder Brother - Moderator13/10/2018 11:54:54
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I agree with Bob. I didn't bother removing the film - it's tiny about in the scheme of things, as long as there is plenty of epoxy on the wing brace an bare faces of the wing ribs (99% of the area I would say) all will be fine. Bear in mind mine has had a lot of "throwing around" - sometime quite violently in it long life, and the wings have always took it!

BEB

Geoff Sleath13/10/2018 11:58:56
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3014 forum posts
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Ron: I certainly hope I don't have to move my tray as It's firmly glued in. I think BEB said his balanced with the battery as far forward as possible.

Bob: That's an interesting idea to reinforce the leading edge tabs. Did you have to widen the slot in the fuselage former? I agree about the small amount of surplus film not being of much consequence. As I would normally cover a wing after joining the two halves on a home build it's not usually a problem. Obviously needing to cover and box an ARTF makes that route impractical in this case.

Geoff

Bob Cotsford13/10/2018 12:48:20
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Geoff, on the WotsWot I used 3mm or so carbon rod which forms the top and bottom edges of the tongue. I grooved the root ribs to accept it so that it's sandwiched between the wing halves and doesn't add to the width of the tongue. I'd have to dismantle the model to get a pic as I store my Wots assembled.

Geoff Sleath13/10/2018 13:00:13
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After Ron's comments re CoG and his need to put the battery much farther back I did a loose assemble of the airframe so I could an idea of where it is on my build. There were no servos or tail wheel etc but I did fit the u/c and the battery of course. It's very slightly nose heavy but not much and most of the bits missing are behind the balance point so I don't think it'll be a problem. In any case very little weight at the tail can make up for extra nose weight if it becomes necessary.

While I was at it I weighed the model. It came out at 4.26 lbs (under 2kg). I think the final flying weight will be around 5lbs so the 700 watts I'm getting should be just about sufficient to get it off the ground

Overall I'm very impressed with the quality of the covering and construction in general. The only fittings I'll replace are the plastic clevises. Everything else is very usable.

Thanks, Bob.  I'll certainly think about introducing some carbon reinforcement.  I should have some in stock.

Geoff

Edited By Geoff Sleath on 13/10/2018 13:02:19

Ron Gray13/10/2018 13:46:16
1159 forum posts
286 photos

Geoff, it was not the static C of G that I had to balance for, I had to move the battery to get it to fly 'correctly'. On its first flight with 'book' c of g it felt very nose heavy so did an inverted 45 degree climb on half power and sure enough she really did pull to canopy. Having moved the battery back it is now a lot, lot better but as per a previous post I also had to raise the wing LE by about 2 mm. Still some fine tweaking to do but getting there and with plenty of power on tap it's a hoot to fly.

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Biggles' Elder Brother - Moderator13/10/2018 13:58:14
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I would agree with Ron here. When I say mine balances fine - it does - but it isn't set at 82mm from the LE as the instructions say. You will find that nose heavy I believe, I know I did. By all means try it, but I bet you move it back!

Personally I think the wing incidence is fine - personal taste of course - but for the CoG I'd say 85mm back is the beginning of the "good zone"! After that it just depends how sensitive you like the elevator to be.

BEB

Edited By Biggles' Elder Brother - Moderator on 13/10/2018 13:59:15

Jonathan M13/10/2018 16:14:06
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All very interesting... I'm 'taking notes'!

Jon

Geoff Sleath13/10/2018 18:06:29
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3014 forum posts
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I'm getting towards the point of needing to remove film from the fin and tailplane. I'm not all that happy using even a fresh blade in a scalpel in case I score the underlying wood. I have thought of using a fine point on my soldering iron to melt the film.

Any tips?

Geoff

Ron Gray13/10/2018 18:14:18
1159 forum posts
286 photos

Geoff, try the soldering iron method, it works really well and has the added benefit of sealing the edges of the film down, if you do try it make sure you leave a gap back from the marked outer edge line to allow for the melting of the film.

Devcon113/10/2018 18:17:32
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Hi Geoff,

Watching with interest, to remove film to a line I've tended to, as you say, use a soldering iron lightly drawn over your cut line.

A couple of questions, what servo are you going to use for elevator and I'd be really interested in seeing a picture of how the two wing halves are joined as I'm struggling to visualise the method.

How is the weight going ?

Thanks

Devcon1

Ron Gray13/10/2018 18:23:47
1159 forum posts
286 photos

@BEB - I decided that the incidence needed changing as when flying straight and level, and after the C of G check it still needed up elevator. It was also quite difficult to get it to spin and I know there are those out there who say that incidence shouldn’t affect that, but after I changed it spins were a lot easier. Still a work in progress as it’s still not exactly as I want it but it’s good fun getting it there!

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