How to chose a motor for quadcopter

[Tamiyacowboy]

hello Tami again. 

 

so here you are, thinking of maybe building your own quadcopter BUT

your very unsure on how best to decide what motor you should use. 

 

so let tami show you how he chooses his motor and what his train of thought is.

 

i built the frame have a controller thingamybob and some 20a esc's but what motor would i buy and why.

so first off wee want to know how heavy we think our machine will be. let us say its 800g a few digits away from a kilo in weight.

 

now lets look at this image

 

 

this prop layout is for the sunnysky 2212 980kv 

now we will use a 3s battery so 11.1v , above you will see 11.1v  and the prop sizes

10x4.7 / 11x4.5 / 9x4.7,reading left to right you can see we also have amps drawn thrust generated RPM and also power in w

the very last reading is how efficent they are

 

now notice how propsize also affect the amps , if we have 20a esc we want to really keep below 10a

so we will say we have 20a esc;s fitted so 9x4.7 props with 3s will give us 9.6 amps thats about half what our esc can handle.

now our quadcopter weights 800g  and if we read across we can see one single motor will produce 680g of thrust ( lift) 

so thats good but what we are going to do is double our weight, we want punch ( if we did not doubleup full throttle would get you just hovering ) so we need to double our quads weight. to 1600g

now 4x motors will give us  (680x4) 2720g, well over what we really want. we could add a little more weight say fpv gear and not worry much at all.

 

so there we go thats how Tami works out roughly what motor he will use to power his quadcopter.

Good Motor makers will have these prop charts either in the box with motors or online. they are your best friend

once you learn how to choose the best motor for your setup. as you can see the motors we choose here are very much maxing out with 11.1v

so we could NOT run say 4s and have that be ok, the motors would/could fail running with to many volts and current flowing through them.

Also remember prop size makes a change to rpm, notice as the props get bigger the RPM comes down, we dont need to throw them so fast to produce lift.

 

hope this helps you all see how i and others match our motors to our setups using prop charts and overal weight of machine

[yoodoo]

Ha ha ha,nice tutorial.

[Tamiyacowboy]

with esc's we dont HAVE to keep half the amps it gives. 

 

now with the above we could run the motors at 11.1v (a 3s lipo ) and have 11 inch props.

this would give us around 17-18amps close to the esc's maximum. we would gain something close to around 240 extra grams of thrust.

but ...................

 

Now problems come, if we say are falling from the sky at a fair rate, we need to punch that throttle.

we are going to pull more amps from the esc, i would say a 20a esc with a burst could hold 25a for a few seconds.

the problem is we would need more than a few seconds of that Maxed punch from the esc, so we could have a Smoke out.

the esc totaly fails and our bird is now falling without control. 

 

Now here is a little tip, if your indoubt of the esc say you think a 20a would work , but your unsure on your caculation.

just grab a 30a or maybe even a 40a esc. there will be a lot of leway for you then and you can rest in mind the quadcopter

will get that required punch and not break out in blue smoke. 

Edited May 26, 2014 by Tamiyacowboy

[yoodoo]

Where did you get all this from??

[jony nitro]

Some say!

[Tamiyacowboy]

all this comes from my head, i see stuff and dont forget it. 

i also have a fondness for arduino flight controllers and spent a long time researching.

i even purchased an arduino board to get my head around defining stuff and seeing how it worked.

 

this same stuff is what controls your quadcopters, companys write their own code and sell it to you the public.

the open source community's are huge 20,000 - 50,000 or more people all like me, have an interst in the hobby

so poke around. one company of 10 people just cannont crowd source code and mass testing like a community

does.

 

Over time  you learn tricks tips and old wives tails same goes for RC , been nearly 30 years in the hobby

can remember when dynotune motors were the danglieys and the best batterys were 1200mah 1600mah at max if you was sponsored

racer. oh and in them days we ran MSC, mechanical speed control slow medum and yeah maybe fast lol. 

[yoodoo]

Well you have a good memory.I was skimming the clubs motors 31 years ago at a two quid a time.But all the multi rotors are new to me.Got me first rc at 10 (37 years ago) it was aTandy 4x4 bigfoot I think.My first "real" Rc was a Tamiya Bruiser that I got for my birthday.Then been into them ever since....what a great hobby!!!      

[Joe Bailey]

A nice simple explanation of what can be a very complex thing, Big thumbs up to you dude. I've been playing with rc since I was twelve, its been 19 years now. I'm amazed at just how fast this stuff is moving forward now and with the huge amount of funding now being poured into battery tech will get our dreams of half hour flight times and light weight before you know it.