Neomags on outside of regular motor for more efficiency/power?

[sloper steve]

Since the J250 does better with the Flux ring could it be possible to increase motor efficiency by placing magnets on the outside of it?

[blue_bull]

Sorry, no. Ring is for giving better flux flowback to internal magnets (to increase section of case material in order to reduce magnetic resistance. You can feel this if you remove ring and touch motor with a screwdriver. Screwdriver will be attracted to motor`s case. If you apply ring, screwdriver will be attracted less or no more(which will be best result). If you add magnets outside motor, case acts as a magnetic shield- motor doesn´t get any improvement.

Herbert

[Bob Chiang]

Hi Steve,

I had asked the same question some time ago and received the same response as Herbert provided. Which led me to the next question for which I received no public response:

http://www.rcgroups.com/forums/showthread.php?t=198212

Fifty cent motor plus several dollars of magnets might result in a nice motor that can run on an inexpensive brushed controller.

[Ron van Sommeren]

Magnets need a closed magnetic circuit. For the magnets on the inside the circuit is: magnet a -airgap b - statortooth c - statortooth d - magnet e - fluxring - magnet a.

Howevever, in the case of external magnets the circuit is:
magnet p - flux ring - neighbour magnet - air outside the motor - magnet p

1- because the path through the air is long, flux is low
2- even if that flux were high, it would have been in the wrong place, you want high flux between the magnets and the stator, in the airgap. That's were the tangential force is produced.

Met vriendelijke groeten ;) Ron
• diy outrunner discussion group (http://www.yahoogroups.com/group/lrk-torquemax)
• int. E fly-in & diy outrunner meet (http://home.hetnet.nl/~ronvans/), Nijmegen, the Netherlands -> 2005

[sloper steve]

Thats makes sense. thanks!

And replacing a Johnson or 280 motors magnets with Neodyms would work great IF you could find magnets sized and shaped the same?

Is the strength of neodyms so much higher than ferrite it may payoff to replace ferrites in a brushed motor with neos?

Just sqeezing this question in between work :)
If it is answered sorry I don't have time to find it in previous posts.

[vintage1]

Basically yes. If yo can incrase the flux density by say a factor of two, you can double the volatge at the same current and get double the power out of the beast at teh same RPM. And potnetially for the same losses, so efficiency is also a lot higher.

I keep thinking wistfully of neo magnetted IPS motors....90% of why brushless are better is that the magnets are better. The lack of brush friction is a relatively minor issue.

If you strapped magnets on outside and wrapped a flux ring from a bigger motor arund, it might work. Better is to machine up a new case to take the magnets and re-use aramature and brush gear from a cheapo can.

I'll do that one day in a dull moment.

[Ron van Sommeren]

... If you strapped magnets on outside and wrapped a flux ring from a bigger motor arund, it might work. Better is to machine up a new case to take the magnets and re-use aramature and brush gear from a cheapo can.The flux from the outer magnets would travel through the inner ring and the outer ring. In fact, the outer magnets are now magnetically 'short circuited'. The flux from the outner magnets will not flow through the stator/airgap, alas.

Groeten ;) Ron

[vintage1]

Theres always a bit of leakage Ron.

However, in general, I agree. What you need is to re-can a can with neo mags.

80% efficiency would be the target, and about twice the 'normal' power output.

[Bob Chiang]

I would think there would be some combination of thin narrow magnets that could approximate the curve of the Johnson ferrite magnets similar to the way flat plates are used in the CD motor conversions.

How do you pry open the tabs holding the brush assembly to the can of a Johnson motor? I haen't found anything that works yet.

-Bob

[sloper steve]

So we can remove the ferrites and placing in several small magnets such as 5x5x1mm magnets (http://slofly.com/index.php?category=cdparts%20magnets) glued around the curve of the can?
A 180, 280 or J250- it sounds like someone here is going to try it soon.
Just think if the bench tests showed increased thrust for the same amps :D

[vintage1]

..but increased volts to get the same amps..if you are going to try this, take the hottest wound motor you can find. .

[sloper steve]

Put the neos in the J250 here:
http://www.rcgroups.com/forums/showthread.php?t=165501&page=35&pp=15