391 replies to this topic

[swodem]

We have had an ongoing issue (not at our track but at others) with 4002 motors getting such a big short it heats the endbell hardware up such it melts itself to destruction (spring).

 

For the first time it happened today at our track.

 

A visitor from another track who isn't a motor fiddler was driving his car and stopped for a while. When he went to go again 'poof' smoke arose from the back of his car and it was all over.

 

The positive brush got flung out by the spring releasing its tension once the screw pulled free of the melted endbell and fused itself to the body - it was that hot! Neither brushes showed an abnormal wear pattern.

 

We put another motor in and got him going and I kept the parts I could for review.

 

A quick autopsy tonight revealed nothing more than a dirty comm (oil?) and some bridging of one comm segment to another.

 

Thoughts on why? It was running strong before this happened...

[Racer36]

I suspect Sam is correct. The brush in the picture is full width and is broken in enough to cause the push start problem, which is nothing but a dead short.

[Pablo]

Looks like it's geared pretty tall for a 4002. Especially with those extra-wide wheels y'all run.
Body cutting a groove in the tires probably didn't help.

Brush marks on comm sure look long. if I'm right, the arm was really sloppy and possible riding hard on one end or the other due to not being centered.
 
These motors do fail sometimes. They look similar to the 4002B but are not even close to being the same quality and care of assembly.

[havlicek]

Whatever the cause, that's a real "1960s" kinda meltdown for a 2017 kinda motor! Mr. Mabuchi would be jealous!

 

-john

[MSwiss]

The car may not have moved when the trigger was pulled and he smoked it.

 
We've been having less issues locally, since I started making the below brushes available.
 
Cut-down brushes for PS4002FK / JK Hawk 6 motors
 
When the car doesn't go, keeping the finger on the trigger definitely isn't a good idea.
 
FWIW, they will "pop" on my King (12.2v, medium-amp power supply, heavy wiring) but do not (that I recall) on my flat track (13.1v hi-amp power supply, very mild wiring).

[Frankie Schaffier]

Steve,

I had exactly the same thing happen to two of my FKs. Both when I pulled the trigger when it wouldn't go. Think I would have learned the first time.

[Brinkley47]

The very first one I bought did this exact same thing. Since then, never had a problem. I always check the hardware and brush arc before running them now. Sometimes magnets will hit the arm generating lots of heat. I believe that was the problem with the first one I had.

[NSwanberg]

"When the car doesn't go, keeping the finger on the trigger definitely isn't a good idea."
 
Absolutely do not hold your controller full open if the car stalls at the start. At Downriver Speedway we call this being FK'd or FK'ing.
 
I find the the trailing edge of the brushes wear and wrap further around the commutator creating a dead short across one of the leaves of the comm. I can usually solve the problem by simply filing about 1/32 of an inch off of the trailing edge of the brushes away. Not a hard thing to do at all.
 
Interestingly enough it seems the well broken-in motors do not FK as often as motors that are in their third or forth race. It is aggravating but I find it can be dealt with. I have never smoked an FK motor. Almost all the ones that I have lost were due to one of the wires breaking at the comm connection. That hurts when it is an exceptional motor that you lose.

The other issue I have is the endbell bushing spinning. Most of the FK motors I have were bought over the counter at Downriver Speedway. I think eight so far.

[willy wonka]

I have about 30 PS-FKs and I've experienced what the OP has as well. I hit the trigger for maybe two seconds, didn't go hit it again and smoke arose. As I take my body off I realized that both wires on the motor unsoldered themselves it got so hot. Also it blew the hardware off the positive side I believe.

Like Nelson I've noticed a lot of the endbell bushings spinning free, some after a very short amount of run time.

Other than that it's a pretty good motor for the money.

[Zippity]

Posted in another thread:

 

Sadly, brushes "cannot be timed, drilled, friction cut, or fitted with shunts" here in New Zealand. 

 

This motor is the mainstay of our 1/24 scale racing.

[MSwiss]

Are you allowed to change brushes and springs?

If so, disallowing cut brushes makes even less sense.

[Zippity]

Mike,

 

The full wording of the New Zealand rule states:

 

1.5 - Brushes and Springs – Brushes & springs may be changed. Brushes cannot be timed, drilled, friction cut or fitted with shunts.

 

I only follow the rules. 

[MSwiss]

Like I said in my thread on cut brushes, the only rationale to allow a change is to improve performance or reliability, so why not allow cut brushes?

Plus, a new brush is essentially a cut brush until it is fully broken in.

[Zippity]

Mike,

 

I'm not disagreeing with you. 

[Zippity]

[swodem]

I'm not yet a believer in the theory that push-starts and melted endbells are..

1. The same thing
2. Due to brushes being so big on a small comm

Reasoning:

1. Many push starts are not shorting out, they don't burn or smoke they just won't go.

2. Why if it's related to brush size are some like it from birth, and sometimes they improve and stop once run in, theoretically they should get worse

3. Why don't they all do it?

I think that push-starts are motors with an elliptical comm that's not getting brush contact on one comm segment when it should - hence no short.

I don't know yet what is creating the short or where it's shorting out, but will look deeper into this melted one I have and try and find out.

[MSwiss]

1. Many push starts are not shorting out, they don't burn or smoke they just won't go

Probably varies by track, depending on current delivery. My King with eighteen 10 AWG taps pops motors. My Flat, with eight 14 AWG taps, doesn't.
 

2. Why if it's related to brush size are some like it from birth, and sometimes they improve and stop once run in, theoretically they should get worse.

The fit of the brush to the hood, varies wildly.
 

3. Why don't they all do it?

Because they all don't have the same good or bad alignment, and, again, the fit of the brush to the hood, varies wildly.
 

I think that push-starts are motors with an elliptical com that's not getting brush contact on one com segment when it should - hence no short

You must be kidding - LOL. Unless you step down the whole segment/essentially remove it, how is the spring not going to press the (unhung) brush enough to find comm? Regardless how could the motor still be fast with an out of round comm?

[swodem]

Quickly, because I am at work, I'm not kidding, see sketch. You could imagine a scenario where com segment 1 gets contact late.

No 'short' involved.

I don't believe lower current tracks wouldn't burn out a shorted motor... even low power tracks have huge amps.

[MSwiss]

Sorry, Steve, but you are 100% incorrect.

A - Again, a motor with a comm that shape would never be fast.

B - You would have to believe that the Chinese elipitical comm somehow only finds its way to the neo mag PS4002FK and JK Hawk 6 armatures, but not other cheap Chinese armatures, including the PS4002 and JK Hawk.

How come there isn't any history of these ceramic mag, non-heavy cogging motors, having start-up issues?

Even low power tracks have huge amps? You can make that claim based on what?

Being to every slot racing facility in the world?

When we started racing Hardbodies on my flat track, along with the minimal wiring, we ran on an equally puny, 12v, 28 amp power supply set-up.

It was adequate to race Falcon 7s and ceramic magnet minimotors.

When we went to the 4002FK, when you had ones that had start-up issues, if they were in that bad spot at the start of a heat or after a track call, not only would they not burn/pop, but the other seven cars would start up slow.

If the non-starting was caused by your elliptical comm theory, no circuit is being made, and the other seven cars, of course, wouldn't be affected.

[swodem]

Gee, you're cranky today, Swiss!!

I'm just trying to get to the bottom of this

Yes, the motor could be OK-fast; even one with a blown pole isn't that slow.

You then please explain to me a push start motor that doesn't short/burn out or get hot.
As I said, not all push-starts turn to sticky messes.

I'm just trying to understand what/where the problem is to be able to rectify it.

You're assuming the ceramic motors came from same factory...

You make some valid points though and I'm not saying you're wrong.

Oh and yes I have been to every track in the world. ;-)

And if 28 amps ain't much, you stick your tongue on the braid and pull the trigger.

[swodem]

Don't do the tongue thing!!!

[MSwiss]

My post #21 debunks your elliptical comm, no connection, theory.

[swodem]

I did read it. It may be a shorting out one (endbell melter) rather than a push-start one

I'm going to direct wire up an arm to our track that has one pole disconnected and replicate my theory and see what happens.

[MSwiss]

And the ceramic motors aren't made in the same factory?

If you don't rotate the arm, you can't tell the difference between the 4002 and the 4002FK.

And the the can ends of both of those, and both of the JK minimotors, are identical.

[swodem]

Maybe it's the same factory.

I'll have a look and compare the Comms. I think they are different (PS~JK).