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Looking at the JK Hawk 7R


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#1 havlicek

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Posted 12 January 2018 - 05:27 PM

     With all the hubbub surrounding the "two-step", or "two speed" issue, I was able to have a racer send me an example of this motor with the problem.  Upon inspecting the motor, I was pretty impressed with how tight it seemed.  There was zero detectable slop in the bushings (*more on this later), and end play was almost nonexistant (!?).  Maybe I got lucky, but then again, this is supposed to be a problem motor".  With this general type motor, I almost never run them and just take them apart for parts, so I don't have a real lot of experience with them.

     So, I put the motor on the power supply and DID get some of the "two-step" thing, and that went away with increasing voltage (*I think, but can't remember exactly, the motor smoothed out above 8V or so).  Just then I remembered that I hadn't oiled the bushings.  I put a light drop on each end, put it back on the power supply...and couldn't repeat the two-step issue.  ***Now, it may be that I warmed the motor enough the first time I ran it to loosen things up, it's not at all  clear that a drop of oil was all it needed...draw your own conclusions.

     Moving on, I grinded off the itty bitty tabs and took the motor apart.  I was really surprised at the commutator.  The brushes were JUST fully seated and the com was dirty with a hard dark coating.  The com slots weren't full of gunk, but the com segments were definitely and significantly dirty, but the com itself wasn't worn, leading me to believe that however the motor was broken-in involved some sort of water or something...* BUT, that's an assumption, although I think a good one.  I metered the arm as-is and was having some difficulty getting a solid reading, but it seemed to stay within a range of around 10 thousandths from pole-to-pole.  Not "awful", but not anything to write home about either.  I cleaned off the com with some 000 Scotchbrite so the segments were all shiny-clean...NOW I got a solid reading on all three poles...and get this...they were all within a thousandth or two.  That to me is mighty impressive, especially for a cheap throwaway motor.

     While the motor was apart, I took the arm and stuck it in the bushing one end at a time and both ends were tight.  You can bet that, with the arm installed and supported by BOTH bushings at the same time, these bushings are for sure slop-free.

     Here's the kicker.  After all this, I put the motor back together with the com cleaned and just held the "end bell" or "end cap" (*or whatever you can that thing) in place.  The motor spun-up just fine.  :)

***Anyhow, I didn't see a real major issue, but I'm not a racer and I didn't install the motor in a car, so you can take all this with a LARGE grain of salt.  I DID see a small issue at first, but it went away as if by magic (!?).  The only hint I see of what *might* be a problem was with what I think was the break-in method.  Years ago, I posted that I thought breaking these things in under water wasn't a good idea.  I was...er...immediately "corrected".  :)  Now, and all these years later, I still think it's not a good idea...but again...I'm not a racer :)  Here's a picture of the motor upon opening it up:

IMG_2444.JPG


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#2 Pablo

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Posted 12 January 2018 - 05:44 PM

That black coating doesn't come from water. It comes from whatever "motor honey" the owner used during break in.


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#3 havlicek

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Posted 12 January 2018 - 05:52 PM

That black coating doesn't come from water. It comes from whatever "motor honey" the owner used during break in.

 

You know far more about these motors and what racers do to them Pablo...so I'll trust what you say!  All of the above is from a disinterested viewpoint.  :)


John Havlicek

#4 Pablo

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Posted 12 January 2018 - 06:32 PM

Hey, I just thought of something  :bomb:

 

JK has announced they may "rotate" the brush orientation in 2018 to make the curvature conform to the comm.

Everything we have ever been taught about slot car motor theory says this would be an improvement.

Theory dictates they should have been built that way from the beginning

 

I do not know if JK has actually tested the theory. Traditional theory may, or may not, work on these type motors.

That's my theory :D Until it has been tested, we won't know.

 

Which brings us to Havlicek, who has one opened up, and, well, you know what I mean :D :dance3:


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#5 havlicek

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Posted 12 January 2018 - 08:27 PM

 

JK has announced they may "rotate" the brush orientation in 2018 to make the curvature conform to the comm.

Everything we have ever been taught about slot car motor theory says this would be an improvement.

 

Well, I for one am not so sure Pablo.  Certainly, if the brushes come pre-radiused to a close fit for the com, I think that would be a good thing.  If they are a poor fit...or worse...have no radius, then I think the way they are might be better.  

 

 

 

Which brings us to Havlicek, who has one opened up, and, well, you know what I mean  :D  :dance3:

 

 

Nah!  ;)


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#6 Fast Freddie

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Posted 13 January 2018 - 12:27 PM

I recently thought I had this two speed problem cured but that was because I never took the motors above 6 volts.  I recently free wheeled 4 of my HR and 4 of my H7 motors to 12volts and found out that they all had a two speed change that came in around 9-11 volts.  Since these motors are run at 12-13.7 volts on the track that could interfere with performance.  I believe the brushes are fully seated on these motors but I'm not 100% sure.  They may not be my eyes aren't what they use to be.  I also took a HR motor that had been through 1 race and had brushes that didn't appear to be fully seated.  I put it through a Simple Green procedure for 5 seconds at 3 volts.  The comm. was clean and the brushes fully seated.  It didn't have a profound two speed problem but it did have a very sight speed change at around 10 volts. I still believe that in order to get rid of the two speed effect the brushes must be completely radiused to the comm.


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#7 gotboostedvr6

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Posted 13 January 2018 - 03:09 PM

That comm looks pretty clean to me. 


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#8 dalek

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Posted 13 January 2018 - 07:54 PM

Last week I took two H7 motors from my old-motors box that were past their useful life for racing.  The positive brush on both motors was mostly worn away (as most of you probably know, the positive brush wears away faster than the negative one).
 
They had been broken in by driving on a track (not by running them submerged in any liquid).
 
The comms were the typical dark color.  The same dark color that starts out as two thin lines that increase in width until they meet in the middle.  
 
The armature shafts had no detectable side play in the bushings (typical).
 
I oiled the bushings with Glidex.
 
On my power supply they both 2-stepped at about 9 volts.  This, from my experience, is typical of most H7 and HR motors, though usually when installed in a car and run on a track it doesn't seem to interfere with performance.
 
I carefully took them apart (trying not to disturb bushing alignment) then put them back together without making any changes.  They still 2-stepped as before.
 
I took them apart again and sanded the armature shafts for a couple of minutes by spinning the arms with a drill and using 1500 grit sandpaper.
 
I pre-oiled the bushings and shafts then put the motors back together.  
 
The first motor no longer 2-stepped.  From 2 volts to 12, at 0.1 v increments, the RPM increased evenly and amperage was normal -- not a hint of 2-stepping.  Normal no-load amperage seems to be about 0.4 amps at 2 volts -- 0.7 amps at 12 volts.
 
The second motor still 2-stepped as before so I took it apart again and used 600 grit sandpaper on the shaft then followed it up with 1500 grit.  When I put that motor back together it no longer 2-stepped.
 
There was still no detectable side play in the armature shafts so apparently I didn't remove very much material.  I dunno -- maybe just enough that more oil molecules had room to get between the shaft and bushings and act like little ball bearings.
 
Note:  Something else I recently tried with several motors was run the voltage up to where they were pulling over an amp and near the point where they would typically shift then giving the motor can a couple of firm raps with a wooden dowel usually would cause it to shift.
 

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#9 havlicek

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Posted 14 January 2018 - 08:05 AM

That comm looks pretty clean to me. 

 

Not to me, but even more importantly, it didn't "look" clean to the meter.  Judging how clean a com is by how it looks... is like judging how good a meal tastes by how it sounds  :D


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#10 Ecurie Martini

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Posted 14 January 2018 - 12:43 PM

I don't play in this sandbox - I've been following this motor issue from idle curiosity fueled only by the fact that as a 1/32 scale builder/racer, almost all of the motors I deal with are sealed cans.

 

From everything I've read, in particular John's observations and the comment about being able to trigger the behavior by rapping with a dowel, my take is that it is a resonance problem, most likely involving the brush springs.  Commutator condition, brush length and bearing fit could all contribute. Hitting the resonance point of the brush springs would induce some vibration that could result in loss of contact.  Higher input voltage would force the motor speed beyond this point and out of the resonance range.

 

EM


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#11 Ecurie Martini

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Posted 14 January 2018 - 12:50 PM

Further point:

 

"Here's the kicker.  After all this, I put the motor back together with the com cleaned and just held the "end bell" or "end cap" (*or whatever you can that thing) in place.  The motor spun-up just fine."

 

Holding the motor in hand could add enough damping to the system to eliminate any resonance effect.

 

EM


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#12 dalek

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Posted 14 January 2018 - 03:30 PM

The motors are pulling current that is above normal just before they jump up to normal speed and current draw.  To me that seems like the result of a mechanical load and my testing of the two motors seems to point towards shaft chatter.

 

Maybe the arm shaft is rolling around inside the bushings like a wheel rolling down the road (metal to metal contact) plus the two ends are out of sync with each other (creating a load) until the point occurs that they start sliding on oil molecules.  I'm no engineer but just wondering.

 

The brush arm resonance theory should be easy to check.  Maybe push on the brush arms with thin flexible plastic toothpicks and see if the motor shifts (aka jumps up to the normal speed and current draw).

 

Or I'll take an old motor that shifts and bend the brush arms so they have more pressure and/or less pressure to see if that makes the shifting go away or move to a different voltage.

 

Or add a big blob of silicone on top of each brush arm and see if that makes a difference.

 

 


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#13 JerseyJohn

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Posted 14 January 2018 - 05:29 PM

John, as there is no balance marks can you have the arm checked for static and dynamic balance to see how accurate manufacturing is?


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#14 Shiggy

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Posted 14 January 2018 - 08:31 PM

That black coating doesn't come from water. It comes from whatever "motor honey" the owner used during break in.


I break in my motors (Hawk 7 and Hawk Retro) dry and all get dark even deposits on the comm.
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#15 NSwanberg

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Posted 15 January 2018 - 04:29 AM

Perhaps the coms are not quite centered on the shaft? I only have one of these in my quiver and it has never been in a car. I am starting to want to take it part just to see what is going on with it.


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#16 havlicek

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Posted 15 January 2018 - 06:50 AM

I'm more than a little worried about adding what would be uneducated guesses to what, if anything, may be going on here, but Alan's comments do seem plausible at least.  Resonance can cause some freaky things to happen, things that can be difficult to track down and/or duplicate.  While these motors are essentially the same as any other brushed DC motor, there are some aspects to them that, by nature, the end user can't easily mess around with.  For one, the brush arms here are much more like those in the old "open frame" motors.  They both locate the brushes, and apply pressure on them to keep them in contact with the commutator.  That pressure isn't "adjustable"; you can't substitute a lighter or heavier spring, so trying to see if there's an issue there at a certain "resonance point" by changing that is a no-go.  Resonance also can easily affect the actual armature in a really slight-but-rapid "back and forth" movement, happening at certain speeds and then disappearing above and below that speed range.  It can also happen as a "wobble" with worn bushings, again at certain speed ranges (*although the bushings here were awfully nice).

***Most importantly, and even though it's been said before, it bears repeating that testing a motor out of a car on a power supply is not anywhere near the same as testing it in a car with a "load" and on the track.  Even a noticeable resonance or other issue could easily disappear with the motor installed, or at least become a non-issue.

Personally, I still think there *may* be an issue with any other break-in than just running the motor in a car slowly for some number of laps, bringing the speed up until you see the car performing at it's best. (*but this is a GUESS)

 

 

John, as there is no balance marks can you have the arm checked for static and dynamic balance to see how accurate manufacturing is?

 

Hi John.  I have no reason to go any further and spend money to have the arm checked...I don't work on these motors, they're not made to be worked on.  I just take them apart for parts sometimes.  :)  Still, I was pretty impressed with the overall tightness of the motor and even more impressed with how consistently the arm metered.  ***What I can not say is what the average across thousands of these things might be.  It's possible I just got lucky with this motor and that others aren't so tight and don't meter as well, but I doubt that because this motor was sent to me as an example of a "problem motor";)  I have used similar "general/industrial" type motors for parts, and after producing millions of these things, it seems the Chinese really have this stuff down and produce a motor that is really good for the price-point.  We are still talking about a very cheap motor meant to be used and then tossed, a motor that...if it could be sent back to the 1960's Mabuchi-era, could have been winning races,  and maybe cost like 25 cents or so???

 

 

I break in my motors (Hawk 7 and Hawk Retro) dry and all get dark even deposits on the comm.

***I think there can be some confusion about "the marks" on the com.  It's one thing to have a nice even brush track on the com...ALL brushes will leave a visible track, but the brushes on these motors are quite small (*although seemingly sized approriately for such a narrow commutator).  If you look at the picture above, the marking on the com is NOT just a brush track (*which you can make out) that corresponds to the contact area of the brushes, it is a "hard-ish" sort of "glazed" looking coating that is much wider than the actual brush track.  That "coating" will have a different ability to conduct electric current than a clean com (probably less) and could easily affect motor performance.  It's important to remember also that the brush arms in these motors can't be so stiff and press the brushes so hard against the commutator to cause them to wear quickly (*not to mention increase drag and current consumption unnecessarily).  When you have brushes being held and pressed with just enough pressure to be a good balance for the particular "motor system" and to make good contact, and then add the coating on the commutator, performance can be hurt.  The good news with the above motor is that, whatever break-in the owner used, the com slots were clean and not full of junk...THAT can only make things worse.
 

 

Perhaps the coms are not quite centered on the shaft? I only have one of these in my quiver and it has never been in a car. I am starting to want to take it part just to see what is going on with it.

I could have put the arm on my com lathe to see if that's an issue, but the arm is in the trash now.  Still I don't think there'/s anything out of the ordinary going on there at all just by looking at the com and having run the motor.  You have to remember that these are NOT precision ultra straight hardened shafts (*"drill blanks) and while the com DOES have a "shoulder" that makes me think it was "trued" during it's manufacturing process, I would be shocked to find that the com was trued on the actual armature blank before winding.  There are going to necessarily be some imperfections here that wouldn't show up on a $100 armature :)

***The last thing I haven't checked and really don't have a good way to check without getting into way more effort than satisfying my casual curiosity is worth ...is that there are two conductors involved with getting good clean current to the spinning armature...the commutator segments AND the brushes.  Everyone looks at the commutator because the metal makes it easy to spot potential issues, but it's not so easy to look at the brushes.  Sintered carbon brushes are porous.  If people are using some sort of "wet" break-in, it seems likely the brushes are soaking-up some of that stuff even if the motor is dried afterwards.  It could be the actual contaminated brush face is then causing com fouling, or adding to it.

I'm only guessing at all this, and am NOT an engineer, so take what I say with an extra large grain of NaCl.
 


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#17 Eddie Fleming

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Posted 15 January 2018 - 07:15 AM

"a motor that...if it could be sent back to the 1960's Mabuchi-era, could have been winning races,  and maybe cost like 25 cents or so???"

 

Thanks for sharing your thoughts and findings John.


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#18 havlicek

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Posted 15 January 2018 - 07:23 AM

"a motor that...if it could be sent back to the 1960's Mabuchi-era, could have been winning races,  and maybe cost like 25 cents or so???"

 

Thanks for sharing your thoughts and findings John.

 

You're MOST welcome Eddie.  Unfortunately, the best I could do after all this was to guess.  I kinda wish I would have found something obvious or more certain, so I could be "the hero", but as it turns out, I'm just another dummy.  :)  Even though I much prefer the Hawk with the actual removable end bell, I at least came away from this with a better appreciation for the 7R.


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#19 Pablo

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Posted 15 January 2018 - 11:10 AM

I break in my motors (Hawk 7 and Hawk Retro) dry and all get dark even deposits on the comm.

I can't explain that, and it disagrees with my knowledge.

I'd like to know what voltage you break yours in at dry where they get a dark deposit.


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#20 Shiggy

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Posted 15 January 2018 - 11:22 AM

I can't explain that, and it disagrees with my knowledge.
I'd like to know what voltage you break yours in at dry where they get a dark deposit.

Most are just put in the car and run in on the track.
I did do one on a power supply at 5v. Three times for 5 minutes and the brushes were far from bedding in.
In the end, they all look the same.

The two "bum" motors that were inspected were described as having heavily contaminated comms. To my eye they looked little different than the good motors I have.
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#21 Fast Freddie

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Posted 15 January 2018 - 11:26 AM

John beat me to it.  After careful consideration a free wheeling motor will see much more RPMs and go through several stages of resonance vibration then a loaded motor.  Chances are you'll never get to the two speed range ever.  Unless the motor is geared very low.  I'm going to leave my two speed motors alone and see if that theory is correct.  I will, however, make sure I have motors that don't have the problem just incase.


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#22 Shiggy

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Posted 15 January 2018 - 11:30 AM

John beat me to it.  After careful consideration a free wheeling motor will see much more RPMs and go through several stages of resonance vibration then a loaded motor.  Chances are you'll never get to the two speed range ever.  Unless the motor is geared very low.  I'm going to leave my two speed motors alone and see if that theory is correct.  I will, however, make sure I have motors that don't have the problem just incase.


My motor issues are usually slow-when-cold. The effect is much more pronounced with short gear ratios and can totally go away with very tall gearing. But with the latter it slows as the race progresses.
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#23 Pablo

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Posted 15 January 2018 - 12:22 PM

I did do one on a power supply at 5v. Three times for 5 minutes and the brushes were far from bedding in.

OK so after your break in, they are still not "bedded in".

To me that means very little material has been removed from the brush faces yet.

 

Yet you say they have a dark deposit on the comm.

You say you broke them in dry.

My question is, where is that dark deposit coming from, and what is it?


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#24 havlicek

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Posted 15 January 2018 - 01:20 PM

I can't explain that, and it disagrees with my knowledge.

I'd like to know what voltage you break yours in at dry where they get a dark deposit.

 

Well, I've never seen a motor that doesn't get a solid brush track showing on the com after some running...so this sounds normal without seeing it!


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#25 Shiggy

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Posted 15 January 2018 - 03:42 PM

OK so after your break in, they are still not "bedded in".
To me that means very little material has been removed from the brush faces yet.
 
Yet you say they have a dark deposit on the comm.
You say you broke them in dry.
My question is, where is that dark deposit coming from, and what is it?

I have been using Hawk 7/Retro motors for 4+(?) years and until last month only looked at the brushes after they were well used to see if the motor needed to be replaced. Always just install and run. Before that I did not even know the brushes were "sideways " when new.
It would/does take 150-200 laps for the motors to speed up and be "broken in." Never looked to see if the brushes were seated.

That one motor I ran on the power supply showed no sign of bedding in after 15-20 minutes. Just two thin dark lines on the comm.
I gave up and put it in a car.

The only place I can see the dark deposits coming from is the brushes themselves.
D. "shiggy" Person





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