391 replies to this topic

[Zippity]

Why did I know that you would ask me that? 

 

Let's wait until the others have posted their times tomorrow night - then I will know if I have something to brag about or not

[Fast Freddie]

Maybe you guys didn't know this or maybe you did but whether or not a certain motor has a push start problem isn't solely due to the brushes overlapping a comm segment. 

 

There is another reason for the push start problem and that's where the arm stack settles within the magnetic field. When a motor stops and the arm settles in a certain position the comm may or may not have a segment touching both brushes.  Some motors, no matter how much the brushes are worn, will stop in such a manner that they will never have both brushes making contact with a single segment. 

 

Then there are motors that will nearly always stop in such a manner that even brushes not completely broken in will have a push start problem. When you consider the small dimensions we work with, something off by .003-.005" could make a difference. So could a 2-3 degree timing variation or magnets not directly parallel and square in the can. 

 

So while aligning the hardware is a great start the absolute best way to prevent a push start without losing performance is to cut one side of each brush and install the cut side as the trailing edge. There is no appreciable performance gain but there is a huge frustration removal gain.

[Zippity]

... cut one side of each brush and install the cut side as the trailing edge. There is no appreciable performance gain but there is a huge frustration removal gain.

 

That statement is fine if your rules allow it - ours don't!

[swodem]

Assuming the above is correct, therefore it sounds to me like the issue also then would be resolved if the motor was timed differently - I.e. 10 or 20 degrees instead of 15 degrees?

[Samiam]

Noting that this motor is very similar to the 4002 that doesn't have the push start issue, what is it about the FK that may be causing this?

 

The wind is close. 60t of #31 vs 65t of #30. Same can. Same EB. The major difference is the poly neo magnets in the FK vs the ceramics in the 4002.

 

I'm guessing it has something to do with the way the magnets are made. As described by another blogger,they are made from a mix of materials. This mix is not always the same and it is not always consistent across the entire magnet. This would explain why some do it and some don't.

 

This is only my guess as I am no expert. But I did stay at a Holiday Inn Express once.

 

Edit: The 4002 has a 20 deg nominal timing. The FK is 15.

[swodem]

That statement is fine if your rules allow it - ours don't!

Let's not distract this thread with who can and can't do what because of localised rules. We are trying here to get to the detail of the problem... rules can be changed accordingly if required to resolve issues such as this, if the fix is effective.

[Greg VanPeenen]

Noting that this motor is very similar to the 4002 that doesn't have the push start issue, what is it about the FK that may be causing this?

 

The wind is close. 60t of #31 vs 65t of #30. Same can. Same EB. The major difference is the poly neo magnets in the FK vs the ceramics in the 4002.

 

I'm guessing it has something to do with the way the magnets are made. As described by another blogger,they are made from a mix of materials. This mix is not always the same and it is not always consistent across the entire magnet. This would explain why some do it and some don't.

 

This is only my guess as I am no expert. But I did stay at a Holiday Inn Express once. 

 

Edit: The 4002 has a 20 deg nominal timing. The FK is 15.

 

The comm is smaller around then the comm on the Puppy Dog and the brushes are the same size. When the brushes seat they overlap on the comm segments causing a short no-run situation.

 

Aligning the brush hoods does help, but is not a cure all. It is that simple.

 

There is a cure that does not involve altering the brushes, but I'am not telling anybody but the new owner of Pro Slot.

 

GVP 

[Samiam]

Greg,

 

I should have been more specific. I was referring to the 4002 with the Chinese arm. The PD is a 4002B or 4002BB.

[gotboostedvr6]

If you reduce the timing of the arm the problem disappears.

[Fast Freddie]

Reducing the timing and even increasing the timing could cure the problem but it all comes down to where the arm stops in relation to the comm. 

 

I had this problem with C-can Contender arms from two different manufacturers. The arms were both 45 degree and both .540" diameter with a .560" hole, Camen magnets, and Red Fox can. One arm was a PS and one was a BOW. 

 

When installed in the same set up the PS arm experienced push start problems while the BOW didn't. The reason for that was the arm web on the BOW was narrower then the PS arm so when the arm stopped rotating on the BOW arm it never settled with the brushes contacting a single comm segment.

 

While it happened nearly every time the PS motor stopped. Even with the brushes and springs removed I could never force the BOW arm to stop in such a manner that the web of the arm would be between the north and south magnet tips. 

 

This happened almost all the time with the PS arm. When that happened the brushes contacted a single comm segment.  I cured the problem by first filing both sides of each brush but realized I was reducing the timing so I went to just one side of each brush and installed that side as the trailing edge and it cured the problem. 

 

You may also like to know that doing this on Mini 12s helps reduce the heat in the motor by reducing the brush overlap. I have two Mini 12s that have the 38 degree PS arm and at first they would overheat badly but when I cut the brushes the heat went down dramatically. This is an added benefit of reducing brush overlap in any motor. 

[swodem]

... it never settled with the brushes contacting a single comm segment...

... When that happened the brushes contacted a single comm segment...

FF, for clarity this means "both brushes contacting the same comm segment at the same time" - i.e. a short circuit, as indicated by the second image on my post #38 of this thread - correct?

[Fast Freddie]

Correct Steve, with the PS arm both brushes made contact with the same comm segment almost all the time while the BOW arm never did.  I knew some racers who ran the same can and arm but they ran different magnets and they didn't have a problem.  So I came to the conclusion that the distance between the north and south magnet tips also affect the push start, particularly with the PS arms.  If that distance is changed maybe the web of the arm won't settle between the magnet tips.  Thing is I never tested that theory as I nearly stopped flat track racing.  Maybe I'll put a couple setups together this year and test the theory.

[Bazzie]

I use my own PWM controller, and those are more sensitive to shorts on motors. This is due to the fact that PWM gives full power but just intermittently. With an analogue controller you're running reasonably high resistance until you hit full throttle. I therefore have to be doubly careful as behind a car battery and some serious wiring, I can send hundreds more amps through my controller than the transistors can handle, even if just for 40% dutycycle. That's enough to blow the controller if you're not careful. So if the car doesn't move, I come off throttle and fix the problem before continuing. I suffer under the same rules as Zip, so I reset my brushes to factory condition. They get shipped with flat tips, it's only when they are fully run in that the tips are not flat anymore and you get shorting across the comm. I used to run only one 4002fk car in all classes and was changing to a new motor every month. Now that I reset the brushes, I've been running the same motors in my F1 and LMP cars for the last 6 months.
We need to fix our ridiculous rules. There is now way I can improve motor performance by trimming brushes, I only give the motor and my controller longer life!
I do have another theory. I use a current sensor in my controller to detect shorts and then remove power. It is basically an extremely fast electronic fuse. I have seen on starting up a G12 occassionally it would trip the fuse, which it shouldn't do, as the fuse is set to 45A. Also, once the motor has run up a bit after that first trip, it would be fine. Dirt in between comm segments, I suspect. Now compare a 4002 to the g12. Tiny comm, lower RPM and less time that the gaps between segments are not covered by a brush. To me it also looks like the gaps on 4002s are slightly narrower, I could be wrong. I hence suspect it is more difficult for dirt to get flung out of the gaps, so you could get more build-up and hence shorts


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[Guillermo Suar]

PS: Find a "push-start" 4002FK. Install a ceramic mag can on it. I guarantee the "problem" will go away.

 

Hope this will add some light. I did not do what Mike says but the opposite.

 

I put a PS4002 (ceramic mags) arm inside a PS4002 FK (neo mags). Motor with ceramic mags did no have any issue. The one assembled with neo magnets had the push-start problem.

 

Same arm and endbell on both. I just transferred the cans.

 

After cutting the brushes per Mike post (somewhere in the blog) the problem went away.

[Fast Freddie]

There is no reason to have a push start problem if a solution is given.  While cutting the brush .010 or less does solve the problem in all cases I understand that some local rules don't allow it and you got to ask yourself, WHY?  If the reason is that not all racers have the technical experience to cut the brushes then I'm sure there are other racers who would help them.  If the reasoning is that it strays away from the motor remaining totally stock then so does changing brushes and springs.  If a motor has an inherent problem that can be fixed without vastly modifying the motor shouldn't the rules be changed to accommodate the fix?  Cutting the brushes will reduce racer frustration and improve the racing environment while also saving money on destroyed parts.  The negligible performance improvement, if there actually is one, is no reason to allow the cut brushes.     

[Jason Holmes]

My 2 cents love these little motors have only ran the in Can-am Plus and can't now    and Grp F so the cars have always been under 90 grams at all the races I've been in I have yet to see any pop or burn I don't trim the brushes just fix the hoods and change out the stock brushes and run them all the tracks that I've ran on have big amps have ran them at 14.1 V down to 13.3 at BPR with over 2500 Amps not a problem   I think it has to do with weight of car and big amps on track This all falls back on a cheap motor which is nice and your choice on what to run If you don't want problems build the motor for more $$ then if not live with it remember there your Dice roll them as you wish

 

Jason

[swodem]

....Dirt in between comm segments, I suspect. Now compare a 4002 to the g12. Tiny comm, lower RPM and less time that the gaps between segments are not covered by a brush. To me it also looks like the gaps on 4002s are slightly narrower, I could be wrong. I hence suspect it is more difficult for dirt to get flung out of the gaps, so you could get more build-up and hence shorts

I don't think that's it mate
Here are two pics from two different melted motors from your track

One has a dirty comm
The other a very clean one
They both melted down the endbells
You'll note they even come from very different batches of 4002 as the comm is quite different.





I'm still not convinced it's solely a comm/brush overlap issue.



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[MSwiss]

 

 

After cutting the brushes per Mike post (somewhere in the blog) the problem went away.

 

 

I'm still not convinced it's solely a comm/brush overlap issue.

You may not be convinced, but the above quoted post disputes that.

[swodem]

Yep that's why I posted this.
I had a motor start a race on Sunday fine. It was a long race. For some period it became a push start, for maybe an hour or so, then went away and was OK.
No brushgear was touched.

I have also seen BRAND NEW motors not run in behave in a pushstart manner. They technically can't bridge a com segment.

Explain if you can....


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[Frankie Schaffier]

Slot car racing is different than all the other types of racing I’ve done over the years. Issues just seem to continue to banter back and forth even when a solution has been given that works, seems like someone is always trying to prove someone wrong.

In this case I’ve only seen one solution suggested that don’t require breaking the seal and low and behold it works. Exactly as has Mike and many others have posted. If you have a motor that needs a push, trim the brushes and the problem is gone. If you don’t want to risk smoking a “good one”, then trim the brushes from the start and you’ll never have the push start motor smoking problem.

I do agree the rules should allow the brushes to be trimmed, your allowed to use different brushes, cut them on the turtle to shorten them, sand them if you wish, etc etc.. I cut them anyway. Go ahead and DQ me from a $10 slot car race for cut brushes. It's cheaper then a smoked $15 motor with replacement brushes and springs.

[MSwiss]

Steve,
On the latter, they may of not had perfectly aligned or formed hoods.

Also, did you examine the brushes in these motors, immediately before the race, to confirm they still had flat spots on the brush face?

At the time of the first pushstart, was the race stopped, and it was confirmed that the brushes still had flat spots?

[swodem]

Mike,
On point 1, I accept that is a likely scenario
Point 2, no. The new unused motor wasn't mine
Point 3, ahhh mate it was a race. 6hr Enduro. No-one stops a race because a car has a problem...


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[MSwiss]

If you have a motor that needs a push, trim the brushes and the problem is gone. If you don’t want to risk smoking a “good one”, then trim the brushes from the start and you’ll never have the push start motor smoking problem.

 

 

Mike,
On point 1, I accept that is a likely scenario
Point 2, no. The new unused motor wasn't mine
Point 3, ahhh mate it was a race. 6hr Enduro. No-one stops a race because a car has a problem...

Of course on 2 and 3.

 

The point is you made your statement  "They technically can't bridge a com segment." without any real knowledge the brushes had flats, other then they might of, because it was early in the race.

 

And in the top quote, another racer chimed in his pushstart issue was cured with shorter height brushes.

[swodem]

Mike
You obviously have a desire to chop me down

My point on non-run-in brushes not technically able to bridge the gap relates to my research previously posted




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[MSwiss]

Mike
You obviously have a desire to chop me down

My point on in-run-in brushes not technically able to bridge the gap relates to my research previously posted

No desire to chop you down.

 

Just 99.9% sure what the sole issue is.

 

What are "in-run-in brushes"?

 

If you mean "not-run-in" brushes, my point is how do you know the brushes in the motors you cite, were not broken in, if you didn't see them?