Brushless motors

[kymbo]

I'm feeling a bit whipped after stacking the ripmax evolution again today. No where near enough power. Everyone keeps telling me I have to go brushless and I will never go back.

Ok I believe you but having a look around Ebay the range is daunting and the way they describe them varies. The one constant seems to be the Kv the motor uses. The truth is I have already gotten a nice little outrunner 1050kv but it seems I can get the 30-40amp speed controller with another motor for about the price of the speed controller alone. Bare with me

Now I have got 6 motor/speed controller choices in front of me which use 30 to 40 amp controllers. But the Kv on those motors range between 980 to 4000. How it work

Oh and prices vary from $16 delivered to $60+
Please no one say you get what you pay for. I'm in a reckless impulse buying mood.

[felix]

kymbo a good person to talk to would be mark (he was the bloke chasing me with the eagle yesterday).he's pretty cluey as far as motors go and will know what site to get it off cheap.

[skyboyken]

Hi Kymbo,

I may be able to provide some help.

Please tell me:

The span and expected RTF weight of the Evolution, and

The battery pack you want to use.

BTW quality equipment is always a good idea. Dead cheap outrunners and ESC's can and frequently do die early deaths. Some people have no problems but if you already have the motor just getting an ESC isn't a bad idea.

For info, 1050kV is what is usually used with a 3S LiPo pack or 10 cell NiMH. What brand of motor is it and what model?

Ken.

[kymbo]

Thanks Skyboyken.

Its a bit hard to resist with the lolly shop of choices available from Hong Kong. Some of their quality seem too good to believe.

This is the 1st motor I picked up

And yesterday I bought one of these with a 40amp esc
Sexy ehh It's 1400Kv

My next step will be to buy some Li Po's and a charger. What does the 15C, 20C etc refer too? The glider in its current form weighs in at 984g's. with its 1800mm span. I know this new driveline will make everything lighter but I intend to use full size servos instead of the micros in the T tail which I dislike.

[skyzking]

Ok, one thing you must make sure is that the motor will actually fit inside the fuselage of your plane. Motors come in 28mm, 36, 40, 45, 55, 65, 70 and on. If you previously had a 400 size brushed then you can easily fit 28mm brushless motors in there. If you had a 540-600 size brushed then you may fit from a 36-40mm diameter brushless.

The kV of the motor is very important. Motors like 4000Kv are built for props not larger than 5 inches (no good for large aircraft), putting a larger prop on this sort of motor will result in an undesired amp draw and you can cook all your electronics instantly.

So for an aircraft of a span of 1.8m, i suggest a low kV outrunner in the (800-1200) range so you can put a decent prop on it which will give you the desired thrust needed.

The new motor you bought (the 1400kV one) is probably the upper limit of what you need. Check the manufacturers prop recommendations and stick to that, otherwise you can cook everything easily.

Also, dont be worried about the chinesse quality, the motors you buy here in the hobby shop are the same but with just different labels on them.

[skyzking]

I just saw you mention "what is 15C, 20C refer to?"

This refers to the discharge rate of the battery. There will usually be two numbers on it e.g. 15/20C. This means that the lipo is capable of 15C discharge constantly and 20C in short bursts.

Heres how you work out the discharge rate. For example if the battery is 2000mAh in capacity and has a discharge rating of 15/20C

2000mAh = 2Ah,
2Ah X 15C=30A - therefore the continues discharge capability of the battery is 30A (A= amps),
2Ah X 20C=40A - therefore the burst discharge rate of the battery is 40A.

Most lipos are capable providing their burst rating for about 10 seconds.

So if your buying a setup which requires around 40A, then id look in to a battery that can provide that much amps constantly.

I hope that helps...

Abdullah...

[kymbo]

Thats great, now I can get my head around it. Thanks a heap.

[kymbo]

Been on a bit of a sebaticle but since Ive been trying to get a fly in the wind hasn't been favourable for the slopes when I have been available to fly so I have returned to the electric flight subject.

I'm currently working on powering up my oz prey. I have made a fuselage to carry all the gear and have been bench testing the motors and batteries. I even made the thrust testing scales I previously mentioned to give me an idea of what the motors where pulling and tonight nutted out the Jap instructions for the Li Po charger.

A couple questions, the instructions are a bit vague on what to charge the battery to. The batteries I have are 3S1P 11.1V 2200mAh 30C.

I did some searches not knowing if I should charge them for a set period of time or to a set voltage. I think Im supposed to charge them no higher than 12.6V is that right?

How often should you balance charge the batteries as upposed to the LiPo fast charge?

Finally Im planning on using the 1050kv motor with a 40amp speed controller and the affore mentioned batteries pulling a 900g Ozprey. What prop would be good?

[windsock]

Hi Kymbo,

I use a swallow charger to charge my LiPos. From memory I charge at 11.1V and do a balance charge around every 10th charge. On my swallow charger there is a setting for charging Lipos which I use.

I would love to see a photo of how you have modified your OzPrey to fit the motor & battery. I have often thought of doing something like you have done but thought it would be too hard.

Gerard

[kymbo]

I will email you some pics Gerard. The "test bed" is the same profile as the Ozprey fuselage but constructed out of 3mm exterior ply. Not the flexible nature of the EPP but by using fillet glue lines like used in boat construction it is very strong. I also doubled up the firewall and sandwiched in the front landing gear. I will use aluminium to make the rear undercarrage. There is plenty of room for the hardware inside. Feel free to stick the pics up if you like.

I don't have a convenient host site.

[kymbo]

Just seeing if I can insert images this way

[kymbo]

Had her maiden today. Very fast. Nothing like on the slope. Glides like a rocket.

Now I have a plane for the no wind days ;D