Trying to understand the Perendev motor

by Jason Owens.
I have been studying the Perendev motor lately to see just how they have the offsets set up on the main wheel. I was also looking at some diagrams Dan made of the offsets and I finally figured out exactly how they did it. I took a clip from the flash video and the video of the working model and I could see just how the offsets were made by doing a cheap line test.


Danís idea came pretty close but from my observations, the distance between the offsets is one magnet width as opposed to half the width like in the diagram. What I did next was make a simple animation that I could study to see just how they accomplished the off balanced effect in the motor:
[Simulating]

I attached the animation to this e-mail so you can look at it but I can see clearly here how the balancing effect is happening. From this idea, I figured out a way to modify my original tri-phase designs so that these three-phase offsets can be applied. I simply segmented the stator magnets up into three sections (to represent the offsets of the three wheels on the Perendev) and I got this final layout:
[Simulating]

This here is also an animation that I attached to the e-mail for you to look at. It basically has the same three offsets as the Perendev motor and beautifully accomplishes the unbalanced effect. As far as I can see, the magnets on two of the stator sets are always helping the third one enter a line up, then the phase shifts and two different stator sets help a third one line up again; and itís all seamless too! I know that this diagram looks like an earlier model that I made but this one appears to actually work just from looking at the simulation animation.


It appears that the motor will cog when the lines of flux are at a maximum density. Besides tracing out the magnetic lines have you done any calculations on the forces?
You can do this by differentiating the energy in the magnetic cicuit.

Georg


Hi Georg,
Unfortunately, I really donít have any means to test the amount of force that the magnets have on each other. I have Maxwell 3D magnet analysis software and I heard that can be used for force analysis but I really donít have any background in the theory and the math necessary to use it. The only calculations (if you want to call them that) that Iíve done was to organize the geometry of the rotors so that they are offset, but I really didnít do anything more high tech than eyeing the picture to see if it looked ok. How do you calculate the amount of force acting on each magnet exactly? Knowing this would take much of the guesswork out of my designs. I really have no idea if it will work until I can bench test it. I did manage to build a rough prototype (which I will be posting picture of soon) but it didnít work mainly because I didnít cut the pieces out exact enough for them to line up like they needed to, but I also noticed the cogging problem you mentioned. Iím still confident that the tri-phase concept works; I just need to design a configuration that will work with it. What do you think about the whole design concept in general? The main idea is to always have two magnets helping to push one magnet past the sticky spot. Iím beginning to wonder if I even need to angle the magnets on the wheel for this to work. But the angles, spacing, size of the wheel, and number of magnets are the variables I have to work with. However, it would be invaluable if I could find a way to simulate the forces that all the magnets exert on each other. If I can do that on the computer, then I wouldnít need to do so many bench tests. What do you think



Some calculations:

Let O be the centre of the field.
Clearly, the angle OAB is equal to the angle OAC. Let the magnitude of AOC be x radians.
Thus, the overlapping area will be a circle sector with radius R and angle 2x (yellow),
plus two circle segments (pink) from a circle of radius r, cut off by the chords AB and AC respectively.



Now, the area of the circle sector is:

The area of each circle segment is: a sector of a circle minus a triangle.




This drawing shows that the angle 2x is 120 degrees and that is equal to 120 * (3.1428/180) = 2.095

Radius = 1 inch /2 = 0.5 inch





The area of the circle sector is: R * R * x = 0.5 * 0.5 * 1.047 = 0,26175

The area of one segment is: the area of the sector / 2 minus the area of the triangle =
(0,26175/2) - (0,5*0,5/2) = 0,130875 - 0,125 = 0,005875

The area of the overlapped area is 0,26175 + 0,005875 + 0,005875 = 0,2735
The area of one complete circle = 3.1428 * 0.5 * 0.5 = 0,7857



Answer on the first question: What is the area of the red that is outside the white circle.
That is the area of a complete circle minus the area of the overlapped area =
0,7857 - 0,2735 = 0,5122 square Inches

Answer on the second question: What is the area of the red that is inside the white circle.
That is the overlapped area =
0,2735 square Inches

Answer on the third question: What is the ratio of the first area to the second area:
That is 5122 : 2735 =
1,873 : 1    or    1 : 0,534