Ok... I admit... I need some serious help with this one

I have recently been running Team Atlas mods... usually 8 Triples... they are a great motor considering the price and I have been having a lot of success with them

HOWEVER.....

for some reason, I now have a motor that EVERY time it hits the track the positive brush shunt AND the positive motor lead unsolder themselves from the motor... I am an experienced racer and also pretty good with the soldering iron so I've already ruled out cold solder joints...

I've also run through all the obvious things like gearing etc

I'd put it down to something wrong with the motor if it wasn't for the fact its not an isolated incident for me... in fact I can think of at least 3 other occasions with DIFFERENT motors where the same basic thing has occured...

The only common thing that I can think of that is the same in all cases, is that the un-soldering thing starts after I've changed to new brushes... each time it was a different brand of brush so I can't see a connection there... I also have a hood aligner, comm lathe and all the good stuff usually touted as necessary for motor maintance

I have NEVER had anything, even remotely, similar happen with Stock motors

So... has anyone any useful insights into just WHAT might be going on?

is the shunt that is coming off the closest to the ground? Is the motor getting very hot? Is the surface you are running on hot (asphalt gets hot in the sun)? Ive seen it happen before and its because of the motor heat and the heat being emitted from the ground. just one possible reason.

This is not too uncommon with low wind mod motors especially on hot racing surfaces. The best way to fix this is to go to a much higher melting point solder. The stuff that I have used actually requires you use flux to make it melt properly.

Both good suggestions but they don't explain why this happens after I have to change brushes and why only the positive shunt AND positive motor wire do it

I am running a pro 4 so both brush shunts are almost equal distance to the ground

AMGRacer is right... This is due to the brush getting hot. There are several reasons for this. There is more efficiency loss from the brush to the com then from the com to the brush. You should also notice that the positive brush wears more then the negative brush, for the same reason.


8 single will draw more torque/current down low then an 8 triple.
Mashing the throttle out of corners can contribute to this as well.
Running high silver content brushes will generate more current/heat.

Easiest way to fix this is to buy real solder, (not cheap shit), and solder the shunt on well, with a significant amount of solder to bond with the end-bell. A good blob of solder here will dissipate the heat better and will be more resilient to temperature.

Put a fan on it and you will never have a problem again.

But have a look at your brushes for colour. If they are getting too hot it will tell here. If they look fine then it's your solder.

Coxy.

over gearing the motor and excessive arcing will can cause this to happen.

1. check the condition of the brush spring, maybe it has been damaged from excessive heat? if the spring goes soft then u will get brush bounce etc.

2. check the comm make sure it is tru.

3. what brushes are you running? with hotter weather u might have to go to a lower silver content brush like the Fantion 321M

4. consider timing the motor down to reduce arcing and reduce heat.

These are two good points. Try some harder brushes and a little less timimg....

Possibly, if the new brushes are serrated and run straight away, without any 2-3volt run in (new serrated brushes tend to have very sharp edges that require at least some low timing run-in period to smooth out the brush face). If the brushes have a full serration with sharp edges - they may be causing excessive arcing when they have to transmit mega amps when you gun the throttle. - thus causing heat etc.

my two cents

I'll check it all bit more throughly tomorrow

The thing I HAVE noticed is the shunts have change colour, but only in the middle of the shunt... they have gone a red/purple colour instead of copper coloured...

I will check brushes and springs better when I get a chance

I always run my motors in for around 10 minutes using a 4 cell pack, usually doing 3 or 4 short runs until the motor starts getting warm then letting it rest... I do this if the brushes are serated or full faced

The solder I am using at the moment is a 1mm, 60/40 mix... not sure of the brand off the top of my head

I usually run Fantom brushes, but at the moment I am using GM simply as they are more available here in WA where I have been doing my RC shopping