Since the sad loss of my Mega powered Global Birdie 10 a few months ago I've lacked a "hack" sports electric model of my own with a decent undercarriage. My normal hack model for winter flying and one which is very popular with sports flyers in the UK is a Wot- 4, pictured below in it's glow guise with a very lovely OS .40SF fitted. This is a 52” span, high wing aerobatic model, representatives of which have been powered with anything from a .35 to a .90! She was a very nice flyer as set up with the .40SF but my gradual switch over to completely electric powered had to be continued with a conversion of this model.

I picked up a Twister 60 brushless motor at the Walsall fly-in this summer and thought that the Wot 4 would be a useful test bed, so spent an afternoon taking out the glow engine, fuel tank, receiver battery, motor mount, throttle servo and linkage and removing the accumulated oily grime, or at least most of it. Isoporopanol came in handy there.

Wot 4s in their natural habitat don't have cowls, or at least don't have cowls beyond their first crash. A look down the flight line at any UK club will confirm this. However I did have a nice GF cowl for a Wot Four, purchased at great expense from the LHS. Unfortunately it was for a later model and didn't fit at all, thereby leaving me free to rationalise motor mounting without worrying about a cowl.

First look was at the AXI space frame mount, that I've seen on some other Wot-4 conversions. This seemed to me to put the motor a heck of a long way out from the firewall, potentially putting it in harms way of a horrible distortion in the case of a prop strike. The Twister had a nice option to reverse the shaft and mount the motor at the rear and with a substantial firewall this looked the best option. So first job was to cut a motor plate, which I did from GRP. The Twister motor was secured to that, the appropriate holes drilled in the firewall for captive nuts and everything looked great. It wasn’t- this is what the eventual set-up looks like, as described below, and the observant viewer will note that it isn’t directly mounted to the firewall.

Then some thought was given to battery location and insertion. Having had it drummed into me by various contributors to these forums that taking the wing off to change a battery is tantamount to clubbing baby seals in the acceptability stakes I looked for a way to avoid this. I’d calculated that a minimum of 16 cells would be required and that the only real option, given the construction of the model, was to insert these from underneath. The Wot- 4 has a quite severely raked fuselage behind the undercarriage plate and that would be the best location for a hatch. This was cut out and a hatch fabricated. I used an offcut of lolly stick as a tongue to retain the hatch at the front and two control horn offcuts which swing into place to retain the hatch at the rear. The location of the hatch can be seen in the picture below.

The fuel tank bay and fuselage in front of the servo tray was the location for the battery pack and in order to feed these in with the greatest ease an angled lightply plate was constructed and keyed into the former at the rear of the tank bay and the firewall and fixed at the rear to some triangular section trailing edge stock. The battery ramp can be seen in the internal pictures. Battery retention is by a combination of a velcro strap and a lightply former that is wedged between the battery pack and two blocks let into and pinned to the fuselage sides. This keeps the battery rigid and immoveable, as it would be a shame if it fell out backwards.

For the power pack two 8 cell CP2400 NiCd packs were joined together to make a long block pack (Pictured) to give the required 16 cells. A 4 cell 650mah AAA receiver pack was installed below the battery tray in the tank bay.

The radio gear was retained from the glow model, comprising a Futaba R128DF receiver and HS300 servos on rudder, elevator and aileron. A Jeti Advance 45 esc was velcroed to the fuselage side, the batteries put in place and the model submitted for balancing.

Did she balance first time? Not on your life. LiPOs? Fergeddabboudit! She was extremely tail-heavy. Armed with a short nose and a very lightweight motor there was no way this particular model was going to get by without a lot of weight up from and even 16 cells in front of the C of G wasn’t enough, with that firewall mounted motor.

Chatting this over at the club the optimum solution (me having discounted ripping out all the radio gear and replacing those standard servos with microservos) seemed to be to bring the motor forward a touch to increase the moment arm for that puny weight to act on. I also replaced the weedy RX pack with a standard one weighing twice as much. The motor was spaced from the firewall with extended M3 bolts and hardwood engine bearer blocks (pictured) that add about an inch offset to the motor. Coupled with a biggish aluminium safety nut on the prop got the C of G in the right place.

The maiden flight was this afternoon and went without a hitch (if not without a glitch). The Twister 60 on 16xCP2400s and 13x6.5APC-E prop pulled 37 amps static at 8400rpm. This allowed an easy ROG from our grass field and a deliberately very steep climb out to about 200 feet in the first circuit. Gigantic loops are a joy to behold and the model does everything she did on glow power. Indeed she seems to have more power and even at an estimated 7.5lbs the Twister pulls her through the air with great authority. I'll try and get some video up in the gallery next time we get down to the field.

Methinks I’ve just found my replacement for my lost favourite sports model

Hi leccy
Your battery hatch is neat - sooner or later, someone will actually build a Foss-il for leccypower, should be interesting to see how they figure out on getting the pack in/out.

Have often pondered on quietening down an AcroWot, which I reckon has to be one of the better looking sports fliers around, but I suspect it would be a very expensive set of templates to haul one to the US. Also, there's odd suggestions that even just publishing photos of such a highly hacked model would cause the Head Foss-il to act like an American and call down all the lawyers in hell for impugning his design

Funny - I recall many English clubs as having a set of WOT4 templates that no-one would own up to until they trusted you enough to know you weren't a FosSpy ...

Whatever, good work on your WOT-E - the world now has another electric kit available to it. Any chance of a cowling in wood now you know it works well?

Regards

Dereck

I'm using the Twister 60 in an ES10 on 14 volts with a 14x10. Pulls 42 amps. I'm happy with it after a season's flying but keep thinking of going to 5S for that extra bit of vertical. My AUW is 75 oz.

Dereck

I wonder whether Chris Foss might ever include a redo of one of his designs for electric, with the strength and weight correctly distributed for the different needs of electric flight. A Watt- 4 perhaps?

Funnily enough the Acro-Wot conversion has been done recently, using the Twister 60 as a powerplant

http://www.rcmodelflyers.co.uk/4um/i...topic=11582.30

agree with you on the looks, I've always liked the lines of the AcroWot.




If you were starting to build one from scratch then it would be possible to keep the weight down, perhaps substitute a lighter tail construction, maybe then you could use LiPos, but as I described above I needed every ounce of those heavy CP2400s to get here to balance.

I might well knock a GF cowl up for the Wot-4, now that I know she works. Though it is in keeping with the prototype in her natural environment to have all the engineering out in the breeze perhaps a more sleek cowled-in electric look could catch on. It might also have the added benefit of allowing me to ditch the receiver pack and fit a UBEC by weight redistribution. I'll also do some experimenting with props as just looking at the numbers these motors are incredibly versatile and I'm not working this one particularly hard yet.

Brian

Hey Brian, you skeered me for a moment with that 1st picture attachment. Good to hear from you!

Great E-conversion, I wish more people would do them and include thier info here.

BTW, it's refreshing to see that some people other than myself still use the "Old" round cells and say so here. I'm sure there are a lot of members of RC Groups that don't speak up about this just because it isn't the latest and the greatest trend. Makes things much more affordable too!

Greg

Those CP2400s were just £2.00 a cell = £32.00 for the whole battery pack (plus maybe another quid for wires, heatshrink and connectors). They will carry on taking charges and providing power until the cows come home. They'll fast charge without complaint and without them this model wouldn't have balanced. I'll use LiPos for jobs that they excell at, and where they are cost-effective, but I'll also continue to use round cells for jobs that they excell at. IMHO it doesn't pay to completely discard anything that works, so my electric models will continue to be powered by a combination of brushed and brushless, NiCd, Nimh and Lipo, plus whatever else comes along.

Brian

Nice job, I like the hatch, my own Wot 4 requires the wing to be removed to change packs. I am also building an Acrowot for electric power (AXI 4120/18, as in my Wot 4)

David S

Brian, Greg
Having looked at the investment and problems associated with big and small lipos (my DuskStik does 15 mins on a pack of ex-phone battery cells, where the plug and lead cost me more than the cells!), plus the possibilities of the Valence "Saphion" pack sitting on my bench, BRJ (Big Round Jugs) are keeping their place in my fleet also.

I run a lot of CP2400, but I have a pack of GP3300 nimh that are awesome in runtime and power delivery.

A Wot4 with a built up wing and a more electric-friendly fuselage wouldn't be that hard! I had a WOT4 with a Merco 61 on it for a while ways back "over there", its biggest snag was getting it to come down and land without taking up the entire field.

Its second biggest was the way it went through a gallon of fuel!

D

If people want to see more of such conversions, here are a few of my own Wot 4, also built and flown as a glow model before i saw the light

That's not me holding it, I was holding the camera!

Dereck - I am building an electric Acrowot with a few mods from the kit with the blessing of CF, though I haven't had any time to visit my workshop recently

Dave s

Dereck

Agreed- those GP3300s are the Bee's knees. Pete Wilson was getting an 11 minute fully aerobatic flight with his AXI 8120/18 powere aerobat yesterday, compared to the 7-8 minutes that he'd been getting on RC2400s. At £3.50 a cell they are still good value and I see a couple of packs of those in my future too, the only downside being the 45 minutes fast charging even at 5 amps.

Dave- I like your cooling duct underneath, a brave man could insert his batteries in there, with a suitable retention system and not worry about them doing an impression of a RAF Hercules doing a low level Landrover drop Nice job.