170 replies to this topic

[havlicek]

... So here's the whole mess all wound and carefully soldered (yes... the wire is rather stout!) and ready to be tied.



Then I tied up the comm and the magnet wire coming off the stacks as neat as I could with Kevlar. This stuff is great, amazingly strong so you can really yank on it when tying things up and heat resistant (a very good thing because this arm will get hot).



... Next epoxy and balancing/finishing touches and a little surprise at the end.

[havlicek]

Some epoxy in a small cup, a wooden coffee stirrer to mix it with, and a toothpick to apply it. Even with non-fast-setting epoxy, the stuff starts to polymerize after a pretty short time (it starts to get a tiny bit "stringy") after mixing. I try and go slow... carefully applying the epoxy, working from the comm tabs down, but you should try and work smoothly and rapidly. I'm also applying less of the stuff now than when I started doing this again... you really only need as much as it takes to cover the windings and the Kevlar. I then put the arm in the oven, standing with the comm up and the oven set to 250 degrees at first. Even though the curing process is greatly speeded-up with heat, at first the epoxy goes through a short period where it's viscosity decreases (it becomes more "runny") so it can soak into the windings and the spaces at the comm... a good thing. You don't want the epoxy just sitting on the arm... you want it to flow sort of how you want solder to flow into a joint.



After a short time, I turn off the oven so as not to overheat the arm and flip the arm so the comm is down and the epoxy will run the other way. You don't have much time as the heat will rapidly "set" the epoxy. Then I flip the arm again and put it back in the oven which is now cooler... maybe a hundred degrees or so (?) and let it stay in there while the oven cools down to room temp again. Resins speed-cured this way will often be somewhat harder... but more brittle than if cured at room temp, but when applying as little as possible and having that sink-into the windings it's probably a good thing. When it comes out of the oven it looks like this:



... Just some balancing and finishing touches to go now.

[havlicek]

So the idea here with static balancing is to find out which side(s) of the arm are heavy because when spinning, those heavy sides will cause vibration... bad for RPM and the life of the motor.

Here's the deal with the R-Geo balancer... the magnetic field is carrying the arm on a single point so it can rotate with little resistance. This can also be done by balancing the arm on a couple of razor blades to see how it rolls across them. When the heavy side is apparent... I mark the center of it by the top (comm) first and drill a little material away to make it lighter. You have to go slow here as the bit can slip off the side of the arm easily. What I do is rest the spinning flutes of the (small) drill bit against my thumb while just applying a bit of pressure. The bit won't cut into your thumb... but this is definitely not a safe way to do this. I don't own a small (or a big) drill press though so I improvise. The process is to try the arm... drill a bit... try it again and repeat until it has no apparent heavy side, marking and drilling as you go.

You have to be really careful not to drill too deep and you must use a narrow drill bit. The narrow bit will remove less material at a time so you don't remove too much and it will be easier to start a hole with. If you go too deep, you can weaken the arm because you'll be into the thin part that gets wrapped with wire. You could also hit the copper windings and the arm is toast. If you wanted to be safe... you could rig a drill press jig to hold the arm and set depth stops. If you still needed to remove more material after going as deep as you safely can... then switch to a bigger bit and your first hole will act as a pilot.



When it's all done, I rechuck the bit in the Dremel and hold a piece of #600 wet/dry paper against it to get rid of the burrs caused by drilling it as well as by engraving the wind and my initials in it, and it's ready to go into a motor. Total time about an hour and a half... I suppose I could go a little faster, but I worry about not doing a good job as I can. Besides... why rush?

[havlicek]

... I don't know if this will work but here's a link to...

THE RESULT.

[Pablo]

Awesome!

Questions:

- Why is only one end of the shaft tapered?
- How do you crimp the comm tabs closed without ruining it?

[havlicek]

Thanks a heap, Pablo.

With the magnetic balancer... only one end of the arm needs to touch the magnet' the other floats in mid air. With this arm, I also tried trimming the shaft on the comm end to only what was necessary for the endbell bearing (plus a little) to see if that makes a difference... it doesn't. :-) On this arm, I tried both the magnetic and razor blade methods... and here they both gave the same results. Maybe I just was more careful because I was working "in front of an audience".

I crimp the comm tabs closed by folding-up a paper napkin into a tight roll and placing that on the far side of the comm. I then use the needle nose pliers to squeeze the tab and the napkin... no marks and no problems. As you can hear from the link... it runs nice and smooth and if there were any problems at all with the comm it wouldn't.

Still... after all the work, you never know if it all worked out until you spin them up.

[Rick]

John,

Let me look around, I can probably rustle up some old 12 arms that are good. You could unwind and wind to your heart's content. 12s have a .350" stack so watch the turns, it will take a few more or smaller wire or watch out! 12s are 50 turns of 29 wire. Something like a 40t/27 would be a start or some double winds...

If I had only kept all the burnt-up arms in my past, you would need a pick-up to haul them all away. Who'd have ever thunk that old arms would have any value in the future...

[Pablo]

I read somewhere the late, great Bill Steube used to file the stack thicknesses to allow more wire.

[Horsepower]

... I don't know if this will work but here's a link to...

THE RESULT.

I don't think it works. I couldn't hear anything.

Where do you get Kevlar thread?

[havlicek]

I don't think it works. I couldn't hear anything.

Where do you get Kevlar thread?

Hmmm... maybe try downloading the file (it's very small) and then playing it. It's just an MP3 so your computer's player should open it. Here's the LINK.
It works fine over here and was a bit of a hassle to record, convert, and post it. I'd hate it if nobody else ever heard it "sing". Just right click and "save target as" should work, then simply click on it and your computer should just play the file.

Switchblade,

I did a google for Kevlar thread and got a neat hit on Amazon for cheap HERE.

... The stuff came in a couple of days and one 50 yard spool will do a LOT of arms. Still... for a couple of bucks I bought two. :-)

[havlicek]

Rick,

That sounds pretty cool. I don't know how easy they'll be to take apart... but I'd definitely give them a try!

[Pablo]

Hi Gary,

Call me, I'll let you listen to it for $1.99 for the first minute...

It sounds like a G12.

[Bill from NH]

Works okay with AOL Media Player.

[havlicek]

Thanks, Bill...

So again, there's not that much involved here and the materials are fairly affordable. The worst part expense-wise is the blank arms and I just ordered some more from Mura and it's like $15 a pop for them (but they are excellent and the result is a better arm). The rest doesn't amount to much... maybe another buck or two per arm for epoxy, sandpaper, Kevlar, and magnet wire. Even the wire was only like $15 or so (I forget) for a one pound spool and that's a LOT of wire.

For double winds (like the #26 dbl pictured earlier in this thread)... you simply unroll enough wire onto a second spool and then feed both as you're winding. It's a little more difficult to keep things straight and neat... but not too bad. You can come up with your own signature winds... mark the arm by engraving it or epoxy-on a tag and really have a blast. For the whole retro thing, this all seems like such a natural... this was after all the way things were done before these arms became commercially available.

Finally... when you get consistent results doing this, treat these arms right and set up the motors properly. I just keep a C and D can motor handy for trying these things out and those cans are sloppy (loads of play, loose tolerances, used brushes, and beat springs), but really set-up well... these things would no doubt perform significantly better. I hope all of this helps the one or two (sigh...) folks who may be interested in trying their hand at a really "retro" aspect of slot car building, especially since it took me all day to take the pictures of the process (I'm a miserable photographer).

BTW... thanks a heap to Cheater for making the photos brighter and clearer so people could see the whole deal better!

[idare2bdul]

For the whole retro thing, this all seems like such a natural... this was after all the way things were done before these arms became commercially available.

The powers that be in Retro Racing cringe at the thought of anybody having to learn about motors. It's OK to be a good chassis builder and to derive an advantage from that, but D3's RetroPro and Big Dog classes are the only retro classes that allow an individual to even blueprint their own motor.

My understanding is that may be changing in 2008 NorCal with the adoption of the 4002C as their motor and rumours of a possible anglewinder class East of the Mississippi river have come to my attention.

[Rick]

The audio works, I was waiting for a VIDEO! (I had sound turned way down) LOL. It sounds good, turn the volume up and BTW it opens up Quicktime Player on my 'puter to run it?...

[havlicek]

Rick,

The video wouldn't be a pleasant experience if my mug was on it. Better to leave it just as an audio file. The file will open with whatever player is designated as your computer's default audio player. It could be Quicktime, Realplayer, Windows Media Player, etc.

[Horsepower]

Thanks for the link to the Kevlar thread! My favorite money pit - Amazon! I should have stock in them. I still couldn't get the audio. Must be somethin' with this computer.

[havlicek]

... No worries, Switchblade, the clip is less than 10 seconds long and it's not exactly off the Deep Purple "Machinehead" album. The people selling the Kevlar were cool... got the stuff cheap and fast. What are you winding? I've gotten some inquiries about doing some of these arms for people and the #24 seems to be the one so far.

[One_Track_Mind]

Hi John,

Very nice indeed!

I'm with Gary on not hearing this arm sing... but I'm sure it does very well. I get the little pop-up window and it goes for 7 seconds but I hear nothing?... Yes, I have the volume turned up.

Keep on winding and having fun! Good to see threads like this come about.

For your efforts, If you're ever in the need for a few vintage Kirkwood comms, PM me your address and I'll send some right over. No questions asked, nothing asked in return.

[havlicek]

... I'm PMing you right after this.

 Soprano_.mp3   170.72KB   143 downloads
PS: I just discovered that the attachment system here allows audio files as long as they're under the limit so I put the "theme song" above. Maybe???

[Cheater]

John,

No problem playing the audio file here on my old Mac.

Yes, non-image files can be attached to posts, so long as you observed the 2,000k size limit.

[Horsepower]

That link did it, John! That reminds me, I have to make a dental appointment!

[havlicek]

That link did it, John! That reminds me, I have to make a dental appointment!

:-)...don't remind me!

Igor and I did some more experimenting in the la-bor-a-tory and did a "fuller" #24 wind (20 turns), just so people don't get the idea that I'm only interested in developing WMD over here . The result is really encouraging...another one that really "sings" as well. I think I'm pretty much "there" at this point and may try some heavier winds like 23awg or maybe heavier(???). The #26 double I did is really nice so I don't see the point (at least right now) in going any lighter.

I hope some of you take a stab at all this because it's great fun, not terribly difficult once you get the hang of it and really satisfying. Thanks to the ideas, requests and info I've gotten from some here, I'm also considering testing the waters doing these things as a sideline. Anyone interested can just PM me and we'll see where that goes.

-john

[havlicek]

I'm sending out the last of my "prototype" arms today as the last part of seeing people's reaction to these things. I've sent out (from what I recall):

*a S24 15T
*a S24 17T
*a S24 20T
*a D26 13T

...just for grins some D Can rewinds with some of those.

...as a representation of various degrees of spice :-) While some of these were done while I was still gathering technique, and bits and pieces (some were tied with fiberglass for example before I got the kevlar...some weren't tied at all, and I later started using less epoxy), I think they should all run well. Hopefully, as I get some feedback on how they perform and in what setups, track conditons, chassis, and track power...I may refine them some more.

-john