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Thursday, February 6, 2025

How Motors Work - some educational links

 

How Motors Work - some educational links

fechter

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.

Correct?

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

Correct?

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"

O.K. Now we're getting somewhere.

Take a look at this motor:

<a href="http://www.lemcoltd.com/lem_170.htm">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.

Agree?

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="http://tncscooters.com/product.php?sku=106170">Cheap Unite Motor</a>

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

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!

See
http://www.consult-g2.com/course.html

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.

Good idea. There's a huge amount of rubbish about "high torque winds" etc..

jonescg said:

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.........

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: http://click.email.globalspec.com/?qs=d3e9f51e6309a68626d10ce47902f8e0d44a2907667d1a69dbff22acfe24780f

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

NOW ON-DEMAND
Available On-Demand Until
January 7, 2015

WEBINAR PRESENTER:
Dr. Jinfang Liu,
Chief Operating Officer

Lori Haley,
Manufacturing Engineer

Karla Takasumi,
Senior Applications Engineer
KEY TAKE-AWAYS:
• 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

________________________________________
Important!
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
requirements.

• Trouble Accessing the Webinar — please copy and paste the URL
below into your browser.
http://event.on24.com/r.htm?e=822688&s=1&k=45EC7C094AB108B5DE482A46AFE86BD7

• Sound/Volume — turn your speakers up to hear the audio.
You will not need to dial in.
________________________________________
ABOUT ELECTRON ENERGY CORPORATION:
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.
________________________________________

Regards,
Dave

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"

These are well researched resources on how Motors work! Thanks for sharing.

Hello,

Please can someone tell me the difference between a unipolar stepper motor and a bipolar stepper motor. I understand that Bipolar motors have a higher torque but can they be used in the same applications?

HarryC said:

Hello,

Please can someone tell me the difference between a unipolar stepper motor and a bipolar stepper motor. I understand that Bipolar motors have a higher torque but can they be used in the same applications?
Here is a pretty good explanation:

I don't see why either couldn't be used for a particular application but the drive circuit will be different.

Unipolar Motors do not require the use of H-bridges, making it simpler to install and operate. According to this website: https://www.accu.co.uk/en/p/95-unipolar-stepper-motors-vs-bipolar-stepper-motors
However, Bipolar motors are generally have more torque and are more efficient than unipolar motors

This is another educational link: http://www.tigoe.com/pcomp/code/circuits/motors/stepper-motors/ this website says you can identify whether its a unipolar or bipolar motor by measuring the coil distance.

Hi Fetcher,

Seems like these are some good content to understand about motors as per the comments. Unfortunately, some of links are not working and not available. Could you please some other alternate links or videos which gives information as the above links. I will be really grateful.

I have been reading APL's and HH's threads and strongly motivated to build an Axial motor. I have a basic question which seems to be almost assumed in the threads. How do we determine the number of turns required and AWG that need to be used? What is the math behind this?

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