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Cox "NASCAR"... what a drag!


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#1 havlicek

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Posted 22 February 2018 - 06:22 PM

     Rummaging through my "pile-o'stuff", down in the FT36D department, I came across a Cox that was asking for help.  The can bushing was gone, the inside of the can was rusty, and the end bell had "The Mabuchi Crack".  Sooo:

1) I scrounged up a $3 eBay Mabuchi, took out the bushings, armature and magnets
2) I removed the stock magnets from the Cox, and then opened up the can's bushing carrier, and soldered-in what was left.
3) Then I epoxied-in the new fixed bushing from the eBay Mabuchi, completing the "bushing transplant".
4) Next up was to grind-off the top and bottom tips on the eBay Mabuchi's magnets to fit (*then washed the magnet dust off my face, because I looked like a coal miner)
5) After whipping-up a set of .008" shims, I epoxied the shims and new magnets from the eBay Mabuchi...more transplanting.

6) Then I drilled the end bell so I could key the bushing to the holes and outer ring to repair the "crack"

IMG_2516.JPG

With a solid setup and muscular magnets, NOW I could make an armature.  Here I chose to also "transplant" the eBay Mabuchi's arm after stripping and cutting spacers.  I had used the arm to set the magnets, and the shafts on these things are pretty dandy.  With a nice sturdy com, all that was left to do was to wrap some magnet wire around the thing.  20T/#24 seemed like "a plan" and, after welding and cutting the com, it comes in at .035 ohms "zackly"

IMG_2517.JPG

Mocked-up to make sure nothing is hitting something it shouldn't be hitting, and all is good.  This arm definitely goes out for balancing (duh!)

IMG_2518.JPG


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#2 havlicek

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Posted 23 February 2018 - 07:38 AM

...oh and I should mention (*I guess?) that of course this motor will be for drags only.  I held myself back a little as I was originally thinking about #23 wire, but only JUST a little.  :D  While the magnets are nice and strong AND I kept the air-gap fairly tight, these wide crown armatures make for very little "cog", and I think the combination here should make for a strong drag motor.


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#3 Foamy

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Posted 23 February 2018 - 12:29 PM

. . .ummmm, the Cox magnets are stronger then the stock Mabuchi magnets. . .


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#4 John Gorski

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Posted 23 February 2018 - 03:18 PM

Nice

John cant wait to see the Blower on top!

John

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#5 Samiam

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Posted 23 February 2018 - 05:33 PM

Most electricians would call .035 ohm a dead short. 

 

John calls it "a plan" for a drag motor. :bomb:  


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#6 havlicek

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Posted 23 February 2018 - 07:53 PM

. . .ummmm, the Cox magnets are stronger then the stock Mabuchi magnets. . .

 

 

ummm, why yes they are!? (*at least the later Hong Kong  ones that were in this are), and these are way stronger than the Cox magnets.


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#7 havlicek

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Posted 23 February 2018 - 07:54 PM

Nice

John cant wait to see the Blower on top!

John

 

 

That would be up to the scratchbuilder...or the body man John!  :)


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#8 havlicek

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Posted 23 February 2018 - 07:55 PM

Most electricians would call .035 ohm a dead short. 

 

John calls it "a plan" for a drag motor. :bomb:  

 

I didn't make this stuff up Sam...just playing follow-the-leader.


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#9 Robert BG

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Posted 24 February 2018 - 11:23 AM

This might be a dumb question.But did you reuse the old com?and did you have to epoxy the stacks again before rewinding?

 

Thanks


Robert Fothergill

#10 havlicek

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Posted 24 February 2018 - 12:23 PM

This might be a dumb question.But did you reuse the old com?and did you have to epoxy the stacks again before rewinding?

 

Thanks

 

Hi Robert,

     No, the com pictured is definitely NOT the Mabuchi 36D com.  I doubt the stock com would last even for a single drag run (!?) with this combination.  The com pictured is from the general/industrial $3 Mabuchi the armature and magnets came from.

     These armatures are powder coated already, and the magnet wire isn't glued or potted so, after dewinding, no coating is required except for the com and tail spacers, so I just covered them with JB Weld.


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#11 Pitt Man

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Posted 26 March 2018 - 09:36 PM

I'm the proud new owner of this screamer.  :sun_bespectacled:

 

What a fantastic build, John!

 

I'm afraid to free run this sweety on a realistic voltage, but it tachs out @ 22,500 on 2.4 volts.  :bb:

 

Oh yeahhhh baby, this is going to be fun.  :shok:  :heat:


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#12 Half Fast

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Posted 26 March 2018 - 09:42 PM


 

I'm afraid to free run this sweety on a realistic voltage, but it tachs out @ 22,500 on 2.4 volts.  :bb:

 

 

 

How many amps did it draw?

 

Have fun

 

Cheers


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#13 Pitt Man

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Posted 26 March 2018 - 09:58 PM

Sorry, no idea on the amps, I break in and test all my motors on nimh battery packs.


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#14 havlicek

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Posted 27 March 2018 - 06:20 AM

I'm the proud new owner of this screamer.  :sun_bespectacled:

 

What a fantastic build, John!

 

I'm afraid to free run this sweety on a realistic voltage, but it tachs out @ 22,500 on 2.4 volts.  :bb:

 

Oh yeahhhh baby, this is going to be fun.  :shok:  :heat:

 

Hi Bob...and thanks.  Yeah, these motors scare me more than any other, even with the very short blasts they're intended for.  Add to that the really high voltages some run them at, and the fear factor goes up even further.  Without a doubt, yours is the hottest 36D I've ever done!


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#15 Dallas Racer

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Posted 27 March 2018 - 10:14 AM

. . .ummmm, the Cox magnets are stronger then the stock Mabuchi magnets. . .

 

How do they compare to Arco magnets?

 

John, what comms do you prefer on 36D motors?

 

Something I've been wondering: What would be the performance difference between armatures with the same amount of turns, but different guage wire? Such as 20T 25G, 20T 24G, 20T 23G.


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#16 havlicek

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Posted 27 March 2018 - 11:38 AM

 

 

How do they compare to Arco magnets?

 

Which ones?  The stock magnets in the Hong Kong Cox motors ("NASCAR") are a bit stronger than the stock Japanese Mabuchi FT36D magnets.  I forget the exact average, but it's probably safe to say they are around 10% stronger.  The magnets I used here are significantly stronger than those, and are "around" as strong as the Arcos.  The Arco magnets are probably 25% or so stronger than the stock Mabuchi magnets...definitely worth it if you can find them.

 

 

 

John, what comms do you prefer on 36D motors?

Really, anything besides the stock ones.  The seemingly strongest com I've seen for the 36D's larger diameter shaft is still the old stubby Kirkwood com that was marketed by Champion and some others.  However, it's really short length makes using it with the Mabuchi end bell difficult and you have to do a lot of internal clearancing to get them to work, and even after all that, there's precious little "wiggle room".  After that, there are several different Asian coms I've seen that are very nice, as well as tall (a good thing for both spacing as well as heat dissipation), but I don't know that they're stronger than the old stubby Kirkwoods.  I've also bored-out 2mm bore coms like the "regular Kirkwood/Mura coms", but that MUST make those coms weaker, so it's not a good idea at all.  There are no modern slot car motor coms made for the larger shaft because there are no modern slot car motors that use that shaft size.

 

 

 

Something I've been wondering: What would be the performance difference between armatures with the same amount of turns, but different guage wire? Such as 20T 25G, 20T 24G, 20T 23G.

 

 

Keeping in mind that good performance for slot car motors is a balancing act between power and revs, and that revs means less turns...whereas power "kind of" involved with more turns, your question is a difficult one.

20/25 would fall right in the range of useful winds for that size wire gauge.  (*of course, stack diameter and length matter a LOT)

20/24 is at the upper limit of the "range" for that wire gauge.  It would still be a brutal armature, but not as fast as some other #24 winds.

20/23 is a LOT of wire for that gauge.  Revs would be down compared to say a 15-16 turn #23 (*as if that would matter ;) ), but I would expect torque to be up (*as if that would matter also ;) )

The general rules that apply (among others) are:

* More turns of wire on either a stationary electromagnet or a spinning one (armature) is that more turns = more generated magnetic strength...more "power", at least potentially.  Current usage will also change though.

* Less turns means the potential to spin faster

***Other things affect a DC motor's performance that don't come into play with a stationary electromagnet.  For instance, timing and "back EMF" (a DC motor is also a generator when it's coils aren't energized), play a large role here.  Part of that also is that we want a motor to not just spin fast and produce a lot of power efficiently (a lot of "watts", with as little energy wasted as heat as possible), but also to have a good balance between those and braking.

***For a better and DEFINITELY more authoritative explanation, it's best to ask a physicist that has done graduate work in the field.


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#17 Geary Carrier

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Posted 27 March 2018 - 12:12 PM

Hi John,

 

Thank you for this excellent explanation...


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Yes, to be sure, this is it...


#18 havlicek

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Posted 27 March 2018 - 04:06 PM

Hi John,

 

Thank you for this excellent explanation...

Hi Geary,

      Thanks, but this is all pretty basic information.  Above all else, I don't want to be seen as being some sort of "expert" on all this.  DC motors, and how they work is an insanely complex subject.  For slots, the whole subject gets even more difficult because we're "used to" running motors that consistently perform in ways that could very well confound trained/schooled experts in the field.  For that reason, guys like Stu Koford and whoever else is still working in slots have a MUCH better handle on all of this than I ever will.  ***I just wind them as best as I can, and hope they work well.  Beyond that, I only have "feelings", "theories" about this stuff.


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#19 Dallas Racer

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Posted 31 March 2018 - 01:57 PM

I forgot about this. Thanks, John.


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