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January 22, 2019, 20:39:05 PM

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Author Topic: Brushless motor equiv for 40cc petrol  (Read 655 times)

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Offline FlyinBrian

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Brushless motor equiv for 40cc petrol
« on: December 24, 2018, 04:55:35 AM »
I have bought a model that was designed for 35 - 40cc gas engines. Its a sports biplane the GP GIANT AEROMASTER
Can anyone recommend a sensibly priced brushless motors will give me similar performance? I would like to use 8 cell lipos as I have several 4 cell batterys that I can use in series.


Cheers



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Offline FlyinBrian

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Re: Brushless motor equiv for 40cc petrol
« Reply #1 on: December 27, 2018, 05:07:28 AM »
Bump
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Offline PDR

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Re: Brushless motor equiv for 40cc petrol
« Reply #2 on: December 27, 2018, 09:11:44 AM »
I suspect that the reason no one has answered is because this is beyond the size where "simple, cheap" solutions are readily available. I've never gone that large with electrics (in the 2.5-3kW region), but suggest that you're probably looking at a 12s setup rather than an 8s one. I know people who have converted 50cc-class aerobats with 12s setups, but it needs some thought and care. Amongst other things you have to start worrying about electrical safety (it's around 50v DC), and you have to think about the safety implications of a motor that large which can spring into life at the nudge of a stick. All the setups I've seen of that size incorporate a "safety plug" in the power circuit - a shorted pair of connectors in series with the battery that ensure the system is only "live" when you connect it.You also need to have "pre-connectors" which initially connect the batteries to the ESC via a resistor to limit the inrush current to the input capacitors of the ESC which might otherwise weld connectors and/or wreck the batteries.

PDR
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Offline itsme

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Re: Brushless motor equiv for 40cc petrol
« Reply #3 on: December 27, 2018, 10:09:30 AM »
My personal opinion is that there is a limit (at the moment) on the size of electric model flying which makes anything over 8s the realm of specialists. Where as any monkey (like me) can safely set up and fly a 40cc petrol model. I can take up the field two models and a can of fuel and fly all day without dimming the lights on a small town.

Offline JohnMac

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Re: Brushless motor equiv for 40cc petrol
« Reply #4 on: December 27, 2018, 12:15:10 PM »
I can recomend a German piece of software called eCalc. It is pretty cheap and allows you to put all the parameters of your model design into it and test various motors, batteries, props etc. I have used it for my next electric project, a 1/4 scale Albatros DVa. I want to use a prop size as scale  as possible and I have a solution that allows me to run a 24" prop on 8s on a large Hacker Motor. Scale would be 27" but I am limited by the relative shortage of low Kv motors available. This motor is certainly not cheap either.
Take heed of Pete words, he is absolutley right about the safety considerations. Jeti make a range of anti spark connectors BTW.
I wish I had had this eCalc when I converted my YT FW 190 several years ago. I calculated everything longhand and it took a lot of time.
Good luck,
John


Offline FrankS

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Re: Brushless motor equiv for 40cc petrol
« Reply #5 on: December 28, 2018, 20:53:36 PM »
+1 for eCalc, but I thought it was Swiss not German, being a .ch website. Good program to use though and like John I use it all the time.

Offline FlyinBrian

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Re: Brushless motor equiv for 40cc petrol
« Reply #6 on: December 29, 2018, 13:59:41 PM »
Thanks all
I have found a HK 1.60 glow equiv that uses 8 - 10 cells and develops just under 3KW, c 4bhp, this might be ok but otoh it may be marginal dpending on the weight of the model and of course being a bipe the model will be fairly draggy. I really did not want to go to 10 - 12 cells for all the reasons  (Good point re the isolation plug!) I am pretty ok with handling c50V although having once accidently touched the terminals of a 3 cell lipo against a steel ruler the sheer violence of the resulting vaporising connectors scared the shi... poop out of me.

With the cost of the batteries (x2) new motor and HV ESC I think petrol may be the better option. I have a JC EVO 28cc which is pretty powerful for its size so may give that a try.

Incidently does any forumite live near Bury in Lancs as the guy I bought this model from works shifts and as he is with the Lancs police his work pattern can and does change so I am loath to travel from Skeg over to darkest Lancs only to find he has been called to work. SO if anyone could collect it who is more available for me to collect from them I would be eternally grateful.

Cheers
BP
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Offline FrankS

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Re: Brushless motor equiv for 40cc petrol
« Reply #7 on: December 29, 2018, 17:21:37 PM »
if a 3kw (4hp) electric motor is going to be marginal hows a 28cc 3hp motor going to be better? Do you know the flying weight of the model? if you do you could put it all into eCalc and it will give you an estimate of the performance on different motors and props.

BTW I run a circa 2kw motor on an 8s setup and the aircraft performance is not far off my DLA 32cc powered one (just a lot quieter!)


Offline FlyinBrian

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Re: Brushless motor equiv for 40cc petrol
« Reply #8 on: January 10, 2019, 11:04:51 AM »
if a 3kw (4hp) electric motor is going to be marginal hows a 28cc 3hp motor going to be better? Do you know the flying weight of the model? if you do you could put it all into eCalc and it will give you an estimate of the performance on different motors and props.

BTW I run a circa 2kw motor on an 8s setup and the aircraft performance is not far off my DLA 32cc powered one (just a lot quieter!)

Frank, good points but my thinking was - The Giant Aeromaster was designed about 20 - 25 years ago when most Gas engines were converted agricultural units developed for longevity and durability rather than power. Modern gas engines are powerful for their size and IIRC Great Planes recommended 30 - 60cc gas motors for this model.

However I have come across a SH reasonably priced 8 cell brushless motor which develops c 3HP on 20 x 10 or 21 x 8 props which about the equiv of a moderate 30 - 35 cc gas engine.

Naturally I will do some tests before installing.

Thanks for all the feedback
Brian

« Last Edit: January 10, 2019, 11:07:17 AM by FlyinBrian »
Basic Research is what I do - when I don't know what I'm doing!.


 

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