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Which motor?

Fans and Thermals.
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StephenB
Posts: 176
Joined: 26 Dec 2018, 08:45
Location: Hungary

Which motor?

Post by StephenB »

I've just taken delivery of the Cliff Charlesworth Schiebe SF-33 short kit from Cliff and starting to put together the various bits and bobs before commencing the build.

The model will come in at around 1.8Kg, I'll use a 3S LiPo but other than that I've no idea of what motor to use. I'll be flying it in a scale like manner so just enough power to get airborne with a little in reserve would seem to be the requirement, but how much is that??

Would, for instance, something like thishttp://www.modelshopleeds.co.uk/catalog ... s_id=22112 do the job or is it too much or too little?

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Peter Balcombe
Posts: 1141
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Which motor?

Post by Peter Balcombe »

Stephen,
I used the following (see SF33 build thread)
“I am using an old Dualsky XM3548 brushless motor with XC4018 ESC supplied by a 3S 2200mAH Lipo.
(There is plenty of space to fit a larger capacity battery if needed).
With a fixed 2 blade 9x6 Master Airscrew prop, this combination gives just over 300w on the wattmeter, with just over 30A at full throttle.
Max motor efficiency current is 35A, so a little more is available, but max current is 40A.

With the model (currently still less it’s tailwheel assembly & Rx) balanced (2200 battery fully forward), the overall weight comes in at 1.8Kg (4lbs), including about 200g of lead hot glued to the bottom of the motor bay.”

The XM3548 looks similar to the referenced one, but as I was only using 300W, you are well within the capability. The Tornado motor Kv is 25% higher so you will probably get more power with the same prop size due to higher revs with same 3S battery.

XM3548 Specification:
KV: 1080RPM/V
Stator Diameter: 28
Magnet length: 26
Shaft diameter: 5
Mounting holes pitch: 19/25
Weight: 165g
Resistance (Ri): 22mOhm
Idle Current (Io) @10V : 2.58A
No.of Cells (LiPo): 2..3
Max. Efficiency Current: 35A
Max. Burst Current (15s): 44A
Max. Power (15s): 650W
Input Connectors: DB3
Recommended ESC: XC4018BA
Prop. Range: 9x6...12x6

Peter

StephenB
Posts: 176
Joined: 26 Dec 2018, 08:45
Location: Hungary

Re: Which motor?

Post by StephenB »

Thanks Peter, although I knew which motor you had used, frustratingly I couldn't find any specs on it when I did a search. So more power will translate in to needing a larger ESC? I was hoping to keep it to a max of 40A.

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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Which motor?

Post by Peter Balcombe »

Stephen,
I think a 60A ESC is recommenced for the Tornado motor (capable of 700w or so), but you don’t need all that power for the SF33. If you are using a lower power ESC then it’s even more important to check the power train with a wattmeter (always a good move with electric flight) to make sure you stay say 20% below the ESC rated current. Check out the current draw & make sure the throttle range doesn’t let you pull too much power with the chosen prop.
It might be worth starting with an 8x6 prop & seeing what max power is pulled with a fresh battery before trying the 9x6. If you only have a 9x6 then make sure you run up slowly with a wattmeter in circuit so that you can stop before letting the smoke out of the ESC ;)
Peter

Jilles
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Re: Which motor?

Post by Jilles »

Not a real expert on this, but the rule of thumb is you need minimum 150W/kg plane to be able to take off . So a 1.8 kg model must have a power plant of minimum 270W.
But this is not the end of the story, on several occasions I have come across models that the owner put powerful motors in the model but does not deliver.
the combination of rpm/v, the battery size and C figure and prop size must all be compatible to get what you need.

StephenB
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Joined: 26 Dec 2018, 08:45
Location: Hungary

Re: Which motor?

Post by StephenB »

Peter, I have a watt meter so can check current draw and wattage when I have all the bits together. From your earlier comment I wonder if this motor http://www.modelshopleeds.co.uk/catalog ... s_id=15968 might be a better bet? It gives around 400 watts with 30A ESC with less Kv.

Jilles, yes it is complicated trying to figure out which combination of motor/prop and battery will give the required watts per lb (or kg).

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: Which motor?

Post by Peter Balcombe »

Stephen,
Personally, I would go for the first motor as I think you will be pushing the 2nd one with 3 cells & end up risking blowing the ESC trying to get enough power. I think it better to have a slightly over capable power train & reduce the power provided, rather than push the components.

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Barry_Cole
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Joined: 10 Mar 2015, 09:30
Location: Hampshire UK

Re: Which motor?

Post by Barry_Cole »

Agreed, you can always close the throttle a bit..

:roll: :roll: :roll: :roll:

BC

StephenB
Posts: 176
Joined: 26 Dec 2018, 08:45
Location: Hungary

Re: Which motor?

Post by StephenB »

Thanks chaps, the first motor it is!

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