14 replies to this topic

[havlicek]

I got a PM about spacing armatures, and since it took the equivalent of the Mayberry phone book to answer it, I figured I may as well copy/paste it here:

Ideally, you want as little extra space as possible without the armature binding.  When the motor is assembled and before the brushes are installed, the armature should spin freely with as little extra slop as possible.

***The idea here is to space the armature so that it sits exactly back and forth where the magnets "want" it to sit.  Here's a procedure:

1)Install the armature in the setup (can and end bell)...just by holding the end bell in place, and give the arm a spin.  After that, lightly press the arm from the commutator end to see how far towards the back of the can it can move from where it stopped after spinning.

2)Estimate how many spacers it will take to fill the extra space at the tail end of the armature, add those to the armature and reinstall it.  If there is still some space, add some more spacers.  If the armature seems like it doesn't need any more spacers...remove one to make sure you haven't overcompensated and added too many spacers.  Do this until the armature rests after spinning with almost no extra space at the tail end.  There are some very thin spacers available...down to .003" if you really want to be anal about all this (*and it's a good thing to be as accurate with spacing the arm as you can be).

3)Once you're confident you have the tail end spaced, start adding spacers to the com end of the armature until you have as close to zero slop as you can come.  If you don't have the right combination of spacers, there are tools available so you can slightly shorten the armature's tail spacer tube...or even the top of the commutator (*on some commutators...some vintage ones shouldn't be shortened).  That way you can fine tune things and be able to add that last spacer that would have bound up the armature.

***The idea here is to have the armature "floating" or being held by the spacers in exactly the same position it would be in if only drawn there by the force of the magnets...BUT without binding the arm.  A little slop is MUCH better than some binding, but the faster the motor, the more important it is to properly space and center the arm.

***On some older motors and some newer ones too, if there's a bit of shaft sticking out of the end bell, and the arm is slightly bound after assembly, you can hold the motor with the end bell shaft pointing down over a hard surface and tap the motor/shaft against the hard surface.     This can open up some space by either slightly bending the can end bearing strap outward or "cupping" the tail spacers to fit the can bushing/bearing.  It may seem brutish and crude (*and should only be done with care), but it will work and should be fine if you don't over-do it.

***It can happen with some motors that either the can or the end bell bushing isn't fully seated.  This is a pretty frequent thing with the current "minican" motors as the end bell bushings aren't held very well by the plastic.  Giving the arm a *light* tap on the can end (flipping the motor overt from the above) of the shaft will confirm that the end bell bushing is fully seated IF YOU FORGOT TO CHECK WHEN THE MOTOR WAS BEING ASSEMBLED. 

***On vintage 16D and 26D Mabuchis with the factory ball bearings, NEVER do the "tap" thing.  These ball bearings have no inner race and the outside flanged metal is *really* soft/fragile.  You're likely to ruin them by doing this.  It's really not a good idea even on modern bearings either, and only should be done (*if necessary and you're used to doing it) with bushings/oilites.

[Robert BG]

Great post John,thanks for sharing.

  If you happen to have meat hooks instead of hands like myself   To make it easier you can use a old pinion that's been unsoldered to help get a good spin on the arm.The little bit of solder usually makes it a nice friction fit and while they make a tool for this.I have one but prefer the old pinion.

[havlicek]

Hi Robert,

     Sure, anything that helps to spin the arm is a good idea.  I don't usually have much trouble doing this except for some motors with extraordinarily strong magnets.  With those motors, it can be hard just to figure where the arm needs to be for it to be centered because the magnets are holding the armature so strongly.

[Robert BG]

I definitely should've mentioned its generally helpful on the stuff with strong mags,but I'm a bit of a scatter brain at times

[Phil Smith]

In the '80s I had a Hi-Pro can and one really fast I15 arm. It was a deadly combo. I raced it for 3 races before rebuilding it. It would eventually develop a lot of side play because the spacer washers would wear. And often the can bushing would be worn and sloppy too, because the arm was a bit pitted in that area. In spite of this it didn't slow down at all. It was still a rocket. Because of this I've never fretted too much over centering and endplay. Not saying it doesn't make a difference, but it didn't seem to on that motor.

[Bill from NH]

Hi-Pro was Walt Labree, a Pratt-Whitney Aircraft machinist out of CT, now retired to FL.

[havlicek]

In the '80s I had a Hi-Pro can and one really fast I15 arm. It was a deadly combo. I raced it for 3 races before rebuilding it. It would eventually develop a lot of side play because the spacer washers would wear. And often the can bushing would be worn and sloppy too, because the arm was a bit pitted in that area. In spite of this it didn't slow down at all. It was still a rocket. Because of this I've never fretted too much over centering and endplay. Not saying it doesn't make a difference, but it didn't seem to on that motor.

 

 

It matters on ALL motors to some extent Phil (*but you already said that!  ).  The faster a motor is, the more it will matter.  How much it matters also depends how strong the magnets are.  Of course, on less critical motors, you can be off a little and likely not notice anything particularly worrisome.  Besides, just reducing friction (*as would increase if the arm is running "against" either end of the setup, it can also matter (*excessive end play) in how the brushes wear against the com, and even mess with a good gear mesh in sidewinder and anglewinder cars...even inlines!

[Richard G With]

Wondering about the effect of angled opinions and spurs? Sealed motors end play can be adjusted by the tapping method, and the RETRO Big Dog motors can be opened and made more precise. But what about the axial thrust caused by the gears?

[havlicek]

Wondering about the effect of angled opinions and spurs? Sealed motors end play can be adjusted by the tapping method, and the RETRO Big Dog motors can be opened and made more precise. But what about the axial thrust caused by the gears?

 

 

Good arm spacing has nothing to do with that, and the above remains the same regardless of whether the motor goes into a sidewinder, an anglewinder or an inline.

[Slot-Racer]

John, nice article that is how I do it, and your steps should be sticky noted.

 

I think what Richard is referring to is when angled gears are used. I've experienced this. Being offset, they are at an angle (of course) and can bind too if they are installed too far in or too far out cause they are not perfectly straight and armature play does add to this. Proper armature spacing would eliminate that when installing the motor and setting the gear mesh initially. 

 

If the motor pinion and spur are aligned, then no there is no effect using straight gears for example as there is no angle between the gears. If you look at angled gears they are taller on one side and shorter on the other. Improperly set, they can bind but if you can get a sweet spot and the motor arm has just the right about of play you can use that angle without any binding.

[havlicek]

John, nice article that is how I do it, and your steps should be sticky noted.

 

I think what Richard is referring to is when angled gears are used. I've experienced this. Being offset, they are at an angle (of course) and can bind too if they are installed too far in or too far out cause they are not perfectly straight and armature play does add to this. Proper armature spacing would eliminate that when installing the motor and setting the gear mesh initially. 

 

If the motor pinion and spur are aligned, then no there is no effect using straight gears for example as there is no angle between the gears. If you look at angled gears they are taller on one side and shorter on the other. Improperly set, they can bind but if you can get a sweet spot and the motor arm has just the right about of play you can use that angle without any binding.

 

Hi Mario...yes...and no.    Really, spacing an armature is only relevant to the motor alone, aside from any chassis considerations.  It may be that some people will space an armature differently for a motor destined for say an inline than they would for a sidewinder, or an anglewinder.  To me, that doesn't make sense...but that's what's cool about all this stuff, "horses for courses". 

[Kim Lander]

Love your articles John...brings back old times when building motors was the thing....with the sealed motors now its almost an art gone south. Somthing else that factors in is whether you have a GOOD EVEN wind on all three poles, inconsistant winds will give strange magnetic fields(your winds DO NOT have that problem), so when the electricity is applied you get mag field to mag field reaction which can make the arm move into another position completely different than  when set without current , that screws up all the spacer work to heck, hahahaha    its what makes motor building so much fun. Love your work and reports.....Kim

[havlicek]

Hi Kim...and thanks!

Of course motor building isn't much of a thing with sealed motor racing, and those who ARE "building" those motors probably aren't exactly advertising.    Still, there's a heckuva lot of motor building going on in group and drag racing and of course with the super high-end stuff and among the vintage crowd also!  The open and eurosport/flat track guys build motors to beyond NASA spec routinely!

[Benno - SAC]

Hi John,

I am always wondering, how much the arm will grow during heating up.
If the slop is too small, the arm will bind after heating up maybe.
Do you have any experience with this?

[havlicek]

Hi John,

I am always wondering, how much the arm will grow during heating up.
If the slop is too small, the arm will bind after heating up maybe.
Do you have any experience with this?

 

Hi Benno,

     Since most of the heat is at the commutator, I guess it's possible that end of the arm (not the shaft) can grow/expand lengthwise on the more extreme arms.  It must be negligibly small though, if it happens at all, because I've never heard of anyone spacing arms slightly loose to take this into account.  Interesting question though!  I'd like to see someone who knows chime in on this for sure.