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Old May 25, 2012, 07:28 AM
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Australia, ACT, Canberra
Joined Dec 2011
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Question
Brushed to brushless conversion

Hello All,

So I was just going through some plans I have and one of them was for a nice basic build of a plane however it was designed for a 540 motor and 6/7 cell nicad (Yeah it's an old plan hahaha). What would this combo translate to these days for a Brushless with Lipo's.

I'm a bit of a newbie when it comes to electrics so any advice would be great.

Thanks.
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Old May 25, 2012, 08:13 AM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
3,684 Posts
That translates into a low power, heavy system. How big is this plane (size and weight) and what kind of flying are you looking to do? Old electric planes, for the most part were designed to just get into the air and stay off the ground... performance was nothing like the electrics of today. The best thing we can do is get an idea of the size of the plane.

I had a geared 550 in my super sportster EP and it made the plane heavy and sluggish to accelerate... I doubled the power with a brushless setup and cut out about 10 ounces from the flying weight by converting.
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Old May 25, 2012, 08:28 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
12,467 Posts
But some of those old short nosed designs worked well with brushed motors, converting them to lighter brushless motors often meant adding some lead to get the CG where it originally was.

Many of the electric powered gliders designed around a brushed motor come to mind, and the WWI short nosed biplanes.

But brushless motor and Lipos do generally mean better flying over the brushed and nicad/nimh set-ups.
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Old May 25, 2012, 08:34 AM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
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Quote:
Originally Posted by eflightray View Post
But some of those old short nosed designs worked well with brushed motors, converting them to lighter brushless motors often meant adding some lead to get the CG where it originally was.

Many of the electric powered gliders designed around a brushed motor come to mind, and the WWI short nosed biplanes.

But brushless motor and Lipos do generally mean better flying over the brushed and nicad/nimh set-ups.
True, some of those designs require lead or very large batteries up front to offset the difference. In the end, you at least get more power at the same weight and probably more run time.

In the case of the SS EP, I had about 3 ounces in the tail to offset the stock power system and after conversion it required no weight to balance.
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Old May 25, 2012, 11:00 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia / UK visits
Joined Jan 2010
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Quote:
Originally Posted by NOI53Y View Post
Hello All,

So I was just going through some plans I have and one of them was for a nice basic build of a plane however it was designed for a 540 motor and 6/7 cell nicad (Yeah it's an old plan hahaha). What would this combo translate to these days for a Brushless with Lipo's.

I'm a bit of a newbie when it comes to electrics so any advice would be great.

Thanks.
What I did was to check around on ebay / Hobby King and various online sites for a brushless motor that was for similar size prop as minimum quoted, with a KV ( this is basically no-load rpm per 1Volt ) of 1000. My brushed was on an 8cell 9.6v pack ... so I went for a 3S (11.1V) pack.

the combo of 1000kv motor, 3S pack for a prop same size proved itself and my ME109 flew an absolute treat.

For the ESC .. I read the specs of the motor and bought an ESC that was rated at 50% higher than the max amps stated for the motor.
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Old May 25, 2012, 03:38 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
5,486 Posts
If this was a conversion of a rubber powered airplane would you ask what brushless system will perform most like the rubber motor did? What would have happened to the P-51 if the British had said we want to put a British engine in the Mustang, what engine do we have that performs like the original Allison?

Don't worry about matching the old power system. It may or may not have been the best match for the airplane. Design the new power system to fit the airplane's characteristics and how you want it to fly. For help on that list the configuration of the airplane, wingspan, wing area, weight and how it should peform, i.e. sport aerobatics, trainer, 3D, etc.

Larry
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Old May 26, 2012, 03:53 AM
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Ok so I had a look at the plans and It's 47" wingspan and weighed in at 2lb 2oz with the brushed setup and 6 cells.

It's supposed to be a tame sports model. Kind of like a next step type of plane from a trainer.

With that in mind what would you recommend.
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Old May 26, 2012, 04:23 AM
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Quote:
Originally Posted by NOI53Y View Post
Ok so I had a look at the plans and It's 47" wingspan and weighed in at 2lb 2oz with the brushed setup and 6 cells.

It's supposed to be a tame sports model. Kind of like a next step type of plane from a trainer.

With that in mind what would you recommend.
Tame sports model around 2lbs a 200W power system is going to be ample.

To run 200W, you could get away with a motor as light as about 70g, but you're likely to run into balance problems as it's replacing a 540 that typically weighs around 180g, so I'd look for something at least 100g, even a bit heavier.

A motor around 1000-1100 Kv will use about 200-240W for a 10x5 prop, or if you can only fit 9", look for Kv around 1200. The Turnigy G10 series at 140g has Kv available of 810, 1100 and 1200, giving you a good choice of prop sizes from 9" up.

To get better advice, decide first up on prop size.
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Old May 26, 2012, 08:30 AM
222 km/hr Parkjet flyer
solentlife's Avatar
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Quote:
Originally Posted by scirocco View Post
Tame sports model around 2lbs a 200W power system is going to be ample.

To run 200W, you could get away with a motor as light as about 70g, but you're likely to run into balance problems as it's replacing a 540 that typically weighs around 180g, so I'd look for something at least 100g, even a bit heavier.

A motor around 1000-1100 Kv will use about 200-240W for a 10x5 prop, or if you can only fit 9", look for Kv around 1200. The Turnigy G10 series at 140g has Kv available of 810, 1100 and 1200, giving you a good choice of prop sizes from 9" up.

To get better advice, decide first up on prop size.
Bringing us back to my post earlier that reckoned on prop size and finding good set-up for that prop as a MINIMUM size. My reasoning for minimum size is as another says - old models tended to be marginally powered ...
Picking the prop as a minimum means most likely being well powered by brushless.

I also believe that powering OVER is far better than UNDER powering ...
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Old May 26, 2012, 09:56 AM
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Blackpool, Great Britain (UK)
Joined Dec 2003
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Quote:
Originally Posted by Lnagel View Post

Don't worry about matching the old power system. It may or may not have been the best match for the airplane. Design the new power system to fit the airplane's characteristics and how you want it to fly. For help on that list the configuration of the airplane, wingspan, wing area, weight and how it should peform, i.e. sport aerobatics, trainer, 3D, etc.

Larry
Absolutely correct.

This applies when replacing any outdated power system; brushed, IC, whatever.

Allow me to repeat. Base the new power system on the needs of the model. Don't waste time searching for an equivalent set-up.
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