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Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

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Old 09-21-2007, 07:05 PM   #1
GB57
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Default Help with Motor/Prop Selection

I have a NIB Whipit HLG kit from 10 years ago. 58" polyhedral wing and (it says) 10-12 oz flying weight. I am interested in building it as an electric sailplane with a brushless motor, folding prop and LiPo batteries. I figure it would weigh from 15 - 17 oz after the conversion. Already have a Hitec 05S full range micro RX and two HS-55 servos. Would like to get a good climb angle and about four pulls up to thermal height (say 500 ft). All suggestions for brushless motor and folding props to match as well as LiPo size and ESC size would be greatly appreciated.

Garry
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Old 09-22-2007, 12:45 PM   #2
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You should have a setup delivering at least 120 Watt I think. If it is 150 Watt you would be pleased with the climbing as long as you choose a motor with low kV, and use a large diameter propeller. On such a "small" plane a 10-12" propeller is big.

How do you plan to install the motor in the plane? If the nose is narrow, and you plan to make a firewall to mount the motor behind, an inrunner might suit best. This is because of where the cables come out on different motors. On the outrunners the cables come out close to the front of the motors, and since their housings rotate the cables can be damaged in narrow noses.

Most inrunners have a too high kV to suit pulling up planes at high angles and slow speed. Therefore a geared version would be the perfect choice.

If an outrunner suits in the plane something like AXI 2212/34 is as lightweight as it can be.
To have more punch available, the AXI 2217/20 will be a safe choice. This is for 2-4 LiPo, but since you want to climb fast and then glide I would suggest 2S or 3S LiPo. This is because you can swing more propeller-diameter at lower voltage, and what brings you vertical is a big diameter

The "perfect" motor is (in my opinion) a Cyclon Elite Mini. You can see it on this page. It is a geared "outrunner", the rear part rotates. It will have to run at close to idle in your plane, but is capable of pulling your next 1,5-kilo model up at an impressive angle. Although; look at the weight: 80 gram! 13 gram more than the largest AXI mentioned above. This is a motor made for one purpose: pull a plane up high at short time.
OK, I don`t have the Mini myself, but soon I will. And why? Because I have tried Elite 10 and Elite 18. I was impressed

2S or 3S LiPo might be your choice, depending on which motor you land at. For the Cyclon I would suggest 2S LiPo. Since I have not had the chance to test one yet I can`t recommend any propeller. But since I said 120-150 Watt for your plane I would have tried to match max 150 Watt.
Remember: even if the motor is able to handle 450 Watt you suit a propeller which suits your needs! If you need 150 Watt then put on a propeller which give you 150 Watt at WOT. In the next, larger plane, add more Volt and a bigge propeller and go flying

A geared inrunner would do the job, but there is one disadvantage: Inrunner with a gearbox in front makes a long installation. Thus you have to move the battery backwards and might have to add led up front.
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Old 09-22-2007, 02:30 PM   #3
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www.hobby-lobby.com/glow2electric.htm

Also try downloading MotoCalc8. Great program.

www.commonsenserc.com also has some useful charts...also google bartus, they make a universal motor calc (Forgot the URL :\)

There is such a word as Jigawatt!!!!


Prject Glbetrtter
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Old 09-22-2007, 08:22 PM   #4
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New strong version of the most impressive motors in the Cyclon Range (NFS). This motor has the ability to deliver more than 300 watts continuous and 450 peak watts yet it weighs only 80 gr. It is the only motor in the world at this time to offer so much power for such low weight. No more comment is needed..

Though I'm sure this is an excellent motor, I just wish that hyperbole and unsupported/unresearched claims didn't have to rear their ugly heads in the advertising.

I think Microdan 2505 Speed (33g) and Littlescreamers SPJ (32g) might like to argue that they can do the 300W continuous at less than half the weight. Lightflight, Justgofly and Medusa (and probably a host of others) have all got <80g candidates too.

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Old 09-23-2007, 07:32 AM   #5
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Originally Posted by Dr Kiwi View Post
Lightflight, Justgofly and Medusa (and probably a host of others) have all got <80g candidates too.

But I don`t think none of them are able to deliver this much power to such a large propeller as Cyclon do! And to pull a thermal glider up fast it won`t help with same amount of Watt delivered to a small high-pitch propeller. The motor also have to be mounted nicely in the nose, attaching a spinner up front and otherwice be hidden inside the plane.

The Microdan 2505 "might" deliver a bit over 200 Watt, to a 5" propeller. Does this suit a glider? NO. Could it easyli be mounted in to a gliders nose? NO.
The Littlescreamer SPJ have a kV of 2350 Should this suit a glider? No way. Could it be mounted nicely in to the nose of a glider? NO.

As I said earlier: "In my opinion" the Mini would be a great choice for the GLIDER. Although there are a lot of outrunners with low kV able to do the job. Why? Because I have tested its bigger brothers, and have seen what they do. Swapping from Jeti/Mega-motors to Cyclon in same plane gave me VERTICAL performance instead of 30` of climbrate WIth 20% more watts only. And in an other I used 20 seconds to 200 meter, instead of more than 50 secs... with equal Watts.

And as I also said: GB 57 needs 120 Watt, but this power should be delivered to a large propeller to do the job in the way which suits a glider.
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Old 09-23-2007, 04:05 PM   #6
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I understand perfectly your argument about getting the power into a large prop for a sailplane/powered glider. But that was not what the "Cyclon" description said - it just said 300W - and that was what I took issue on.

I know its a ridiculous comparison, but I have regularly put 300W+ into a 33g Microdan 2505 Speed (yes, I agree, with only a 5" prop!).

For a more sensible comparison, I have just tested a Suppo H2212/5.5 geared 2.43:1 (65g incl. gearbox) and it ran happily at 363W with a 9x5 GWS HD on it. I will admit that 483W with a 10x6 GWS HD was really far too much!
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