An Eleccy WOT4XL - with a twist!

[Biggles' Elder Brother - Moderator]

As many will know I like the WOT4 - a no-nonsense model, easy to fly if you want but can "do the book" in the right hands. I've had my current balsa ARTF WOTTY for about 3 years now, its seen a lot of flying in that time, many hours, and is starting to look a little tatty.

I wanted a winter hack and took a look on BMFA Classified for something suitable - a tidier WOTTY maybe? Well I found a very tidy looking WOT4XL in Cheshire - not far from me - so decided to take a look.

The seller wanted £160, which considering that included: the airframe, a very nice AXI Motor, ESC, rudder servo (though no elevator or aileron servos) and a good 6s battery thrown in (all with only a handful of flights under their belt) this looked a bargain.

Why only a handful of flights? Well the chap selling was an experienced modeler, but on big petrol jobs and gas turbines etc., this was a dedicated IC man!

The WOT4XL was his first foray into electric power and was very much an experiment for him. But it turned out to be a failed experiment. With flight times of 4 minutes or so, a need to fly on full throttle and a generally lack-lustre performance he was not impressed! His conclusion "Electric power is rubbish I just want rid of it - hence the price" (Well he didn't say "rubbish", he used another word, but I can't put that here!)

So I took it off his hands - seemed to me to be an act of kindness really! But in reality, having looked over the conversion and what he had done, I was convinced we could do a lot better and turn this into a viable electric powered aeroplane. Besides that - I like a challenge!

So this thread is the story of me doing that. To begin with I'll review the model as I got it and examine the conversion for areas we could improve on. That will be the next post.

Just before we start I want to make something very clear. This is not in any way intended as knocking the guy I bought this from, he's a very accomplished modeler and understands aspects of the hobby I don't. Nor is it about a "electric is better than IC" thing. It is about showing what a broad church our hobby is these days and how knowledge (good as it is) doesn't always transfer well from one sphere to the other. Creating electric power systems and implementing them is a very different knowledge and skill set than setting up a big petrol aerobat - though both are challenging. So I'm hoping to illustrate some of the differences and so help folks achieve that first conversion successfully or at least appreciate better what is involved and what considerations are important.

Hope some find this interesting, let's get on with the review of what is there now.

BEB

[Bob Cotsford]

Looking forward to this one BEB, I've thought about 120 4stroke equivalents but decided they're bigger than I really want these days so I'll be interested in seeing how you come up with your final solution.

I do still have a 1.20 size Edge airframe, I just can't make myself let it go despite a club member saying that he has ready cash available for it.

Edited By Bob Cotsford on 16/09/2018 22:59:46

[Chris Jones 7]

Love my electric Wot4 XL. Certainly not under powered on 8s with a nice eight minute duration. Enough power to drag up a decent sized glider but still slows to a brisk walk for landing.

[Biggles' Elder Brother - Moderator]

Right well starting at the tail end the first thing you'll notice are these to cut-outs (there is another on the opposite side):

In the original model out of the box there is a single elevator servo located amid-ships. It drives the elevator, which is in two independent halves, via a push rod assembly in which a single rod from the servo is forked into two rods. He obviously didn't like this arrangement (TBH is does have its down side!) and has replaced it with a solution very common on larger petrol aerobats - two servos mounted in the tail.

Now this is definitely a more precise solution but it has the serious disadvantages for electric power that: a) it doubles the number of servos, adding more weight, and b) it shifts that weight right to the back. Now an electric motor is significantly lighter than am engine, we usually have problems with conversions threatening to come out tail heavy anyway - this isn't going to help!

Next up is the battery placement. This is vital in electric conversions, we need to use the considerable weight of the battery as a means to help balance the aircraft correctly. Given the potential tail heavy nature of most conversions we normally want battery about as far forward as possible. But the original converter didn't see it that way, he located the battery at the desired CoG!

This is a classic big IC solution if you think about it. The battery is the "fuel tank", the fuel tank empties during the flight so it makes sense to locate it at the CoG so it won't cause a balance shift. Er,...but batteries don't change weight as they discharge, so that isn't needed. It also misses out on the opportunity to use the battery as useful weight ballast.

Now let's shift our attention forward:

A ventilated spinner no less! One thing I did like about this, the screws where cap screws with an allen key drive recess. Much better than usual cross head screws used to hold the spinner on. I don't know if this was original to this spinner or a modification, but either way its an idea I may well copy!

Removing the spinner we find a rather nice aero-naut carbon fibre prop that has been well balanced:

No expense spared here!

Continued in the next post,....

 

Edited By Biggles' Elder Brother - Moderator on 16/09/2018 23:21:04

[Biggles' Elder Brother - Moderator]

On the removing the cowl I found what "hefting" the model suggested was there, a lot of lead:

That is just under 1.3 pounds of lead, 0.58Kg to be precise! Wow! It's not there now - I've removed it!

Next let's take a look at the motor mount:

Erm,...does that look like upthrust to you? A closer look reveals that the lower stand-offs are indeed "shimmed" by a nut packing:

Very strange! I'll remove that I think as part of the overall work and see what see flys like without it. Given the huge shift in weight distribution I'm planning (discussed later) and the generally slimming down of this at present fairly porky aeroplane, it's likely we can restore the original thrust line.

Finally he has added what I can only assume is extra ventilation, first at the fire wall:

And then under the fuselage:

Not the neatest of jobs!

OK that's the lay of the land and what we have to work from. What can do with this?

Continued,...

[Biggles' Elder Brother - Moderator]

OK, so taking stock, what have we got?

The current all up weight is 4.6Kg. Allowing for the missing servos and sundries that will come out at about 4.8Kg in flying rig (10lb 12oz) . The weight suggested by Ripmax in the literature is 3.85Kg (8lb 8oz),

So she's well overweight, by about 20%. But she is fitted with basically the specified power train for the design weight. No wonder the performance is lack-lustre!

The current wing loading works out at about 26oz/sqft, not bad in itself - but I think we can do better!

So where can we shed, or usefully relocate weight?

1. Restore the single elevator servo and resite it in the centre of the model. This is a saving of about 41g - OK not much, but the real benefit here is the relocation out of the long tail which will help us to shed a lot of that lead up in the nose. For the elevator I'll use a plain vanilla Futaba S3001, no frills here! For the ailerons I will use two Savox low profile jobs from my used servo box:

2. Relocate the battery up as far forward as possible. No weight loss, but a major benefit in losing lead I hope.

3. Relocate the ESC up in the cowl, it's currently in the fuel tank bay. OK small impact, but every bit helps.

After these steps we'll review the situation again.

Right, that's the plan, work starts tomorrow!

BEB

[john stones 1 - Moderator]

It's one of the reasons I dislike the pre fitted servo trays, I want my gubbins where the weight works for me not against me.

[Geoff S]

Out of curiosity I Googled the Axi4130/16 motor and found that you did indeed get a pretty good deal! Looking forward to reading more about this. As it is you're doing exactly what I would do.

All my electric conversions have needed the battery as far forward as possible and as little weight as possible right at the back. Might it be possible to get it actually under or over the motor by cutting an aperture in the firewall? I did that with my most recent conversion (a 58" DB Cirrus Moth) and got away with no extra ballast at all. You may then be able to effect battery changing through the front with hatch in the cowl.

A big advantage of fitting the esc in the cowl is better cooling with the draft from the propeller as well as getting its weight forward.

Did you check the power consumption before you started surgery?

Geoff

[Biggles' Elder Brother - Moderator]

Hi,

well today I majored on sorting the rudder and elevator servo. Reinstating the elevator in the centre instead of in the tail. I also ended up replacing the rudder servo - for various reasons. So I now have two Futaba S3001's up there and all seems to working well.

The only real issue was getting the two pushrods down the fuselage. I use 3mm rods for these with a Blackhorse style clamp that was designed for 2mm and I drilled out. All fixed wih blue Locktite so nice and secure.

A bit difficult to photo all this, so here is a short video. First we see the resited servos and then a shot of the tail with the rudder and elevator cycling driven by a tester.

Onward and upward! We'd better have a look at the ESC siting tomorrow.

BEB

[Rich too]

Interesting thread, even for a petrol head like me! And probably all the shortcomings directly contributed to why he didn’t like the plane! 8 can’t believe he added all that lead with the battery over the cog!

[Biggles' Elder Brother - Moderator]

Yes Rich it is a bit hard to fathom isn't it!

OK on with progress - or at least what progress there was today! We all have those days when our plans to get in the shed and sort stuff out all goes awry - today was one for me! In the end I managed maybe an hour to an hour and half total!

Anyway here is what I did,... as mentioned above today was to be "move the ESC day". Why do we have to move it at all? Well the fact is it's currently occupying a prime bit of realestate - the fuel tank bay:

Its in the way of the planned new battery location there and the cooling isn't great either. So it's shifting into the cowl. Well that should be straight forward enough shouldn't it - Ha!

So, first step remove the ESC, here it is out:

I've put a 12" (30cm) rule in the shot to show you how big this ESC is - its massive, sitting there like an octopus! Its quite unusual for a FW ESC in that its loaded with the SimonK software - more common on MR ESC's?

Have a good look at the picture, there is something else very strange about this ESC, take a look at the connectors, they are male bullets!! I have never seen male connectors on an ESC before! So of course the motor has to have sockets - equally unusual!

Now I suppose there is no fundemental reason why you shouldn't have this arrangement, but it certainly runs against the standard convention and left me with a problem. You see that ESC is so big it won't fit in the cowl! So I want to change the ESC for another I have in the box - I would normally be able to just slip a replacement in, but of course the connectors don't fit!

So soldering iron out, motor taken off and new male connectors fitted:

I've briefly tested this out (outside the model) and it works fine. I have porogrammed my Tx for the model (not hard as I already had the program for the conventional WOT4 - so just a copy. Obviously the throws and that need to be set but it's basically there). Reassuringly the Tx version works fine on the throttle as well.

So, some progress; not much but it is progress at least.

Tomorrow is "hole patching" day. The thing is like a sieve in places!

BEB

[Callsign Tarnish]

I'll enjoy this. Having looked at some of the butchery and basic errors I'd disagree with him being an experienced modeller!

[Devcon1]

Following with interest, particularly how the Centre of Gravity develops.

Intrigued to find out what the twist will be and the performance.

[Richard Ashworth]

Another addict signed on. I am trying hard to understand the whys of the plane when you got it. I do leccy and I can only guess that I would be likely to make a similar mess of a big petrol or turbine if I was to try without a lot of reading up first.

Fly the foamie and ARTF 4s, so desperate already to see the end result.

[Nigel R]

Nice project for the £160. Watching with interest.

Some seemingly nonsensical choices have been made during the fitting out, for sure.

What's the power figure with the setup as it stands? Somewhere around 1.5kW?

[Biggles' Elder Brother - Moderator]

Posted by Devcon1 on 19/09/2018 02:56:58:

Following with interest, particularly how the Centre of Gravity develops.

Intrigued to find out what the twist will be and the performance.

 

 

Sorry if I dissapoint you Devcon - but the "twist" is just that I think its a bit unusual to be doing an electric conversion of an electric conversion!

Re Performance, well I'm aiming for 4Kg all up (that's about 8.8lb). Allowing for a max current of 60A - which the motor is comfortably capable of - and the fact that I'm using a 6s battery - I should have a maximum power of around 1.3kW - that would be 150W per pound - loads of power! But all that of course depends on getting it to 4Kg and that will mean little or no lead - the battery placement will be crucial here.

BEB

Edited By Biggles' Elder Brother - Moderator on 19/09/2018 11:45:44

[Shaun Walsh]

There's probably a small but lucrative market for Tungsten spinners!

[The Wright Stuff]

Posted by Biggles' Elder Brother - Moderator on 19/09/2018 11:44:33:

Posted by Devcon1 on 19/09/2018 02:56:58:

Intrigued to find out what the twist will be and the performance.

Sorry if I dissapoint you Devcon - but the "twist" is just that I think its a bit unusual to be doing an electric conversion of an electric conversion!

Edited By Biggles' Elder Brother - Moderator on 19/09/2018 11:45:44

...and here I was wondering whether the 'twist' was in the wing or in the fuselage, and how it was going to be straightened out...

[Kim Taylor]

Re Performance, well I'm aiming for 4Kg all up (that's about 8.8lb). Allowing for a max current of 60A - which the motor is comfortably capable of - and the fact that I'm using a 6s battery - I should have a maximum power of around 1.3kW - that would be 150W per pound - loads of power! But all that of course depends on getting it to 4Kg and that will mean little or no lead - the battery placement will be crucial here.

BEB

Edited By Biggles' Elder Brother - Moderator on 19/09/2018 11:45:44

I'm definitely interested to see where you end up with the weight.

My own electric Wot4 XL ended up nearer to 5Kg than 4 - this was with an E-Max 4020 motor and 5800 6s LiPo.

No lead used to balance

I got it down to 4.5Kg by using a carbon fibre undercarriage which was loads lighter than stock and could, I suppose have shaved a bit more by not using a separate Rx pack and doing away with the arming plug and associated wiring, but both of those seemed a bit risky with a model this size.

It was drawing over 1400W at full chat on a 15x8 APC E prop and was pretty much unlimited vertical.

I've never heard of or seen one get down to the box top weight, even with a .90 2 stroke fitted (and there are many in my club).

Kim

[Biggles' Elder Brother - Moderator]

I agree Kim, the box top weight is 3.85Kg, I'll never get it to that!

But I hope to get as close as I can to 4Kg.

BEB

PS Doing some major surgery at the moment, will report in later!

[stevan Lewis 1]

BTW BEB, the spinner looks like the Turnigy Turbo spinner from Hobbyking, they have cap head bolts.

Steve

[Biggles' Elder Brother - Moderator]

Thanks for that info Steve. I do like that arrangement.

BEB

[Biggles' Elder Brother - Moderator]

So, today was supposed to be "ESC fitting day" - but when I got into the shed I realised that I was just dodging a job here. You see doing the ESC is easy, sorting the battery isn't!

"So let's all go and do the ESC?" No, let's be grown up, grasp the nettle, and sort this battery. I can't properly site the ESC, with the right length leads etc., until I know where the battery is going to be anyway!

Basically its going in here:

The fuel tank bay. I'd love to get it right up in the cowl - but it's just not possible. The cowl is too narrow and there is no space between the standoffs etc. So the fuel bay it has to be.

For some reason there is a whopping big thick chunk of hairy balsa there - epoxied in. Oh joy! I don't know why, it only held the old ESC which, although large, wasn't that heavy! I need to get this block out, its taking up space I want to use for something else.

Boy it was a job and a half! It was stuck in there never to come out and of course access was tricky. But a combination of a scalpel, stout knife for levering and eventually a pair of long nosed pliers finally won the day!

I have it back as it was originally!

So, why am I so concerned to lose this block? Well, after much squinting and eyeing up, I think that if I cut a hatch in the top of the black covered fake windscreen I could get a 6s battery in though there! It couldn't be a long hatch, or wide, but it is deep giving us maneuvering space. So battery nose down first and than wiggle it into position. If that works there would be no need to take the wing off to change the battery!

So I marked out the position of a hatch on some masking tape over the "windscreen":

Took a fresh scalpel blade and a very big breath,..... and started cutting - the moment of commitment. You have to do this very gently I find, using very many light strokes - you don't want to dig in. I was surprised at how thick the top wood was, I had to swap over to a longer scalpel blade at one point. But eventually I got there!

And here is the hatch cover,... basically the cut out piece!

You can see how thick it is. I now need to trim that a bit - it's a very tight fit! - and fit some pegs and catches to retain it.

Does it work? Can I get the battery in? You bet yer!!

You could hold a dance in there!

So, pleased with that, once we get it fitted probably we can look at battery retention but I don't foresee any big issues there.

Phew! Time for a bottle of Spitfire I think and a nice sit down!

BEB

[Ron Gray]

C’mon BEB, my standard size WOT4 has 6 cell batts in it, the XL should swallow them! (yes I know mine are only 3000Mah). I made a battery tray that allows the batt to be slid in and out, much like the leccy conversion but longer.

[Devcon1]

Not at all disappointed about no twist as the suspense would have been too much for me.

We must be telepathic as I'm at a very similar stage on a standard Mk 3 build hence following with interest.

I notice from the instruction that Chris Foss advocates, for those brave enough, an option to cut rectangles out of the foam cores to remove some excess baggage. Not sure if this is referenced for it's bigger brother.