Li-Po and ESC/motor compatability

[JC]

Gents

Just got used to brushed motors and nimh ect and now its all gone lipo and brushless. I've been reading the articals in RCME and I'm finding it a bit confusing. Is there any easy way of working out what amp esc to use with a lipo of a given C / voltage rating or an equasion to use. The instruction in RCME is very good but I just cant get to grips with it. I have just bought a West wings Toucan and have got a 7.4V 1000Mah lipo rated at 15C continuouse discharge. If I put a 480 brushed motor in it what amp esc should I use (lipo compatable obviously) or what rated brushless motor and esc should I use.

Yours a tad confused

Jon 

[Tim Mackey]

The C rating is not really anything to do with it Jon, this only tells you what current the battery could theoretically be discharged at. Put simply, the ESC should be able to handle comfortably the maximum current that your motor will draw, and that depends on the motor specs, and especially the prop you put on it.

Brushed motors are dead ducks really, and with prices on brushless so low these days, frankly you are mad to even think about using an inefficient noisy sparky carbon burning dinosaur.

However...if you insist, a brushed can 480 size motor is good at approx 8A up to around 20A and a prop of about 6 X 3 or 6 X 4 is normal, with an absolute maximum current limit of 30A.

Therefore get an ESC that will handle 25A as minimum, better still, get a 35 or even 40A one, then, when you eventually see the light and get a proper motor , you will have bags of room to spare, and the cost will be only slightly more than a 25A anyway.

Incidentally, I am pretty certain that brushless speed controllers are actually now cheaper than brushed ones ( you do know you cant mix them dont you ? )

Brushed ESCs are holding their price due to their antique value

[JT]

Timbo - you say: 

"Therefore get an ESC that will handle 25A as minimum, better still, get a 35 or even 40A one, then, when you eventually see the light and get a proper motor , you will have bags of room to spare, and the cost will be only slightly more than a 25A anyway. "

and then:

"Incidentally, I am pretty certain that brushless speed controllers are actually now cheaper than brushed ones ( you do know you cant mix them dont you ? )"

Is this a contradiction or am I missing something?

[JC]

Timbo

Many thanks. I'm still not too sure on how to ensure that I dont draw too much current from the battery and wreck it. The Kv ratings on brushed motors are still a mystery. I'am happy that a brushless esc wont work with or fit a brushed motor and visa versa.

Cheers

Jon 

[Tim Mackey]

I think I see what you mean James and if he did NOT follow my first bit of advice and get a brushless motor to start with then the mixing bit would tie him up as it were To clarify then JON

 A 40A ESC will have room to spare if used on a 25A setup of either brushless or brushed type.

You cant mix a brushless ESC  with a brushed motor, and viccky verkky

Brushless ESC is almost certainly cheaper than brushed if you shop carefully

Thanks James.....now get back to songwriting, been nothing decent from you since "you got a friend"

[Tim Mackey]

Jon. The only really safe way to ensure you dont exceed the current capability of your battery ( which is what the max C rate means ) is with a whattmeter or similar. Otherwise, fit the prop and battery size recommended by the motor supplier. If you still doubt this wisdom, check thisPOST

KV means the revs per volt of power supplied....600KV motor will spin 600 RPM for each volt, so on 10V = 6000 RPM. This will vary a bit with different prop sizes. Crudely speaking...

Low KV=more wire on the motor, large props, lower A, lower rpm, higher torque, big floaty scale jobs

High KV = less wire turns, small props, higher current, high rpm, lower torque IE fast hotliners.

[JC]

Timbo

Thanks again that makes things a lot clearer.  I will give brushless a go. I dont fancy taking out the brushed kit I've allready fitted so I guess I will just have to get another model. What a shame. I'm sure the wife will understand.

Cheers mate.

Jon

[Tim Mackey]