13 replies to this topic

[Matt Sheldon]

OK I have a question that I have wondered about for years, but sealed racing forced me to forget. LOL.
 
What is the difference between a Hemi wound arm (don't tell me it was spun by an elephant's trunk) and an arm that was wound conventionally? What are the performance and pros and cons of a Hemi wound arm?

[SlotStox#53]

I think Hemi wound armatures differ from standard winds by the way the direction the wire is wound on the arm and how they're terminated at the comm tabs. Although I have no pictorial evidence to show/prove it!
 
As for any performance pros and cons, I don't know and I'm sure the motor experts will explain properly, Matt.

[raisin27]

The Hemi winds I remember from the 1980's were GP27 arms that had the windings wrapped in the opposite direction from a conventional wind on the laminations.

The theory was that in Group 27 racing where the number of turns had to be 27 you could get slightly less wire from the same number of winds using this method.

[MSwiss]

Correct.

You're not crossing over the center of the lam on the first turn so you're saving a miniscule amount of wire.

It must not be practical to do, machine winding, as the only arms I remember that were hemi-wound were Pro Slot G27s.

[MSwiss]

Of minor note, the wind was 38 turns of 27 guage.

[Danny Zona]

I'm pretty sure RJR arms were all hemi wound from 16D and up.

[raisin27]

Thanks, Mike, a brain fart on my part.

[MSwiss]

I'm pretty sure RJR arms were all hemi wound from 16D and up.

Like I said, what I remembered.

I wasn't involved at all in that type of racing.

My point (sort of) was why wouldn't P/S do their other (restricted) arms that way?

[Matt Sheldon]

Thank you, that makes sense. I found 20 RJR & Viper 16D/S16D arms and they are all Hemi wound. I will be using them in my bracket drag setups so they should work good for my application.

[havlicek]

The Hemi winds I remember from the 1980"s were GP27 arms that had the windings wrapped in the opposite direction from a conventional wind on the laminations.

 
That's just the way those in particular were done. A "hemi" wind has nothing to do with winding the arm either CW or CCW,  and neither offers any performance advantage or disadvantage... just a matter of preference or machine setup (in the case of machine wound arms).
 

Correct.

You're not crossing over the center of the lam on the first turn so you're saving a miniscule amount of wire.

It must not be practical to do, machine winding, as the only arms I remember that were hemi-wound were Pro Slot G27s. 

 
Bingo. I don't know about whether or not it's problematic for machine-wound arms, but it does become a little more fiddly when you go to terminate the coils at the comm.

 

Also, because the ends of the wire are headed straight up (rather than crossing over each other at the top of the coils), you do need to be careful not to stress the wire ends when tying.

 

For machine-wound arms where the comm is installed after winding with the wire ends just loose, I suppose you could do them either way.  I

 

n any case, it is a little more bother for what's probably at best a tiny advantage. Even if there is some advantage, that would be more the case with spec wound/tagged arms where you could do a specified number of turns and still have a tiny bit less wire. You can get to less wire by neater/tighter coils (not to mention more consistent results from pole-to-pole) than *just* hemi winding.
 
-john

[macman]

The RJR hemi-winds were, and still are, rockets!!! I have a 16D that is faster than some Super 16Ds.

[Danny Zona]

Revs Just Right.

[havlicek]

The RJR hemi-winds were, and still are, rockets!!! I have a 16D that is faster than some Super 16Ds.

 
No doubt, but there are so many things that add up to a fast arm, so I think that it may be jumping to conclusions that hemi-winding played a major role in that.
 
-john

[Ramcatlarry]

Basic physics: when you wrap a coil in one direction, the polarity is opposite that winding a pole the other way. Since most 'hemi wound' arms are 'special', they may also be wound with more care and likely to be neater and with less resistance... and maybe faster. 

 

Bottom line is that the polarity is also likely to be backwards and if you blindly solder the leads on and not test, the car could try to back up on the starting line, especially in you also are used to N/S magnet in the can standard convention.

 

Rewinding error #1: Wind two poles one way and the third pole a different way... arm will not self start or run well.