Electrifying a Wot 4

[Danny Fenton]

we might just try and do that, good excuse for me to get yet another model, whats this dynamic soaring about then

[Tim Mackey]

You will have to ask Andy E about that - serious hooligan territory - I am more into informal fun and laughs

[Danny Fenton]

The Fury would PSS if I took the prop off

[Tim Mackey]

It probably would indeed...but undercarriage is obviously a no no.

Don't worry about having suitable models, there will be plenty to share from us lot.

[Danny Fenton]

If you had ever seen me twiddle the sticks you wouldn't make that offer lol, you said you can fly either mode, I can barely fly ANY mode LOL

Chris is already digging the slope soarer out of the attic while we speak...............

[Chris Bott - Moderator]

Timbo - I'll be there, like a shot. Just as soon as I can, which at the rate I'm going won't be before the Autumn

I've sloped in the Yorkshire Dales, Long Mynd, Devon, Cornwall, Dorset and Burton Dassett but never yet in Wales. At the moment work seems to be taking me near Cardigan quite a lot, but you never know, there could well be something I need to do in the North...

Thanks for the invite. One way or another, we'll take it up

If all else fails, I'll wave on the way to Gleneagles..

[Tim Mackey]

Heres the latest results with one of the 2 new motors ( KMS).The 670Kv 1400 watt motor has been returned - loose magnet . When I get the replacement  it will be trialled with..... 

1) 6s genuine A123s.   2 ) 4s softpack Lifes  3) 3s LiPo

The results here are from the larger 1500 watt 480Kv version ( see picture )

Trialling with:

1) 8S softpack Lifes.   2) 6s LiPo.   3) 4s Lipo   4) 6s A123s 

Its a nice motor, throttling smoothly  with very little "notchiness" and a quality appearance.

40A constant, with 60A burst, its only "ticking over" with likely props. I originally aimed for around 500 watts pp but having tried it with a higher RPM - it flys better with higher pitch speed. 

First up is 8s Life on a 12 x 6.This is quite a bit more powerful ( and thirsty of course ) than my Turnigy 400Kv on a 13 x 6 prop ( posted earlier ).

The KMS on 12 x 6 showed  11500 RPM and over 1kw but drank 47A at peak, so the bench test was limited to 1 minute and obviously I didnt bother with the 13 x 6 !! I dont really want to drop the prop size as the wotty prefers a largish prop, and besides, the revs will climb further and it all starts to get a bit noisy etc. On the 8s pack, my best results have been with the lower Kv Turnigy 400....which was destined for my Hangar 9 Camel - I may decide to use this new KMS in the camel insead which will be 4s lipo powered, and use the Turnigy in Wotty.

Next test  is on a 6s LiPo and the same 12 x 6 prop - seems quite promising with 43A, 950 Watts and 10800 RPM at peak - only downside is the 43A, again a little high for good duration.

Third up was just for interest.....I tried a 4s Lipo with a largish 14 x 7 prop - power was a bit low at 440 watts, with RPM @ 6700 and current @ around 32A. It would obviously give a decent flight time, but power is marginal.... I know its still around 80Wplb, but she just feels better with a bit more - heavy old IC conversion you see. I think a 14" prop is about the limit for this bird, and I didnt have a higher pitch one to try. A 14 x 8 might just be good ??

I cant do the 6s A123s test yet, as I am still waiting for 2 more cells.

Finally, a minor disaster struck later on in the day when during the 8s  LiFe pack testing, the 1kw + power pulled over the workmate whilst my back was turned - the prop driver dug into the floor covering and ripped a greta big chunk out, prop broke, motor stalled and consequently fried my 80A ESC. My other high A ESCs are only good up to 6s LiPo so I can't trial the 8s Lifes further yet. Hey Ho

More gremlins on the none too reliable Eagle Tree Logger I am afraid...For some strange reason it is playing silly blighters, on one test showng a high RPM of over 46k and it refuses to graph the data...simply saying " No data points displayed ". The "dial style screens"  are fine - see picture -  Danny / Chris - any ideas ??

Got fed up - so hit the sticky buns and coffee for comfort - closed workshop for the night ! Pooh

[Bruce Richards]

Timbo,

I am building a light weight WOT4 and have been trying to decide what engine to put in it. Reading this thread I decided to go electric instead. My plan is to go 2 X 3s2p with my standard 2200mah packs. It will be interesting to see how well the batteries fit and how the model balances.

I have purchased this motor and  this ESC. What prop range do you think I should try? Any other comments on my intended set up would be welcome.

[Danny Fenton]

Timbo you are just not destined to get any readings from Eagle Tree  I must confess to never having used any of the additional sensors, despite having them. These additional sensors seem to be causing you the erroneous readings, I have an rpm sensor but have not figured out an easy way to connect it in circuit, a recently acquired temp sensor is also yet to be tried, though it will be easier as it just needs to be in contact with the surface to be monitored. It would be nice to see the way the rpm is affected in relationship to current when the prop unloads during flight, so I will have to make up some 4mm male to female adaptors to attach the RPM sense leads.

Thats some serious power to pull your workmate over, bet that made you jump!

you have turned to sticky buns, I am working in Dublin this week so have turned to the Guinness

Bruce that motor is the one I have fitted in my Sea Fury, running on 8 A123 cells and a 14 x 7, its a good motor and will probably perform better with the lower voltage, just worried 3S may be slightly too low, 4 may be better. It goes fine in the Fury but just feel the higher revs cause a few energy sapping vibrations.

As Timbo says if the motor/prop combo is noisy then there is wasted energy, a quiet set up is usually more efficient.

With the A123 I only have 2300mah so you may be better using a 4s1p 2200 and a 13 x 6??

Anyway let us know how it goes?

[Tim Mackey]

Hi Bruce, not sure whether you are intending 2 x 3s in series or parallel. The motor is very close to the 2 Turnigys I have ( 1 x 400Kv and 1 x 600Kv ) The latest motor in the tests above is 480 Kv so very close to your 500kv job. They are great value motors. The Turnigy plush controllers are also excellent - I have this exact same one destined for my  large EDF Hawk and it throttles very smoothly and runs cool at around 45A.

If you are using 3s configuration, then you will need a pretty darn big prop to get the power up on that lowish Kv - and the pitch speed may be too low. See the results here from a 4s with the 480 Kv.

4s Lipo with a largish 14 x 7 prop - power was a bit low at 440 watts, with RPM @ 6700 and current @ around 32A. It would obviously give a decent flight time, but power is marginal.... I know its still around 80Wplb, but she just feels better with a bit more - heavy old IC conversion you see. I think a 14" prop is about the limit for this bird, and I didnt have a higher pitch one to try. A 14 x 8 might just be good ??

If you consider that I was achieving very close to the Kv with the 14 x 7 prop ( 6700 RPM / 14Volts = 478 kv ) and apply this reasoning to your 3s battery, you get only 5250 RPM ( 500kv X 10.5Volts = 5250 RPM ) In the perfect zero drag and 100% prop efficiency world, you can calculate the model speed from (( RPM x pitch) /1056) = speed in MPH.  In your case that would be just 34 MPH...too low for a Wot4 really, as would be the low wattage ( remember I only got 440 peak and thats with 4s ) - If you increase pitch much more, then current is going to get high.

Of course,all that could be useless waste of sleeping time if you intend to use the 6s configuration. However, then you may need to prop down to keep power / amps manageable. ( I was at 43A remember on 6s, and with a slightly lower Kv motor, so I expect yours will be quite thirsty on 6s - and do you really want a smaller than 12" prop on a wotty ?

Finally, what AUW do you aim to achieve, cos yours may be lot lighter than mine and therefore the lower power of the  3s and slightly larger pitch prop might work .

[Tim Mackey]

Danny...yep jumped out me skin I did - thank god the wife had left our car in the drive, or it would have been smack in line when the lot went over

The RPM sensor I use is simply tapped into any 2 wires on the motor or ESC output wires. I use a little harness made up from a short length ( 3" ) of light 2 wire cable (  servo lead is fine ) soldered to 2 modelling pins witha little jst bec style plug on the other end. The sensor unit has the other half of the jst plug. I simply stick the pins into the cables, and remove after use...easily moveable from model to model then.

Guiness eh.... give me a nice coffee any day....and a bun of course

New ESC just ordered ( up to 7s lithium compatible) from foamy jets.

50 - 60A opto £16, not bad I suppose.

Didnt use H/C 'cos I just ordered a load of stuff 2 days ago and its aready shipped.

[Danny Fenton]

Hi Timbo, thats a great idea using pins like that, I will make up a harness when I get back, i had been pondering that problem since I got the rpm sensor

[Bruce Richards]

Laying in bed last night mulling over the day and I realised that 2 X 3s2p was a bit of a confusing term. What I meant was 6s achieved using 4 3s1p packs. 2 in series, parallel with another 2 in series.

 Thanks for the pitch speed calculation very useful.

I was hoping to use 14X7 21V X 500 =10500 RPM  10500 X 7 /1056 = 70mph. If it pulls to much current I can try 12X7 or 12X6.

I wish I had some idea of the target AUW I have never weighed any of my models but I keep meaning to invest in a set of scales. Maybe this time. Looking at the WOT4 instructions it suggests and AUW of 70-90oz. I guess I would be aiming for the lower of these weights or slightly less. I have cut holes in the wings as suggested in the back of the build instructions to save 4oz and I will be using 3/32 balsa for the fuselage sides instead of 1/8 that is supplied. I will probably  cut holes in the tail and fin. However I do not think I am a very good t building light I tend to use too much glue and find it hard not to add a bit of extra "strength" here and there.

 I just worked out the weight of my planned battery set up. 26oz batteries leaves only 44oz (under 3lbs)is not much for the model and the radio so I may have to think again.

[Chris Bott - Moderator]

Gents, our "Standard" 40 - 50 sized setup which works well in many many models is the Thunderpower 670Kv gold coloured motor and 6S A123's or 5S Lipo's.  We use 12x6 13x6.5 and 14x7 depending on power requirements. We've used this in Wot4's, YT 3Demons, Hangar9 Showtime 50, DB Tiger Moth,
X2 in Ripmax DH88, and many more. On 14x7 and 6S A123, it pulls around 1KW which is pretty good for a 600W motor. It doesnt seem to trouble it at all, AS LONG AS throttle management is used to keep the average power well down.

[Tim Mackey]

Danny Fenton wrote (see)

Hi Timbo, thats a great idea using pins like that, I will make up a harness when I get back, i had been pondering that problem since I got the rpm sensor

As they say...a picture's worth a 1000 words.

bigger if clicked.

[Tim Mackey]

Bruce Richards wrote (see)

Laying in bed last night mulling over the day and I realised that 2 X 3s2p was a bit of a confusing term. What I meant was 6s achieved using 4 3s1p packs. 2 in series, parallel with another 2 in series.

 Thanks for the pitch speed calculation very useful.

I was hoping to use 14X7 21V X 500 =10500 RPM  10500 X 7 /1056 = 70mph. If it pulls to much current I can try 12X7 or 12X6.

I wish I had some idea of the target AUW I have never weighed any of my models but I keep meaning to invest in a set of scales. Maybe this time. Looking at the WOT4 instructions it suggests and AUW of 70-90oz. I guess I would be aiming for the lower of these weights or slightly less. I have cut holes in the wings as suggested in the back of the build instructions to save 4oz and I will be using 3/32 balsa for the fuselage sides instead of 1/8 that is supplied. I will probably  cut holes in the tail and fin. However I do not think I am a very good t building light I tend to use too much glue and find it hard not to add a bit of extra "strength" here and there.

 I just worked out the weight of my planned battery set up. 26oz batteries leaves only 44oz (under 3lbs)is not much for the model and the radio so I may have to think again.

I think many people find the AUW of their finished masterpiece is very much down to how little epoxy is left in the bottles after building. Mine is around 5.5lb - but was a slimer when born, and has been over-engineered a tad. I usually allow around 30% of aitframe weight for powertrain. The AUW of my electric version was the same as the IC ( 52 engine ) . I use a UBEC to save weight of radio battery. I expect you will be around the 4 1/2 - 5lb mark - thats a prettty big motor remember. Pitch speed is theoretical and in reality will be lower, and wotty is a bit draggy by todays standard. You are also assuming ( as I did ) that your batteries will hold 3.5v per cell under a heavy load, and also that the motor will maintain it's Kv. I hope you have a whattmeter or similar, and you can see why I have rather a large range of props - nothing like the actual testing to show what will really happen in a particualr combo.

PLUS how it behaves on the bench ( or attacking  the floor ) is always different to how it behaves in the air, and I dont just mean through unloading. Keep us posted. I personally reckon that 6s on a 500Kv motor will be a bit too much, but it will sure go well, if for not very long flights.

As Chris says, throttle management will be vital, which is not a natural process when flying a Wotty

[Bruce Richards]

I have a watt meter I would not be without it. I was planning to use the UBEC on the ESC do you foresee a problem with this?

My old WOT4 has and Irvine .53 up front so I am used to working the throttle. I found on WOT it would disappear and just keep getting faster and faster.

I will keep you posted on how it works out. If it all goes wrong I will stuff an IC engine in the front.

[Danny Fenton]

I must confess that I don't use the ESC UBEC on anything more than three cell lipo models, I either use a seperate UBEC or a Rx pack. I just feel a little safer that way. If you do use a seperate UBEC make sure it can handle the current. As Timbo has outlined elsewhere on this forum servos can draw an alarming amount of current and some of the UBECs are really not up to it. I believe, though have never tried it, you can use the watt meter to measure Rx load??? is that right Timbo??

PS don't give up on the leccy wotty, its a really good model made convenient..........I am not sure I agree with your comment about it being draggy, mine is ballistic, razor sharp trailing edges, and no ironmongery hanging outside the cowl help  I have considered fitting the wings with some flaps to slow the landings down a bit.

[Tim Mackey]

razor sharp L/E on a wot 4 ? - must be a different version to mine which is very blunt and rounded. You cant use the whattmeter to measure servo current - well you could...but its messy, and a simple DVM set to current measurement would do the job ( static only of course ). The eagle Tree has a servo current sensor which actually plugs into the receiver between your supply ( battery or BEC ) and logs current used during flight. I have also asked eagle trees Bill Parry for a sensor to monitor receiver VOLTS rather than current - especially in view of reported Spekky brown outs, and he assures me its on the way. I actually found that the servos used a lot LESS than previously thought, and I did a thread over here which makes interesting reading. Also an earlier one here

I have used some ESCs BEC power on 4s packs, but many ESCs are limited to only 3 or 4s if wanting to use the BEC.

See this other thread here ( I really must get out more )

I would NOT use the inbuilt BEC on a 6s Pack Bruce....even those ESCs which claim to use switching regs and be useable with high input volts recommend a standalone unit for more than 4 cells.

[Danny Fenton]

razor sharp Trailing edges Timbo lol the bits at the back of the wing!!! everybody takes a sharp intake of breath, mumbling about flutter, but if the linkage is slop free, I have never experienced flutter. (you watch Wotty will get it now!)

I knew Timbo would have a bag full of links to servo loading LOLOL I had forgotten about the ability to monitor the current within Eagle tree, must try that one day.

[Tim Mackey]

oops....sorry - must read more carefully in future

Do you have the current monitoring module then Danny? - I think it might also be useful to try it inline with the bec INPUT when using a seperate one....cos the current drain on that side of the bec should be really low, especially if fed from a high voltage flight pack.

[Danny Fenton]

Unless i have the completely wrong end of the stick (highly likely) then I thought the latest Eagle Tree could monitor the current in the servo circuit, it certainly has a connector to monitor throttle position. I must confess to only ever really being interested in current/volts and mah consumed.

[Tim Mackey]

Yes it can...but you still need the sensor module which connects between the bec and the receiver.

heres a piccy of various sensors - servo current monitor top left

[Danny Fenton]

ahhh righto, you did get a full kit of parts didn't you

I would be lost with all those toys, poor Wotty lugging all that test gear aloft ;) Performance and c of g will change when you remove it

[Bruce Richards]

Will the Turingy 60A speed controller handle 6s? The spec seems to suggest not. Any suggestion for Cheap 6s capable UBECs the Giantcod ones I have say up to 22V and 6s is 24V?