339 replies to this topic

[havlicek]

PM sent Marty

 

-john

[Hermit #1]

 Every once in a while, I'll go down to "the dungeon" and start looking at parts for inspiration. 
<SNIP>
That way, even though it's so incorrect on the inside it would make a purist cry, it'll at least look the part on the outside  Anywho, this one oughtta really dim the lights in Fresno, since it's a #28 double wind!  So that's my story and...oh yeah...here's a super secret spy photo.  

 

 

-john

John:

Since this is one of the old low-profile B cans, did you have to bore/hone/relieve the inside of the top/bottom of the can to clear the large diameter blank?  MURA ended up cutting the inside of the cans to better clear then-standard .510 dia. arms - I'd think a .560 dia. arm would actually hit the inside fo an unrelieved can.  Or did I misinterpret your ".560 x 460" dimensions, and the arm is actually .460 dia.?

I didn't find any follow-up posts regarding this project - I'd be interested in hearing how it came out.

Cheers!

[Bill from NH]

I think that's a Mura A-can rather than a 'B'.

[SlotStox#53]

I think that's a Mura A-can rather than a 'B'.

Sure looks like it to me, Bill.   I think that motor John finished and sold either on ePay or was in the last motor auction on here.

[havlicek]

Yes...it's the Mura "A" as Philippe tagged them...a Mura "D"-sized motor.  As for how it turned out, it's a deadly missile of course (    ), but has been sold.  Of course, being a "D" sized motor, the very strong Parma magnets are pretty much a drop-in and a good match for such a hot wind.

 

-john

[Hermit #1]

     Every once in a while, I'll go down to "the dungeon" and start looking at parts for inspiration.  Sometimes it's for a "more or less" correct project, sometimes it's for one of those "well, if I cut this and sand that, I might be able to fit the other doohickeys to the whatchamacallit" projects and sometimes it's for one of my "I don't give a dang" projects.  So last week, I found a pretty nice Mura "B" can with a butchered end bell.  The can got stripped and flattened, and I installed a nifty ball bearing in it rather than replacing the *REALLY* worn bushing, but the end bell's screw holes were all stripped and there was no hardware!?  Since Mura C hardware will fit (I know...the period police will gasp!), a running motor could easily be fashioned, but it would have to be an "I don't give a dang" motor.

    So, after staring at the pieces for a while, I started to look for some nice magnets and I do have some...BUT...I also started staring at some D-motor magnets which are PLENTY strong and sort of a good fit (actually...a little too tight with the thin metal "clips" normally used with those).  My demented brain (or what's left of it) started considering options and I came up with the formula: B+D+BDA/KDW= NP (B motor + D magnets + Big Diameter Arm divided by some Krazee Double Wind = New Project).  So I sez to myself..."self, make an arm and do a fairly stooooopid double wind, then stuff that thing in the B".  Being totally oblivious to the concerns regarding the B motor's proclivity for getting into BBQ territory, I dun-did me a #27 double wind on the .560" x .460" blank I cobbled together for this "I don't give a dang" project.

O.K. John, 'ya fooled me!  Next time I'll look at the picture more closely - thanks to all who pointed out the error
Now that .560 arm diameter makes more sense ...

So John, just how would you get a .560 dia. arm into a MURA "B" can - if you had to?

P.S.  I'd just finished reading all 120 pages of "Arm Winding #1" plus all of "Arm Winding #2" to date, so I was a little dazed and cross-eyed.  What a monumental collection of worthy info - amazing!

[havlicek]

Hi Dave,

 

     I don't think it's possible to get a .560" diameter arm in a Mura B.  I think the inside height dimension is smaller than the arm OD and to make things even more difficult, the magnets with the correct arc segment to match the arm's OD would be too tall.  I'd have to check and recheck all the dimensions but, aside from basically turning the B into a very large strap motor (and there'd be no real point in doing so), I don't think it's do-able.  Sure, the magnets could always be machined down and the can holes made MUCH larger, completely removing the can flats at the end bell so the arm could be inserted, but I'd hate to wreck such a nice motor as a B.

 

     Thanks for reading the"Arm-Winding" threads too.  I'd hate to think I posted all that and nobody looked!  It's been a long road since I decided to get back into rewinding/winding.  Of course, I never got so deep into all this as a kid.  We basically just rewound Mabuchis and whatever else we could figure out how to destroy...er..."modify" and hopefully put back together and get to work a little.  I found myself caught up the further in I went because I'm a "tweaker" by nature.  I was also spurred on because:

1)Motor work, one of THE most basic parts of the hobby seems to have completely disappeared (except in the higher classes) with cheap disposable Chinese motors being available.
2)Some routinely asked me "what's the point?" which, to this day confounds me when the whole purpose of the hobby is tinkering

3)Some also make the point that they actually prefer slower motors and racing which is fine (and why classes in all kinds of racing will allow different levels of speed and budget).  This of course ignores the whole point of "tinkering" and the reward of feeling good about making something with your hands.

    I still get a fair number of messages from people about all this, but gathering all the information I could, as well as trying and failing until things began to work has been...to put it mildly...ridiculous.  Anyway, people such as yourself who have done this stuff can certainly dig in as the basics haven't changed (because they're based on physics).  Even people who have no experience but enjoy tinkering and are willing to dive in can find a lot of enjoyment and ultimately...satisfaction in all this.  ***We (meaning slot racers) used to do it all, scratchbuilding chassis, winding motors (or at least tearing them apart and building them to a higher standard) and painting bodies.  I never got used to the idea that you just bought stuff and assembled these, OR just purchased a complete R2R unless you were just starting out.  Even then, you put that new R2R on the track and got lapped many times and you immediately wanted to "make it go faster"!  THAT was what I grew to know slots was all about, and it also drove the retail aspect for the track owners who were more than pleased to sell lots of parts, including arm blanks and coms

 

-john

[Bill from NH]

If you cut that B-can to make it a strap can, the .560 dia. arm might fit, but probably it would drag on the track too.

[havlicek]

So it's getting cooler and there's a slight chill in the air.  That's when a man's fancy turns to thoughts of...MOTORS!  Here's a fairly nutso #27 doublewind, fresh out of welding and tying/epoxing.  It has to go out for balancing because static ain't gonna cut it for this missile.  The doubles almost never come out quite as neat as single winds, but the proof is in the pudding and this one reads a fairly ridiculous .085 ohms exactly per pole.  ***This oughtta dim the lights in Fresno for sure


 
-john

[SlotStox#53]

That is all !

[Hermit #1]

John, does the engraving on that stack say 19T-D27?  The blank looks like one from Bill Bugenis, or maybe a recycled Pro Slot S16D, what with the groove running down the center of each pole piece on the O.D.

Please tell us more about the set-up - is that a MURA C-can, which magnets, etc.?  How did it run on the test bench?

Cheers!

P.S.  Very neat winds for a double - you've got the touch!

[SlotStox#53]

Hermit, John hasn't run it up yet, the arm is being sent out for dynamic balancing as its such a hot wind/armature

[havlicek]

Hi guys...Dave, the setup is your typical (sexy) Mura 2-hole C can/end bell with "elephant ears" heatsinks, although the bussbars are (I think) Champion.  The magnets are the correct  (and strong) Muras and should provide plenty of pushback against the field generated by such an armature.  The lams are from Bill (I think the lams are originally Viper or something), and I pressed them onto a drill blank shaft (.460" long as is "proper").  The wind is (as you mentioned) 19T/D27 and we're down in S24 territory here.  The motor will be a beast.  Resistance would have been even lower on a .440" or shorter stack, but it's close to dead-short-land as-is.  Leaving aside the few #23 and #24 singles I occasionally do for the terminally insane, this is as hot as it gets.  Timing advance is around 25 degrees CCW.

 

The groove on the outside of the stack is pretty much the way modern arms all are, and it helps keep the drill bit from walking when balancing.  It doesn't serve any other purpose as far as I know.  Then again, when you see old Mura arms that were drilled with that very low angle wide bit (spot weld bit) all over the crown and not even necessarily the center, seems clear they had a jig and a drill press.  Of course, the old Mura lams had a thick winding leg and crown, so drilling didn't need to be quite so precise.

 

-john

[Bill from NH]

Viper bought out Robert Root of RJR, so those lams might have originally been RJRs. Are the Mura magnets used their current  Red Dots or the Blue Dots (cryogenized to help the magnetism last longer)?.

[havlicek]

Are the Mura magnets used their current  Red Dots or the Blue Dots (cryogenized to help the magnetism last longer)?.

 
No, those would be shorter (and possibly thinner... I forget). 
 
-john

[Hermit #1]

<SNIP>
The groove on the outside of the stack is pretty much the way modern arms all are, and it helps keep the drill bit from walking when balancing.  It doesn't serve any other purpose as far as I know. 
<SNIP>

 

There's some interesting info on magnets and motors on Slick 7's website. One part really caught my eye: Bob Green always told me that the performance of the motor was based on the tips, and this is the reason why, the armature is turned off when the poles get to the middle of the magnet. The real work is done when the poles are closer to the magnet tips.

That got me to wondering if the groove is not only there to aid drill centering when balancing, but to "diffuse" the magnetic field on each pole away from the core and towards the tips, making the arm a little more efficient.
 

SlotStox#53 said:  "Hermit, John hasn't run it up yet, the arm is being sent out for dynamic balancing as its such a hot wind/armature :D"

 

I really goofed on that one, Paul, mabe I should get to bed earlier and not post when tired. Thanks for the wake-up call! 

Cheers to all!

[havlicek]

There's some interesting info on magnets and motors on Slick 7's website. One part really caught my eye:  Bob Green always told me that the performance of the motor was based on the tips, and this is the reason why, the armature is turned off when the poles get to the middle of the magnet. The real work is done when the poles are closer to the magnet tips.

That got me to wondering if the groove is not only there to aid drill centering when balancing, but to "diffuse" the magnetic field on each pole away from the core and towards the tips, making the arm a little more efficient.

 
These sorts of things are basically useless to even wonder about (and the groove in the middle of the crown isn't at all analgous to the tips of the arm poles). Besides the fact that Bob Green knew more about motors than most all of us here combined, the grooves are there and will be on most lams you'll be able to get. Here are a couple of more tidbits:

1) The shape of the tips of the magnets has changed radically over the years, going from thick/blunt and even grooved, to very thin, and those thinner tips will extend the "reach of the field" a bit and smooth the transition from polarity to polarity as the arm rotates. Result: much less cog, even with today's much stronger magnets. The width of the crown certainly has an impact on performance, and skewed lam armatures can "imitate" some of the really wide crown lamination benefits without adding mass.
 
2) The shape of the tips of the armature lams on the other hand can't reasonably change that much, because you're limited by what you need to do with the armature, that being winding wire in there. Sure there are wider and narrower crowns and thicker and thinner winding legs and crowns, but lam design has pretty well settled on a compromise between performance subtleties and optimizing for winding (ie: enough room in there).  
 
3) Some of the best performing laminations over the past several decades were the Mura .007" lams (and if you could get them, the .005" Champion ones), and those were/are thick blunt things with diagonals between the poles back by the shaft hole. A PITA to wind, but they worked. That may have been at least as much because of the thinner lamination steel and even the type of steel as it is due to the design.  

Anyway, whether or not the "groove" does something positive, negative or nothing at all to performance is arguable, but doesn't matter because you're not going to find many lams available without the groove (although they are out there). I think that the Eurosport and open wing guys might have better information, but often even those guys just see what someone else does who wins... and then they want the same stuff he uses.   

 

Anyway, they're way out on the bleeding edge of the technology, running motors that would make Klingons envious.
 
-john

[Coal Train]

Have you ever tried soaking the wire in Xylene to remove a small amount of insulation to lower the resistance?

[Robert BG]

John,

 

I may have missed it as it's taken a while to read both threads. But what do you use for a spacer on arms?Like on a short stack 12 style arm.

 

Thanks.

[havlicek]

Hi Robert,

While the manufacturers generally use aluminum tube spacers, and thin-wall aluminum tube at that, I never found any back when I was looking. I settled on two things. The first is K&B brass (NOT copper) tube. There's a thinwall that, when you do the math and subtract the wall thickness, has an ID just a bit over 2mm. This place has one of the best selections of all the K&B stuff, and at good prices/quick shipping:

Hobbylinc.com
 
I mainly use pre-cut brass tube "beads" with a 2mm ID and a 5mm length. The 5mm length is very close to working on all kinds of arms... sometimes with no trimming, or very little. You can get them on eBay for cheap, and the pre-cut length saves time and effort for sure. Even if you have to trim them, I just stick them on a spare shaft and spin them with a Dremel disc. Final touch-ups can be done with one of those "drilled-out" end mills. Here's the "beads/spacers":

Brass "Tube Spacer" 2 MM I/D X 5 MM Length Pkg. Of 100
 
For the FT36D, I just cut brass tubing that has an ID that fits... I forget the size.

[Robert BG]

Thanks, John.

I just posted in another thread but I also have some old Mura arms laying around that I'm thinking to salvage parts from and I was going to dissect them. But I'd hate to waste them if it's little more then a crap shoot.

[SlotStox#53]

Sorry if this has been asked/answered before but couldn't find it.

Regarding triple winds... what is the formula or corresponding wire size? I know the double wind is three sizes bigger as in a double #27 = single #24.

Got a spool of Mura silver triple wire that I'm going to use and wanted to make sure beforehand. Also got a RAM seven-pole arm I'm gonna have a stab at, too.

[MSwiss]

Here's the "beads/spacers":Brass "Tube Spacer" 2 MM I/D X 5 MM Length Pkg. Of 100

What is the OD of these spacers?

[Robert BG]

What is the OD of these spacers?

I'm wondering if they're similar to the Camen .30 long brass spacers that Joel turns down.

[MSwiss]

What is the OD of these spacers?

Hi John,

Could you please measure the OD of the 2MM ID spacers you provided a link for?