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Hawk 7 fast after it warms up - any idea why?


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#1 MarkH

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Posted 01 February 2017 - 07:11 AM

First, lets not turn this into yet another $13 Chinese motor thread.

 

I am just curious if anyone else is seeing these motors pretty far off the pace for the first 10-20 laps and then they come up to expected performance. I do not understand what is going on to cause this issue but I have had five of the last seven motors behave this way. One of those had soft brushes and the rest had hard brushes.

 

To be fair, I build cars for another racer and just pull a motor out off the peg board and put one in. Fortunately for him he has been getting the "cherries." They are fast at power on and seem to be lasting a long time. The last one I put in for him was just next on the board and it also had hard brushes and it is very fast at power through the whole of our long races.

 

The last two I put in my cars have been thrown away due to losing too much at the start of the race.

 

Your thoughts...


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#2 dalek

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Posted 01 February 2017 - 09:46 AM

Although it doesn't seem to make any sense, it is possibly hardware related.
 
I had three Hawk 7s that all took about a minute or more to get up to full power, each lap I could hear them revving higher down the straight, and of course, lap times were dropping.
 
I was putting them into a JK Indy car (screw-in mounting), and had put Sonic 10t lightweight pinions on them, mated to a 37t Cahoza spur. I haven't used those pinions before or since.
 
I didn't use any of the motors, but just marked them "slow cold" and put them back in my box.
 
Sometime later, I put one of them in a GT1 RTR car and it didn't have the "slow cold" problem.  
 
I don't positively remember the fate of the other two motors, but I think the outcome was the same, or at least similar (only three or four laps to get up to full power).

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#3 tonyp

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Posted 01 February 2017 - 12:01 PM

When running motor when it heats up the spring arms lose tension and RPM increases. I had a couple of motors that would need to warm up before they ran well.

 

What I did was break in the brushes a lot more which will decrease the tension and it made these motors fast right off the bat.


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#4 slotcarone

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Posted 01 February 2017 - 12:09 PM

A very common problem with FK motors in general. I have not found a solution except what Tony said.

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#5 Taylor Davis

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Posted 01 February 2017 - 12:45 PM

I had a Retro do that for about the first 30 seconds of every heat last month, with three heats to go I had my pit man douse the comm with lighter fluid while it was running between heats and it went away.

 

Maybe just a dirty comm. Or brushes?


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#6 DOCinCocoa

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Posted 01 February 2017 - 04:01 PM

This business of running slow at the beginning of the heat for maybe 30 seconds (it's not real bad) is why I do not cool down the Hawk Retro between heats any more. All of these motors have been the older version of the Hawk Retro.

 

I have not seen this with the 7R version, but I do not have a lot of experience with the newest version. Of the five 7R motors that I have run, they have been very consistent in performance and have not exhibited the slow/fast phenomenon.

 

Are you cooling the motor down between heats?


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#7 Taylor Davis

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Posted 01 February 2017 - 04:11 PM

No, it was the older version, I think, but I'll have to check. I have only purchased one 7R 7R and it's been okay/middle of the road for me with the extremely limited experience with them.



#8 MarkH

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Posted 01 February 2017 - 05:04 PM

The spring tension sounds right to me. Thanks, Tony.

 

I am not using a cooling fan between lanes but the motor does not take as long to go fast after running a lane. This adds more evidence to the spring tension changing.

 

Maybe I can dig out the last one I tossed in the can and see if more break-in will work. These are motors with 7777 acid etched in so I think they are from a current batch.

 

Funny thing is when they are running as expected they are very fast.


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#9 MarkH

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Posted 01 February 2017 - 08:18 PM

I took a good look at the brushes. They are already worn down to around 25% left. This was a brand new motor with brushes that took a bit longer than normal to break in. Not sure why they would have worn down.

However, it took 23 laps for the car to finally get up to speed and could run easy 3.65 on my track. I cooled off the motor and put it back on the track, 4.15-4.20. Sixteen laps later it heated up and was again running in the mid 3.6s.
 
So I took a pick and raised and lower each spring in an attempt to reduce the tension. No change in performance.

I then heated the wire post up with a soldering iron at 420c and let them cook for 3 seconds each. The thought being extra heat might release some tension. Nope, same story.
 
So, I grabbed another motor, broke it in, and mounted it in the same car with the same gears and tires. First laps were in the low 3.7s. After 5 laps easy 3.63-3.64. Let it cool off after the 20 lap run. Put it back on the track and had instant 3.65s and few in the 3.5s without trying very hard. So maybe I finally have a winner.

I know at one point a couple years ago a batch of 10 or so H7 I bought were all bullets except one and it was very good. I guess it is just the law of averages.
 
Thanks for all who gave advise.
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#10 Samiam

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Posted 01 February 2017 - 09:23 PM

I have seen racers running their cars on power supplies between heats in an attempt to keep the motor from cooling off. Is that effective?


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#11 Taylor Davis

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Posted 01 February 2017 - 10:56 PM

I do this in wing car racing to clean the comm on low voltage due to the high amp draw during race power, don't know if it would effect such low drawing motors as much though...

#12 slotcarone

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Posted 01 February 2017 - 11:11 PM

Happens with the 7R motors, too! :)


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#13 Jay Guard

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Posted 01 February 2017 - 11:24 PM

I'm not really convinced that the brush holders/springs are really the cause of the slow/fast phenomena. Generally speaking the characteristics of spring quality brass is not affected much at all by the kind of heat that these motors see. Unlike most steels, brass is work hardened and not heat treated to gain its spring (i.e. hardness) qualities.

 

I tend to like the theory that when the motor heats up it is essentially softening the glue around the comm and allowing the timing to shift slightly. I've got no hard data to back up the "glue melt" theory but to me it seems a bit more likely than the spring tension theory.


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#14 MSwiss

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Posted 01 February 2017 - 11:58 PM

I've had one Retro Hawk that ran that way.

My money is on something to do with the comm connection.

Next time I email my old boss, I'll ask him if he has any insight.

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#15 NSwanberg

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Posted 02 February 2017 - 03:51 AM

When running motor when it heats up the spring arms lose tension and RPM increases. I had a couple of motors that would need to warm up before they ran well.

 

What I did was break in the brushes a lot more which will decrease the tension and it made these motors fast right off the bat.

 

How do you know the spring tension was not getting higher?

 

I have often thought this problem was related deformation of the brush tabs/spring occurring while soldering wires to the tabs that essentially serve as the brush springs as well. 

 

Is there enough experience out there to say it does not seem to happen to racers that use clips to the tabs verse soldering the lead wires to the tab?

 

AJ Hoyt seems to prefer the clips. I don't see his motors suffering this problem as often but I still think it has happened to his motors.

 

I prefer soldering and I try to do it quick!


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#16 MSwiss

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Posted 08 February 2017 - 07:59 PM

Next time I email my old boss, I'll ask him if he has any insight.

 

His reply was "odd."

 

Possibly something to do with the formulation of the brushes.


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#17 MarkH

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Posted 08 February 2017 - 08:17 PM

Perhaps the thought is some materials used to make brushes will conduct better at higher heat. If there is more of that in the mix that makes some sense.


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#18 zipper

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Posted 09 February 2017 - 07:05 AM

Carbon resistance has a negative thermal coefficient.


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#19 MarkH

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Posted 09 February 2017 - 07:18 AM

So negative thermal coefficient would support hotter brushes conducting better or worse?

 

Sometimes engineering terms mean the opposite of what they appear to say.


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#20 gotboostedvr6

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Posted 09 February 2017 - 07:56 AM

I can't think of any material that will reduce resistance as its temperature is increased from room temp. At least nothing that would be used in a brush.


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#21 Brian Cochrane

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Posted 09 February 2017 - 01:11 PM

For educational purpose only, take the problem motor apart and take another motor apart and swap endbells and retest it. And then swap brushes and retest it. See if you can find the problem that way.

 

I think if it's not the brushes or the brush arms/springs, It's probably is the wire connection at the comm. It is not making full contact and when the motor gets some heat in it the contact increases which makes the motor "wake up."


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#22 MSwiss

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Posted 09 February 2017 - 01:59 PM

Even though Stu guessed brushes (note, a guess without much conviction) I still say comm connection, based at how abruptly the motor speeds up.

If the OP has two that he's given up on, if he can send one to JK and one to me, maybe we can get to the bottom of it.

I would take the arm out of the motor and check for resistance, look for anything odd, and hit it with a heat gun to see if any of the resistance readings go down.
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Mike Swiss
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#23 gotboostedvr6

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Posted 09 February 2017 - 02:00 PM

I agree, it sounds like a poor magnet wire to comm tab connection. Once it gets hot the metal expands and makes a stronger connection.

Maybe you can sneak a soldering iron in there...


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#24 MarkH

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Posted 09 February 2017 - 04:54 PM

I know they were tossed in the trash. Pretty sure the can has not been dumped and would be happy to send you guys these for expert evaluation.


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#25 MarkH

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Posted 10 February 2017 - 11:29 PM

OK, I found the two motors in the trash. I can send them your way if you still want to investigate.


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Mark Horne

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There are only two things in life that make me feel alive. Racing is one of them.


#26 MSwiss

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Posted 12 February 2017 - 10:21 AM

Big thanks, Mark.

Mike Swiss
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Mike Swiss
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Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516. Make checks out to Chicagoland Woodworking, Inc.


#27 MarkH

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Posted 12 February 2017 - 10:37 AM

Copy, I will box and send this week.


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Mark Horne

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#28 Samiam

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Posted 12 February 2017 - 11:11 AM

This is how it should be done.
 
Mud ducking on social media is useless and solves nothing.
 
Brian's idea of swapping out parts to isolate the culprit is a good idea. It would also work with the push start 4002 FKs.
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#29 MarkH

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Posted 12 February 2017 - 11:15 AM

Yes, sir.
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#30 Randy Tragni

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Posted 12 February 2017 - 09:41 PM

I'm guessing that TonyP is right but if not it could also be thermal expansion finally closing the brush hoods and making a better contact. You might want to measure with a digital VOM and see if there is a connection issue.



#31 MarkH

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Posted 16 February 2017 - 06:30 AM

Motors are going out USPS today to Mike and JK. Looking forward to your expert evaluation.


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#32 swodem

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Posted 28 February 2017 - 06:01 AM

...I tend to like the theory that when the motor heats up it is essentially softening the glue around the comm and allowing the timing to shift slightly. I've got no hard data to back up the "glue melt" theory but to me it seems a bit more likely than the spring tension theory.

 

I find that theory impossible to consider;

1. timing movement would have to be wild

2. how could it be so consistent

3. what weird force sneaks in and resets it as it cools?


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#33 MarkH

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Posted 28 February 2017 - 06:08 AM

I sent the motors off to JK and Swiss. When they have reached a conclusion, if one can be found, we will have a better idea what is really going on.


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#34 Racer36

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Posted 28 February 2017 - 11:47 AM

We had an erratic power situation with a RH up here and we finally figured out what was going on. The plastic bushing that holds the terminal and the brush internal was loose and the brush was dancing around on the comm. No idea if it was loose from production or if it was overheated during soldering, but at least we now know what was up.

No need for a federal investigation, just thought I would share what we found.

Cheers


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#35 swodem

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Posted 03 March 2017 - 12:26 AM

We had an erratic power situation with a RH up here and we finally figured out what was going on. The plastic bushing that holds the terminal and the brush internal was loose and the brush was dancing around on the comm. No idea if it was loose from production or if it was overheated during soldering, but at least we now know what was up.

No need for a federal investigation, just thought I would share what we found.

Cheers

 

I have pulled these motors apart, removed the armature and watched the brush arms while i torture the terminal with a soldering iron - they don't even waver or show any signs of distressing.

 

I don't believe the whole 'soldering the lead wires can change the brush tension' - no way. Not enough heat for long enough by a country mile.

 

And, the heat of an iron (400 degrees) isn't enough to mess with the metallurgy of copper or brass 

 

Next theory please...



#36 MSwiss

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Posted 03 March 2017 - 12:43 AM

I got in the motor and put it on the power supply.

Free reving, it didn't seem to change rpm as it warmed up a but.

I even hit it with a heat gun.

No change.

I took the arm out to meter it.

The arm, once I pressed it fairly hard, against the contacts, read normal across all 3 poles.

Whether it required any more pressure to get it to read normal, it's hard to say.

So, really nothing here.

Maybe Tim at JK will come up with something.

He was out of the country on business, so I doubt he's had a chance to look at it.

Mike Swiss
IRRA® Components Committee Chairman
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Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516. Make checks out to Chicagoland Woodworking, Inc.


#37 gotboostedvr6

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Posted 03 March 2017 - 10:42 AM

What about hot resistance readings
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#38 Racer36

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Posted 03 March 2017 - 11:00 AM

 

I have pulled these motors apart, removed the armature and watched the brush arms while i torture the terminal with a soldering iron - they don't even waver or show any signs of distressing.

 

I don't believe the whole 'soldering the lead wires can change the brush tension' - no way. Not enough heat for long enough by a country mile.

 

And, the heat of an iron (400 degrees) isn't enough to mess with the metallurgy of copper or brass 

 

Next theory please...

I did not maintain that an issue was created in the metal through soldering, just theorized that the plastic bushing may have been melted during soldering allowing  the brusharm to move around. With the motor on the power supply there was an obvious change in rpm and sound if you put pressure on the negative terminal. If you actually read my post you will see I refer to the plastic bushing.


Dennis Dominey

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#39 MSwiss

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Posted 03 March 2017 - 11:15 AM

What about hot resistance readings

Thanks for deleting your tactless post and replacing it with the above.

 

I'll address the above question when I have more time.

 

I have a lot of track prep to do right now, for a GL ISRA race, tomorrow.


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Mike Swiss
IRRA® Components Committee Chairman
Five-time USRA National Champion (two G7, one G27, two G7 Senior)
Two-time G7 World Champion (1988, 1990)

Eight-time G7 King track single lap world record holder (pointless era - LOL)
 
Chicagoland Raceway
17B West Ogden Ave
Westmont, IL 60559
(708) 203-8003
mikeswiss86@hotmail.com (also my PayPal address) 
Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516. Make checks out to Chicagoland Woodworking, Inc.


#40 gotboostedvr6

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Posted 03 March 2017 - 03:33 PM

Functions of erratic motor power output on FK motors ;

Measured resistance changing more then expected from room temp to Operating temperature on one or more poles, excessive TIR of the motor shaft, comm runout induced by the combination of shaft runout and unnecessary extra v block spacing or collet positioning during comm truing.

There are other things but I feel that these are the most overlooked.
Thomas Jefferson: "Paper is poverty. It is only the ghost of money, and not money itself."
-David Parrotta

#41 swodem

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Posted 03 March 2017 - 03:48 PM

Functions of erratic motor power output on FK motors ;

Measured resistance changing more then expected from room temp to Operating temperature on one or more poles, excessive TIR of the motor shaft, comm runout induced by the combination of shaft runout and unnecessary extra v block spacing or collet positioning during comm truing.

There are other things but I feel that these are the most overlooked.

 

Wow you can Comm-true a Hawk 7 on your Hudy??

 

I think the above are things that may make a motor perform less than optimum, but not sure how they would make it erratic? Its more likely to be consistently poor



#42 swodem

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Posted 03 March 2017 - 03:49 PM

I did not maintain that an issue was created in the metal through soldering, just theorized that the plastic bushing may have been melted during soldering allowing  the brusharm to move around. With the motor on the power supply there was an obvious change in rpm and sound if you put pressure on the negative terminal. If you actually read my post you will see I refer to the plastic bushing.

 

I wasn't making my comments solely on what you posted, but the common theories that the brush arms get less 'spring' due to current and soldering heat....



#43 gotboostedvr6

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Posted 03 March 2017 - 04:17 PM

The manufactures that produce fk130 motors true the comm before assembly yes?

They use some method and my investigation has shown it is flawed right from the bag.
Thomas Jefferson: "Paper is poverty. It is only the ghost of money, and not money itself."
-David Parrotta

#44 swodem

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Posted 03 March 2017 - 06:23 PM

I doubt it's trued like in a lathe
More like just formed round


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#45 JK Products

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Posted 05 March 2017 - 12:15 PM

HI Mark,

 

Sorry to be slow in responding, just getting unburied from being gone. We initially inspected the motor and could find nothing that looked bad (damaged or fouled commutator, etc.) before testing it. On the power supply, with two different loads, we couldn't find a significant change in performance after running for over 10 minutes at different voltages. Like Mike, we tried hitting it hard with a heat gun and again, no significant difference. Do you think it could have been something on the set-up of the cars? When you swapped out these motors, were the other motors fine? If yes, did you happen to put one of these motors back in and did you see them repeat the same change in performance? Was it only when the car was being raced that you saw this (maybe a track power supply change?)?

 

Sorry I can't be of more help but I can't find anything on my end. 


Tim Homola
JK Products

#46 MarkH

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Posted 05 March 2017 - 02:35 PM

We run 4 tracks in our series and I have a specific setup for each track. The motor was put in the car first for my track and then setup to run at a second track. It acted the same on both. About 20-25 laps from cold and came to life and was as fast as expected. Clean braid, good wires and solder and a free axle. I did bring it back to my track and run it one more time. 90 amp PS and 2 farad cap by my self.

It is a mystery and I am sure you would have preferred to find something so it could be addressed.

 

The last two H7 out of the bag have performed as expected with no issues. There is hope we will not see this issue for a long while.

Thanks for looking into it.


Mark Horne

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"Racing is life... everything else is just waiting." Steve McQueen - LeMans
There are only two things in life that make me feel alive. Racing is one of them.


#47 gatormark

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Posted 09 March 2017 - 08:24 PM

We run these cheap motors on a 200 ft engleman and everybody has seen the power jump. Now some that have com from a guy that's zaps them and breaks them in under water seem to be more consistent.


Mark Conner

#48 Big Booty

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Posted 11 April 2017 - 05:31 AM

Semi conductor materials have a negative coefficient of resistance.  e.g. Carbon, germanium silicon to name a few.  So hotter carbon brushes conduct better than cold ones.

 

Bare copper comms have a very high coefficient of friction.  Copper oxide coefficient of friction is a lot lower.  As the electrons jump off the brushes and onto the comm the arcing promotes an oxide layer to be formed.  The tension on the brushes then scrapes this layer away.  Too much tension and you scrap away all the oxide layer.  Not good.  Not enough tension and too much oxide layer forms.  Not good.  Get the tension jut right and you scrap away the same amount as you are making.  Perfect.


Rick Smith


#49 havlicek

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Posted 11 April 2017 - 06:01 AM

Seems to me that this is probably not an "issue" at all.  These are just inexpensive, but "high-value" (ie: performance/price is pretty impressive) motors built to a spec that allows racers to "use them and toss them".  That they run as well as they do at all for the price is remarkable.  That some of them may have quirks should be expected.

***People who build motors, even the high-end NASA-spec stuff, know that even a big budget and a lot of work still won't make every motor perform the same.  Sometimes, it just is what it is.


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#50 Tim Neja

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Posted 11 April 2017 - 08:55 PM

I've experienced slow cool motor and speeding up after it heats up with a few motors. I know a few others have seen this as well here at BPR>  I'd estimate it's been less than %2 of the what I've run.  None have been fast enough to race anyway---but it hasn't been a really unusual phenomenon! I'm  NOT complaining--I don't have any problem with the current  Retro Hawks and I hope Tim doesn't make any more changes! Bottom line--we are NOT going to get better motors than we currently have. There's going to be some manufacturing and performance variables in a $13 motor no matter what we do! We have them in $200 motors too!! Welcome to racing! :)


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She's real fine, my 409!!!





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