My 13t maxx cobalt,has been running uneven @ half throttle for some time.Today it will not start without moving the prop.Always it happens in the same position.
I guess I have a bad winding.Is it able to be fixed.Or is a new brushless in my future?

Sounds like your comm is dirty, which would require disassembly and cleaning.
Or if you want to dump some coin in to it, get the comm turned and a new set of brushes.

already took it apart.The comp was pretty clean.Then I sprayed it down with electronic cleaner.Still same problem!

Wow, I would of thought for sure it was a brush to comm contact fault. If I recall, the 13 turn has some pretty heavy windings, don't they ? Burn out possible I guess if it got really, really hot.

Maybe a busted solder joint ?

ensure there is no shorting between commutator contacts with a meter

Hi Budd,

It maybe one of the windings. That would make it not start in one particular place.

If this is the case you can rewind it!!
Heat the tabs that hold the wire down to the comm with a flame (lighter etc) until you see the blue colour start to appear. Quickly dunk in water as you don't want to over heat the comm. You can now lift the edge of the tab with a small screwdriver and remove the wire. DON"T BREAK THE TAB!! Count the number of windings and the gauge and rewind the motor. Just bend the tab back when you are finnished (make sure to remove the varnish where the tabs are).

I just finished rewinding a speed 480BB race and it got a few Neo magnets for good luck. It goes fantastic!!

Best of luck
Phil

I've had one of these that had so much solder in the shunt (that's the woven wire that runs to the brush from the power terminal) that the brush would hang up in it's holder from the stiffness. The behaviour was much like what you described, budd. I've been too busy to pester Maxx about spare brushes. I was unable to fix the original one, so the motor is in the junk drawer for now, but a new brush would make it good as new again.

PDK - where did you find Neo magnets that will fit a Graupner 480????

Thanks all! already replaced the motor with one of my many can motors laying around.Almost runs as good, but better duration.I may play with the rewind. but really wanted a excuse for getting a brushless. After i burn up all my can motors.

Hi uscra112,

One of our local suppliers has 25x9x3mm block magnets. There are 6 of these in a motor (instead of the two semicircle ones).

I got them from Magnetic Force but I would try Here next time (I would ge the high temp ones as well).

Changing the magnets changes the motor dramaticaly and you may have to rewind the armature to get the motor you are after.

Enjoy!!!

Phil

Hooo Boy! New life for all those ferrite 480s I bought when I didn't know better!

You lay three of these long magnets in to replace each semicircle magnet? Do you glue them in with epoxy, or what?

Is the 25x9x3 specifically required for the 480 motor? I didn't see that exact size on the engconcepts website, although he's listing similar sizes as being suitable for outrunner motors. Haven't gone through the Magetic Force site yet. 'Course I'm in the US so I ought to troll the stateside suppliers.

Good job to figure this one out, laddie !

Also a Phil

I fixed my motor.one of the 5 spots on the comm was dead. I lifted the tab that holds the wire.Cleaned it real good,bent the tab back down.And the motor works again and much smoother.I will flow some solder in it later to keep it clean.

Hi,

Good job Budd, glad you are flying again.

Yes three side by side for each semicircle magnet. Just make sure that all the magnets on one side are the same way eg, north facing in and the other set of 3 the other way eg, south. When you get the magnets, stack them all together (they will sort themselves out) and mark the top face of each magnet. Then just make sure that one group of three has the mark visible and the other not.
To fix the magnets I put the outside magnets of a group in the can (they will repel each other). Then wrap the third in plastic food wrap (to stop the CA sticking to it) and put it between the outer magnets but up the wrong way. This will attract the outer magnets to it. Tack the outer magnets with CA and remove the middle one. remove the wrapping and put back in the right way up (more CA). Then repeat with the other side. To finnish off I use some good 24 hr epoxy around the outside of the magnets. I have also used polyester fibreglassing resin thickened with talcum powder which also works well.

The 25x9x3mm magnets seem to be a perfect fit, nice and close to the armature and takes up a similar radius to the ferrite ones. I e-mailed George at engconcepts last year about getting some magnets for my first outrunner, and he said that he could get them (or have them made) any size. He said that custom sizes are not more expensive and I could expect to pay about the same as a similar sized "standard" magnet. I would e-mail him and see!!. Go for the "SH" high temp ones though. I don't know how much difference in performance there would be between the N45 and N40 grades (the N40 are much cheaper) but my guess is not a great deal.

Remember the motor will be very "Hot" after you put new magnets in you may have to rewind (which is not hard) just don't break the tabs
I used 40 turns of .4mm. The motor is quite "cool" power wise ie, high torque and it turns a 8x4 slim prop at 11 amps on 8 cells and will replace my geared 400 (weighs the same no GB noise!!!). I have not used the high temp magnets so I don't want to use it for high power.
If i can get my camera working i will post a pic or two.
Good luck.

Phil

Good description of a clever technique - I will have to try this out after Xmas is over.

I was going to ask about the way the stronger magnets affect the performance parameters. I should try it first with a mild armature, not the 4.8v 4800BB race, huh? My intent would be to get a "cool" setup also, to power some future scale projects. One would have a pair with 3:1 belt drives and 10x7 three-bladers. This works now, what I'd be looking for would be higher efficiency, not more raw power.

Is that 40 turns per pole?

Wonder if George could make drop-in semicirculars? Nah, if the bars work, why bother. . . .

Hi uscra112,
The 480bb race winding would be ok if you planed to use something like a 2x1 inch prop!!!!!!!

Yes it was 40 turns per pole. Three poles. I should have noted that it is a good idea to put a bit of the epoxy on the windings as well.

If you are gearing your motors you can go for a hotter wind (because the gearing reduces the load). Efficiency goes up (and torque down) with the hotter winds, while torque increases with the cooler winds.

Should be fun working out what will work best for you. While testing your winds I would recomend NOT folding the comm tabs back down until you are happy with the motor. Just make sure the wire is tight around the tab. You can run the motor like this for a short time.

Good luck
Phil

Thanks for the info.

I'm quite familiar with the business of motor parameters and the correlations to performance, although I'm just a greasy mechanical penguineer and not an electrischer. And I almost never run any motor DD anymore, except outrunners.

What I'm excited about is the prospect of having a boxful of useful rare-earth motors instead of a boxful of well-made but wimpy ferrite 480s. I've been playing with some of the commercial "400-size" cobalts, and find them as useful as brushless when properly geared. They aren't quite as efficient, but what with these new high-current LiPos and NiMH cells, they no longer require unacceptably heavy batteries. But the selection of winds is limited, and they're still 50 bucks apiece. I can rework a half-dozen 480s for 50 bucks.

I'll start with your 40T formula and see how it goes.

Have you had any armature balance problems?