3573 replies to this topic

[havlicek]

Hi Tony. Is it part of what a Hemi is that it must "run in the opposite direction", or just because of the way the wire comes off the com tab? I have wound them with the wire coming straight down off the tab as you said (I normally don't), but with the arm timed to run either CW or CCW. It's a little awkward with that wire hanging there like that, but it can be done. With "regular" winds, I've also wound them in either direction (either CW or CCW around the poles) and with the wire crossing over the stack and the arm timed to run either way also.

Anyway I'm probably mistaken, I just figured that the "Hemi" thing was only about the way the wire comes off the com tab and doesn't cross over the pole???

-john

[havlicek]

Hi Tony. Is it part of what a Hemi is that it must "run in the opposite direction", or just because of the way the wire comes off the com tab? I have wound them with the wire coming straight down off the tab as you said (I normally don't), but with the arm timed to run either CW or CCW. It's a little awkward with that wire hanging there like that, but it can be done. With "regular" winds, I've also wound them in either direction (either CW or CCW around the poles) and with the wire crossing over the stack and the arm timed to run either way also.

Anyway I'm probably mistaken, I just figured that the "Hemi" thing was only about the way the wire comes off the com tab and doesn't cross over the pole???

-john

[tonyp]

I think just the nature of the wire pattern makes it run the opposite direction. Of course you time the comms on slot motors so it doesnt matter. On the R/C stuff the comms are/were at zero degrees, so a hemi arm when used had to have the magnets reversed 180 degrees to run correctly. Stock motors had a 27 degree built into the can. If you stuck a std arm in a hemi stock motor can, it runs backwards.

[tonyp]

Gus, I dont think there is more chance of throwing the wind as the wire runs straight to to tab, no loop over the stack at the top to loosen up. A hemi makes it easier to get the wires up to the comm, plus you eliminate the chance of coil shorting the wires where they cross over at the top going to the comm on a standard wind.

[havlicek]

Thanks for the info Tony!

I finished redoing this burned-up Mura sent to me:




...it was gone gone gone and I couldn't reuse the arm or the endbell (regular Mabuchi FT16D endbell) as they were both fried.

I built a new stack with a drill blank shaft, added a Bugenis com and did a 55T/#29 wind, replaced the endbell and soldered the hoods and clearanced it inside. Cleaned up the can and magnets and set them to center the arm in the field. I also sleeved the spring posts because the wind is pretty hot for the endbell:




Amazing how much different this wind is with the Mura can and magnets as opposed to the Mabuchi stuff. It's just about a 1 amp motor and it really screams and runs super smooth...but I worry about the Mabuchi endbell, although it doesn't seem to get scarey-hot now. After some more break-in it should calm down a bit more but, fingers crossed!

-john

[havlicek]

...and I finished up a nice old 26D for JHW and it's another...you guessed it...#29 wind. This is a wind that I'm confident can live well in a 26D onnacounta it's what's in my proxy motor, This baby sounds sweet and draws exactly 1 amp no load with no break in to speak of other than running it at 5.5V for about 3 minutes. Can by Mabuchi, magnets by Champion (Arcos), endbell by Champion and springs by Fender Musical Instrument Corp. (I made 'em):




-john

[Jairus]

And blank arm by FRENCH!
(unless you used something else....)
Looks BEAUTIFUL, thanks John.

[havlicek]

You're most welcome Jairus and yes, arm blank by French

-john

[gascarnut]

I think just the nature of the wire pattern makes it run the opposite direction. Of course you time the comms on slot motors so it doesnt matter. On the R/C stuff the comms are/were at zero degrees, so a hemi arm when used had to have the magnets reversed 180 degrees to run correctly. Stock motors had a 27 degree built into the can. If you stuck a std arm in a hemi stock motor can, it runs backwards.

The "reverse rotation" comes from the fact that the current flow in a hemi-wound armature coil is opposite to a regular-wound armature. So as the coil energises, instead of the current flow generating a North-out magnetic field (for example) it generates a South-out field. Therefore it is necessary to change the relationship between the magnet polarity and the voltage polarity to get the armature to rotate in the same direction as a regular-wound armature, either by swapping the magnets over, or by swapping the lead wires over. For RC motors, because of the mechanical timing between the can (magnets) and the endbell (brushes), you have to swap the magnets.

[Gus Kelley]

Hey Guys! Thanks for all the info. I remember doing some winding like that as a kid but didn't realize a name put to it. I thank Oscar Morales and Jerry Davis for initially providing info and the rest of my friends here on the blog for finish clearing up the loose ends. Gus in Sacto.

[Don Weaver]

Dennis explains the physics of this well. I would also point out that some of the posts here seem to indicate that comm timing determines rotation.....it does not. Advancing the timing in the direction of rotation will speed the motor up. Retarding the timing will slow the motor down, not change it's direction of rotation. Like putting a TSR in a Flexi chassis....it runs slower and heats up more.

Don Weaver

[havlicek]

I would also point out that some of the posts here seem to indicate that comm timing determines rotation.....it does not.

I'll have to go back and re-read this all since I didn't see that (or remember saying it) but, timing doesn't determine rotation direction, polarity does. Timing only determines which direction the motor spins faster.


-john


PS...thanks for the explanation Dennis!

[gascarnut]

You're welcome, John.

Now that everyone is either thoroughly informed or thoroughly confused, shall we start talking about "star" winds?

[havlicek]

You're welcome, John.

Now that everyone is either thoroughly informed or thoroughly confused, shall we start talking about "star" winds?

Sure! I've even got one I've never seen described in the books that I use from time to time to solve problems with getting a certain number of turns on a particular blank. I didn't "invent it" though, I discovered it when I took apart an old motor that didn't look rewound but must have been.

-john

[Gator Bob]

Sorry, guys, I tried my best and failed. The drill kept coming out the side of the wire when it got to the hook part.

Start at the other end.

[Don Weaver]

I'll have to go back and re-read this all since I didn't see that....

John,

Here are a couple of posts that "seem" to say timing determines rotation:

".....but with the arm timed to run either CW or CCW."

"Of course you time the comms on slot motors so it (direction of rotation) doesn't matter." I inserted what "it" refered to.


Don Weaver

Don Weaver

[havlicek]

Hi Don,

Nah...I think most everyone here (for sure Tony P and myself) assumes that means timed to run better CW or CCW, as timing only determines that, not actual rotation. Tony even went further in the post you quoted to say:

On the R/C stuff the comms are/were at zero degrees, so a hemi arm when used had to have the magnets reversed 180 degrees to run correctly.

Good to clear up though!

-john

[havlicek]

So it's getting to be that time when I have to re-order epoxy, and I just hate that even the "sample pack" I get costs $80. Anyone know of another high-temp/lo viscosity epoxy or any other high temperature lo-viscosity clear potting compound...one or two part, that can easily be cured in a non-industrial setting like at home, that is suitable? If so, any links? TIA

-john

[Alchemist]

What is a "Star" wind please? I'm presuming you're "criss-crossing" the wire between the poles?!

Oh, and Thank you Dennis for adding to my confusion - LOL!!!

John, purple is my favorite color and that motor looks too good!! Another jewel!

Ernie

[gascarnut]

What is a "Star" wind please? I'm presuming you're "criss-crossing" the wire between the poles?!

Oh, and Thank you Dennis for adding to my confusion - LOL!!!

John, purple is my favorite color and that motor looks too good!! Another jewel!

Ernie

Ernie, in a "star" wind each pole is connected to only one comm segment, the other ends of the wires around the poles are soldered together and wrapped around the tail end of the stack. It makes for a slightly milder armature on the same wire as a regular arm , as I recall, but it's been a long time since I wound one. The real high-speed stuff didn't ever use this technique because of the balancing problem of having the "tail" of wire around the tail spacer.

[Alchemist]

That sounds unique Dennis. Would you have a photo of this type of wind please?

Thank you for taking the time to explain this procedure Dennis.

Ernie

[tonyp]

Dennis we did some star winds on rc motors but never got them to run really well. They always seemed to be less efficient so were not suited to the application.

[Gator Bob]

So "Hemi" is a winding technique And a product name?

The Strombecker kit instructions are not real specific other then wind the wire CCW. Have some Mura blanks too.. called Hemi which look like fancy repackaged Strombecker (or Iguanas? )

Also found a new "Hemi wound" Super Wasp. What the heck ???


I prefer the 426 version... "let it go Bob, just let it go".

[Robert V.]

Hi John

I got my epoxy resin off ebay i paid about $32.00 for about a quart so far it works pretty good check it out do a search (epoxy resin high heat) it's called Max HTE it's a 2 part clear amber, i cured at home with no major problems for that price it may be worth a try, if you are not shore i can send you a small amount to try let me know.

[havlicek]

Hi Robert,

That's an excellent price for so much of the stuff. What I use is considerably higher temperature rated (around 500F depending on cure), although I have at times messed up the mix proportions causing some problems with foaming...I'm more careful with it now. The other thing is, I have never even come close to using up the pint I buy before the material should be discarded because of passing it's shelf life. I've since re-ordered and it should be here in a couple of days coming from Brooklyn. Thanks a heap for the information though, and you should be set for a long time with that much. Heck, you could glass a decent-sized surfboard with that much!

-john