Electric newby starting a Wot4 E and requiring advice please

[keith ellis 2]

hi. am just getting back into flying and have seen a few threads about the new wot4 e , having a 53 powered origional from years back plus restrictions on noisey flying thought i would give this a go.

i have no experiance of electric flight and no idear on what electric power costs. could someone in the know point me in the right direction as regards to cost and the right motor and matching esc i would need, am a complete novice regarding electrics so any information in idiot format please..

i have followed another thread on here about the wot4 but a lot of the electric speek is a bit over my head untill i pick up the basics

regards keith

[Biggles' Elder Brother - Moderator]

Hi Keith,

well we could just say "buy this, this and this" but frankly that won't get you very far forward in terms of understanding. So let's try and do this step by step. I'm assuming you are talking about the wooden Wot4e not the foam one.

The starting point is the all up weight of the model. For very basic performance (just about able to fly!) we need about 50W of power for every pound of model weight. For a steady, basic, performance about 70W per pound. To have enough power to be able to fly comfortably, and do basic aerobatics, about 100W per pound is the usual amount.

The spec weight for the Wot4e Mk2 is 3.2lb. So we need to put in a power system that will give us about 300-350W. Let's call it 350W for the purpose of our calculations.

Now, the power, in watts, is equal to the current, in amps, multiplied by the battery voltage. The manufacturer states that we should use a three cell lipo - something like this - Lipo batteries such as this are rated at nominally 3.7v per cell. So three cells in series (which this battery has) means a nominal voltage of 11.1 (It will be a bit more freshly charged and a bit less when partially discharged). So as;

Power=amps x Voltage

The power we need is 350W and the nominal voltage is 11.1, so that means we'll have to run a current of 350/11.1 which equals about 32amps. This figure will help us select the speed controller we need.

We need the ESC (electronic speed controller) to handle 32amps. But its wise to spec the controller with some "headroom" so we should be looking for an ESC that can handle say 40amps. Something like this would be fine. Not the cheapest - but a good make.

Now we come to the motor - again its the amps that mainly govern things here, but some other factors need to be taken into account. We need the motor to handle about 32amps comfortably and dish out about 350W. Now an important figure in the motor spec is the kV number. This tells us how many revs/min we'll get per volt applied. We want max revs to be about 10,000rpm, with a voltage of 11.1v that means we're looking for a motor with a kV value around 10000/11.1 or about 900. In pratice anything between about 800 and 1100 will be fine. Something like this would fit the bill - a good make and its in the sale! Max current ( for a max of 60secs) is 46amps and at 1100kV it will give us a healthy max rpm.

With 10x5 prop this motor will give you around the 350W you want. But,...and here's the fun bit, take it up to a 11x7 and this will dish out well over 400W. At that power the Wot4e would be sparkling! So, you could fit the 10x5 to start with and then up the prop as your confidence grew for better performance. You'll find electric power very flexiable in that way.

So, there's a basic spec - hope you find it useful. Obviously you don't have to select the items I've pulled out - they are just meant as examples - though they should be OK - although given that motor I might up the ESC to 50A instead of 40A - just so I could change the prop safely and have fun later! I've stuck with Giant Shark simply for ease of being able to find stuff quickly for you - I have no connection with GS and there are plenty of other dealers that could supply stuff just as good.

BEB

[Concorde Speedbird]

There is a glossary here if there are some words you do not understand. We have a Wot 4 e, but we put a Saito 45s on it so I don't know the electric setup, BEB's post is very good for you though.

Have fun!

CS

[keith ellis 2]

thanks for the simplyfied explination BEB,

i know having read through other eleccy posts that there is much to electrics than first appear .

one thing i have seen is ESC with a BEC attatched, which if i have read this rightly allows you to power your rx from the same power pack, Something we used to do years back with Cars but with a very simplyfied stepdown resistor.

Question i have about this is , does the ESC have a processor of sime kind that still keeps enough power in store to power the RX even if the motor has run down the power pack to a certain voltage .

On a car that wouldnt be so much of a problem it just grinds to a halt and the servo's run very slow,, but obviously on a plane if the volyage droped to a certain point you could loose control. or is it best to keep rx power supplies sepperate.

[Keith Berriman]

I would suggest a basic start point of 350 watt motor prop to match motor and 50 amp speed control and 2700 3 s liipos and some Hitec hs82 metal gear servos along with your radio . If possible show your loaction and see if your local club has a flyer with one to look see and watch

[Olly P]

Keith - The ESC has a cut out function so the motor would go 'dead stick' but still supply power to the radio system.

RC Plane, I thnik that is what BEB has explained above....

Keith, any more Q's please ask away!

[Keith Berriman]

Hi OP whoops should have read the thread start to finish, trust my last sentence may help Keith

Edited By RC Plane Flyer on 04/01/2013 09:49:27

[keith ellis 2]

i have read through several times the formulas for working out the size motor requird which i understand ok,

But i am having trouble with regards equating the kv 1100 values to the motors that they show for sale, some motors have the same kv with the same 11.1 volt supply but have different ranges of amps ,,and throw much diffent size props.

, what am i missing.

Also the prices of motors seem to vary massivly from £!5.00 to £100 , what is the possable differences in such motors to warrent such a wide variance in prices, if it was an ic i would go for a 46 - engine, but elec seeems to have much more variables.

i can see this going to take me a bit of reading up on to get my head round it all

[Steve Hargreaves - Moderator]

Just to add a couple of points to BEBs Masterclass above......

First & most important.....always remove the prop during set up etc & only re-fit it once you are ready to do a bit of testing......spinning props bite very hard & it is amazingly easy to start them up without meaning too. Once the battery is plugged in treat the whole power train as you would an idling IC engine.....I can't stress this point enough Keith......any & every EF flyer will tell you tales of near misses with accidentally started motors......I myself have had several all without serious mishap thankfully. I can practically guarantee that at some point in your EF career you will hear that motor whizz into life unexpectedly......when you do I hope you will have followed this advise & say to yourself "Thank God I removed the prop"

Right...down off the soapbox.....BEB suggests a 10x5 & I'm sure this will be a great starting point....but it will be just that...a starting point. To measure the current drawn by a motor we need a wattmeter...this fits between the ESC & battery & tells us what current is being drawn, what the o/p voltage of the battery is & how many watts of power are being consumed.....you really can't do much in EF without a wattmeter so buy one now. You will then be able to experiment with different props to get an optimum set up & ensure that none of your components are being overloaded.

Final thought & this is really nitpicking but I thought I'd share it with you.....although BEB correctly quotes the nominal voltage of a 3S Lipo as 11.1 volts you will find that under load the output voltage of the battery will drop...probably to around 10.5V.....personally I always use 10volts for 3S Lipos cos it makes the maths easier.....

Keep thinking & reading & asking questions Keith....its the only way to learn. The thing to understand about EF is that its all very flexible & has a lot of variables so inevitable you hve to make a few assumptions......the technical word for this is "guessing" & with experience you can guess pretty accurately but there is no hard & fast guaranteed formula......we make an educated guess & then fine tune it with a wattmeter & some practical tests.....

Thats what makes EF so facinating if you like a bit of experimentation & so frustrating if you don't.........enjoy!!

[Steve Hargreaves - Moderator]

Just to answer your last post Keith then I don't think you are missing anything.....look at the trees & see the wood......

As BEB noted the kv is the rpm per volt that the motor will spin at......apply 10 volts to a 1000kv motor & it will spin at 10,000 rpm (nearly.....but don't worry about that bit) now add a 9x6 prop & it will take a certain amount of power to spin the prop......lets say 25A. Take the prop off & fit a 15x6......the motor will try & spin it at the same speed as the 9x6 because you've applied 10 volts but a 15x6 will take much more power to spin at the same speed as a 9x6 so the motor will need to draw much more current to provide this power. Power equals volts x amps.....volts is fixed by the battery so to get more power it must draw more amps.

So if our motor is rated at 25A or so then it will turn the 9x6 no problem....fit the 15x6 & you will exceed the max current rating of the motor & it will release the magic smoke & stop working....

Does that help...?

Motor pricing does vary enormously......you pays your money & you takes your choice really.....I have found the budget motors & ESCs to be great provided you don't overload them & operate with a bit of headroom....

[keith ellis 2]

steve,

thanks for the heads up advise on safety regards props and eleccy motors i will bear that very much in mind,

regarding the watt meter i was looking at those earlier and can see and fully understand how the use of these is needed so will be on my order along with the motor.

i can see where you are comeing from now with regards to the currant draw and motor ratings now, nothing like an ic engine where there is a limited hp where if you over prop it it will only turn at a certain rpm where as an electric motor will pull as many amps as it can to still turn at the same rate,

would it be a good assumption to over allow by some 15-20% on the ESC to allow for prop upgrades , is there any down sides to having too big an ESC. say a 60 amp rated for a 40 amp motor.

im presuming the wat4e must be a lot lighter than the ic version as im sure that is much heavier, as i have a irvin 52 powering that which is just right .. and the motor that BEB recomends would be for a much lighter plane

[Steve Hargreaves - Moderator]

I've no direct experience with the Wot 4e so wouldn't like to comment specifically however the watts per lb rule is a good one so keep this in mind & you'll be fine.

Personally I would allow 15-20% headroom on an ESC as a minimum......a good bit more if you plan on experimenting. Running any component flat out will inevitably shorten its life & you simply don't need to run stuff at its limit these days. In t' olden days EF was marginal & every gram counted so you ran things flat out & hoped!!! Nowadays we have a surfiet of power so this isn't an issue.

Certainly no downsides to having a large ESC....other than the physical size & weight.....a 60A unit is a good bit bigger than a 40A unit.....

Now...just to give you something else to contemplate....if you were to approach the current limit of your ESC you could swap to a higher voltage battery (assuming the ESC was rated for the higher voltage) & get the same power for less current flow (Power = Volts x Current remember). To do this you would also need a smaller prop too as the higher voltage battery would make the motor turn faster.....

I mention this because the relationship between battery voltage, motor kv & prop size is absolutely key......get your head around this & you are well on the way to true enlightenment in the ways of sparky-ness....

[Biggles' Elder Brother - Moderator]

Hi Keith,

lots of good stuff above - I'd double underline Steve's point about never connecting the battery (hence effectively powering up) in the workshop unless the prop is removed! As Steve says all EP flyers have had the experience of a motor suddenly, and completely unexpectedly, bursting into life. Its not that electric power is unpredictable - its just that we're all very prone to absent mindedly making mistakes!

Here is a point in case - my own near squeak with mutalation via electric model! I was just finishing off an electric powered Tiger Moth, the battery was connected and so was the prop, the model was sitting on the bench of my workshop - which in those days was a small bedroom.

I use Futaba radio and I had initially set the model up with a Y-lead on the ailerons and so both ailerons were connected to channel one. I was setting the throws and decided that I'd really like some aileron differential. Now that's best put in with the ailerons on separate channels (one and six). So I duely disconnected the battery, pulled the Y-lead out added two short extentions to channels one and six on the Rx and then connected up the ailerons. Fine, so far. I then reconnected the battery to test my new aileron set up. Only one aileron worked! Well of course - stupid! I had to change the model type in the Tx didn't I - from "1-aileron" to "2-ailerons" - obvious. So, I nipped into the appropriate menu on the Tx and switched the model type......whoooooooo! The motor immediately shot to full throttle! I'm in a small room with a model aeroplane frantically trying to fly off of the bench with a 12" chain saw on the front!

How had that happened? Well if you use Futaba gear one of the things you'll learn is that for 99.99% of ESC's the throttle has to be reversed in the Tx - its just the way life is. I did indeed have the throttle reversed - at the beginning. But what I had forgotten was that in changing the model type all the controls automatically switch back to default - ie non-reversed! So, the instant I pushed the button to change over, although my throttle stick was "closed" the model was reading WOT!

It's so easy done. You can believe that since that day (when fortunately the only casualty was my pride/self-composure, and the only damage the fact that every loose item in the room had been blown into the far corner!) I have never worked on a powered up model in the workshop with the prop attached. It's quite funny in retrospect - but it certainly wasn't funny at the time!

Actually, I go one stage further these days. During general servo and control system testing I attach a standard 5 cell NiMH pack to the Rx and power it and the servos through that. It's only when I come to testing the motor that use an actual power battery.

BEB

[keith ellis 2]

im gald you said about reversing the throttle positions, i never knew they read the positions in reverse

is there any reason for this,

sounds like you got off lightly...

i think for ease of use and safety i would use a seperate rx battery in any case as it seems from what i have read up un the BEC can be unreliable if you are running too many servo's or if their currant draw becomes too high.

i also read that you can pre program the ESC with basic functions like voltage shut off values etc.

i am running an old futaba FF6 computer tx so am hopeing the recievers for this are still ok for the modern day ESC

[kc]

I did exactly what BEB did......finished setting up the model and then put the prop on and connected battery again......then I just went into the Futaba menu to double check what settings I had made....woooshh... model took off out of the model stand and hit the carpet. Fortunately I was standing behind the model! Smashed prop, wrecked Lipo, damaged model but no personal injury except shock.

BEB's explanation (above) is excellent but I think that 'kV value around 10000/11.1 or about 900' should be clarifed by using ' divided by ' instead of / We are not all academics!

Similarly using WOT in a WOT4 thread is confusing! Wide Open Throttle is still a bit odd when IC people have for decades used Full Throttle as the term.

[Steve Hargreaves - Moderator]

Not dis-similar to one of my own errors BEB......model powered up & sat on the bench for set up minus its wings.....I found I needed to reverse the rudder but accidentally selected Channel 3 (throttle) instead of Channel 4 (rudder).....the motor went from zero to full power in the press of a button, shot off the bench & across the workshop before smashing itself into the far wall & thrashing itself to death on the floor.

It took me a whole minute to realise what I had done & about 10 seconds to realise how stupid I'd been and another 10 seconds to realise how lucky I had been as the prop missed me!!!!

Scary....

[Biggles' Elder Brother - Moderator]

Hi Keith,

I really wouldn't bother with a separate Rx battery in the WOT4e. Modern ESC's are very good at cutting motor power whilst ensuring that you have enough left to power the Rx and servos. I do sometimes use a separate power supply, but only with much larger models, for example the Twin Otter I've recently completed has the Rx and servos separately powered via a 2s lipo and voltage regulator. But that has 9 servos!

You're right all ESC's are programmable - and things like the cut off voltage are usually preset at sensible levels anyway. Remember, say your cut off is set at 3.4v (that's conservatively high!) the ESC will cut the motor power at 10.2v, but once the motor comes off load the battery voltage will come up again. Also, you have your timer - electric fliers tend to make extensive use of Tx timers so they can be sure to land with the power on!

So I'd follow the KISS principle with the WOT4 - I have models which demand a lot more of their servos that the WOT4 will running perfectly happily off just the power battery!

One more point, I was an earlish adopter of 2.4GHz and I've never flown electric with 35MHz - all my 35 stuff was IC. But I do know that many 35MHz users complain of "glitching" (sudden twitches of the control surfaces) when flying electric. I've never experienced this with 2.4. Something to consider.

BEB

[Steve Hargreaves - Moderator]

Posted by keith ellis 2 on 04/01/2013 12:00:06:

im gald you said about reversing the throttle positions, i never knew they read the positions in reverse

is there any reason for this, its just how it is Keith......for Futaba sets you need to reverse the throttle channel in 99.999999999% of cases

sounds like you got off lightly...

i think for ease of use and safety i would use a seperate rx battery in any case as it seems from what i have read up un the BEC can be unreliable if you are running too many servo's or if their currant draw becomes too high. Amazingly the ESC will still power the prop using the Rx battery assuming you are using the BEC on the Rx.....I still can't believe this but I have proved it to myself....if the ESC is connected to the Rx & you plug a 4 cell battery into the Rx as well the ESC will beep & prepare for action & if you advance the throttle the prop will turn.....not very fast & not with much power but it will turn. Removing the prop is the ONLY safe option. Yes you are correct about overloading the BEC if you have too many servos.....up to about 4 mini servos I'd be happy to use the BEC...more than that & I'd look at a stand alone BEC or a seperate battery. Aeromodelling lore tells us we should disconnect the ESCs on board BEC if we do use a seperate supply by removing the positive wire from the ESC to Rx lead. Personally I use a short extension lead to do this so the ECS lead/plug stays intact for future projects.

i also read that you can pre program the ESC with basic functions like voltage shut off values etc. Also true. Most ESCs are plug & play & will work fine out of the box...no programming needed.....they auto-detect the battery voltage & set a safe cut off voltage for the battery (usually around 2.5 to 3.0V per cell for Lipo) When the battery reaches this voltage it will cut the motor but still power the Rx/servos.....the wise EF flyer will not allow his battery to drain so far however......try to use a max of 85% capacity of the battery & it should reward you with a longer life

i am running an old futaba FF6 computer tx so am hopeing the recievers for this are still ok for the modern day ESC H'mmm it should all work OK but you can sometimes get problems with 35MHz gear in EF.....the high switching frequencies of the ESC/BEC can interfere with the radio signal.....hard to tell until you try it. I have EF models that will fly fine on 35MHz & some that just sit there & jitter. 2.4GHz sets are almost immune to EF interference so are to be preferred but they are by no means essential.....

Hope that helps!!!!

[Steve Hargreaves - Moderator]

Ooo cross posted BEB.....

I must learn to type faster......

[keith ellis 2]

im running with duel conversion recievers, so hope they will be ok but if not i have found that a tx combo on 2.4 arnt that expensive. plus am going to have to upgrade at some point anyway so wont be the end of the world ..

the site flying site im trying to get back in with have limited ic flying times which is why im going half n half with electric , so i am able to get more chance of flying, otherwise a combination of work, flying restrictions and bad weather means not much flying time.

considering the prices im seeing for batteries, ESC's and motors i can see the electric power versions working out cheeper over all than an ic motor especially with fuel costing around 17 quid a gallon and you still need a flight box chargers for the nicd's and glow start

[Steve Hargreaves - Moderator]

Try it & see Keith......it may be fine....D/C receivers are no guarantee unfortunately...I've had S/C, D/C & PCM Rxs fall over in EF models & I've had them all in work in EF models......generally the higher reving motors like EDF etc are the wost culprits......2.4 is pretty much obligatory in these.....

Don't try & build a cost argument around either method of propulsion......just use either & enjoy...both IC & Electric bring something unique to the hobby. Personally I prefer IC cos I like messing with engines but electric models do fly superbly & you can't argue with the concenience they offer......plus when you get the set up wrong, the smoke trails & flames from an electric model looks very convincing.....especially if its a warbird......

[Biggles' Elder Brother - Moderator]

I agree, in practice I've found there isn't much to choose between them on cost grounds. Electric tends to have higher initial costs - you'll need 3 or so of those batteries for example - but its really like buying all your fuel "up front"!

Remember you'll also need a Lipo charger and a good supply of connectors etc. And if you get serious about electric flight a field battery is a good "add-on". So costs can mount.

BEB

[keith ellis 2]

i already have a flight box with field battery and fast charger but it only charges nicads, nimh and another,, lithion iron which im presuming is nothing like a lipol battery..

i was going to ask about charging of these lipol batteries as mainly being a nicad , and only just recently moved onto enloop for rx packs which am yet to try

[Steve Hargreaves - Moderator]

H'mmm "lithion iron".....is that a mistake in the instructions?? Could it be Lithium Ion??

LiPos...or Lithium Polymer batteries are a type of Lithium Ion batteries but there are several types all of which have different chemistry & charge at different rates etc.

DO NOT TRY & CHARGE LIPO BATTERIES IF YOU ARE UNSURE OF THE CHARGER. ONLY EVER USE A LIPO CHARGER TO CHARGE LIPO BATTERIES.

Lithium Polymer batteries can burst into flames if incorrectly charged....hence the stern warning. If you are unsure about your chargers abilities to charge LiPos then get it checked by someone who knows about these things.....

[PatMc]

Keith, which fast charger do you have ? Someone here is sure to know of it & whether it's OK for lipo or not.