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Discussion Starter · #1 ·
hi! ive just rewound an old johnson 111. i want to put a couple of small round samarium cobalt magnets on the sides of the can. hows the orientation, do i stick the cobalts together pull them apart then stick them on the cans, or do i have them repelling each other and then stick them on the cans that way or third do i stick them on with one atracting and one repelling. thanks in advance. john.
 

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I seriously doubt that you will get an increase in magnetic flux in the air gap as a result of this. Normally the return path for magnetic field lines is through the outside of the can. Mounting magnets externally you will have the return path for the mag lines now going through air for a large proportion of the time. Try it Id be interested in finding out if it yields an improvement.

cheers
rick1776
 

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You may get an increase in RPM, just tried it. However the torque fell significantly. I suspect the mag flux lines are severly distorted with the addition of the external magnets.

cheers
rick1776
 

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Discussion Starter · #6 ·
hi rick, what rewind did you use. i rewound 100t of 30 swg, havent tried it on the rpm checker yet. im just rewinding a hornet arm to go in a superwasp with shorted windings 50t with 30 swg. john.
 

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QUOTE (stoner @ 11 Jul 2011, 04:53) <{POST_SNAPBACK}>hi rick, what rewind did you use. i rewound 100t of 30 swg, havent tried it on the rpm checker yet. im just rewinding a hornet arm to go in a superwasp with shorted windings 50t with 30 swg. john.
III cans used to be quite popular with cobalt magnets fitted inside the can (as with all can magnets, they worked best fitting so the magnet gap to the arm was constant)
Magnets inside the can are the way to go, extra magnets on the outside can be expected to produce much inferior results.
To run hotter arms it was normal to discard the standard lll brush gear and replace it with something more suited to the higher current.

QUOTE (rick1776 @ 11 Jul 2011, 04:09) <{POST_SNAPBACK}>You may get an increase in RPM, just tried it. However the torque fell significantly. I suspect the mag flux lines are severly distorted with the addition of the external magnets.

cheers
rick1776
A stronger magnetic field gives more torque and less free running rpm.
Reducing the magnetic field round the arm will give increase in RPM and less torque.
If you are putting the cobalt magnets outside the can in addition to the feeble standard magnets, if the cobalts attract to the side of the can it'll probably reduce the magnetic field round the arm and if the cobalts repel the side of the can it'll probably increase the magnetic field round the arm
Sounds like your experiment has reduced the magnetic field round the arm.
 

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QUOTE (john's slotracing @ 11 Jul 2011, 11:10) <{POST_SNAPBACK}>III cans used to be quite popular with cobalt magnets fitted inside the can (as with all can magnets, they worked best fitting so the magnet gap to the arm was constant)
Magnets inside the can are the way to go, extra magnets on the outside can be expected to produce much inferior results.
To run hotter arms it was normal to discard the standard lll brush gear and replace it with something more suited to the higher current.

A stronger magnetic field gives more torque and less free running rpm.
Reducing the magnetic field round the arm will give increase in RPM and less torque.
If you are putting the cobalt magnets outside the can in addition to the feeble standard magnets, if the cobalts attract to the side of the can it'll probably reduce the magnetic field round the arm and if the cobalts repel the side of the can it'll probably increase the magnetic field round the arm
Sounds like your experiment has reduced the magnetic field round the arm.

I suspect that I am getting a very small (cross sectional) effective magnetic field with the externally mounted button magnets. The mag field lines are now basically the width of the button magnet and not the height and length of the can. RPM went up significantly, measured with an optical tacho but stall torque was severley reduced. This was on a std scaly mabuchi with 2 button mags placed centrally on the outside of the can. Weird thing was that the button mags stuck no matter which way around!! One orientation produced a small decrease in RPM the other orientation almost doubled the rpm. This was at 6V. I didnt measure the stall torque for the decreased RPM only for the increased rpm orientation. Torque was reduced from about 95gcm to about 33gcm.

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rick1776
 

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Magnets outside the can isn't an ideal solution, but if it is the only practical option to give you a bit more power, it does work.

We used to do it a lot when we were racing with plastic track, and wanted more power from a standard fitted motor

From memory, just clamping them on how they felt like it (opposing surface poles attract), you get more revs, less torque in a crude sense. reversing one or both of them, and taping them in place to stop them springing away produced less revs, more torque.

You'll feel it as you turn the armature by hand with the motor out of the car.
I recall a certain Ninco Mosler with about 8 magnets holding it on the track, over a Kg of downforce, and I think the NC-6 had about 3 extra sets on the outside. Which was okay untiul it deslotted and attempted to simultaneously self destruct, bore through the barrier walls, the garage wall lining and to impale marshals and any small children within range.

NC-6s are ther "Vanguard 6" motor of the slot car world LOL; lazy, lumbering, and mostly indestructible.
 

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QUOTE (rick1776 @ 11 Jul 2011, 12:43) <{POST_SNAPBACK}>I suspect that I am getting a very small (cross sectional) effective magnetic field with the externally mounted button magnets. The mag field lines are now basically the width of the button magnet and not the height and length of the can. RPM went up significantly, measured with an optical tacho but stall torque was severley reduced. This was on a std scaly mabuchi with 2 button mags placed centrally on the outside of the can. Weird thing was that the button mags stuck no matter which way around!! One orientation produced a small decrease in RPM the other orientation almost doubled the rpm. This was at 6V. I didnt measure the stall torque for the decreased RPM only for the increased rpm orientation. Torque was reduced from about 95gcm to about 33gcm.

cheers
rick1776
Guess it must be doing something very weird to the magnetic field to produce that effect.
Weird thing was that the button mags stuck no matter which way around!! Yeh that justifies several exclamation marks.
Rare earth button magnets are way stronger than the original Johnson 111 ones - maybe they are so much stronger they can locally reverse the field in the 111 mags - which just might explain how the button magnets can attract both ways.

Reducing torque from about 95gcm to about 33gcm is a huge reduction, those button mags must be doing the magnetic field round the arm a whole load of no good.

QUOTE (slotcrazy @ 11 Jul 2011, 13:43) <{POST_SNAPBACK}>Magnets outside the can isn't an ideal solution,
Masterpiece of understatement!
There are so many better ways of increasing motor performance.
 

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Discussion Starter · #12 ·
hi eddie, typo 100t of 36 awg. the magnets are round 3mm by 5mm tall about £4 for 10. the cheapest neodymium proper shaped mags are about a tenner with p&p, as for samarium cobolt your talking lots of money and you only need those for qualifying a wing car, eurosport and drag raceing. well out of my price range or needs, i was just looking at pepping up weak mags.what would the result be if i drilled through the can and mag and inserted the cobolts flush with the id. i could regain a bit of torque by reducing the air gap. keep the explanations comeing i find it very interesting. thanks john.
 

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Discussion Starter · #13 ·
hi 300slr, just read your post. what are the better ways of increasing motor perfomance other than blueprinting it,very cryptic, now you have got my curiosity really going. regards john.
 

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QUOTE (stoner @ 11 Jul 2011, 16:48) <{POST_SNAPBACK}>hi 300slr, just read your post. what are the better ways of increasing motor perfomance other than blueprinting it,very cryptic, now you have got my curiosity really going. regards john.
At the Johnson 111 end of the performance spectrum there are plenty of replacement motors available for under £10 that have a higher spec, - check out the Scale Auto range. If that's sort of power your cars need, then I wouldn't bother tuning an existing low end motor.

Most things about a motor make a differance to performance, for example (in no particular order)
Armature - wind, lamination thickness, trued stack, trued comm, balance, comm timing, straight shaft
Magnets - strength, shape, magnet gap
Brush gear - spring tension, alignment, brush material
Can - alignment of bearings, quality of bearings

Just picking out one or two of those probably won't help much, often several have to be done together.

QUOTE (stoner @ 11 Jul 2011, 16:34) <{POST_SNAPBACK}>hi eddie, typo 100t of 36 awg. the magnets are round 3mm by 5mm tall about £4 for 10. the cheapest neodymium proper shaped mags are about a tenner with p&p, as for samarium cobolt your talking lots of money and you only need those for qualifying a wing car, eurosport and drag raceing. well out of my price range or needs, i was just looking at pepping up weak mags.what would the result be if i drilled through the can and mag and inserted the cobolts flush with the id. i could regain a bit of torque by reducing the air gap. keep the explanations comeing i find it very interesting. thanks john.
Gotta wonder if you've got another typo or two in there, you seem to be saying cobalts are way out of your price range then describe how you are going to fit them.
 

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QUOTE (stoner @ 11 Jul 2011, 16:34) <{POST_SNAPBACK}>hi eddie, typo 100t of 36 awg. the magnets are round 3mm by 5mm tall about £4 for 10. the cheapest neodymium proper shaped mags are about a tenner with p&p, as for samarium cobolt your talking lots of money and you only need those for qualifying a wing car, eurosport and drag raceing. well out of my price range or needs, i was just looking at pepping up weak mags.what would the result be if i drilled through the can and mag and inserted the cobolts flush with the id. i could regain a bit of torque by reducing the air gap. keep the explanations comeing i find it very interesting. thanks john.

From memeory and without going into the shed to and looking at one I think the old JohnsonIII motors had the mags aligned so that the armature butted hard up against the can end bearings. Remove the brushes and spin the arm by hand. Which end does the arm butt up against? If its the can end then move the magntes about 0.5mm towards the endbell end. Repeat this until you have the arm centrally located so that it is not bvutting hard up against the bearings. Add washers to take up the slack.

You might try and place some mild steel shims behind the mags to reduce the air gap. This should give you slightly better torque at the expense of some rpm. Make sure the material is "magnetic" though. You should be able to fit 0.2-0.3mm thick shims. Of course you could argue that its not worth the effort given its a Johnson youre trying to extract extra performance out of.

cheers
rick1776
 

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Discussion Starter · #16 ·
hi rick, ive got a ton of 111 motors theve got outer brush gear easy to up grade . all the ones you mentioned have got the standard closed can mabuchi blob of carbon on a steel-brass?arm and you have to disassemble the can to clean the com properly. i allready discussed closing the airgap. ive read several articles on 40000 rpm johnson111 that dont sacrifice much torque for this tune. if you read my post ive got 10 samarium cobolt 3mm round by 5mm long for £4 i didnt say any thing about the samarium cobolt- can- mags, just how expensive they were. so its only the one typo, let me ask you this why do you bother to scratch build bodies when you can buy ninco scalextic etc bodies that look so much better, paint, tampo, detail and then you can scratchbuild a chassis to make them run better. is it satisfaction in creating and running something youve built yourself. because thats the same as me. thanks for tip abought centering arm. im after knowledge from people who,ve done it or cleverer people than me who explain why you cant do it. i,d prefer constructive criticision to nit picking, you never stop learning and no matter how silly it seems to some people i,d rather ask. love you all, john.
 

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Hey dont get me wrong John. Go for it. An old trick from the 60s was to put the can in a vice and gentley squeeze it. This would close down the air gap and give ypu some extra torque. Be careful though.

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rick1776
 

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Discussion Starter · #18 ·
hi guys, i dont fully understand the flux lines using the can as a path. strap motors have no can to speak of, so back to , would drilling through can and mag inserting the the cobolts inside the mag, or would it be better to use full mag length flat neos on the outer can. thanks john.
 

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QUOTE (stoner @ 14 Jul 2011, 11:15) <{POST_SNAPBACK}>hi guys, i dont fully understand the flux lines using the can as a path. strap motors have no can to speak of, so back to , would drilling through can and mag inserting the the cobolts inside the mag, or would it be better to use full mag length flat neos on the outer can. thanks john.
In strap motors the main function of the "can" is to hold the other bits of the motor in place sufficiently rigidly. The "can" makes little differance to the flux lines from the samarium cobalt magnets.
Samarium cobalt and other rare earth magnets are much stronger than the ordinary ceramic magnets fitted to the lower cost motors. Modern C can motors (with ordinary ceramic magnet) have the can extensively cut away such that it can no longer make much differance to the flux line. The light weight and extra cooling seems to be more important than any extra magnetism a "full" can might contribute.

Magnet gaps are important. Looking up the sizes of magnet hone that suppliers produce give a good idea of what magnet gaps motor builders want. The typical range (each side) is from about 0.15mm to 0.4mm. To answer your question, cobalt magnets outside the can is way to far away, they'd work much better inside the can, and better still honed to give a suitable constant magnet gap.
 

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Discussion Starter · #20 ·
hi 300slr, i cant afford to put cobolt or neo can mags in, so would drilling through the can and mag and inserting the cobolts flush with the outer edges of the original mags leaving a slight deppresion in the middle of the tiny cobolts do any good. i see the older builders useing a neo across the back of the old triang ect motor for a little help for tired magnets, so in reality will any of my sugested thoughts work. the cobalt mags have slightly less magnetism than neos , but they handle a higher heat tolerance than neo,s which go kaput over 200c. or if any body really doesn,t know i,ll take any informed guess work as a start point. thanks all. john.
 
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