20 replies to this topic

[havlicek]

(In my best Rod Serling) "Imagine if you will, a world where people race with wild abandon. This is a place where racers feverishly build the night before the big race, not knowing if their efforts will pay off, or result in violent destruction. You're about to enter that world... a world that reaches from the pit of your deepest fears to the limits of your imagination, a place we call "The Big Wire Zone."

OK, that was stupid, but after years of typing about this stuff, I get a little goofy sometimes looking for new angles.  
 
The subject here is a pretty ordinary C motor. The can was one of the unwelded RJR cans I got from Bill Bugenis. I clamped and brazed the seams shut, then cleaned off all the brazing crusty-goop the process leaves behind. I epoxied-in a fresh 2mm x 5mm bushing and sprayed a coat of a deep green hi-temp auto paint.
 
These cans produce a hole about 4 or 5 thousandths smaller than many others that I've used that are already welded at the seams. I'm not sure why, but it must be that most cans when welded aren't held tightly closed, as these are when I braze them.  
 
Whatever the reason, the hole with the magnets installed is around .525", which is pretty nifty. A regular Mura endbell tops off the setup... again, nothing "special," but I like them. They're beefy and just plain "work."


 
Hey, wait a minute. Those coils visible at the back end look awfully heavy-freakin'-duty! OK, cat's out of the bag. The heart of the beast is a 19t/24 on a longish .475" stack, with a comm from Dan Miller.




 
No doubt, this will be a violent motor; there's no other way to put it.   With the arm coming in at .038 ohms, we're pretty close to dead-short territory... current coming in pretty much just leaves, but not before converting a lot of amps into a lot of rotational force, or something like that.

While I doubt whether shunts are necessary in many cases. I think this motor will get a pair. With all it's glorious excess wrapped in an ordinary-looking package, I call this one "Cheep Thrillz."  


 
-john

[Pablo]

The glory days are back!!  

[havlicek]

Well, at least in the imagination of the few of us old codgers (like you and I) who do our best to ignore convention... and reason, Pablo.  
 
-john

[Bill from NH]

If these cans' tightness causes a problem, they could easily be stretched using a can straightening mandrel and a small hammer after brazing.

[havlicek]

Well, sure they could Bill, but a few thousandths under isn't a problem at all. Of course, pressing or tapping in a mandrel would almost certainly break the brazed seams open, because these cans are pretty darned straight as-is and something would have to give.

It is an odd thing (although not a problem) though as I've not had a problem installing endbells. They're not even a tight fit the way the old Mura endbells often were on the Green Cans. Those were sometimes really tight.
 
-john

[Steve Deiters]

Smokin'!

[havlicek]

Oh and I forgot to mention, I installed the bushing with one of those alignment tool things after brazing and cleaning up the can. It fit a little snug, but wasn't a problem to install or remove.

 

The only thing I can figure about where those few thousandths go is that some aspect of the forming (the corners where the flats meet the radii, maybe even the actual radii or something) is slightly different with the RJR cans. I have some of the finished/welded ones kicking around, and should do some more investigating.

 

-john

[havlicek]

Smokin'!

 

... figuratively speaking!

 

-john

[Pablo]

  Never mind conventional or rational - lay down more Koford heavy and get down with the sickness. 

[old & gray]

The only thing I can figure about where those few thousandths go is that some aspect of the forming (the corners where the flats meet the radii, maybe even the actual radii or something) is slightly different with the RJR cans.  I have some of the finished/welded ones kicking around, and should do some more investigating.

 
John,
 
From my machine shop experience, an inside corner (in sheet metal) where a radius meets a flat will have a radius as the metal transitions from face to face. The outside corner of the magnets will have a sharper (smaller radius or chamfer) than the sheet metal. The result is the magnets are pushed away from the sides of the can reducing the size of the hole.
 
I remember when the RJR motors were first introduced their fit and ease of assembly raised the bar in the Boxstock class.

[Geary Carrier]

Hi John,

 

What size Kevlar did you use on this beastie and do you use the same size for all your motors?

 

Thanks,

 

g

[gotboostedvr6]

I have tens of thousands of yards of Kevlar if any of you guys need some. Just cover the material and shipping cost and i'll get some out to you.

[B.C.]

Never apologize for big wire arms. Seems like you did a big wire double wind sometime back.

 

Looked great. A big wire arm in a C-can wound out on a long straightaway sounds so nice, only thing better is several of them at once.

[havlicek]

I remember when the RJR motors were first introduced their fit and ease of assembly raised the bar in the Boxstock class.

 

Yeah, the cans are really nice... still!
 

What size Kevlar did you use on this beastie and do you use the same size for all your motors?

 

Beats me. I just order the stuff "by eye" and hope it comes to me the same thickness as I hoped it would be. I use a thin Kevlar thread on the tamer arms, and I have some in between the two for the not-as-crazy-as-this-one arms.  
 

Never apologize for big wire arms. Seems like you did a big wire double wind sometime back.

 

Looked great. A big wire arm in a C-can wound out on a long straightaway sounds so nice, only thing better is several of them at once.

 

Thanks, Brian.  It's been so long since I've heard that sound, your post brought a smile to me!
 
-john

[havlicek]

The only thing I can figure about where those few thousandths go is that some aspect of the forming (the corners where the flats meet the radii, maybe even the actual radii or something) is slightly different with the RJR cans. I have some of the finished/welded ones kicking around, and should do some more investigating.

 
So, I built another set-up using a plated/welded/finished RJR can with the same magnets, and got pretty much the same result, even after grinding down the inside of the welds and the seams.  

 

Whatever the reason/cause, the RJR cans definitely produce a slightly smaller hole than say the various Mura cans. After inserting a C-can mandrel, I had one heckuva time...I  mean one heckuva time getting the thing out, and the hole was still about the same few thousandths under.  

 

Again, this isn't at all a problem, nor would it necessarily make for a better-running motor. 
 
-john

[Bill from NH]

Who made the mandrel you were using? If you had trouble getting the mandrel out, you must have had problems getting it in, too. Did you just force it in or use something for a hammer or press? That's not what you want to do.

 

You want to finger insert, not force, the mandrel part way into the can, then hammer on the can's top/side bends in the area where the mandrel is in until you can slide the mandrel in a little further, then you hammer the bends again and insert the mandrel a bit further once more. The number of times you'll have to partially insert the mandrel and hammer the bends until it completely fits will depend on the can's trueness to begin with. Having to do this four or five times on one can is not unusual.

 

I've not had any mandrel stick in a straightened can that I couldn't pull out with my fingers. Only a few Mura C-cans I've had were straight when they came from the factory. The only cans I've had split at the weld were Slotwork 16D cans. The few that did, I silver soldered the seam on the can's outside. End of problem.

[havlicek]

Hi Bill,

 

Long story short, I understand all of the above, and if the mandrel went in easily in the first place then the can most likely wouldn't be under by a few thousandths.

 

-john

[zipper]

From my vaults: #23 Rocket, #25 and #23 wound by me 45 years ago. Crap epoxy, just heavy duty thread round the comm and just comm solder. Not used, just a trial on power that wasn't too succesful.

 

But some Finnish Championships were won with my #25 and #26 winds - no epoxy and no balance allowed... After that self-wound arms were forbidden...

 

[havlicek]

Nice looking arms, Pekka!  Mura blanks and comms?

 

-john

[zipper]

Yes, were the comms made by Kirkwood?

[havlicek]

Probably (?). There was a time period when the Mura comms looked a lot like Kirkwoods, and then they looked a little different... that was all before Mura went to those "Diamond Trued" comms that were especially chubby.