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Info Required on Motor, Battery, ESC and Prop Combo

Old 09-13-2017, 07:42 AM
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Default Info Required on Motor, Battery, ESC and Prop Combo

I have a Martin Mariner, Keith Sparks design, completed and ready to fly. I downsized from over 100" span to 82". It's been finished for a few years, but music overtook me, became proficient playing saxophone, and I'm just getting back into flying.

Currently I have 2 RCV 60SP's mounted, and the weight of the aircraft is about 15.5 lbs. The props are 4 blade, 13 X 13, and the prop tip clears the water by about 2", perhaps a little more, so the prop shaft to water is about 8.5". I figure the weight of the RCV's will be about the same as motors, batteries, ESC's and props, 15+ pounds.

I chose RCV's so they would fit nicely inside a cowl, and turn a scale prop, being geared to 50%. I'm not keen on the engines, so am considering moving to electric.

Electrics are a mystery to me, being an old nitro head, and no doubt in time, electrics will be as simple as nitro engines have become, but right now, I'm lost!!

I'm looking at a motor, ESC, battery and prop combination, and the extent of my knowledge is that I am going to need a total of about 100 watts per pound, so will need close to 1600 watts, or about 800 watts per motor.....big motors.

Is anybody able to give me solid info on the actual numbers....sizes, even model numbers of what I will require? Naturally I would prefer 4 blade props, but if not available, then 3??

I'll 'reverse engineer' from there and see if I can figure out why they were chosen.

I've done some research, and come up with this motor

https://hobbyking.com/en_us/turnigy-g60-brushless-outrunner-500kv-60-glow.html[/url]

this 70 Amp ESC

https://hobbyking.com/en_us/turnigy-trust-70a-sbec-brushless-speed-controller.html[/url]

this battery

https://hobbyking.com/en_us/turnigy-battery-nano-tech-4000mah-5s-35-70c-lipo-pack-xt-60.html[/url]

and the prop a 13 X 8 2 blade, but I'd be looking for a 4 or 3 blade.

Am I on the right track??

Thanks for any assistance anybody is able to offer.

Last edited by Semi Retired Aviator; 09-14-2017 at 08:16 AM.
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Old 09-13-2017, 10:05 AM
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solentlife
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Your friend in all this is "eCalc" .....

It costs only a couple of $ to register and you get one of the most comprehensive calculators to sort out combos you can imagine and its so easy to use.

You input weight
Battery
ESC
Motor
Prop

out comes an answer .... you adjust each until you get a clear working result.

Attached is a quickie I knocked up on eCalc ... Test for WF

Shows a 6S battery with 80A ESC's, Turnigy 5050 580kv, 12x7E props .... gives more than enough grunt ! The slightly smaller props help with water clearance as well.

I then compare to your links : Test 2 for WF

You are just on limits of current through the G60 ... and that's with a less prop than your 13x13 - which I don't think you need as big.

Nigel
Attached Files
File Type: pdf
test for WF.pdf (1.20 MB, 73 views)
File Type: pdf
Test 2 for WF.pdf (1.17 MB, 47 views)
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Old 09-13-2017, 11:52 PM
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Thanks Nigel.

Being new to electrics, I didn't realize that eCalc existed. I'll take a look.
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Old 09-14-2017, 12:03 AM
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ron_van_sommeren
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Originally Posted by Semi Retired Aviator View Post
... Electrics are a mystery to me ...
Is it wise to start your e-career with such a setup?
I think it would be much much safer/better/simpler/easier/cheaper/safer to start with a less powerful plane, single motor setup, learning curve and all. To get some e-routine and e-knowledge with a simple cheap setup and plane?
I would learn the (e-)ropes/routine/knowledge/experience with a less powerfull model, cheaper setup.
E-motors can start all of a sudden, without warning, with full torque available right from zero rpm up to full rpm, merrily hacking away at fingers, leg, private parts, with full and unstoppable force.
Motor and/or controller can go up in smoke in an instant, without the warning you get when an IC motor starts to run lean. And once the smoke is out, you can't put it back in.

Originally Posted by Semi Retired Aviator View Post
... Electrics are a mystery to me ...
Some well-structured reading and handy e-tools for rainy/windy days. Will save you, and us , a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools - RCG

And please, please, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the best setup.

Originally Posted by Semi Retired Aviator View Post
... Naturally I would prefer 4 blade props, but if not available, then 3?? ...
Nice 2,3,4,5 blade CW&CCW adjustable pitch prop$
Varioprop - RCG

Originally Posted by Semi Retired Aviator View Post
... Currently I have 2 RCV 60SP's mounted ...
Extend motor wires, and keep the battery wires short. Keep controller(s) close to battery(s):
Too long battery wires can kill ESC over time: precautions, solutions & workarounds - RCG
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Old 09-14-2017, 12:37 AM
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Hi Ron,

Thanks for the better than great information.

I omitted to say that I've been flying a couple of electric foamies for a while, but know nothing of the calculations required for the components, hence the enquiry. They are PNF's so all components were supplied except the battery, and a particular capacity was recommended so I went with that.

I'm sure that with the info you and Nigel have provided I'll be able to find what I'm looking for.

Last edited by Semi Retired Aviator; 09-14-2017 at 08:17 AM.
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Old 09-14-2017, 07:13 AM
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A Wattmeter is the first item on the list .... that item alone will save a lot of heartache.

It not only tells you the motor draw so you can setup motor / battery / ESC / Prop combos ... it also tells you battery state for storage / charged etc. Its the universal box of tricks !

Along with eCalc ..... you'll be well on the way to discovering the range of e-power.

Nigel
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Old 09-15-2017, 12:34 AM
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My favourite quote
Originally Posted by scirocco View Post
Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, eg limited prop diameter if it's a pusher, or you already have a bunch of 3S packs and don't want to buy more, and so on.

While an absolutely critical part of the system ...
... Kv is actually the item one should choose last.
  1. Decide your peak power requirement based on the weight of the model and how you want to fly it.
  2. Pick a preferred cell count (voltage) and pack capacity for how to deliver the power.
  3. Pick a prop that will a) fit on the model and b) fly the model how you want - often as big as will fit is a good choice, but if high speed is the goal, a smaller diameter higher pitch prop will be more appropriate.
  4. Look for a size class of motors that will handle the peak power - a very conservative guide is to allow 1 gram motor weight for every 3 watts peak power.
  5. Then, look for a motor in that weight range that has the Kv to achieve the power desired with the props you can use - a calculator such as eCalc allows very quick trial and error zooming in on a decent choice. For a desired power and prop, you'd need higher Kv if using a 3 cell pack compared to a 4 cell pack. Or for a desired power and cell count, you'd need higher Kv if driving a smaller diameter high speed prop compared to a larger prop for a slow model.
The reason I suggest picking Kv last is that prop choices have bounds - the diameter that will physically fit and the minimum size that can absorb the power you want. OTOH, combinations of voltage and Kv are much less constrained - at least before you purchase the components.

So Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, eg limited prop diameter if it's a pusher, or you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS
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Old 10-08-2017, 06:24 AM
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Well the wattmeter has arrived, I've subscribed to eCalc, and I'm having an interesting time playing with various combinations there.

I propose using two batteries, to increase flight time, and since I was going to use RCV 60SP's, I have plenty of weight to play with. There doesn't seem to be provision for 2 batteries on eCalc, so I've entered one motor, and half the weight of the aircraft.

Does that sound reasonable, or are independent batteries not recommended?
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Old 10-08-2017, 06:27 AM
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For eCalc ... just add the two battery's together and use that as the total. Leave motors / weight etc as actual.

Nigel
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Old 10-08-2017, 07:48 AM
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Thanks Nigel.....again!!

Last edited by Semi Retired Aviator; 10-11-2017 at 03:05 AM.
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Old 10-26-2017, 04:27 AM
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Well I've tried to make electrics work on the Mariner, but it doesn't look as though I will be going down that path. I really needed to plan on electrics from the beginning, principally for cooling the ESC's which would be in the fuselage. Short of major surgery on the fuse, I can't achieve that.

I'll take Ron's advice, and start the path to electrics by assembling a Classic 40 I picked up at a sale and working through that project.

Thanks to the members who spent time giving me advice, and I've printed the text of the links provided to me.
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Old 11-16-2017, 11:23 PM
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Old 11-17-2017, 02:28 AM
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