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Techniques => How to... => Topic started by: angry_muppet on June 16, 2016, 21:22:34 PM

Title: Choose an electric power setup?
Post by: angry_muppet on June 16, 2016, 21:22:34 PM
I know it was suggested to keep the Euro Trainer I'm trying to get flying as an IC model...  But as I'm new to the whole hobby, I'd like to stay clean with electric, at least at the moment.  When I have more money (i.e. in 40 years when I'm retired...) I can go IC then!  ::)

Anyway, how does one choose from the plethora of options on our favourite Hong Kong site?

The EuroTrainer stats are thus:

Wingspan:1500mm
Mean chord:290mm (or thereabouts)
Wing Area:43.5dm2
"Empty" weight:1.6kg
Expected "flying" weight:Approx 3.0kg (~400g motor, 900g battery, 100g wires etc)
Wing loading:approx 69g/dm2 (22oz/ft2)

Using google, it suggested this http://flbeagle.rchomepage.com/software/webocalc_1.5.2/html/webocalc_metric.html (http://flbeagle.rchomepage.com/software/webocalc_1.5.2/html/webocalc_metric.html).

This calculator suggests (using a 6s battery, chosen so I could use one pack across several models in my "Dream hangar"):

20C30C
Motor900kV760kV
Prop10x510x5
ESC70A60A

Would that seem to be in the correct region?

What would the effect be if I use a higher "C" rated battery with the low "C" setup?  Would it just be less stressed?
Title: Re: Choose an electric power setup?
Post by: EI1638 on June 17, 2016, 09:02:35 AM
I would have expected the higher C to be associated with the higher current setup. What's missing from the info is the motor wattage. It's usual to derate the ESC (electronics don't like heat), and to give substantial overhead in terms of the esc.e.g. estimated peak current 50 A,  esc rsted 75 A. In many electronics designs it's not unusual to derate electronic devices by 50%, and sometimes more.

Based on the weight it looks like you need a 400, 500W system, as in the battery needs to be able to supply 500 watts for the expected flight duration, without damaging itself, the ESC, or the motor.

An example of a suitable system is the power pack for the Multiplex Acromaster. If I recall correctly this is around the 450 W mark, runs on 3S batteries. I'm not saying buy this as it is kind of expensive, being multiplex, but it is an example, with battery recommendations, of a motor, prop and esc that will provide what seems to be the right amount of power. Once the battrry and esc are sorted I find I sometimes replace the motor with a higher KV motor after a few flights. That would be because I dont want to overload the motor by moving to a higher pitch prop.

Chris
Title: Re: Choose an electric power setup?
Post by: Happy Days on June 17, 2016, 17:55:37 PM
A wing loading of 22oz/sq ft is a bit heavy for a trainer David. :o Ideally you'd be looking for no more than 15oz /sq ft. ;)

What size prop is on the model at the moment?

Keith
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 17, 2016, 19:22:25 PM
As is, the plane is a OS Max 40FP on a 10x6 prop.

Am I correct is assuming that a 1.6kg "empty" weight is realistic?  Obviously weighing on kitchen scales isn't the most accurate for a model plane...  ;D

The setup I was looking at was:

5000mAh 6S 40C http://www.hobbyking.com/hobbyking/store/__9965__ZIPPY_Flightmax_5000mAh_6S1P_40C.html (http://www.hobbyking.com/hobbyking/store/__9965__ZIPPY_Flightmax_5000mAh_6S1P_40C.html)
800W motor http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=17354 (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=17354)
or a 1350W is cheaper? http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18171 (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18171)

An ESC can be bought to suit when the motor and battery is sorted.
Title: Re: Choose an electric power setup?
Post by: goreyflyer on June 17, 2016, 20:00:46 PM
I have a sk3 motor in my 73" exrtra flying on 10s and its very good.

How about the easy match range:

http://www.hobbyking.com/hobbyking/store/__19028__Turnigy_G46_Brushless_Outrunner_420kv_46_Glow_.html

Fly on 5s

The higher c rating is needed for 3D and helis!
We use 20c on f3a planes!!
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 17, 2016, 21:11:31 PM
Would the easymatch motor generate enough thrust though? Is rated at 2650g on a 14x10 prop... It'll only be spinning a 10" prop.
Title: Re: Choose an electric power setup?
Post by: Happy Days on June 17, 2016, 21:12:16 PM
Ha!!! At just short of one kilowatt it would be the most powerful trainer I've heard of. Not even the Model County's club trainer has THAT much power and that plane can almost prop-hang on a 13x8 prop. WWEeeeeeeeee!!! ::) ::) ::)
Title: Re: Choose an electric power setup?
Post by: goreyflyer on June 17, 2016, 22:34:14 PM
Electric props are lighter than glow props.
So you will have to by a prop!
I'm sure you would have enough ground clearance with say the 14x10 they list plus these esc's are good the plush 60a.
I think I have one of those with a programming card too which I can do you a good deal on? 8)

Title: Re: Choose an electric power setup?
Post by: Happy Days on June 17, 2016, 22:39:56 PM
Hang on David, there's more to be considered than just power. ???

Learning to fly a model plane is about making corrections from both pilot and nature. In essence the student pilot is learning how to instinctively react to the models actions.

Stick a novice in the seat of a racing car and he will probably crash it. Place that same student in a slower car and he will find there is time to asses errors and discover a way to correct it. (Just bear that in mind while you read the rest...)

If you fit a big motor and a big battery into your Robbe you will increase it's AUW.
As the wings are of a fixed size this increased AUW will also increase the wing loading.
As the wing loading increases, so does the stall speed of the model.
As the stall speed increases so does the landing speed. So if the stall speed is (say) 25Kph you will never be able to land the model at 10 Kph.

Therefore; it is advisable to have as lower wing loading as possible, so the model flys as slow as possible, so the student has a s much time as possible to make corrections, before the model hits terra firma.

A 6S 5000mAh battery alone will weigh the best part of 1Kg (And that's just the battery!)
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 18, 2016, 09:32:32 AM
I do have a couple of 3S 2000mAh batteries, a 30A ESC (which probably won't suffice) and a motor of unknown power...

At the least then, I need a new ESC and a motor of known power (approx 500W?) and a prop...

Looks like a 14" prop would fit.  I didn't think it would as the 10x6 for the glow motor was within 1" of the ground.  I suppose the prop shaft center is in different locations depending on the motor and orientation of fitting...  8)

And if I so desire later, 2 3S batteries in series = 6S
Title: Re: Choose an electric power setup?
Post by: selleri on June 18, 2016, 12:56:29 PM
That size of a plane should easily fly on 3S, any bigger and you're just adding weight and expense!

This one with a wingspan of 182cm flies on 4S and has plenty of power.

(https://frettavefur.net/Forum/uploadpic/2013/1372688595_5.jpg)
Title: Re: Choose an electric power setup?
Post by: Happy Days on June 18, 2016, 16:41:08 PM
Looks to me like Black Horse Liberty 182 :-\ Selleri, and I agree with you entirely vis the power train needed.

So, a motor of something like a 2826/12 would do you fine David. (28 = the diameter of the outrunner's rotating  'cylinder'. 26 = the length of the 'cylinder'. 12 = the number of turns of wire on each of the motors internal coils) The above should produce around 3-400 watts of power and have a rpm per Volt of around 8 or 900. (rpm/V)
Also you need to make sure that the shaft of the motor will fit the 10x6 electric prop. If it doesn't you may need a prop adapter to do the job. You will also need some method of securing the motor to the firewall of the model.

A brushless ESC with a BEC capable of  min 3S and handling around 40 (or more safely 50) amps should see you right.

With 3S batteries of 2000mAh capacity you might find the flight durations are a little short, but if both batteries are of the same age and make you could connect them in parallel to make a 4000mAh set. If the batteries are in good condition that should give you about 12 -15 minutes flight time as a trainer. If you want to 'beat up the sky' with aerobatics expect half that flight time.

Sorted!  :)

K.
Title: Re: Choose an electric power setup?
Post by: selleri on June 18, 2016, 18:26:29 PM
Quote from: Happy Days on June 18, 2016, 16:41:08 PM
Looks to me like Black Horse Liberty 182
Keen eye mate! 
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 19, 2016, 10:15:47 AM
Ok, I don't know these dark arts of motor selection, so based on what Keith has suggested there are three, two realistic:

Aerodrive SK3 3542-800kv (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=80679) 493W, 49A (Way too powerful?  8))
Turnigy G10 810kv (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=19020) approx 3540, 375W, 42A
Aerodrive SK3 2836-1040kv (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18158) 335W, 12 turns, 28A (This would be it?) :)

It's like me and cars...  I don't want to have "enough" power, I like to have an abundance of it.  Then again, I did start off in a 85hp car... and worked my way up :D  I should bear that in mind!

So based on the SK3 335W unit, I'd need about a 45A ESC (round up from a 50% safety factor) to be safe?

And batteries...  I don't have anything bigger than 2200mAh, and they're all different...  :( So no joining up for me.

The question is, would it be worth purchasing both SK3s and basing the ESC on the higher draw, then I can replace the motor when I want to progress, or at the very least, purchase the higher rated ESC...
Title: Re: Choose an electric power setup?
Post by: Happy Days on June 19, 2016, 11:02:40 AM
I'd say the Aerodrive would suit, provded it can fit into the airframe and you can find an appropriate prop to fit the shaft. :-\

If one of the other motors can be fitted into your model then yeah, try one of those if you want. I can only repeat that (I.M.O.) it's easier to learn to drive a low powered car, than it is to drive a high powered one. Bigger motors need bigger ESC's and bigger batteries which all adds weight and consequently makes the model harder to fly. Whether you can use the same equipment in subsequent models will depend HOW MANY times and to what extent they get damaged WHEN you crash the trainer :-[. Flying aeroplanes, even flying them acrobatically,  is more about subtly, than "peddle to the metal". ( Any fool can do that. )

Keith.
Title: Re: Choose an electric power setup?
Post by: goreyflyer on June 19, 2016, 20:11:02 PM
Spoken like a true motorcycle instructor!!!!



But power is brilliant !!  ;)
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 19, 2016, 22:35:05 PM
Oh what fun!  :)

4000mAh battery (http://www.hobbyking.com/hobbyking/store/__32210__ZIPPY_4000mAh_3S1P_30C_Hardcase_Pack_UK_Warehouse_.html)
Aerodrive SK3 - 2836-1040kv Brushless Outrunner (http://www.hobbyking.com/hobbyking/store/__36822__Turnigy_Aerodrive_SK3_2836_1040kv_Brushless_Outrunner_Motor_UK_Warehouse_.html)
30mm stand off mounts (http://www.hobbyking.com/hobbyking/store/__57169__Stand_Off_Mounts_4pc_30mm_UK_Warehouse_.html) - The motor "can" is 40mm; the available space from the front of the fuselage to the firewall is 80mm; is there any issue with using these little guys  (http://www.hobbyking.com/hobbyking/store/__65406__NTM_42_Motor_Mount_Spacer_Stand_Off_10mm_4pc_UK_Warehouse_.html) as well? (10mm spacer)
Prop adapter w/ Steel Nut 3mm shaft (http://www.hobbyking.com/hobbyking/store/__39878__Prop_adapter_w_Steel_Nut_3mm_shaft_Grub_Screw_Type_UK_Warehouse_.html) This lad will allow me to use the original spinner (I hope)
14x7 prop? (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=28724) Unfortunately, it's the only prop that might be suitable I seem to be able to find in the UK warehouse...?

So far, I estimate an AUW of approx 2.1kg; this gives a wing loading of ~48g/dm2 (15.8oz/ft2).  Slightly heavy, but reasonable.

I'll also need bolts?  :-\
Title: Re: Choose an electric power setup?
Post by: Happy Days on June 19, 2016, 23:11:24 PM
Motor mounts.....Best to keep the motor as close to the firewall (and consequently as close to the CoG) as poss.

4000mAh battery?.......that's a big battery for such a model, 3000 or 3500 would be lighter. (Your choice of course.)

14x7 prop...Hmmm The motor is designed for a max load of 28amps. I would have thought a 14x7 prop would likely overload it. :( If the model was last flown with a 10x6 that's the size to be aiming for really. You'll get a longer flight time with a smaller prop as an added bonus! ;)

15.8oz / sq ft is a good wing loading for a trainer! 8)

Goreyflyer;...yes my days of wheelies, stopies, and burn-outs are long gone,...along with my handsome looks and masculine physique! (But I'll have the memories forever ;D )

K.
Title: Re: Choose an electric power setup?
Post by: angry_muppet on June 20, 2016, 06:53:46 AM
The reason for the stand off mounts is that the "nose" in front of the firewall is 80mm. As the motor is only 40mm, I either need to use stand offs or cut the nose back; I'd prefer not to modify the airframe too much.

I wouldn't be particularly concerned about the CoG; the original OS motor is 250g and the SK3 is only 80g.  Putting it further out should approximately replicate the glow motor and reduce the need for ballast?  I assume using the stand offs does increase the potential for "flex" in the motor position?