Joined Aug 2012
Wanna learn about moto specs
More than just telling me which motors you'd recommend in a given craft, can someone point me to an article or discussion that explains how to determine what will work well? I really want to understand the specs for motors and what kind of lift I can expect from a set of motors/ESCs/props.
I'd like to build a 60-70cm- hexcopter initially using a kk2.0 for control and a turnigy x9 rx/tx. Eventually, I plan to switch over to an arducopter board. I want a good solid platform with plenty of lift so I can heft a FVP system and as a platform for some serious tinkering. (I'd like to play with sonic obstacle detection.)
A friend is planning a similar system, but wants to go a bit bigger and octo to start. Although both of us have experience flying both fixed wing and rotor rc, neither of us know how to determine what motors, esc's and props to use on a given project.
Joined Feb 2003
>>More than just telling me which motors you'd recommend in a given craft, can someone point me to an article or discussion that explains how to determine what will work well? I really want to understand the specs for motors and what kind of lift I can expect from a set of motors/ESCs/props.<<
Unfortunately that can be quite difficult without getting into all the math. However if you browse around you can get a very general idea on what may work on various applications. Then the rest will depend on some personal experiment unless you are fairly close in duplicating what some one else has used.
That is the reason why sometimes posters will ask for specific hardware and their compatibilities.
>>I'd like to build a 60-70cm- hexcopter initially using a kk2.0 for control and a turnigy x9 rx/tx.<<
The only thing that matters to what motors and prop to use will be the final projected weight of your project. 60 to 70 cm hexa can have a pretty large range. You can use 6 each 2216 size motors and some 10" props to some 2820 size motors and some 13" props. The weight difference will be substantial.
You may be using skinny 12mm round tubes for arms or up to 21mm Trex 700 tail booms for arms.
>> Eventually, I plan to switch over to an arducopter board. <<
Again the flight controller is a flight controller. They all work once you know how to tune them properly.
>>I want a good solid platform with plenty of lift so I can heft a FVP system and as a platform for some serious tinkering. (I'd like to play with sonic obstacle detection.)<<
As least you are not talking about lifting a Canon 5D mark 2 like most other posters.
>>A friend is planning a similar system, but wants to go a bit bigger and octo to start.<<
The number of motors do not necessarily translate into size. you can have a tiny Octo or a very big quad.
>> Although both of us have experience flying both fixed wing and rotor rc, neither of us know how to determine what motors, esc's and props to use on a given project.<<
That is a great start. At least you know about RC in general and how it works.
The multi rotor motors are really more focused on kV or RPM per volt as you know from your single main rotor helicopters. However since the multi rotor uses motor to drive the propeller directly a lower kV motor is more desirable.
Through the history of electric flight motor sizing has been the most non-standardized situation. Most manufacturers come up with all kinds of way to name their motors which is very confusing for users. In the older brushed motors days you have motor sizes such as 700, 600, 500, 480, 380, 280 etc. Then some brushless motors started using the same number system and they still do. For example if you look at some of the motors sold by Hobby King it will same a Park480. Same thing if you look at some eRC motors sold by Hobby Lobby.
However most other motors start to use a different numbering system. Some use a four digit number which signifies the stator size and the kV after the dash. Some manufacturers will number their motors by the outer diameter of the motor can.
Regardless almost all motors used in multi rotors are outrunner because they generally have a lower kV. You also start to see more and more pancake outrunner motors which give even lower kV plus higher torque.
For me the simplest so far is to find the stator size of the motor and and the kV and I use them as a reference. The taller the motor the more powerful. The bigger the diameter the more torque. The kV pretty much is governed by the windings and if you get into the specific of the windings it gets even more confusing. You have single wire wind, multi wire wind and you can connect the three phase in a Y configuration or a delta configuration. All of those will dictate the rpm per volt. So it is much simpler to temporarily ignore the winding informations and just find out about the kV.
To start the 22mm diameter stator is the most popular for a mid size multi rotor. The smaller 22mm diameter 8mm tall motors are the smaller work horses for smaller machines or larger machines with 6 to 8 of them together. They can spin some 8" props on 3 cells. These are good for 18" diameter quads.
The 2216mm are the mid size motors for mid size machines. They are about the most popular for a 20" diameter quad to 22" quad. They are great for 10" props. on 3 or 4 cells.
Then you get the 2814 motors which are starting to get a bit larger. They generally like 4 cell battery if the kV is in the 700 to 800 rpm per volt range. 11" to 12" props are the normal. These can power quads around 26" to 32" diameter.
Then you have the 2820 motors which are the power house for heavy lift machines. They swing any where from 13" props to 15" props. 4 of these can lift a DSLR. 6 to 8 of these can lift a fairly heavy movie camera.
As far as kV range. You want to stay with 3 cells pack when you use motors in the 900 to 1200 kV range. From 800 kV to 900 kV you may consider trying either 3 cells or 4 cells pack to see which works better. For 600 kV to 800 kV you need 4 cells to generate enough RPM for lift.
So that is a really simplified and general summary of some of the motors we use. One thing to play is to try eCalc and plug in different motors and check out what thrust they say you will get. That way you can have a general idea. Just be aware that eCalc may not be the most precise tool and you do need to do some experimenting to fine tune your setup.
Motors and props depends on it.
What is the common all-up weight of a 60-70cm hexa with FPV gear, I don't know, maybe 2000g.
Owners of such set-ups could give more precise values.
At hover, motor-prop combo efficiency is usually between 7 and 8 g/W.
For 2000g you need 2000/7.5 = 267W
You will have 6 motors = 45W per motor.
Motors max power depends of your flying style.
If soft, it should be 2.5 times hover power = 110W (each motor max power)
If more dynamic, 3 times = 135W
If acro, 4 times = 180W
Secondly, you will have to choose the right prop for your motor.
It has to give you access to the full power of your motor, no less no more, and a good efficiency at hover.
There are tests and calculators to help you with that.
I have forgotten: KV between 700 and 1000, props probably 10X4.7.
This needs to be stickied or something. This is more information on motor selection in one place than I have seen in another thread in RCgroups.
Also, for the easy part, once you have a motor picked select an ESC with a higher max amperage than the max amperage the motor is rated for.
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