Motors

[HoverRound]

Sorry for the really novice question. I'm contemplating my very first build of a small mulitrotor to get a sense of all that is involved in owning, maintaining, and enjoying one of these. I will be building mine from scratch as it will probably be a slow process due to lack of funds.

I've been doing a lot of reading here over the past month or so (I know, not very long) and one of my first problems is figuring out the differences in motors. I see most people refer to motors by what I assume is a model number, but there are so many. Is there some kind of code or do the numbers mean anything, or are they just the number the manufacture puts on them? Is there any standarization to these numbers? Is there a guide somewhere that I haven't found yet that can help me select the right motor for what I want to do?

My long term goal for my second build is to have a heavy lift, self built multi sometime next year- hope that's not too ambitious.

 

[Electro 2]

"Is there some kind of code"

Sort of.

"do the numbers mean anything"

Yes they do

"are they just the number the manufacturer puts on them?"

Sometimes.

"Is there any standarization to these numbers?"

Sort of.

"Is there a guide somewhere that I haven't found yet"

Not that I'm aware of.

Sorry to be a wiseacre, but. 5 seconds with motor numbers: They break down like this. I'll use a fake number as an example e.g. 2830-11 with a Kv rating of 1000. With many manufacturers the first two digits are the O.D. of the outer case, hence a measure of total swept magnetic area, here 28mm. The second two digits are the height of the case, here 30mm. Total swept magnetic area would be 28 x 30 for a swept area of 840 square mm. This gives us a basic idea of transduction ability of the motor if all other things were held constant (they aren't). This said, as near as I can tell, some manufacturers specify *armature* dimentions and some specify outer case dimentions. Obviously armature would be the best so as to null out case and permenant magnet field thickness. The dash 11 part varies with manufacturer again. With some, it means the motor is wound for a nominal operating voltage of 11 volts, i.e. a 3 cell pack. With others, it must be the phases of the moon or something, as it seems to bear no relationship to anything. The K-sub-v rating is a legitimate defined figure, it's RPM per Volt. Under no load conditions, our hypothetical motor will turn 1000 RPM on a 1 volt source. This is tantamount to optimal wind operation voltage. For typical multirotor max prop speeds, 3 cells (11.1V) = 750-1000Kv, while 6 cells (22.2V) would work with around 350-600 Kv. I hope some of this makes sense.

 

[HoverRound]

Yes, that is helping a lot. Thank you so much for taking the time to elaborate a little.

Again, not being from an RC background, when I think of motors I would relate that to the something like an engine in a car. And when I think of car engines, more is always better, meaning a bigger engine normally means more power which will make it go faster or work harder. But it seems that bigger doesn't always mean better in the world of multirotors. I am understanding the prop speed/voltage a little bit more, but the last few sentences lost me. I guess since we're dealing with single speed it's not like car which typically have transmissions to keep the motor operating within it's torque curve.

So, lets say I want to build a quad and my goal is only smooth, stable flight- more or less a cinematography rig. Since I know it will need to carry a DLSR it will need to be in the medium to large size. I think I read that you should try to start with knowing your approximate final weight, then choose a prop, which will determine the length of the arms and size of the motor and batteries. So I guess my next thread should be about props and how they relate to thrust?

Thanks so much Electro 2

 

[Electro 2]

"I guess since we're dealing with single speed it's not like car which typically have transmissions to keep the motor operating within it's torque curve."

The characteristics of electric brushless motors bears *no* resemblance to an internal combustion engine. Forget what you know about them as it will only confuse you.


"I want to build a quad and my goal is only smooth, stable flight- more or less a cinematography rig.
"will need to carry a DLSR it will need to be in the medium to large size"
"I think I read that you should try to start with knowing your approximate final weight, then choose a prop, which will determine the length of the arms and size of the motor and batteries."

Uhhh, no. You would start with total weight. But, since you have stated where you want to go, I'll save you the trouble. Your DSLR capable rig will be a 700-1000mm Hex, maybe Octo, with an AUW of roughly 8-12 lbs, or so. Motors will end up being 40-50mm with 14-16 in props and 6 cell, 8-10 Ah packs. Boom, done. A more or less standard rig for this kind of work. I'm building one now. You might be able to get by with a smaller rig, but the flight envelope will be limited and less suitable to a wide variety of shoot environments. Also, you don't state whether you are doing motion picture work or stills. If it's movies, add a three-axis stabilized brushless drive gimbal system into this too.