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Hawk 7 two-speed "wall" syndrome


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#1 dalek

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Posted 14 November 2017 - 10:30 AM

There is a phenomenon consistent with JK Hawk 7 (and JK Hawk Retro) motors that I'll refer to as a wall.
 
If you have a "two-speed" or a slug H7 or HR, or just would like to verify what I'm saying, you can perform the testing described below, using your power supply and any Hawk 7 or Hawk Retro motor, whether it's one you're still racing or one that you're not racing any more because the brushes are mostly worn out or the motor has bad brakes.
 
Beginning at 5 volts or less, increase the voltage at the rate of about one volt per 4 seconds. Typically, the motor begins to encounter an internal load, a "wall," so to speak, at about 9 volts, that causes the amp draw to increase but the RPMs don't increase very much.
 
Continue increasing the voltage and then at usually about 10 volts, you will hear the motor RPMs suddenly increase and see the amperage drop back down to normal.
 
I assume that this "wall" syndrome, (or you might call it a characteristic), when it's bad enough in a particular motor, is the cause of what we call a two-speed motor. A two-speed motor is one that causes a slot car to suddenly increase in speed, part way down a straightaway.  We've had a few of these.
 
When the "wall" is really bad, you can increase the voltage all the way to 12 volts and the motor rarely jumps to the higher RPM, so it'll be a slug, all the way around the track (I bought one of these a couple of weeks ago). Last night I discovered that when I get the voltage up to 12 volts, I can tap the motor shaft a few times and get the motor to jump to the higher RPM (and of course the amperage drops back down to normal – about 0.7 amps).   wonder if this indicates there is an armature shaft harmonic vibration occurring inside of the bushings that causes the "wall."

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#2 Racer36

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Posted 14 November 2017 - 10:37 AM

Every single two-speed motor I have seen is as a result of someone using too much heat when soldering wires on and melting the nylon bushing. This de-stabilizes the brush arm and allows the brush to walk around on the comm, effectively changing the timing.

 

Personally I think the rest of your theory is a bunch of crap, but that's just my opinion.

 

And again, you should stop running the voltage up beyond 5 volts with no load.


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#3 MSwiss

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Posted 14 November 2017 - 10:43 AM

Slotbloggers,

 

Do not free-rev your motors to 12v, as the OP indicates he does.

It may damage the motor and does nothing to indicate motor performance on the track.

The motor, under no load, at 12v, will reach much higher RPM than it will running on the track at 12-14v, where the motor has a considerable load from the gear train, tire to track surface adhesion, and downforce from the body.


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#4 Gator Bob

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Posted 14 November 2017 - 11:13 AM

Are the comm tabs crimped (insulation displacement) and soldered ... or just crimped (folded)?


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#5 jimht

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Posted 14 November 2017 - 11:31 AM

My experience is that a motor that suddenly speeds up at a certain point when unloaded is out of balance, has a bent shaft, loose bushing(s), or an out-of-round comm.

 

Seems that it sometimes can't get past that point (i.e. wall  :) ) on the track and so is a dud, speed-wise.

 

The issue is obviously not easily fixed with a sealed motor.


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#6 Danny Zona

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Posted 14 November 2017 - 11:52 AM

I've had a few gear shifters lately.

I'm not knocking them. I just have dealt with them lately more often than not.

No biggie to me though.

It's just how it goes dealing with a mass-produced cheap motor. I take the good with the bad as long as everyone is dealing with the same problem.


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#7 JK Products

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Posted 14 November 2017 - 02:46 PM

JK Products does not support operating our motors in the method described by the the OP and we also disagree with his conclusions. As I indicated in a recent post by the OP, I think the "two-step" issue some complain about is possibly the result of improper gearing. 

 

If your motor is geared too tall (< 3.3 gear ratio), you can experience the car starting the straight slowly and then accelerating quickly as the RPMs finally pick up because they started too slow coming out of the turn.

 

If someone sees the two-step issue, please change the gear ratio to something higher, like 3.5 and check the motor again. If after doing this you believe you still have a two stepping motor, please PM me and we will be happy to investigate the issue.

 


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#8 dalek

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Posted 14 November 2017 - 03:10 PM

Here is a YouTube link of a video I made of one of the good performing Hawk 7s I bought a couple of weeks ago.
 
It seems to show the tendency of the Hawk 7 motors to inherently be two-speed. 
 
I did the same test using an old Falcon 7 motor and the RPMs increased steadily all the way from 2 volts to 12 volts and, as expected, the amperage increased evenly also.
 


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#9 JK Products

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Posted 14 November 2017 - 03:49 PM

Dale, please do track testing as everyone has recommended.


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#10 Racer36

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Posted 14 November 2017 - 03:54 PM

The audio reminds me of a trip to the dentist. In fact the whole thread is about as pleasant...


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#11 olescratch

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Posted 14 November 2017 - 05:21 PM

Just the sound of that motor revving gave me chills! I was waiting for the smoke! Not a good practice in my opinion???


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#12 dalek

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Posted 14 November 2017 - 05:35 PM

Dale please, do track testing as everyone has recommended.

 

I *have* done track testing – that's what got me here.

 

I believe I'm conservative saying that one out of 20 Hawk 7s have problems on the track.


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#13 dalek

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Posted 14 November 2017 - 05:41 PM

Here is the link to a video I made of the bad Hawk 7 I bought last week.

 

I bought three. Two are good in my JK Indy car, and one is not.

 

The previous video is of one of the good ones but shows the inherent "two-speed" tendency.

 

This video is of the bad motor. The text in the video explains everything.

 


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#14 JK Products

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Posted 14 November 2017 - 05:42 PM

Hi Dale,

 

I really would like to help.

 

From my earlier post:

 

"If someone sees the two-step issue, please change the gear ratio to something higher, like 3.5 and check the motor again. If after doing this you believe you still have a two-stepping motor, please PM me and we will be happy to investigate the issue."

 

Tim


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#15 Brinkley47

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Posted 14 November 2017 - 06:04 PM

Sure, gear the motor to run slow and no surging worries. That makes no sense. This is another issue of the manufacturer dodging the problem or not knowing how to fix the issue. Blame it on the customer. Smart business practice.


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#16 Dallas Racer

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Posted 14 November 2017 - 06:15 PM

I don't understand why some of you are giving Dale a hard time.


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#17 Cheater

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Posted 14 November 2017 - 06:46 PM

Will, 
 
I guess you're reading a different post than I am:

"If after doing this you believe you still have a two-stepping motor, please PM me and we will be happy to investigate the issue."
 
Wanna explain in English just how that is blaming the customer and dodging the problem?

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#18 JerseyJohn

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Posted 14 November 2017 - 06:49 PM

OK just my opinion. I have experienced that sudden rise in RPM, drop in amps and smother running in every Series JK Hawk since before the R motors. I believe its either a brush float issue or a balance harmonic. Ever have a tire on your car vibrate at 60, worse at 65, smooth as silk at 70.
 
Also once the brushes are fully seated that two-stage goes away.
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#19 Gator Bob

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Posted 14 November 2017 - 06:53 PM

Here is a YouTube link of a video I made of one of the good performing Hawk 7s I bought a couple of weeks ago.
 
It seems to show the tendency of the Hawk 7 motors to inherently be two-speed. 
 
I did the same test using an old Falcon 7 motor and the RPMs increased steadily all the way from 2 volts to 12 volts and, as expected, the amperage increased evenly also.

 
A video is worth a thousand words. Clear to hear the shift.
 
The two-stepping FK deal isn't new or unique to Hawk 7.
All the investigations have not proved out anything concrete to prevent its recurrence... if it's back again.
 
It does make sense to see if it is a 'shifter' motor in the comfort of your own power supply.
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#20 Brinkley47

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Posted 14 November 2017 - 06:55 PM

Wanna explain in English just how that is blaming the customer and dodging the problem?


if I was a manufacturer, I think these posts on multiple cases warrant an investigation. If he is waiting on a customer to tell him how to fix the problem, he may have a long wait.
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#21 Brinkley47

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Posted 14 November 2017 - 07:03 PM

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I am no English major, Greg. Does this sound like blame to you?
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#22 Cheater

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Posted 14 November 2017 - 07:03 PM

Investigate exactly what, Will? Every motor in his inventory?

I haven't noticed that Dale has offered to send JK that motor to check, have you?

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#23 Brinkley47

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Posted 14 November 2017 - 07:06 PM

The surging issues with the new Hawk motors. There are three threads about this topic. Or... you could blame the customer and pretend like nothing is wrong. Ask anyone at the Brawl how many 7Rs burnt up on Friday. Probably the most I have seen at a Premier event. No worries, nothing wrong here... LOL.
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#24 Cheater

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Posted 14 November 2017 - 07:10 PM

Fair warning, Will, you're stepping real close to the line in terms of lack of civility IMO.

Might want to turn the dial a litle more in the adult discourse direction.

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#25 Brinkley47

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Posted 14 November 2017 - 07:18 PM

Facts hurt sometimes. I personally seen ten 7R motors burn and I am confident there were many more. I know one racer who burnt three out of his three hand-outs. How would you feel if that happened to you at a big race?

You are defending a topic you have little experience with. Let the racers handle this one.
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#26 Cheater

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Posted 14 November 2017 - 07:23 PM

Will, I was racing slot cars when you were in diapers. And I have burnt up my share of motors, believe me. I recall one enduro in South Georgia where we burned four or five motors just in practice for the race and decided to DNS.

I am not defending anyone. There may be a problem with the motors or there may not be, I have no opinion.

But what I do have an opinion on is the standard of discussion in my little house. Ridicule and insults don't sit well with me, nor, I am pretty sure, with a large portion of the members here.

Keep in mind that this isn't Facebook.

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#27 Brinkley47

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Posted 14 November 2017 - 07:27 PM

So jumping on the OP is OK? Got it. Your playground, Greg. Just dont be surprised when you are the only one in the sandbox.
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#28 Cheater

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Posted 14 November 2017 - 07:32 PM

So jumping on the OP is OK?


Show me where that occurred, Will. I don't think you can.

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#29 Noose

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Posted 14 November 2017 - 10:16 PM

I had the two-step dance with Rs and putting them on low voltage (2 volts) for around 20 minutes cured the problem.

I know motors blew at the Fall Brawl but I cannot say all were 7Rs. I will say that the Simple Green method works but great care to thoroughly clean it out is a must. Thus one can conclude Haste makes Waste if not done properly as one tries to hurry to get motors broken in.


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#30 Kevin Donovan

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Posted 14 November 2017 - 11:16 PM

I had some of these two-speed issues and fixed it by putting a drop of superglue on the leadwire tabs.


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#31 slotcarone

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Posted 15 November 2017 - 12:01 AM

Thanks for the info, Kevin. I will find a two-stepper in my box and give your method a try!

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#32 NSwanberg

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Posted 15 November 2017 - 02:37 AM

On my chassis dyno, with a complete car, I quite often find cars that will be smooth at near 4 volts and then buzz like crazy until I get to 7 volts where the car will suddenly smooth out. The current draw of the motor will drop and the output voltage of the dyno will suddenly increase as well. I attribute it to harmonics in the drive train, including the motor, that cannot be accounted for. The final test should always on the track. 
 
How can we expect non-epoxied winds to stay in place and an armature to remain in balance through an RPM range? Most armatures are never in prefect balance and will have a critical RPM where the unbalanced condition is apparent. Getting that imperfection out of the usable RPM range for these cheap little sealed motors seems almost a crap shoot to me with the winds flapping in the breeze.
 
Switch oil and see if it changes.
 
You can bet I am going to try super glue on the tabs to see if that helps!


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#33 Zippity

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Posted 15 November 2017 - 04:21 AM

Please remind me.

 

Are we talking about $12 motors here, or have I missed something?


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#34 raisin27

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Posted 15 November 2017 - 05:49 AM

Although super gluing the tabs or windings is probably undetectable wouldn't that be considered illegal for sealed motor racing?


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#35 Racer36

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Posted 15 November 2017 - 05:56 AM

Superglue on the wire tabs fixing the problem just confirms what I stated earlier. Too much heat when soldering the wires melted the nylon bushing and destabilized the brush arm. With proper prep and clean work it should take less than a second to solder wires. Any more is just asking for trouble.

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#36 Kevin Donovan

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Posted 15 November 2017 - 06:02 AM

Although super gluing the tabs or windings is probably undetectable wouldn't that be considered illegal for sealed motor racing?


It's easy to see the superglue on the tabs so I guess thats up to the interpretation of the tech guy.

What bothers me the most is that I don't remember these issues with the old Falcon 7 or earlier Hawk7.
I never had one two-speed and they didn't require such elaborate break-in.
I remember just running them in on the track and they usually ran great.
Supposedly the brushes are harder now but I dont think the new motors are as good.



#37 Kevin Donovan

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Posted 15 November 2017 - 06:12 AM

I think the tabs are loose and the leadwire movement causes the problem.
The car speeds up and slows down in the same sections of the track lap after lap.
I’ve never seen this running a motor with conventional endbell.

#38 slotcarone

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Posted 15 November 2017 - 06:52 AM

Superglue on the wire tabs fixing the problem just confirms what I stated earlier. Too much heat when soldering the wires melted the nylon bushing and destabilized the brush arm. With proper prep and clean work it should take less than a second to solder wires. Any more is just asking for trouble.


This happens even before the motor has been installed in a car!! No heat on the tabs!
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#39 havlicek

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Posted 15 November 2017 - 07:18 AM

My "take" on all this after watching the video is that this is a *very* common thing.  I've frequently seen this sort of behavior with motors from:

1) Slight bushing misalignment (can sometimes be self-corrected by running-in the bushings).
2) Dry bushings
3) Armature imbalance (again, even slight)
4) Brush/spring problems... hung-up (not the case with this type motor because the brushes aren't located within hoods), brush "bounce" (can be caused by different things like weak springs, out-of-round comm, or sufficiently "untrue" shaft; in this type motor, loose spring arms).
5) Too much end-play and/or arm not centered in the field (tightening the end play on sealed motors by banging the can or pushing the bushing and then trying to "reset" the bushing can make this better or worse).

I may be forgetting some possible causes, but it's also quite possible that more than one of the above is in play here, and how the motor is installed could make the behavior more noticeable or not. I honestly think this sort of thing is probably way more prevalent than many people might think with "all" inexpensive sealed-type motors. Motors with actual endbells *might* be more easily improved depending on the skill of the person and what the cause is but here's the thing:

On motors (more $) and in racing classes where the motors are meant to be opened and checked/worked-on, a lot of the basic "tuning" steps a builder might do would normally take care of this sort of thing. The behavior of the motor in the video is the same as you would see with some older, less expensive motors from Mabuchi, Mura, Champion, etc. As you got into the more expensive motors from any of those manufacturers, you *hopefully* got motors that needed a drop of oil and not much more because of tighter tolerances/specs, but even then racers just opened-up the motors to get things as right as they could.

 

While I believe this behavior is probably way more prevalent than people might think and is really to be expected from such low-cost motors just because of "chance," that same "chance" means that the presence or absence of the general type behavior and to what extent it's there almost definitely will vary from production run to production run. To put it simply, it's mostly just "the nature of the beast." 

 

All of this type motor and those with an actual endbell are made to a similar general spec because they have to be! The biggest mistake would be to think that one brand or the other has some sort of advantage, when they're all subject to "chance" from production run to production run. The other way to state that is that they're all exceptional performers... all things considered.

On a side note, I get asked to make "special" motors all the time (of course, I don't do that... ever) because there's the impression at least, that some people have a motor "advantage." This kind of motor would naturally be more difficult to "improve" in a way that's hard to notice, but I have to assume that some people have figured ways to have at it. Personally, I think that it's far more likely that people work around these variances by buying a whole bunch of motors, and there goes the whole "even playing field" and/or "taking money out of the equation." The answer to that is just hand-out motors, but everyone already knows that. There will still be some "cherries," but at least everyone has the same chance of getting one.


John Havlicek

#40 Kevin Donovan

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Posted 15 November 2017 - 07:21 AM

Never had the two-speed issue on a Falcon 7. Soldered the same way with them.



#41 havlicek

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Posted 15 November 2017 - 08:00 AM

Personally, and having seen motors do this many times, none of what I think might be causing this has to do with "user-error." The soldering thing "might" be the case for some people (I wouldn't know honestly), but with the very thin brass brush arms in these motors that probably does happen sometimes. 

The superglue thing seems like something to try anyway because it's easy to test.
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#42 John Streisguth

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Posted 15 November 2017 - 09:57 AM

I have seen the 'two-speed" phenomenon, and IMO John H probably has explained most of the possible reasons. Cheap motors, lots of variation in production. They are what they arre.

 

And at the Fall Brawl, I know that some people were pushing the envelope of gearing to gain an advantage on the big Engleman track, so that may explain some of the magic smoke escaping LOL.


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#43 JerseyJohn

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Posted 15 November 2017 - 11:01 AM

And at the Fall Brawl, I know that some people were pushing the envelope of gearing to gain an advantage on the big Engleman track, so that may explain some of the magic smoke escaping LOL.

 

A lot of 10/28 and 10/27, John.


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#44 Fast Freddie

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Posted 15 November 2017 - 11:39 AM

I've had several of these two-speed motors and I concur with Jersey John. Once the brushes are fully seated the two-speed effect is gone, at least that has been what happened on all of my HR and H7 motors. 

 

One other thing that has happened on several of my motors is that when the two-speed effect goes away the magnetic "cog" seems to increase. I only have 20 motors so that is only what I have experienced with my limited supply of motors.


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#45 JK Products

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Posted 15 November 2017 - 11:59 AM

Thanks, John(s), and we know this is done often.

 

A gear ratio of 2.7:1 or 2.8:1 is really tall gearing and significantly outside of the recommended 3.3-4.2:1 operating range for these motors.

 

Can you do it? Sure.

 

Will it work sometimes? Yes.

 

Will you blow up more motors as a result? You bet.

 

Is this a defect in the motor???


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#46 willy wonka

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Posted 15 November 2017 - 12:27 PM

I've seen this many times, even with the older versions. I usually marked it and just keep trying them and over time some would come around, some would not.

The smoke show at the Brawl I would say was either because over-gearing or the car on too soft of tires causing a lot of heat in the motor.
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#47 Fast Freddie

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Posted 15 November 2017 - 12:51 PM

I noted this on the other thread but which has the most effect on the motor gear ratio or FDR (final drive ratio)?  A gear ratio of 13/36 with .720" tires has a FDR of 3.85. The most popular gear ratio in Retro racing is 9/28 with .8125" tires and the FDR is 3.83. I have run an HR motor with that first gear and tire set-up, in a major race, with no adverse problems and the car ran very good. I have also run a HR motor with a 10/35 gear set and .760" tires. The FDR in that case was 4.61. Since it was virtually impossible to hit a good FDR with such a small pinion gear I relied on the overall gear ratio in this case.
 
Like John pointed out above 10/28 or 10/29 is the wrong gear ratio for .8125" tires. Both 9/28 and 10/31 yield nearly the same gear ratio and FDRs of 3.83 and 3.82 respectively.
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#48 willy wonka

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Posted 15 November 2017 - 12:57 PM

A lot of 10/28 and 10/27, John.


9/27 for me.
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#49 Pablo

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Posted 15 November 2017 - 01:05 PM

The video may well show the best method to turn a good motor into a "two-speed" by abusing it.

Would you rev a race car engine to redline in neutral under no load?
 
Ever if the rev limiter didn't prevent it, they aren't designed to perform that way.


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#50 John Streisguth

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Posted 15 November 2017 - 01:05 PM

A lot of 10/28 and 10/27, John.

 

I didn't race Coupe, but it seemed that's where people were taking the risk, if they had a motor that didn't have good speed. Not sure about Can-Am, I wasn't paying attention as I had my own problems LOL.


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