Electric Acro Wot ?

[260 Flyer]

Looks good Jon!

So whats the finished AUW?

[Jon]

ok ok every body wants to know the total weight.....So here it is...

Fus ...fully covered with Profilm, plus a pilot and his canopy, the out-runner Motor and its adjustable mounting, ESC with leads and gold plugs etc, RX On / Off switch and leads to the Synth Receiver with an ariel tube plus leads to, 2 x standard servos which are connected to the rudder and tail plan horns via 2 x Gold-N-Rod control rod sets, Full glass under carriage and tail wheel, 12 x 8 prop and mounting. Also the underside of the fus has been filled in with 1/32 ply to form the battery box which is complete with packing foam and battery straps. Also the battery box sides have 1/32 ply added on the insides.

Total weight is 3Lb 3&3/4 oz

Wings... Fully covered with Profilm plus 2 x servos and "Y" lead, 2 x sets of horns and 2 x sets of micro wing servo mounts and control rods.

Total weight is 1LB 8&3/4 oz

Power Batteries.... 1 x Lipo 4s 2500mAp plus leads & 2 x Y connectors held together by a rubber-band

Total weight is 1LB &3/4 of an oz

Rx Battery.... 1 x 4.8v 1100mAh Ni-cad plus lead and connector

Total Weight is 4&1/4 oz

So the All Up Wieght (AUW) is 6LB 1&1/2 oz

or 5LB 9oz if flow with only one battery and I could run the RX off of the main battery and save a further 4&1/4 oz ie 5LB 4&3/4oz ....but I will be flying with 2x Lipos and the RX battery fitted.

Hope the above break down helps if your planning a like build.

So now the $75,000 question, how much lighter would It have been if I had used an I/C engine and fule tank giving about 15 - 20 mins flight time ?

Jon

[Always broke]

Dose it really mater, Yes it would have been lighter but then you would not have built it.

IC models converted to electric are nearly always going to be heavier as they were designed to take the forces/vibration from a smelly dirty power plant.

[Jon]

but by how much? ab

[Mike Rolls]

My electric AW weighs 5 lbs 11 ounces which includes 4 ounces of nose weight  () to get the CG right. My IC version (ST 51) weighed 5 lbs with an empty tank. 8 ounces tank so about 5lb 6 ounces with a full one.

Mike

[Always broke]

Well its easy really.

What is the weight of your motor /esc and flight packs x2 . At a guess 1200g

If you used a 46 engine that would weigh approx 450g or a 61 700g. add say 283g (10oz) to 397g (14 oz)  fuel .

So 46 powered  is 733gram

so 61 powered is 1097gram 

So it is 474 g heaver than a 46 powered one and 103 g heavier than a 61 powered one Approx 

[Jon]

Thanks Mike, just gives me an idea of how it may feel as I have flown a mates I/c version ......just hope it flys ok thats all

jon

[Jon]

Thanks ab    as long as i have not wasted my time...

[Mike Rolls]

Jon

I should also have said that I've known a number of folks with AWs that flew fine at 6-7lbs all up with a vareity of motors in the 46-60 range.

Mike

[Jon]

Well I have just completed the first test

To recap.

The Motor is a E-Flite Power 46 670Kv (800w) Brush-less EFLM4046A (Motor Rated for up to 7lb planes) (My E-Acro has an AUW of 6lb 1&1/4 oz )

The ESC is HM Pro 80A 2-6s S-BEC

The Prop used was a 12x8 E

The Battery pack used was 2 x matched Flightpower EVO 2500 mAh 18C (Rated at 45Amp Cont 28C 70Amp max bursts) 4S LIPOs ie: (5000mAh @ 14.8v)

Watt meter at start showed the voltage was 17.6v

Held at 1/2 throttle for 30 sec I measured 9.2A @ 16.1v 148w & 85mA consumed

Held at 3/4 throttle for 30 sec I measured 22.3A at 14.6v 328w & 298mA consumed

While held at Full throttle for a further 8&1/2 mins I measured a peak of 35A at 13.9v 487w at 1500mA consumed

during this 8 min period the power dropped back to 410w at 13.2v with 3900mA consumed

I switched off at the 10 min point when the battery was quiet warm and the voltage was down to 12.4v after 5 sec the battery was reading 13v but still quite warm

Both the motor and the ESC was cool....

Using Timbo's 50% rule the estimated flight time would be 14-15 mins... but would there be enough power at the prop to fly?.....The set up could be used with 5s or 6s batteries if I spent more money..

So....What do you think?

[Always broke]

In all honesty if it was my model I would want at least 100w per Lbs min so 650w just to fly around gently. If I wanted to do more than that then 150 to 200w per LBs.I do like lots of power. But it will fly on 450 ish  watts just dont expect very startling performance . You could try a bit bigger prop to up the current a bit, perhaps a 13x8 or 15x8 . You only need lots of power for climbs. I would think you are going to end up adding another cell or two to the set up.Your voltage is dropping quit a bit . My W4 is on 5 cells and is just about 41/2 to 43/4 Lbs ready to fly. Your set up on 5 cells would give around 640w for the same current draw.     35 amps is very low for max current. Most of my similar set ups are around 60A  max current .

Simon

[Jon]

So your saying that it may be better to fly for slightly shorter spells on a bigger prop or use 5s or 6s batteries or even both!   oh dear more Christmas expense

thanks for your comments Simon... I don't have any larger props to try as yet but will get a few asap

Anyway having only just passed my "A-FW" it may be just as well I wont be doing any fanncy stuff for a while

Got it all to look forward to...

Merry Christmas Jon

[Ben Mullins]

Well, if the acro-wot is flyable on that amount of power why not give it a go. As long as you're not underpowered it should'nt be a problem, should it? You could see what its like as it is. On the other hand do you really want 15mins of loops etc so soon after your 'A'. In my opinion I would want shorter flights on the bigger prop and have more power, just incase anything does go wrong!

That is how i would feel. But in the end its upto you, do you want to spend more money?!

Merry Christmas and a Happy New year to all

 Ben.

[Jon]

I have ordered a 13/8 & 15x8 prop to pay with but am a little undecided re the 5s & 6s choices

 During checking some battery prices at BRC I found the following

A 4270mA 6s 20/30c 85/128A 487g =£119.00

A 5350mA 5s 17/28c 90/149A 590g  = £115.00

A 5350mA 6s 17/28c 90/149A 699g = £135.99 (cant understand how the output is the same as the 5s)

2 x 2500mA 6s 20/30c 50/75A 736g = £127.98

All will fit in the battery box no probs     but which to ask Father Chrismas for? he'll only let me have one!

Which way would you go chaps and why?

jon

[Always broke]

Have a look at this link to Giant Cod.

These are good packs. I have had good success with them. JSTXH balance connector.

Giant Cod

A lot Cheaper.

 or Hobby City

Hobby City

Just a couple of suggestions. Look around there are some good cells at a lot lower prices.

6S will allow you to run lower currents. I use 6S 3700 in my Angel S and it  gives ample flight times and it saves a bit of weight. If you use 5S then you may be better with 4200ma packs as the current draw would be more.  I am sure there will be plenty of suggestions

Simon

[Jon]

Weight: 604
Capacity: 4300mAh
Voltage: 5S1P (14.8v) 4 cell
Discharge Rate: 20-30C
Size: 155x45x43 (including cell spacers for ventilation)
Charge Plug: JST-XH
Discharge: t-connector (Deans style)
Charge Plug: JST-XH
Discharge: t-connector (Deans style)

Just looked at the first one and it says its a 5s but then says its 14.8v 4 cell?   see spec copied above

jon

[Jon]

ps whats a JST-XH ?

[Mike Rolls]

Jon

Just the name of a particular type of balance plug. Sadly, there is no universal standard for the damn things.

Mike

[Tim Mackey]

Well IMO that motor  is too low a Kv for 4s, definately need 5 or even 6 cells ( TBH I would probably go 6S ) on something like the Acro Wot. These models are crying out for fast and responsive power, and stooging around the sky is just not gonna cut it. I used a similar Kv motor in my Wot 4 ( albeit a bit heavier ) and found 8s A123 cells gave nice power and decently high revs. 7s would probably be better, so therefore think in terms of 6s LiPo. Would you consider A123s instead of LiPo ?

At least with these you could get away with one pack as they can be recharged in 15 minutes - in situ

( providing your charger can pump out the electrons fast enough )

If its Li-Po then why not try 2 x 3s or a 3s + 2 s pack in series for trial purposes - at least that way you get to measure WOT bursts and assess the RPM and wattage.IF you go 6s , you woould need to prop down abit or you are likely to exceed the maximum current rating of the motor. The Eflite 46 is not really big enough for really high performance on a 7lb sport 'plane, so eI expect you will end up on 5s with a prop that will pull maximum current allowed ( around 45A or so ? ) Assuming you get 5s propped to give 45A contimuos, then that should show around 780 Watts.....which is more like it.

450 W will definately NOT fly a 7lb Acrowot well - again just my opinion - but then I like plenty of power on tap when needed.

[Jon]

Hi Chaps

Thanks once more for all your very helpful input

I have just been doing a bit of reading about A123s (link) ... Some of it was a bit deep for me so will need to read it once more. Did search this forum for info on them    but the search returned nil. 

Some of the main points of the blerb was the fact that A123s are bigger but cheaper than Lipos, cell  voltage is a bit lower, flat discharge curve, much quicker charge time, better chance of withstanding a crash, new charger may be required, 1000 cycles claimed (not like 10 - 50 only for Lipos)...

On the face of it apart from the fact that they are a bit bigger (got to fit inside my planes battery box) I can see there are a good few benifits but what about the draw backs?...

It very much looks like I have to go for 2 or more large 6s lipos anyway so am contemplating the change to A123

I currently have just 2 flight packs of 2 x 4s 2500mAp Lipos and a Imax B6 charger (12v or 240v) which has given me very good service so far.

Where can I read more?. Is what I read upto date?. What would any of you do?

In the meantime I am charging my second pair of 4s 2500mAp which unlike the first pair I tried which were older and 18c rated, these are 20C rated and quite new... I'll then re-run the tests with the second pair to check the numbers.

jon

ps sorry if there are any spelting erroors, did try the spelting cheker but it didnt worked!

[260 Flyer]

Jon

I too have been pondering A123s as an alternative power source for an Acro Wot!

It's all getting a bit mind boggling!

To fast charge two 6 cell A123 packs in parallel at 20A will need a charger capable of around 600W. The largest I can find are 300W so 2 will be needed. Or use one to charge for twice as long.

To power the charger for up to 4 charge cycles will require a battery of at least 50 Ah capacity (allowing 25% for heating the flying field)

So to add it all up,

2 X A123 6 Series 2300mAh. .£132

2 X i-Charger 1010B plus. .......£240

1 X Leisure battery ......................£60

Total. ...........................................£432

Add on another £30 or so for shipping and 4 X 6S1P 4300 Lipo's from Giant Cod for £360 start to look attractive!

Rob

p.s. Or how bout one of THESE?

[Jon]

Hi Rob

But to re-use the batteries only 100 times makes the A123s very attractive.. you could have needed to replace the Lipos  a few times by then... above 100 cycles of a A123 and there's no argument  is there

I'll have a look at your link now..

Jon

[Jon]

Ha Ha ....very smelly and over 80dbs most of the time... no thanks

Jon

[Jon]

Well I have just completed the 2nd  test

The Battery pack used this time was 2 x matched Flightpower EVO 2500 mAh (not 18C as used before) but a little higher rated at 20C 50Amp Cont 30C 75Amp max bursts 4S LIPOs ie: (5000mAh @ 14.8v)

Watt meter at start showed the voltage was 17.6v  No change

Previously   Held at 1/2 throttle for 30 sec I measured 9.2A @ 16.1v 148w & 85mA consumed

But this time Held at 1/2 throttle for 30 sec I measured 10.7A @ 16.8v 180w & 55mA consumed 

Previously   Held at 3/4 throttle for 30 sec I measured 22.3A at 14.6v 328w & 298mA consumed

But this time Held at 3/4 throttle for 30 sec I measured 28.3A at 15.2v 430w & 230mA consumed

Previously held at Full throttle for a further 8&1/2 mins I measured a peak of 35A at 13.9v 487w at 1500mA consumed 

But this time held at Full throttle for a further 9&1/2 mins I measured a peak of 39.9A at 14.8v 590w at 1300mA consumed                                                             almost 100w per 1Lb !

When I switched off this time the battery was not as warm as before and the voltage was down to 12.5v 

Both the motor and the ESC was cool....

So the boy done good.. but only just a bit good-der-rer.

Could it be the C rating... think its more probable that the first pair are shot.... what say you?

So 5s or 6s or A123....What do you think?

[Tim Mackey]

5s LiPo ...or 6 x A123. There is quite a lot of stuff on here Jon about A123s actually... I will see if I can find them.

heres one

there are others...search via gogle for A123 and modelflying .co