Effects of Running Higher Power through Kollmorgen Motors

knoxie

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Hello

This happened after about a week of running the Kol motor at 60V, this is quite common if you really turn the wick up on these motors, I have found a place that will make the rotor from a magnet! this would be great and would mean you can run higher rpms without the magnets flying off.

Sensible power limits still need to be adhered to of course but it would make this nice cheap little motor virtually indestructible for PA use.

See Pictures.

Knoxie
 
If all the magnet pieces are there, you might be able to glue it back on (with better glue).

How many volts were you running when it flew apart?
 
Hi Richard

Yes I was running 60V @ 35A when this one went, it didn't do any damage to the motor body as far as I can tell? I have found a place that says they can make a magnet to any shape you like! they can machine a rotor out of a Neodymium Magnet tube and cap it with some mild steel, I would also get them to key or weld the out put shaft to it, a complete one piece rotor would be ideal.

It would make the motor pretty bullet proof then, it may be possible to glue the rotors magnet pieces back on but they material itself is slightly springy, I would need to find some very high strength adhesive to do it and it would need like a filter wrench or some sort of tube compression clamp wrapped around it. I may just try it Richard.

Can anyone suggest a high strength adhesive that will stick a ceramic magnet to a steel rotor?

Cheers

Knoxie
 
I've used epoxy and also a two-part flexible polyurethane to glue magnets. Epoxy seems to work fine as long as the surfaces are roughed up with sandpaper and there are no traces of oil.
 
that looks like a neat motor to work on. you could probably buy some better magnets for it i mean the individule ones, you would have to find how many poles are in that one piece magnet and you could probably get some really good strong glue thats good under high temps and glue them on at the right angles. you could even test how strong the glue is first at a certain temp before it breaks and calculate the force the magnet will be under at the highest rpm you want and see if that glue is good enough.
 
Hi all
Knoxie said I put plates on the kolls I convert for myself, true but the main reson was 2 fold one I did not want to spend time scraping out the old controller and two since the internal controller was self contained in the lid I could use it as an emergency backup and limp home on 24 v if it was the controller that blew and the reason it blew was fixable.I use NiMh so can go down to 24 is no problem those running lipos wouldn't have this option.I would not put the lid back just use it as an external and leave it in my panier with leads going to and from it. After I had one speed controller blow on me I have always done this but never had to do it.

Knoxie I'm very interested in this new rotor you have found out about (price avalibility), do you think it could allow a koll to be pushed to 72v with the HT chain I've found it could allow a uspd based system to do some serious damage to the max wattage level in the UK eg x10 (2000 w max in UK 200w). Force cooling would be a breeze as the coils are on the outside.
 
Hi

Yes I have sent a drawing off to someone who machines magnets, they can make the rotor body from one piece, the motor drive shaft can then key keyed to fit the rotor as well, it really would make them a tough motor to break then, it may also be possible to fit new magnets or retro fit the existing ferrous magnets with new glue but I feel they would still crack.

As soon as I get a price back I will let you know, it may be a bit pricey but it would make for one reliable unit, I also had an Idea about water cooling these motors as well!! ha ha

Never throw any old motors away as you can normally always bring them back from the dead!!

Im off out for a ride its actually not raining!

Knoxie
 
they know that the rotor isnt just one big magnet right? the black one looks like it but its actualy 12 - 17 magnets alternating polarity around the circumfrence, are they able to do that with a one piece rotor?
 
dirty_d said:
they know that the rotor isnt just one big magnet right? the black one looks like it but its actualy 12 - 17 magnets alternating polarity around the circumfrence, are they able to do that with a one piece rotor?

Hi

No not on this rotor? this is a one piece magnet polar direction is the same all the way around?

Knoxie
 
the motor wouldnt be able to turn if it was north or south all the way around and there would be no point in having so many windings on the stator since there are 18 windings there should be somewhere between 12-17 poles on the rotor, a bldc with the rotor on the inside always has less poles than the number of windings in the stator, if you take a small magnet and move it around the rotor it should be attracted then repeled as you move it around, you will be able to find the numebr of poles like this.
 
also putting in new magnets can cause some problems having to do with the lines of magnetic flux not being concentrated in the hight place and complicated stuff like that, but rc airplane guys make there own motors with regular neodymium magnets so theres a good chance it will work fine. another thing is if you use stronger magnets it will change the charactaristics of the motor, with stronger magnets the K constant of the motor will be increased meaning you will get less rpms at the same voltage but more torque.
 
I've built several brushless motors for R/C airplanes using standard neodymium magnets. I used JB Weld to hold them on. They have been working very well on the 3 motors that I've made most of which are in the 12-18 turn range using 18-22AWG, 9 stators, 12 pole, outrunner configuration (magnets on outside). The biggest is in the 300W (peak) range (12V@25A) and run at about 7000rpm (peak) in use.

I've never had a motor go bad for electrical reasons. I've had a bearing freeze (not frequent enough oil) and I've bent a couple of motor shafts (crashing planes), but never burned a coil, or pulled a magnet.

One obvious difference, though, is that all my motors are outrunners and so the magnets are pushed into place by centripetal force. Still, JB Weld has always held very well for me.
 
i was wondering is there a rule to figure out the number of poles on the rotor based on the number of electromagnets on the stator for a 3-phase brushless motor with the rotor on the inside? would other numbers of poles work with the same number of electromagnets?
 
For a 3 phase brushless motor, the number of stator poles must be a multiple of 3. The rotor poles (permanent magnet part) must be an even number. There are a large number of possible valid configurations.

The Kollmorgen motor rotor has many poles, I could count them later as I have one half apart in the garage. The magnet is a single piece physically, but is magnetized with many poles. I'd guess there's 16, since that's what the BMC motor has.
 
Hi all
had to find the nimber of poles for a Koll once for a device that mesured rpm using back emf, was told to turn the rotor round one revoloution ad count the number of bumps (times it becomes more difficult to turn and then gets easier) the results was 16 this I was told would mean 16 poles.
I then set up the device and found it had a max of 14 poles in its seting so I set it to 8 and divided the number that was on the reading by 2 giving an acurate rpm of the motor to 12.5 rpm, this will only work with a high reving motor the direct drives rev too slowly for this system to be used.
 
Knoxie,

Some motors wrap the rotor with kevlar or carbon fibre to stop them bursting. I have some kevlar that would make a very good wrapping, just wind it on with some slow set Araldite, send me a PM if you would like me to send you some.
 
fechter said:
For a 3 phase brushless motor, the number of stator poles must be a multiple of 3. The rotor poles (permanent magnet part) must be an even number. There are a large number of possible valid configurations.

Thanks for the correction, Fetcher. I'd written 10 stators. It's 9. I was counting through a couple of little holes and I miscounted. They are all in planes so it's a bit hard to count. I was rotating and counting... guess I went one click too far.
 
patrick_mahoney said:
One obvious difference, though, is that all my motors are outrunners and so the magnets are pushed into place by centripetal force. Still, JB Weld has always held very well for me.


That's a HUUUGGE difference!

I was thinking of wrapping something around it like mentioned already... Or put small holes in them and use copper wiring to tie it in (pulled out of my dark spot idea, locknut style).... not sure about that

Kyle
 
I'd try some carbon fiber thread. Bet that'll hold up pretty well. Not too pricey in reasonable lengths, either.
 
knoxie said:
...I have found a place that says they can make a magnet to any shape you like!..

Picture a typical geared hub motor's gearbox:
What would happen to friction/efficiency, wear, noise if all the gear teeth were North and repelled each other..? :)

One may not even have to get fancy:
All the outer facing surfaces of the gears could be N and the inner S so the one side of a tooth was N and the other S.
As long as its put together: N-N and S-S so the teeth surfaces repel each other...
Thrust washer/bearing load and the load on the gear cage will likely increase and need to be considered.
 
I got about 50x Kollmorgen motors new in box if anyone else wants to go back in time and mess around with them…PM me 😂
 
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