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Old Feb 15, 2015, 11:05 AM
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New motors same as the old motors?

After many years I decided to take up RC flying. Back in the 60s I would watch with fascination as older people fired up little nitro engines, wound up rubber band motors on and on. Never forgot it. Then I when I was about 10 I got a plane with a nitro engine and crashed it in 20 seconds.

Now that I am 60 I am getting started, late life crises or something. So I find everything is now electric. I have spent many hours in the Electric Motor Design Thread learning what I can. Total over load with a million new terms and such. And with over 60,000 posts going back years just canít read them all or find the ones which have answers to specific questions.

Back in the 70s I studied electrical engineering and well remember my class in electromechanical devices so I know what 3 phase power is all about and I work on single and 3 phase induction motors in shops all the time. After reading all this RC stuff it occurred that that no matter what the terms itís still motors only smaller.

So I kind of backed off reading and trying to learn all the new terms like ďESCĒ and such. So I have reached this conclusion, these RC motors are really just plain old 3 phase motors driven by some little DC powered 3 phase converter with frequency control to regulate the speed.

Am I close? Is an ESC the same as a VFD only tiny? At any rate these little motors are amazing and the new batteries are a lot easier to deal with then those old small cans of cox nitro with that silly pump. Itís a wonder I didnít cut off all my fingers starting those old motors.
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Old Feb 15, 2015, 11:51 AM
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Close, but not quite. See http://www.aerodesign.de/peter/2001/...l#Anker1591256 for an insight of how the esc works, it is not a VFD.
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Old Feb 15, 2015, 12:13 PM
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Thanks, I guess with micro processors available for pennies these days almost anything possible.
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Old Feb 15, 2015, 12:59 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
11,190 Posts
Our PM BLDC (Permanent Magnet, Brushless DC) motors just brushed motors with electronic commutation (ESC) instead of mechanical commutation. Both brushed and brushless motors follow the same formula
rpm = Kv ◊ (voltage - Rm(Im-Io))
Note that Kv is not a rating. About choosing Kv
www.rcgroups.com/forums/showthread.php?t=2220657&pp=10#post30754159

I take it we don't have to tell you how to reverse rotation on a brushless motor ? Brushless motors are three phase (brushed are three phase too, internally) and can operate on/from a VFD. However, RC controllers are not VFD's, it's the motor that 'tells' the controller when to commutate. The controller reads the voltage induced in the phase that is unpowered at that time to figure that out (→ BEMF signal & zero crossing detection). More in this excellent and active diy brushless controller thread
www.rcgroups.com/forums/showthread.php?t=200567

More about brushless motors, pictures, drawings, exploded vieuws, diy
www.aerodesign.de/peter/2001/LRK350/index_eng.html



And for a rainy day(s) ...

E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
The Ampeer
→ Electric Power Basics


followed by
The Ampeer
→ Everything youw wanted to know about e-flight (Ed Anderson)
Table of Contents
  • What You Need To Know About Receivers
  • What function goes on which stick?
  • Battery Basics
  • Amps Versus Volts Versus C
  • Lithium Battery Chargers
  • ... ...
  • Understanding the Electronic Speed Control (ESC)
  • the Low Voltage Cutoff Feature (LVC) Of Your ESC
  • The Role of the Battery Eliminator Circuit in Your ESC (BEC)
  • Sizing Power Systems for Electric Airplanes
  • Prop Versus Amps
  • What Do the Kv Numbers On Motors Mean?
  • Who Needs a Wattmeter/Power Meter? (everyone!, RvS)

www.scriptasylum.com
→ RC calculations
→ electrical
system wiring
respectively ...
LiPo pack wiring
respectively
chargers (2 menu items)
The other menu items and demos are also veeeeery handy/instructive for e-folk, add site to your favourites?

www.ezonemag.com
→ FAQ

Vriendelijke groeten Ron
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Last edited by Ron van Sommeren; Feb 15, 2015 at 02:37 PM.
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Old Feb 15, 2015, 01:51 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
11,190 Posts
Quote:
Originally Posted by lhedrick View Post
... Itís a wonder I didnít cut off all my fingers starting those old motors.
Electric motors are riskier than IC engines. An IC engine can't start al of a sudden, whereas an e-motor can, without proper precautions and good routine. And contrary to an IC engine, an e-motor has all torque available at low rpm, unstoppable.

Also, an e-motor or controller can go up in smoke instantly, batteries can take a bit longer to die.

Vriendelijke groeten Ron
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Old Feb 15, 2015, 02:17 PM
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Not sure why I wanted to know other then it's just my nature.

And yes, nothing magical about direction of rotation.

It's been 40 years since I was in those EE classes and difficult to imagine that I was able to do all the math once upon a time. After college I migrated to network software engineering where I stayed for 25 years. I spent enough time in wood shops over the years to keep my working knowledge of how to deal with induction motors in the 1 - 5 HP range. I watched a member of our shop try to hook up a 3 phase motor table saw to a 2 phase circuit for a few days until I told him to buy a rotary and stop tripping the breakers every 30 minutes.

Now that I am looking into RC components, it's clear that a lot of EE types dropped out of boring big corporate environments and moved down the ladder to things which are much more fun. The components which are available are amazing.

Thanks
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Old Feb 15, 2015, 02:41 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
11,190 Posts
Two outrunner magnetic field strength simulations.
Magnetic field rotates faster than shaft.

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Last edited by Ron van Sommeren; Feb 16, 2015 at 07:10 AM.
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Old Feb 16, 2015, 07:10 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
11,190 Posts
Quote:
Originally Posted by Ron van Sommeren View Post
... it's the motor that 'tells' the controller when to commutate. ...
PM BLDC systems are not synchronous, not a-synchronous, they are iso-synchronous.

Some excellent reading, enjoy.

Vriendelijke groeten Ron
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