How Motors Work - some educational links

Electric Motors and Controllers
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How Motors Work - some educational links

Post by fechter » Feb 02, 2007 10:39 am

Here's a very detailed and well illustrated tutorial on the basics of AC induction motors and brushed DC motors. You can learn a lot from this.
If you're not the techie type, ignore the mathematical formulas and just look at the pictures.

Here's a resource for brushless motor theory for engineers:
another nice one here: ... 00885a.pdf

A more basic explaination is here:

A nice animation of a brushless motor: ... motor.html

To calculate speed, acceleration, current, and voltage, the famous 4QD calculator:

another excellent simiulator to help evaluate how different motor, battery, and controller combinations will perform on an electric bike:

A tutorial on motor calculations:
Last edited by fechter on Jun 21, 2007 9:49 pm, edited 7 times in total.

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Post by Volt » Feb 03, 2007 1:29 am

I thought this was also kinda interesting

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Post by Beagle123 » May 27, 2007 4:28 am

I read the links provided, and they were interesting. However, I'm more interested in data that will help me build a better bike.

Fetcher, check me if I'm wrong, but I've concluded from reading that dc motors will increase their RPMs proportionally with voltage.


Also, an increase in current producess more torque (?)


Thses kinds of principals are really helpful to me when I'm trying to design a bike.

Another really important point is that every motor has a range of RPMs that are very efficient. Knowing where that band is, and how to change/optimize it is very useful information.

I can't say that I understand it all yet, but when I do, I'd like to write a guide to help people choose and work with dc motors. It seems like its pretty easy to run your bike in an inefficient manner (but maybe not).

For example, suppose you have a 24v motor, and you want to run 20 amps through it at 36v. How will that change the numbers for the motor?

I wrote a topic on my current situation "here"

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Post by fechter » May 27, 2007 9:21 am

Beagle123 wrote: Fetcher, check me if I'm wrong, but I've concluded from reading that dc motors will increase their RPMs proportionally with voltage.


Also, an increase in current producess more torque (?)

Correct. Those relationships are very nearly linear under normal conditions.

Yes, it's very easy to get into an inefficient operating zone. Gearing for too high of a speed is the most common mistake.

The overall system dynamics can get very complex and don't always lend themseves to calculations or simulations. They will get you in the ballpark though.

I'd like to make a better reference page, but that's a lot of work and will take some time.
"One test is worth a thousand opinions"

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Post by Beagle123 » May 28, 2007 3:56 am

O.K. Now we're getting somewhere.

Take a look at this motor:

<a href="">LEM-170</a>

At the bottom of the page are three Excell Spreadsheets that show the motor's performance at 24v, 36v and 48v.

Would you agree with tise statement?:

Eventhough this motor looks excellent, its a bad choice for a scooter becasue its too big. If you look at the graphs, at 48v the motor "barely gets off the ground" at 50 amps. This motor performs best at 150 amps, so its better suited for a motorcycle etc.

Do you agree with this?:

The biggest problem with electric motors is the "accelerating from a stop" phase. So smaller motors may be better at getting up to the speed they need to perform best.

And, motors perform best when they have a significant load. I.e. taking a 750w motor and making it put out 400w. This would favor the smaller motors as well.

It seems like choosing a motor that's too big could easily be a problem.


Also, I think that Lemco page I found could be a good resource to write a guide for choosing how to run a motor. Or perhaps the rule of thumb should be "go with the higher voltage."

Thanks fetcher. You're really help a lot of us on this site. I hope I can contribute more in the future as I learn more.

By the way, I'm considering this motor for my next proiject:

<A href="">Cheap Unite Motor</a>

If I'm correct, it should produce nicely when asked to produce 600w or so.

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Re: How Motors Work - some educational links

Post by SolarTriker » Feb 15, 2010 2:28 am

Ooooooh I'm loving this stuff fetcher!!!!

Thanks for posting this! Really going to have to put in a few hours and get my head around it all. I'm in no real hurry with my build - just really want to think it through and design it so it works first time. This is probably going to be the slowest build in the world - will take a few months! I love the evlogix current control switch sold on that one guys! I want to model an Astro 3210 on a 24V setup limited to 250W and gear it to do ~20Mph on 27 speed 16in wheels. Don't laugh! i'm not taking a monster recumpence creation and turning it into a schoolgirl - I just like wearing a frock sometimes! You guys should try it get in touch with your feminine side! haha!

Thanks for your help and inspiration!

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Re: How Motors Work - some educational links

Post by ron van sommeren » Jun 09, 2011 1:33 pm

1.1 Introduction
1.2 Magnetic circuits and the design equations
1.3 Sample calculation of magnetic flux design in a gap
1.4 The B-H curves of PM materials
1.5 Excursions of the operating points
1.6 Energy product and maximum energy product
1.7 Intrinsic and normal B-H curves
1.8 Magnetic forces on permeable materials

2.1 Magnetically hard (PM) materials
2.2 Magnetically soft materials

3.1 Intuitive concept of flux
3.2 Reluctance and permeance
3.3 General formulation of reluctance
3.4 Roter's method
3.5 Numerical calculations of magnetic fields
3.5.1 Finite difference method
3.5.2 Finite element method

4.1 Force and emf generation
4.2 Transformer operation
4.3 Instruments of magnetics

5.1 Magnetizing requirements
5.2 Current vs. time in an ideal magnetizer
5.3 Real magnetizers
5.4 Optimization
5.5 Other considerations
5.6 Forces on conductors and coils
5.7 Winding patterns

6.1 Force production
6.1.1 Forces between a conductor and steel
6.2 Energy considerations
6.2.1 The force equation
6.3 Torque balance equation
6.3.1 Dynamic determination of torque
6.3.2 Torque development by 2 fields

7.1 Introduction
7.2 Overall dimensions
7.3 The magnetic circuit
7.4 Magnet performance
7.5 Design features
7.6 Motor winding
7.7 Winding connections
7.8 Motor characteristics
7.9 Loss calculation
7.10 Armature reaction and demagnetization
7.11 Acceleration
7.12 Designing with computers

8.1 Introduction
8.2 Laminations
8.2.1 Die punching
8.2.2 Chemical etching
8.2.3 Laser cutting
8.3 Stator stack
8.4 Winding
8.5 Magnet magnetization
8.6 Bearing assembly

9.1 Types of drives
9.2 Speed control
9.3 Sensorless control

10.2 Torque characteristics
10.3 Electromagnetic principles
10.4 Stepper design tips

11.1.2 Basic principles
11.1.3 Shorted turn
11.1.4 Equivalent circuit
11.1.5 Static magnetic circuit
11.1.6 Coil construction
11.1.7 Improving linearity
11.1.8 Actuator dynamics
11.2 Solenoids
11.2.1 Introduction
11.2.2 First order force calculation
11.2.3 Idealized model
11.2.4 Bobbin and winding
11.2.5 Packing factor
11.2.6 Gap location
11.2.7 Plunger face shape
11.2.8 Remanence and sticking
11.2.9 The plunger-wall flux crossing region
11.2.10 Solenoid drive circuit consideration
11.2.11 Solenoids operating against springs
11.2.12 Constant force variable position solenoid
11.2.13 Solenoid actuation speed
11.2.14 Some other solenoid types AC solenoids Rotary solenoids
11.2.15 Testing of solenoids
11.3 Linear multiphase motors
11.4 Other actuators
Vriendelijke groeten ;) Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC

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Slow wind and fast wind explained.

Post by jonescg » Nov 19, 2012 4:41 am

I noticed a post about "slow winds" and "fast winds" and I got to thinking, I should really make a post so the average punter can make sense of the slang. Shoot me down if this has already been done, but there is a lot of misleading crap out there about how electric motors work...

Lets say we have 5 kg of copper, and you can beat it into any sized wire you like. Use this wire to wind up say a 12 pole motor.

Using thinner wire, your 5 kg of copper can be wrapped around the armature 10 times per pole. Lets call this a ten turn motor.

Using thicker wire, your 5 kg of copper can only be wrapped around the armature 5 times per pole. This is a 5 turn motor.

The torque characteristics of these motors are going to be very different. The 10 turn motor is going to have a higher torque constant than the 5 turn motor - that is, more torque will be produced per amp of current. Torque constants are expressed in Nm per amp.

We also know that volts and amps are related, and torque and motor speed are related. So torque characteristics may also be expressed as voltage constants. In our case above, the 10 turn motor will have a lower voltage constant than the 5 turn motor. Voltage constants are usually expressed as rpm per volt. That is, the 10 turn motor will spin slower than the 5 turn motor per volt applied.

So when someone says "I prefer a slow wind" they are referring to a motor which has more turns of wire per kilogram of copper, and thus spin slower at a given voltage. At that same voltage, a "faster wind" will spin faster.
Last edited by jonescg on Nov 19, 2012 6:17 am, edited 1 time in total.

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Re: Slow wind and fast wind explained.

Post by Miles » Nov 19, 2012 5:18 am

Good idea. There's a huge amount of rubbish about "high torque winds" etc..
jonescg wrote:So torque characteristics may also be expressed as voltage constants. In our case above, the 10 turn motor will have a lower voltage constant than the 5 turn motor.
I think it's better to use the term velocity constant rather than voltage constant. Firstly, it's consistent with the expression of terms in the torque constant. Secondly, it doesn't equate to the true voltage constant (Ke in V/1000rpm) because of the voltage drop from the parasitic torque. Thirdly the abbreviation for volts is upper case V, which also adds to the confusion...

I also think Km should only be used for Nm/✓W and not as an alternative to Kt.

Anyone disagree?

You could argue that angular velocity should only be expressed in radians/sec.........

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Re: How Motors Work - some educational links

Post by h0tr0d » Dec 04, 2012 9:44 am

Really awesome video found by NJay:

Also see other videos from the same YT user...

Thank you Justin! Life is so much sweeter with this forum... ;)

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Re: How Motors Work - some educational links

Post by Drum » Oct 09, 2014 3:01 am

Hi All,

Here's a link to a Webinar about using Rare Earth magnets efficiently. It is available online until January 2015.

I do not know enough to judge how useful this will be to other members, but hopefully some may benefit from it. It is presented through "Globalspec" by Electron Energy Corporation.
Here's the link: ... acfe24780f

and here's a copy / paste of the e-mail from Globalspec:

Available On-Demand Until
January 7, 2015

Dr. Jinfang Liu,
Chief Operating Officer

Lori Haley,
Manufacturing Engineer

Karla Takasumi,
Senior Applications Engineer
• Understand the magnetic properties of rare earth magnets and learn how they impact magnetic circuit design and analysis
• Learn how to design using FEA to improve performance of magnet systems
• Case Study using FEA analysis of Halbach designs to increase magnetic flux density 40% without changing overall dimensions

System Requirements & Compatibility Check
• System Requirements — to ensure successful access on the day
of the webinar, test your system to see if it meets the system

• Trouble Accessing the Webinar — please copy and paste the URL
below into your browser. ... 46AFE86BD7

• Sound/Volume — turn your speakers up to hear the audio.
You will not need to dial in.
EEC Magnets and Assemblies ITAR/DFARS Compliant

Superior magnetic properties, ultra-high temperature tolerance and excellent reliability make Electron Energy Corporation magnets ideal for motors, actuators and generators.

Founded in 1970, EEC is dedicated to improving rare earth magnet performance to meet the most technically demanding applications in aerospace, military, medical, electronics, and motion control markets. As world-renowned experts in material sciences, testing and 2-D/3-D Finite Element Analysis, our vertically integrated operation provides you with the full range of services to meet your magnetic needs.


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Re: How Motors Work - some educational links

Post by spinningmagnets » Oct 09, 2014 12:43 pm

You could argue that angular velocity should only be expressed in radians/sec...
I am searching for the correct engineering term that would describe the speed of the magnets in a PMDC motor. It relates to the amps that the motor demands when bogged down, and three comparative examples to hopefully highlight what I am looking for are:

1) Small diameter direct drive hub in a 26-inch wheel (408?)...

2) Large diameter hub (Magic Pie?) in a smaller wheel (20-inch?)...

3) Hub-motor used as a non-hub with a high reduction to a small rear wheel.

I have come across the term "tangential magnet speed", but I regretfully didn't save the link. I am hoping to form a user-friendly term along the lines of the motors' "magnet speed per meter of wheel travel"

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Re: How Motors Work - some educational links

Post by jpgey » Mar 20, 2015 8:12 am

Very usefull link, with interaction and phase schema, delta, star, sinus and sensorless, Stepper and BLDC Motors Animation ... animation/

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