3573 replies to this topic

[Slotgeezer]

Lesson here?...everything counts and, .......I'm a dummy

-john

Hey, no more so than "yours truly", smokin' that 29-double you'd sent me, by doin' the same thing w/ the brush hood!

Life sometimes seems to test our ability to deal w/ adversity...

IMHO, I hope I pass the "test" soon... I keep studying, & I'm gettin' pretty tired of the failin' grades, eh?

Keep pluggin', John!... We're w/ you, all the way, buddy!


Jeff Easterly

[havlicek]

I finally finished off "Son of Walnut" and as per my previous post, this nutjob is an SCX RX42b-based walnut even shorter, thinner and narrower than it's precessor C-can based walnut. These SCX motors have magnets that are strong-enough (they measure almost 1000 on my meter), that I figure the RX42 would be a good candidate for a hot short stack. This one is a #26 wind just like the first one that measures .2 ohm. The com (yikes! ) had to be cut down. along with the can and magnets. The arm started out as a new Mura .007" blank that I shortened to (I think) around .365". Endbell is a ProSlot that was shaved almost 1/16th on all four sides to fit the SCX can. The airgap in these motors is tight, so shaving the endbell is kind of tedious. Being off a little (I don't have a lathe or milling machine) might leave the arm hitting the magnets.

Anyway, here's the arm:



Here's the finished motor (I like this purple)



Here's the motor next to an FT16D for a sense of scale/size:



-john

[Ed Miller]

John,
Your work is amazing on any motor that you put your hands on.I would like to thank you for all of your hard work.I'm glad you are still toying with the SCX motor.
In the last few years on this forum I have got to know alot of very nice people, and the knowledge on this forum is unbelievable .
Just to mention a few people I have found you (John H) and have talked to you on several occasion about arms /motors you are the MAN when it comes to rewind and balancing.
Then just recently I contacted (Jeff E.) about building me a scratch built chassis ,well let me tell everybody something this guy knows what he is doing, he is hands down the best chassis builder that I have seen so far.He sent this baby to me and told me to try it out,well my slot car arrived on saturday ,so I left it get to room temperature and ran this car on our track,we were blown away with the handling of his chassis and how fast it was with a used falcon in it WOW.
So you two guys are the MEN of slot car racing in my book. I always look forward to reading all of your posts and I just sit here amazed and thank GOD that we have met each other on this great forum!

Take care,
Ed

[Krash]

John,

Thanks for the feed back. I made an error in my first post it should be 30 AWG and not 31, but I don’t think it will make much difference at this wire size. I assume that by “50T of #30 sounds awfully light” you mean not enough winds per gauge of wire?
As you said this is all in trial and error, it was my first attempt winding / epoxy / solder an arm, so if it runs I think I will be happy.
If I may ask what you’d recommend for both a single and double wind?

Thanks for your time and knowledge

Kelly

[havlicek]

Thanks Ed, that's more than a little over the top but thanks anyway

Hi Kelley,

The arm looks great...even more so for a first attempt. If you have a multimeter, set it on "continuity", hold one probe against a com segment (use the side of the probe instead of the point so you don't mar the com) and touch the other probe to the stack and the shaft. You should get no reading, if you do...there's a short somewhere and most likely where the wire crosses over the edge of the stack. If you have a short, the arm will either not run or will run poorly. If you have no shorts, the arm will run and that's pretty much how easy it is to tell if the arm is OK. The rest of it is a balance between resistance (measured in ohms) and power (a function of how many turns you have). Fatter wire will be lower in resistance per length than skinny wire...BUT...more turns means more power. An electromagnet with more turns of wire will be more powerful than one with fewer turns...but longer lengths of wire (more turns) will have more resistance to current flow. Since we're dealing with (usually) 12V, you'll fall into a "range" of winds for that voltage that will work with varying degrees of either power or RPMs, leaving aside other considerations such as magnet strength, airgap, spring tension and brush size, can efficiency for producing a strong field etc. That's as much as I have figured out so far

you mean not enough winds per gauge of wire?

Yes, 50 turns of even #30 wire will be pretty light. 50 turns...even 55 turns of #29 is a nice wind. Don't worry though, try the arm out and see what happens. It's not like it should vaporize or anything. It's a good idea to run these things slowly at first when testing on a power supply, but it's a real thrill when they spin-up for the first time! Expect some arms to fail (I have had MANY), but try and figure out why they failed and your next arms will get better and better.

If I may ask what you’d recommend for both a single and double wind?

As per above, a good all-around single wind for many different types of motors is 50 turns of #29...you could even go as low as 45 turns as long as the motor is epoxied and tied. If you want to try a double wind, try 26 or 27 double turns of #29 or 35-ish double turns of #30. These are only suggestions and you may add or remove a wind as you see fit. Use more caution when spinning these up though as they will be fast winds. Be sure to tie and epoxy these winds especially before spinning them up as they will definitely have enough RPMs to throw a wire. The faster the motor runs, the quicker the weak points will show up!

If you have a multimeter, you can also touch a probe to two segments at a time while the multimeter is set to resistance (ohms) and at the smallest range the meter has since you'll be reading tenths of an ohm. Down in the .1-.2 ohm range is HOT, .6 to .7 is mild. Some inexpensive digital multimeters will give good readings even at those low ranges.

-john

[Alchemist]

""you are the MAN when it comes to rewind and balancing. ""

I concur with you Ed!

John,

If you hadn't blown up a motor or two - we would think you were holding back - LOL!!!

[Slotgeezer]

Love the SCX shortie, John! ... I can foresee a great future, if these were available... As short as you made that set-up, it'd be a "natural" for both 1/24th & 1/32nd CanAm & Coupe builds...

Ed... Thanks for the kind words... There are MANY, many great builders who post here, on Slotblog... I was happy to put something together that worked so well... I know it'll get "well-used" ... ( aka - run to DEATH! )

Keep on windin' John!... We ALL love to read the latest "poop", on the horse-power front!...


Jeff Easterly

[havlicek]

Thanks guys,

I just wanted to add one more thing about winds in general. The other variable is the gauge (thickness in cross section) of the magnet wire. Less turns of thicker wire will pass more current at lower resistance. Since Watts (power) = Volts X Amps, more current means more power and RPMs. Downside is that more current flowing through the motor means more heat as well. All wire has resistance and as the current flow goes up, the resistance causes heat to increase.

-john

[Alchemist]

Hi John,

" Downside is that more current flowing through the motor means more heat as well. All wire has resistance and as the current flow goes up, the resistance causes heat to increase. "

Would the remedy be to use a heat sink to keep the "motor heat issue" under control?

Thank you.

Ernie

[Slotgeezer]

Hey, Ernie....

Now maybe you can understand why they run chokes in Gp7 racing... By restricting the amount of current, they can help reduce motor heat... As a consequence of adding "choke", they also reduce the voltage going to the motor... That, & the reduction in current, helps control heat...

I stopped running the big fat lead wire on my RetroPro motors... I'm using stuff about half that size now, & the heat problem has diminished greatly... A slot car motor is just like a dog... If you've got X - amount of amps of current available, that motor will "pull" every last bit of it.... So, by restricting the current flow, you can better control heat, & increase motor life...


Jeff Easterly

[havlicek]

Would the remedy be to use a heat sink to keep the "motor heat issue" under control?

Hi Ernie,

Yes. Jeff's right about chokes as well. A heat sink (like "elephant ears" or the clip on radiators they use for retro) will help take heat away from the motor because aluminum is a great conductor. By placing the heatsinks between the endbell plastic and the brush hardware, you constantly radiate heat away from the hottest part of the motor. There's even aluminum com-coolers that go on the arm shaft at the endbell side that may even help more ...in any case they look cool as heck too It's also sometimes necessary to do some can and even endbell cutting and drilling to help with airflow.

-john

[Alchemist]

Hi Jeff,

Thank you for defining "choke". I've heard the term used at the track but I've never inquired as to what that meant. So, choking the controller is a good thing?!! Referencing your "big fat lead wires" - if you're using about half the size of that wire - what gauge wire would that be please?

Sir John H.

Would you have a picture or two of this "aluminum com-cooler" please? Have you used these on any of your hot-wound motors?

Thank you.

Ernie

[havlicek]

Hi Ernie,

I can do better than a picture, as you'll have one in front of you before long

-john

[Pablo]

Somebody put a Havlicek 36D motor in my hands at the Thomasville, GA race on Sunday, just to look at.
Baby Blue paint, Giant wires, super strong magnets.
Dogs were barking, Cats were screaming, and grown men were crying.
It was the most beautiful motor I have ever seen.

[JoB]

Hi again John,

Just like a clarification on this answer of yours:

"To glue the stack together again, I use epoxy applied only to the interior faces of the three poles and only enough to cover so it doesn't drip and make a mess. Of course, care needs to be taken not to glue the clamps to the stack. Epoxy works very well for this because as it thins out with heat, it will get into all the little spaces of the stack and really bond it well. Often it will penetrate well enough to bond the stack not only to itself...but also to the new shaft."

"Yes I do glue the com both so it doesn't move around while winding...but also to keep the arm's timing set. I also use a tiny drop of epoxy for this...as well as the tail spacer and the com spacer (if used). To be sure the epoxy does it's job, I rotate the com and spacers as I seat them so that a bit will even get inside between the shaft and the hole." 


Is this regular epoxy like araldite 5 min cure or is the duralco stuff, I got a tiny sample from a firm here in Stockholm that sells it? What temp in the owen?


Also I've seen on some pics here that the inside of the stack is coated with some white stuff? Epoxy with paint or...???

Also what does a #29 single means? How many turns? Is it always equal turns on a single 29?

What arm would fit a PS4002 since regular Mura arms like Gr20 wouldn't fit, their just to long?... and the com doesn't fit either, just to thick?

Appreciate truly your help 

Thank you

[havlicek]

Hi Jens,

Is this regular epoxy like araldite 5 min cure or is the duralco stuff, I got a tiny sample from a firm here in Stockholm that sells it? What temp in the owen?

I use the Duralco for everything and bake it at 250 degrees for 15 minutes. This isn't a full cure, but get's it pretty close. It will cure more as the motor heats up with use.

Also I've seen on some pics here that the inside of the stack is coated with some white stuff? Epoxy with paint or...???

I use a high temperature paint that is normally used on barbeques and automotive engine parts. It adds some insulation, but I really use it because the wire stays put more easily as I wind it. The paint sort of provides "traction"

Also what does a #29 single means? How many turns? Is it always equal turns on a single 29?

That means #29 gauge wire (AWG or American Wire Gauge) single wound instead of a double or even a triple wind. In other words, it's just a normal wind with a single piece of wire going around each pole. For a #29...it can be anywhere from 45-55 turns depending on the motor.

What arm would fit a PS4002 since regular Mura arms like Gr20 wouldn't fit, their just to long?... and the com doesn't fit either, just to thick?

If the arm is too long, you can easily remove stack laminations ("plates") to shorten it before you epoxy it. For the com you have several options. You can open up the space the com fits in with a Dremel and a fine diamond point or abrasive bit, making sure that you clean out any burrs from the brush tubes so they don't get hung up. You can use a narrower com...the one that comes on the PS should be fine for many winds...they seem pretty good to me...you could even see if a different endbell fits if you have any lying around. There's nothing wrong with mixing parts as long as they fit well.

-john

[JoB]

HI again John,

Thanks for the answer, appreciate it.

With 255 degrees I assume you mean Farhenheit. We use celsius as you know.

Anyway no problemo since I have the formel for converting it from F to C.

Another query, which end of the stack is good to start drill in for balancing? Towards the com or opposite?

Regards

[havlicek]

Hello Jens,

With 255 degrees I assume you mean Farhenheit. We use celsius as you know.

Yes, Farenheit...I always forget about that.

Another query, which end of the stack is good to start drill in for balancing? Towards the com or opposite?

Funny you should mention that. I always start towards the com end because I figure the weight of the arm (discounting the shaft) is centered closer to the com area. It's really silly though because an arm doesn't need balance longitudinally as far as I can tell so it's just a habit.

-john

[Champion 507]

Jens -

If I have a small amount to remove from a pole, I will drill in the middle. If the pole is heavier at one end and I remove material at the other end I will mess up the dynamic part of the balancing even further. By removing weight from the middle, it is the best compromise I know of. I've seen factory balanced arms that looked like there was more wire hanging out the back of the arm, but they removed material at the comm end to dynamically balance that pole, so you really can't judge just by looking at it. If more epoxy got applied to a pole at the back end of it and less at the comm end, it would make sense that the back end would be heavier. But since we can't measure that with our razor blades, we can't balance dynamically...only statically.

Do you know the difference between static and dynamic balancing? We do static balancing with the razor blades. We can find the heaviest pole or poles when arms stops rolling. With dynamic balancing, you need an expensive sophisticated machine made to do that type of work and a skilled operator that knows what he or she is doing. Not only does the machine find which pole or poles are heaviest, it will also sense which end...either the comm end or the back end is heavier...thus being balanced dynamically.

If I have to remove a lot of material on one pole, I will drill 2 holes...one at each end of the stack and try to get them as close to the same depth as I can. Again, I don't know if the comm end is heavier than the back end, so I try to remove weight as equally as possible.

I hope this helps.

[havlicek]

Interesting stuff Doug

Jens,

There are all kinds of factors that come in to play here, many of which we can only guess at when balancing an arm (static). There are two kinds of balance/unbalance...the condition (static balance and dynamic balance) , and the process to correct the condition (static balancing and dynamic balancing). We can only detect static imbalance and correct it using our static (the arm isn't being forced to rotate other than by gravity) balancing jigs. Having a guess at dynamic imbalance is more likely to produce greater errors than it fixes so in practice it's probably more accurate to ignore possible dynamic imbalance than to have a go at it with a static balancing jig.

Using the out-of-balance of a car tire as a familiar example, if there were a heavier spot on one side of the tire exactly centered over the tire's axis of rotation...the tire would be statically unbalanced. If the spot were closer to the outside or the inside of the tire (off the center of rotation) the tire would be dynamically unbalanced. Dynamic balancing (the tire is rotated so that detected moments of inertia can be read) would tell the operator both the amount of the imbalance as well as the angle of the imbalance relative to the axis of rotation (draw an imaginary vector from the axis of rotation through the point of imbalance). The bottom line is that we can't know anything about dynamic imbalance using a static balancing jig. We can significantly improve the smoothness of a spinning arm though with static balancing. ***However, it would only be by pure luck that we could get a result nearly as accurate as that of a skilled operator using a dynamic balancing machine. Dynamic balancing should about always produce more accurate results. Of course, none of this is really relevant to what we're doing

-john

[havlicek]

I also need to say that there are aspects of dynamic balancing as it applies to motor armatures that I'm completely in the dark about. For example, the tire example doesn't actually hold since a tire is, for matters of practicality, spinning around a single point, whereas an armature is spinning around two points (the bearings or bushings. Being out of balance dynamically could make an arm not only want to wobble, but to oscillate back and forth as any endplay in the setup would allow. Then to complicate matters even more, there's the question of whether or not the arm is reasonably well-centered in the magnetic field. That could make that oscillation worse or better depending. I don't know how...or whether dynamic balancing machines and operators take all this into account but given how fast even a "mild" slot car motor can rotate, it's probably all significant. Again though (and realizing and accepting the limitations of static balancing), none of this applies to us "basement mechanics". It is interesting to think about anyway!

-john

[idare2bdul]

I also need to say that there are aspects of dynamic balancing as it applies to motor armatures that I'm completely in the dark about. For example, the tire example doesn't actually hold since a tire is, for matters of practicality, spinning around a single point, whereas an armature is spinning around two points (the bearings or bushings. Being out of balance dynamically could make an arm not only want to wobble, but to oscillate back and forth as any endplay in the setup would allow. Then to complicate matters even more, there's the question of whether or not the arm is reasonably well-centered in the magnetic field. That could make that oscillation worse or better depending. I don't know how...or whether dynamic balancing machines and operators take all this into account but given how fast even a "mild" slot car motor can rotate, it's probably all significant. Again though (and realizing and accepting the limitations of static balancing), none of this applies to us "basement mechanics". It is interesting to think about anyway!

-john

If the arm isn't magnetically centered it will jump substantially when the motor is started. Slot drag racers have figured out that if you space the motor for this in the first place you pick up substantial top end and ET. In the late 70's when we marked the arm and hit it with a strobe while running there was no perceptible wobble while running; likely because the small amount of possible imbalance on a balanced armature was overcome by the magnetic field. We didn't try it with an unbalanced arm.

If you want to send a drag arm that has been statically balanced we could do a test on ET and MPH before and after a dynamic balance.

[Prof. Fate]

Hi

John, actually before dynamic was commonly available, we usually did the longitudinal balencing as well. Later, after "group" racing, "Group 12" was defined as an unbalanced arm. The conventional wisdom being that hotter than 65/30 wouldnj't survive without balence. So, SOME of us went back to building 29s and 28s and going through a static then longitudinal balence apparoach with weighted epoxy rather than drill holes.

It isn't as good as a proper dynamic system with a good operator, and it is time intensive. But it does give an "edge". The "proof" of the pudding is that they changed the rules to the tagged arms of today.

Have I ever steered you wrong?

Fate

[Slotgeezer]

If you want to send a drag arm that has been statically balanced we could do a test on ET and MPH before and after a dynamic balance.

& knowing Mr. Boemker personally, you'll only get the truth, not some percieved notion there-of !


Jeff Easterly

[idare2bdul]

Rocky said,"SOME of us went back to building 29s and 28s and going through a static then longitudinal balence apparoach with weighted epoxy rather than drill holes."

Since we are confessing...
There was a track that required unbalanced arms in a class. when you use epoxy balancing on the ends of the stack where it was hard to see and then the dynamic balancer checks it and adds or subtracts epoxy where needed you get an arm worth more than a tenth faster at the time with an American 16D.