# How to "Smoke" an armature !



## 1scalevolvo (Feb 5, 2004)

I have found out the technical problem regarding the tendency of MMT+ armature's to "Smoke" them selves to death.After much testing of 2 cars using the MMT+ chassis i come to the conclusion that the problem is 2-fold.
the solder they use has an excessively low "eutectic point" .That is the solder melts at too low a temprature in contrast to that used on a stock Aurora T-jet or AW Arm'.If you ever noticed after a "smoke out" there are pieces of solder all over the inside of the chassis from the centrifugal force.
Also the wire to the commutator is merely laid down & soldered at the connecting point on a MMT+ Armature. An Aurora or AW arm' has the wire wrapped around the connecting point using a superior brand of solder.When a MMT+ armature heats up the solder melts & the wire lets go. If I ever have the time I would like to experiment by soldering with a good brand of solder a smoked MMT+ arm to se how it works out. I do have a spare new commutator plate to use also.
Usually when I smoke one, I either repair it with a good used T-jet arm & new gear or I can adapt a T-jet gear plate/arm' assembly to the MMT+ chassis by shaving down the square mounting pegs that face inside towrds the armature to make it fit.

Neal:dude:


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## dlw (Aug 17, 1999)

The T+ chassis I run originally had the bad arm, but I didn't smoke it. After replacing it with a new MM arm, it hasn't even gotten warm. So I'm guessing the only smokers out there are those bad 50-ohm arms. could it be that the 50-ohmers cause sufficient heat to melt the solder? Has anyone out there smoked a 16-ohm arm and melted the solder?

Just a thought....


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## 1scalevolvo (Feb 5, 2004)

dlw said:


> The T+ chassis I run originally had the bad arm, but I didn't smoke it. After replacing it with a new MM arm, it hasn't even gotten warm. So I'm guessing the only smokers out there are those bad 50-ohm arms. could it be that the 50-ohmers cause sufficient heat to melt the solder? Has anyone out there smoked a 16-ohm arm and melted the solder?
> 
> Just a thought....


I think even the 16-Ohm smoked out too !:hat:

Neal:dude:


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## Gear Head (Mar 22, 2005)

Yeah...I've smoked about 20 of them. And yes Neil your right...I finally figured out that it was the low melting point solder as well. I confirmed this by ohming one out about 16 if I remember right, and then intentionally ran it into the ground with a heavy body and tons of laps until it had smoke coming out of the windows. Then I pulled it apart and resoldered it and it was OK. All the other ones that i have, i disassembled, resoldered and balanced. They are now some of the fastest cars that i have. I'll take one of the Tplus chassis any day over a JL/AW. Even if you melt it there are far more usable parts left to donate to other chassis. I have never seen the so-called 50+ohm arms that folks speak of.


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## 1scalevolvo (Feb 5, 2004)

Gear Head said:


> Yeah...I've smoked about 20 of them. And yes Neil your right...I finally figured out that it was the low melting point solder as well. I confirmed this by ohming one out about 16 if I remember right, and then intentionally ran it into the ground with a heavy body and tons of laps until it had smoke coming out of the windows. Then I pulled it apart and resoldered it and it was OK. All the other ones that i have, i disassembled, resoldered and balanced. They are now some of the fastest cars that i have. I'll take one of the Tplus chassis any day over a JL/AW. Even if you melt it there are far more usable parts left to donate to other chassis. I have never seen the so-called 50+ohm arms that folks speak of.



I have found that the MMT+ axles are that much thicker than stock T-jet, so when I convert a AW/JLTO chassis to stock wheels I use the MMT+ axle as the rear axle as a way to compensate for the somewhat expanded holes in the crown gear.

Neal:dude:


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## Gear Head (Mar 22, 2005)

...hadn't noticed that, I'll have to try it. I've been using crazy glue in the JL/AW axle holes...ghetto, but it works.


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## Grandcheapskate (Jan 5, 2006)

Hi Guys,
I took out the one T-Plus I have as a runner and decided to ride it around a while. I had never noticed any problems with this chassis before, though I use it very little, and I always wondered why guys said they smoked the armature.
Taking a really good look at it, I saw a couple things right off the bat. The armature shaft was very loose in the gearplate hole so the arm would wobble a lot. Although the arm shaft was flush with the top of the armature gear, I needed to push it though a little more. This seemed to cure the wobble; at least, it doesn't wobble any more than a standard Aurora.
I ohmed the armature and found all three poles even at 16-18 Ohms. Just wanted to be sure this wasn't one of the 50 Ohm "Ooops" armatures.
The next thing I saw was that both the front and rear axle were very tight. In fact, the front axle didn't turn at all when the car was running. Removing both axles was a little bit of a task as they were so tight, they didn't want to come out. I then ran a 1/16th drill bit through the holes; this bit already fit with no problem. So I then opened the axle holes to 5/64th and reinstalled the axles. Now they turned freely.
So, I assemble the chassis, adjust the brush springs and the car flies around the track. I'm thinking - "Good job old boy". Even have a little bit of coast.
After a number of laps, I see the car slowing down to the point where it's about to stop. I get the car off the track (wow - it's hot) and quickly ohm the armature - no problem here, the poles are still at about 18 Ohms. The axles turn freely and the geartrain is loose. Hummmmm.
After a few minutes I reassemble the chassis and put the car back on the track. Weeeeeeeeeeeee, we are flying again. After about 3-4 minutes, it happens again. Go through the same procedure and everything looks fine.
Put it back on the track and we're off to the races. 3-4 minutes later, we're about to cook the chassis again.
Strange.

Thanks...Joe


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## AfxToo (Aug 29, 2003)

If you've taken the big friction contributors out of the drive train the next step would be to test it with a good set of brushes to make sure you are not coating the commutator with soot. For longest motor life the brush-comm interface will film up and have a slight gray cast to it, as slippery copper oxide molecules coat the copper comm surface. A dark sooty coating on the comm means higher resistance and heat. A bright, shiny comm where the brushes contact the commutator mean greater comm wear, something you may be willing to live with for the extra horsepower. I'd try JBs and Wizzards high copper compund brushes if they fit.

If the brushes look okay, or changing them does not make a difference, the next most likely culprit for heat build-up that occurs for an entire batch of motors is excessive core loss due to inferior lamination material or defects in the laminations. The lamination material for electric motors is a specialty steel product that is available in several grades. If these motors were built using lower grade material or material not specifically designed for laminations, heat could be a factor. If the insulation material between the laminations is breaking down or missing, heat would most definitely build up with continued operation of the motor. The lamination material is definately a big factor but seldom talked about. Manufacturers of high-end, custom wound HO racing motors spend the extra money upfront to upgrade the lamination material to produce a cooler running and more efficient motor.


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