What about motor rotor size?

In summary, the conversation covers the topic of rotor size in brushless DC motors and its impact on calculations of angular velocity, voltage, current, and torque. The participants discuss various equations and factors involved, as well as the relationship between rotor size and speed. They also mention the importance of considering rotor inertia and recommend using resources such as the Drives Engineering Handbook and literature from Rockwell Automation for further information and assistance.
  • #1
SpaceLight
11
0
Specifically, this is all to do with rotor size of brushless DC motors and how it plays a part in calculating angular velocity / volts / amps / torque.

There is no single equation to be solved here.
Any relating information or equations..., any and all, please jump in.

I've been looking at all kinds of equations -- angular velocity, moment of inertia, torque, angular momentum, so on, and all interrelating factors --, but I'm not 100% on how rotor size effects the results of these equations, in more of a collective manner, so to speak. Radius is a variable in finding linear speed, but for finding angular velocity, radius variable seems to disappear. To some frail extent I realize that DISTANCE is transferred to ANGLE, but it's one big grey area for me.

In motors, one might be inclined to think that a smaller rotor would result in higher speed. Simply enough: The circumference is less, so less time to travel per revolution. You have stator electromagnets interacting with rotor magnets; call it a force pulse, if you will, created between them, and given that pulse of force the rotor proceeds to spin around until the next pulse initiated by commutation. The smaller the rotor, the more rpm; hence, more pulses initiated, more CEMF, so forth, so on, all due to increased speed by the rotor being small.

I've gone a fair distance so far, in physics and in motor design, I understand quite a bit, but I'm intermediate at best, I digress, I can't nail it down when it comes to the relationship between rotor size, force (as stated), angular velocity.

It's very important to what I'm doing; I'll take any input on the matter.
Thank you very extremely much indeed!
 
Engineering news on Phys.org
  • #2
I'm sorry - was there a question in there?
Electric motors, even simple ones, can get quite complicated - as well as the bulk of the rotor, you'd also have to consider the interaction with the magnetic fields.
What calculations you need depend on what you are trying to achieve.
 
  • #3
oy

lol
 
  • #4
https://www.physicsforums.com/attachment.php?attachmentid=60534&d=1374879190Drives Engineering handbook
https://www.physicsforums.com/attachment.php?attachmentid=54974&d=1359050037

these might help, check rotor inertia in the second article, the articles are a bit big to directly attach to PF but they are from the Rockwell knowledge base they have a comprehensive list of DC Brushless motor literature there

here is the link to their free Literature

http://literature.rockwellautomation.com/idc/groups/public/documents/webassets/browse_category.hcst

also look at their product manuals as different types of DC brushless motors have different rotor characteristics IE low inertia vs high inertia rotors. So you have to be careful what series of DC brushless motor to inertia and torque specifications you need.

you will have to create and account for their knowledge base literature but its often worth it.

Your best bet is to call them and describe your specifications, they will give you a list of recommendations
 
Last edited:
  • #5
Nice engineering handbook.
Refreshing to have equations compiled as such. Thank you.
Have bookmarked Rockwell as well.

Just have to wade through the fog here a bit...
Presently looking through inertia & power...

Cheers, Mordred
 
  • #6
no problem glad to help
 

1. What is the significance of motor rotor size in a motor?

The motor rotor size is an important factor in determining the performance and capabilities of a motor. It affects the torque, speed, and power output of the motor, as well as its efficiency and heat dissipation.

2. How does the size of the motor rotor affect the torque?

The size of the motor rotor directly affects the torque output of the motor. A larger rotor size will generally result in a higher torque output, while a smaller rotor size will result in a lower torque output. This is because a larger rotor has more surface area for the magnetic field to act on, resulting in a stronger force and therefore higher torque.

3. Is a larger motor rotor always better?

Not necessarily. While a larger motor rotor can provide higher torque and power, it also increases the weight and size of the motor. This can be a disadvantage in certain applications where space and weight are limited. It is important to consider the specific requirements and constraints of the application when selecting a motor rotor size.

4. Can the motor rotor size be changed or customized?

Yes, the motor rotor size can be customized to suit specific needs. This can be done by adjusting the number of rotor poles or by using different materials to make the rotor. However, altering the rotor size can affect the overall performance and efficiency of the motor, so it should be done carefully and with consideration.

5. What factors should be considered when selecting a motor rotor size?

When selecting a motor rotor size, factors such as the required torque and speed, available space and weight restrictions, and the type of load the motor will be driving should be taken into account. It is also important to consider the compatibility of the rotor with the rest of the motor components to ensure optimal performance and efficiency.

Similar threads

Is a Larger DC Motor Needed for Low Wind Speed Power Generation?
    • Mechanical Engineering
Replies
34
Views
2K
Induction motor rotor design features
    • Electrical Engineering
Replies
4
Views
1K
Automotive Cancelling effects on a larger brake rotor
    • Mechanical Engineering
Replies
14
Views
1K
What type of motor would have the highest Stalled Torque?
    • Mechanical Engineering
Replies
8
Views
2K
Question about magnet flux and saturation in a motor
    • Mechanical Engineering
Replies
2
Views
2K
Engineering How to calculate rotor flux of the three phase squirrel cage induction motor?
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Automotive Poor Man's Hydrostatic drive: power steering pump as motor?
    • Mechanical Engineering
Replies
19
Views
869
How to select a stepper motor and gear ratio?
    • Mechanical Engineering
Replies
2
Views
3K
How to Measure Torque Required for motor to spin a rotating shaft?
    • Mechanical Engineering
Replies
3
Views
2K
Help Walk Me Thru Motor Sizing Calculations Please
    • Mechanical Engineering
Replies
14
Views
2K

Hot Threads

Recent Insights

Back
Top