391 replies to this topic

[Bazzie]

Point taken Ron, I was thinking next time I'll ask more questions, if at all

 

The next bit of discussion is purely scientific, nothing to do with any specific melt-down. I've not had one by the way, had push-starts-a-plenty, but I usually take care of that before it causes damage.

 

So here's a bit of science and food for thought:

 

I did an interesting experiment. I put a soldering iron to an old 4002 endbell. It doesn’t take much to melt them. We’ve measured on a normal C43 LMP up to 130deg on the 4002. That's normal operating conditions on a C43 chassis. I tested with my adjustable soldering iron which is supposed to be very accurate, at 170deg it makes just a small mark with quite a bit of pressure. At 180 it starts melting it, tiny bit (very scientific ). When you hit 200 the plastic just collapses. I did the same test on a Parma (read also cheap) G12 endbell. At 190deg it barely marked the plastic. 200deg, still almost nothing. At 210deg it starts to react like the 4002 endbell at 170deg. At 230deg the plastic started melting like it did at 190deg on the 4002. The 4002 will not be very tolerant towards overheating brush gear, as a result.

 

​40deg is quite a big difference in tolerance to a bit of abnormal heat. Again, if you look at this scientifically (Ohm's law, that's probably high-school physics), resistance causes heat when you start to draw adverse levels of current (obviously to a point, beyond which the current will become too low to generate enough heat). Factors that could increase the system resistance (excluding things that can go wrong with the armature) could include:

• Dirty brushes
• Type of brushes (one type of brushes could have higher resistance than another)
• Dirty brush hoods
• Dirty comm
• Play between brushes and hoods - if a brush cocks it could mean less contact area between brush and hood, i.e. higher resistance.

The other factor we're looking at here (that will cause excess heat) is increase in current, so things that could cause an increase in current could include:

• Faulty armature (which sometimes manifests as a motor suddenly running really fast, but not for long!)
• Adverse load on the system, e.g. larger tyres, lower gear ratios (e.g. 3:1 vs. 3.5:1), track conditions, chassis set-up, basically anything that causes more load / drag
• Dirty comm (brush material in comm slots)
• Overlapping of brushes over comm

So there are quite a few factors (and I'm sure the above points are not exhaustive) that could contribute to brush gear overheating, and out of those follow some things we could do to limit the risk.

 

Also following out of that is that a lot can be solved by just regular cleaning. A PITA, but what I've also found is that replacing the brushes with better ones (Gold Dust, Big Foot etc.) helps keeping the comm clean for longer. Also, the fact that we now know the endbell melts at significantly lower temperatures, means we need to pay even more attention to keeping everything well-maintained and operate within more strict parameters.

 

It would furthermore be interesting to compare the resistance of the stock brush hoods on the 4002 with the copper retro-fit ones available, as that could contribute to the overall system resistance and produce more heat in the brush gear. Also, copper dissipates heat more readily, so it may remain a bit cooler than the stock gear.

 

Another thought, and here I don't have much experience. What is the impact of arcing on the comm? There's a reason arc-welding works - it generates heat. So could there be scenarios where you get more arcing than usual? E.g. load conditions, RPM, etc.  I've noticed that in these chassis, probably because they are so much lighter than the CTF, motors do rev higher on average, as there is less load on them. I've also noticed that most of our motors arc more at higher RPM.

 

I hope that's more useful to some...

[Bazzie]

Add to the factors, brush spring pressure, and from what I've read, less pressure causes more heat, which makes sense if you consider that with untrued comms (which these should be) you could start getting bounce, causing more resistance and more arcing.

[Bazzie]

It didn't melt down, and just a tiny bit of smoke escaped, but a perfectly good, 1 month old motor suddenly developed a push-start problem. I backed off on the throttle but probably a bit too slow. Afyer a push the car was really slow. Never done it before in many 100's of laps. I pulled the brush gear off, cleaned the comm. The arm looks good, no blackened wires, feint smell of burn. I replaced the brushes with new Gold Dust ones, ran them in under water, but the motor is now a slow one... It also draws around 0.8A @ 3V, a bit low for a 4002. It may have lost a winding on one of the poles. Dang, and it was a fast motor...


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[NSwanberg]

 

Bazzie, on 26 Sept 2017 - 04:21 AM, said:

Bazzie, on 26 Sept 2017 - 12:21 AM, said:

It didn't melt down, and just a tiny bit of smoke escaped, but a perfectly good, 1 month old motor suddenly developed a push-start problem. I backed off on the throttle but probably a bit too slow. Afyer a push the car was really slow. Never done it before in many 100's of laps. I pulled the brush gear off, cleaned the comm. The arm looks good, no blackened wires, feint smell of burn. I replaced the brushes with new Gold Dust ones, ran them in under water, but the motor is now a slow one... It also draws around 0.8A @ 3V, a bit low for a 4002. It may have lost a winding on one of the poles. Dang, and it was a fast motor...


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Were the rear wheels ever off the track under full throttle?

Of the PSFKs I have lost two of them I could tell the very instant it happened. When the rear wheels returned to the track after a fender to fender I could tell it was no longer the same motor. Went through all the motions of trying to restore it before pulling it apart for a postmortem. In both cases a pole was open. On one of the motors I could see the wire just broken at the com connection.

 

Seems like it always happens your best motors but then  those are the ones we race.

[Pablo]

"So here's a bit of science and food for thought:

 

I did an interesting experiment. I put a soldering iron to an old 4002 endbell. It doesn’t take much to melt them. We’ve measured on a normal C43 LMP up to 130deg on the 4002. That's normal operating conditions on a C43 chassis."

 

There is no such thing as "chassis normal operating conditions" in regards to motor temperatures.

I'll admit it is humorous.

 

"I tested with my adjustable soldering iron which is supposed to be very accurate, at 170deg it makes just a small mark with quite a bit of pressure. At 180 it starts melting it, tiny bit (very scientific ). When you hit 200 the plastic just collapses.

I did the same test on a Parma (read also cheap) G12 endbell. At 190deg it barely marked the plastic. 200deg, still almost nothing. At 210deg it starts to react like the 4002 endbell at 170deg. At 230deg the plastic started melting like it did at 190deg on the 4002. The 4002 will not be very tolerant towards overheating brush gear, as a result."

 

​You are comparing the endbell on a $13 motor to one on a $44 motor.

That's even worse than "junk science" - it doesn't even qualify as "science"

 

[smichslot]

"A bit of Science".

 

Given that it was supposed to be "a bit of science" I think that it lives up to what was intended and gives results that are valid: It is relatively safe to conclude that the plastic on a PS4002-endbell are melting at a lower temperature than a bit more expensive endbell from a Parma G12-motor.

 

Those that have studied the science of science are now getting ready to repeat the tests in order to see if their results are the same, in which case the theory on the cause of the meltdowns of the PS4002-endbelts is gaining ground.

 

That is how science works. It has improved many things in our lifes. And now it might help us to get better PS4002's!

 

Steen

[MSwiss]

A few things;
What is a Parma G12 endbell?

I wasn't aware they made one.

The temp the endbell melts at, isn't an issue, IMO.

The only ones I've seen melt, were at startup, when the motor had a massive short situation, the car didn't move, and the user kept his finger pressed on the trigger.

And it has only been on my heavily wired King track.

Never on my extremely lightly wired/current limited, flat track.

We race these motors twice a week at my raceway, in two wildly different cars, and once a month, in a third type of car.

The issue is clear.

Too tall of a brush, with too small of a comm, accentuated by the heavy neo cog.

The similiar 4002,with the same tall brushes, the same small comm, but with ceramic mags, never had a problem.

The fix is easy.

Reduce the height of the brushes, by notching them, and change them out before they are "tall" again.

[MSwiss]

Bazzie, on 18 Sept 2017 - 8:14 PM, said:

Add to the factors, brush spring pressure, and from what I've read, less pressure causes more heat, which makes sense if you consider that with untrued comms (which these should be) you could start getting bounce, causing more resistance and more arcing.

I'm confused by this post.

Are you saying the motor doesn't come with a trued comm?

If so, you are incorrect.

[MSwiss]

NSwanberg, on 26 Sept 2017 - 05:43 AM, said:

 

 
Were the rear wheels ever off the track under full throttle?

Of the PSFKs I have lost two of them I could tell the very instant it happened. When the rear wheels returned to the track after a fender to fender I could tell it was no longer the same motor. Went through all the motions of trying to restore it before pulling it apart for a postmortem. In both cases a pole was open. On one of the motors I could see the wire just broken at the com connection.
 
Seems like it always happens your best motors but then  those are the ones we race.

Hi Nelson,
Thanks for stopping by the raceway Saturday night.

So you are saying you get in some sort of special wreck where both braid are still in the slot, but the rear tires are up on the air, free reving at 12-14V?

Sort of like traversing the slot in a reverse wheelie?

That seems highly unlikely.

Wouldn't you hear a high pitched revving sound?

I've stood in the Deadman a good portion of the last 12 years of my life, race directing/marshaling, and I've never witnessed any sort of phenomena like that.

[Bazzie]

Mike, what I meant is that almost all comms need a re-true after some running, and rules don't allow that on our classes using 4002s.

I agree the problem is not the lower melting point, but it does mean when things go wrong, it goes bad in a greater hurry. Also fully agree on the brush reach around the comm exacerbated by the strong magnets being the cause of push starts.

Lightly wired tracks won't cause as much damage, the problem comes with car batteries and powerful PSUs paired with heavy wiring allowing many hundreds of amps to flow into dead shorts.

A good 4002 arm, even under stall conditions will not conduct enough current to cause such problems, unless if stalled for a really long time, so everything still points at brush reach around the small comm. That, as well as brush gear alignment and brush cocking is why I believe this happens. I've had motors that you just can't get right without breaking the rules. >0.5mm play in the brush hood, angles that you can't correct without cutting the plastic brush hood locators. I suspect that was what happened with my motor, as soon as it had settled down completely the problems showed up.


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[Bazzie]

NSwanberg, on 26 Sept 2017 - 05:43 AM, said:

 
 
Were the rear wheels ever off the track under full throttle?

Nope, I've never had that problem. I guess that would also get worse if you run @ higher voltages. We run 12.5v


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[Bazzie]

MSwiss, on 26 Sept 2017 - 4:21 PM, said:

A few things;
What is a Parma G12 endbell?

I wasn't aware they made one.

This is the one I tested



I suspect it may be a PS then? The can is badly twisted and it doesn't seem to be as well made as a Cahoza for instance


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[MSwiss]

Not a Parma.

 

But not a big deal.

 

Really nothing to do with the issue.

 

I'm guessing the ones that have the little pop, that fail, have comm connections that aren't as solid as ones with better connections.

 

Those are the ones that probably melt the endbell at unsuccessful startup.

 

A higher temp endbell might give you a split second more of holding the controller down, before melting, trying to "make it go".

 

Edit-someone did point Parma markets a G12 motor. Regardless, it's a repackaged item.

[swodem]

MSwiss, on 26 Sept 2017 - 4:28 PM, said:

I'm confused by this post.

Are you saying the motor doesn't come with a trued comm?

If so, you are incorrect.

This is an image of a lightly used arm from a PS4002FK



Mike - Does it look 'trued' to you!?

Not as I know truing. That baby has not been near a lathe of any kind
Its just formed to shape when the whole com was manufactured

Don't believe me, get a brand new one, pull the arm and do a light skim and see how 'bad' they are

I still stand by this is the biggest issue with these motors.
The problem doesn't exist with Hawk7 or Falcon7 or Hawk Retro because the brushes are so much smaller they follow the imperfection, rather than being held off the early contact with the next segment - which in my mind is what causes the short.





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[gotboostedvr6]

The pattern on the comm suggests something other then a cutting tool was used at the manufacturer for the initial "true"

[MSwiss]

swodem, on 26 Sept 2017 - 8:04 PM, said:

This is an image of a lightly used arm from a PS4002FK



Mike - Does it look 'trued' to you!?

Not as I know truing. That baby has not been near a lathe of any kind
Its just formed to shape when the whole com was manufactured

Don't believe me, get a brand new one, pull the arm and do a light skim and see how 'bad' they are

I still stand by this is the biggest issue with these motors.
The problem doesn't exist with Hawk7 or Falcon7 or Hawk Retro because the brushes are so much smaller they follow the imperfection, rather than being held off the early contact with the next segment - which in my mind is what causes the short.

That comm does not look awful at all.

 

That comm has been obviously trued.

 

Maybe not the greatest job, but it is trued.

 

IIRC, but don't quote me, typical mass produced arms are trued with some sort of abrasion device.

 

I've set G7 World Records with comms looking way worse than that.

 

As mentioned before, your theory doesn't make any sense.

 

Imperfect enough to confuse the commutation, but still a rocket motor?

 

Blown G7 motors, with comms .002" or .003" out of round, still start up fine, but run much slower than a 4002FK.

 

Essentially the same motor, the 4002, but with ceramic magnets, has never had the problem.

 

4002FK's, with shorter height brushes like I sell, never have the problem.

 

And Falcon 7 type motors never need a push start, because with the small brushes, there isn't any overlap, NOT because they are not confused by the less than perfect comm.

 

One way to prove it to yourself.

 

Get a chronic "needs a pushstar"t motor, while it is still running well, true the comm, and see if it cures it.(without realigning the hoods, replacing the, brushes, etc.)

 

Cure 2 or 3 motors with chronic pushstarts, with a comm true, and then your theory will hold water.

[swodem]

Mike. I don't think your first sentence is true.

Regards your last sentence, If I had a pushstart motor that's what I would do.


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[MSwiss]

I misunderstood your comment "Not as I know truing.".

 

I took it as you admitting you haven't done it much, or witnessed the results of ones you've run, after knowing the exact condition of the comm, by truing it yourself.

 

I'll omit that comment.

[swodem]

Here are three motors that were all meltdowns.
I have given them all just a light skim



Now obviously there is a chance their out-of-round may be a result of the heat from the shorting out, I can't rule that out, but they definitely are all far from true, with a definite high segment. The cutting tool had not touched the other two segments


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[MSwiss]

If comm tool hasn't touched the other two segments, and the motor was normal/fast up until then, I'm 99.8 % sure, the lifting occurred after the shorting.

[idare2bdul]

You know if we just put the nice American made Big Dogs in these critters you would have the right sized comm a smile and a much shorter thread.  

[Samiam]

.....and have an approved refurbisher put a seal on it. Yeah....let's do that. Sounds like a great idea. That shouldn't generate any controversy. 

 

 

But seriously folks. The problem was examined, a simple solution devised, rules revised, problem solved.

 

Only thing missing here is a thread drift into some sort of food.

[Samiam]

OK, I was wrong.

Pablo, on 31 Jan 2017 - 2:09 PM, said:

 A clove of garlic tied to your controller handle with catgut.
- A sprig of parsley wrapped around the positive lead wire.

No more push-starts.

[Bazzie]

Haha, I missed that one Sam


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[Bazzie]

So my new approach is:
Align brush hoods as well as possible
Immediately replace brushes with gold dust / big foot
Once run in, keep brush tips trimmed.
Reason for point 2 is it only takes about 150 laps for the stock brushes to run in again. Becomes a schlepp to trim that often


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