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Oct 26, 2014, 11:19 AM
Wisconsin
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Discussion

Newbie to Newbie: Motors and Electronic Speed Controllers (ESCs)


The batteries supply power to a number of components but the common ones are the motors for every craft. RC hobbyists use a direct current (dc) brushless motor most commonly. This motor is controlled by sending it dc pulses that turn electro-magnets inside the motor on and off in a pattern that gets the motor spinning. There is a round cylindrical housing that is lined with permanent magnets and rotates. This type is called an "outrunner" because the outside of the case rotates. Some are the reverse and they are called "inrunners".



In an Outrunner there is also a fixed star-shaped assembly, called a stator, that has wires wound around a form that, when powered with an electric current, causes a magnetic field to form. You turn on one set of windings to cause a momentary magnetic field which attracts the winding to the next magnet on the housing, and the rotating part then moves toward the next magnet. Then you pulse another winding and cause it to move toward the next magnet on the housing. By turning the windings on and off, that form multiple temporary magnets, we can get the rotating part to begin spinning. We need to have a controller that will send pulses to our motors in a precise fashion.

This is called an electronic speed controller (ESC). We supply raw power, directly from our battery, to the speed controller and it precisely times pulses that are sent via three wires to parts of the rotating stator. By sending pulses on the three different wires we can get the motor to turn and, if we change the order of any two of the three wires. we can get the motor to turn in the opposite direction.
http://en.wikipedia.org/wiki/Electronic_speed_control

There is a signal wire going to each ESC from the Flight Controller(FC) that allows the FC to tell one or more of the ESC's to startup the motors when it needs to control flight. It is the small orange wire in the photo above.

It can be difficult to understand the specifications of motor vendors. Many use the stator size as a model number for the motor while some have no system that helps you distinguish the specifications from the model name. For example, a DJI 2212 has a 22mm stator height and a 12 mm diameter; it is taller than it is round(on the right in the picture above). A Tiger MN3508 has a 35mm diameter stator and is 8mm tall, more like a pancake, as it is sometimes called(on the left in the picture above). Another motor specification is the KV. For those already familiar with electronics this is not kilovolts; it is a term coined to describe the speed that the motor rotates for a given voltage. For example, let's say you choose a 1000kv motor. This motor will spin at 12000 rpm when powered by 12v or a 3S battery. You multiply the Voltage used by the specified KV to determine the RPM. Each motor has a characteristic KV which determines how fast it will spin when used with a given battery.

Different types of flying need different types of motors. If you want to fly acrobatically (ACRO), you will need a motor that changes speed quickly so you can flip and bank rapidly. It will not need a lot of torque but it will need to go fast and change fast. On the other hand, if you are only interested in an aerial camera platform and will hover most of the time, but need to carry a heavy load, you will need a different motor. You will need lots of torque to carry the heavy load but you don't care too much about speed or changing rapidly. You want efficiency so you use as little power as possible during flight to allow your flight to last as long as possible with a heavy load. For longer flight you need slow moving, low RPM, motors and big props. For acrobatic flight you need high rpm turning smaller props. It is important to note that to get long flight times you need slow moving low rpm props, not necessarily low kv. If your target rpm is 7200rpm you can get that in multiple ways. At 24v (6s), 7200rpm=24v x 300kv but you can also get 7200rpm by(3s) 12v x 600kv or by (4s) 14v x 515rpm. All of these combinations rotate the prop at exactly the same speed.

Next: Propellers
Last edited by mike_kelly; Mar 19, 2016 at 08:46 AM.
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Oct 27, 2014, 08:30 AM
Registered User
Very nice, thank you
Oct 27, 2014, 08:29 PM
Wisconsin
Thread OP
Quote:
Originally Posted by Joachim84
Very nice, thank you
Joachim,
Thank you for reading it!
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Nov 29, 2014, 10:19 PM
Registered User
Nice job on the write-up.
Nov 30, 2014, 10:42 AM
Wisconsin
Thread OP
Quote:
Originally Posted by arizona98tj
Nice job on the write-up.
Thanks for the note. Makes it worth while to know it is useful.

Cheers
Latest blog entry: UC4H: Gimbal flight test
Jan 21, 2015, 01:26 PM
Registered User
For those interested on technical aspect, I think what in RC field is named "Electronic Speed Controller" is what in eletric cars field is named "motor controller", actually made of a "controller" (low voltage signals) and a "driver" (high power) circuit:


This is the shape of the three waves produced by the controller, which control the high-power mosfets:


But some cheaper models just use simple DC motors, but I don't know how they are controlled.
Jan 21, 2015, 02:10 PM
Wisconsin
Thread OP
Quote:
Originally Posted by jumpjack
For those interested on technical aspect, I think what in RC field is named "Electronic Speed Controller" is what in eletric cars field is named "motor controller", actually made of a "controller" (low voltage signals) and a "driver" (high power) circuit:


This is the shape of the three waves produced by the controller, which control the high-power mosfets:


But some cheaper models just use simple DC motors, but I don't know how they are controlled.
Nice addition, thank you. Good example of the square wave signal, not AC, but similar in that it changes like AC but not a sine wave.
Latest blog entry: UC4H: Gimbal flight test
Oct 12, 2015, 08:29 AM
Zarapa's pilot !
Oscar Jr.'s Avatar
Hi, I'm becoming frequent user of this thread and thank you for that. Could you please explain a little bit about Opto ESC, regular ESC with BEC, PDBs, PDB with BEC and how they are related between them? I mean, what I really need to put into a quadrotor frame with your own PDB (referring to ESCs)?

Thanks!

Later I got this excellent video that helps a lot : https://youtu.be/-gOupB8xnlM?list=PL...o4Xr3lNUc8PFpc
Last edited by Oscar Jr.; Oct 12, 2015 at 03:25 PM.
Oct 16, 2015, 07:48 AM
Wisconsin
Thread OP
Sure. The term opto is misused in this hobby so it makes it a little difficult. Before computerized flight controllers there was no need for anything but one battery to power your prop. Simple. Then folks wanted rectractable landing gear and maybe some lights and if they ran off a different voltage you had to add another battery just for those simple accessories. So some vendors added a simple voltage regulator to their ESC's so you could eliminate the second battery. Hence the BEC or battery eliminator circuit. But they were not high quality regulators and modern flight controllers are computers and need good clean power to operate. So people started to use external regulators called ubecs or power modules designed to provide high quality power. Soon ESC vendors realized they could save a little cost by not including a bec with their ESC because most people were no longer using them. Unfortunately they called these ESC's opto. The real meaning is optically isolated. This means that the input is not electrically connected to the output but instead information is transfered by a light beam. It is used to prevent noise from being transfered through the device.
It is really hard to determine if an ESC vendor means optically isolated or just no bec.

The PDB is a power distribution board and is used to take your battery power and conveniently connect that power to multiple devices. It is not required but can make your installation neater. Some new PDB include extra features like video filters or led controllers or regulators for extra voltages etc.
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Oct 16, 2015, 11:33 AM
Zarapa's pilot !
Oscar Jr.'s Avatar
Well, my knowledge has grown a lot at last couple days and now is quite good. Thinking in my second quad (the first one will be LaTrax Alias) I chose to use a PDB with BEC, an Emax Skyline32 Advanced FC, 4 DYS SN16A opto ESC (yeah, opto means no BEC) and 4 Turnigy 1806-2280kV to lift a not chosen frame (250 class). I think that combo will be fine to improve skills that I do not have yet !

Actually, I was in doubt between SimonK vs BLHeli firmware, but it doesn't matter, I'm not a expert in electronics and just wanna have fun !

Cheers!
Last edited by Oscar Jr.; Oct 16, 2015 at 11:44 AM.
Oct 16, 2015, 12:15 PM
Wisconsin
Thread OP
Good attitude. Many people obsess over very tiny differences in things like the BLHeli and SImonK but most of us will not ever see the difference. You will have a great time with your 250 class quad. They are so much fun to fly. Enjoy the building too!
Latest blog entry: UC4H: Gimbal flight test
Nov 19, 2015, 08:55 PM
New Lawnmower
I appreciate this well written article on the motors and ESC's. I had been wondering about the kv and now I know. Thank you very much for taking the time to explain it to us!
Ken
Nov 19, 2015, 09:27 PM
Wisconsin
Thread OP
Quote:
Originally Posted by Bug Eyes
I appreciate this well written article on the motors and ESC's. I had been wondering about the kv and now I know. Thank you very much for taking the time to explain it to us!
Ken
Thank you for taking the time to read it.
Latest blog entry: UC4H: Gimbal flight test
Mar 04, 2016, 04:01 PM
On the ol' Interweb
Do BLHeli multirotor ESCs work on a standard PWM receiver, like Spektrum, but without a flight controller? I'm wanting to use a 3D BLHeli ESC and high KV motor for a fixed wing foamie application.
Mar 04, 2016, 06:34 PM
Wisconsin
Thread OP
Quote:
Originally Posted by T.A.Z
Do BLHeli multirotor ESCs work on a standard PWM receiver, like Spektrum, but without a flight controller? I'm wanting to use a 3D BLHeli ESC and high KV motor for a fixed wing foamie application.
They are standard Pwm esc's but that said they have a lot of features you would probably not want on a plane, like braking. They are made specifically for multi rotors.
Latest blog entry: UC4H: Gimbal flight test


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