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Can you fix a Hawk 7 with a gear change?


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#1 dalek

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Posted 20 November 2017 - 11:50 AM

I've had two things happen, regarding Hawk 7 and Hawk Retro motors, that seem to imply that there can be a relationship between the motor problems we've been seeing and the gears and gear ratios we're running.  I'm beginning to think that it's an issue of harmonic vibrations.
 
The motor problems include: 
-- "slug"
-- "2-speed"
-- "slow-when-cold"
 
1st thing:
A few months ago, I had a Hawk Retro in my NASCAR.  The car ran fine but I decided to try a different gear ratio.  When I put the car back on the track, it was doing the "two-speed" thing.
 
I assumed the cause was that I had damaged the rear magnet with the heat from unsoldering and re-soldering the motor.  I didn't troubleshoot the problem so the motor is now somewhere in my "worn out (and weak brakes) junk motors" box.
 
What I now believe is that the change in gearing caused a change in harmonic vibrations.  And that those vibrations played on the inherent "2-speed" tendency of the Hawk 7 and Hawk Retro motors.  
 
2nd thing:
A couple of months ago my JK Indy car (Hawk 7 geared 37/10) was "slow-when-cold".  
 
Every lap for about 15 laps, you could hear it rev a little higher down our longest straight.  However, after a two-minute lane change, it was  deja vu all over again.
 
The next week, we raced JK GT1 RTR.  I don't know why, but I put that Hawk 7 from my Indy car into my GT1 (geared somewhere around 37/12) and, yep, you guessed it, no more slow-when-cold symptom.
 
It gets better -- the motor was a rocket to the point that I set a new qualifying record.
 
Here is a link to a video I made that demonstrates that inherent 2-speed tendency (I've checked probably 20 or more motors,  from new to worn out), and they all do it to one degree or another.
 
The video is the same one in post #8 in the thread:  http://slotblog.net/...-wall-syndrome/
 
 

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#2 Fast Freddie

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Posted 21 November 2017 - 11:45 AM

Just so you know standing gear ratios without a tire size mean little to nothing in the overall picture if you're looking for answers or a cure to your problems.  The H7 motor has less wire on it than an HR motor but just for some info here is what I run on my HR motors.  These are 64 pitch gears, LMP uses 10x34-35 with .750 tires and NASCAR uses 13x36 with .720 tires.  This worked good for me and nothing burned up.

Two things to try on your two speed problem.  Make sure without a doubt that the brushes are "fully" seated with no evidence of double tracking.  If that doesn't do the job then lightly tap each end of the arm shaft to ensure both bushings are seated fully.  If the problem still exist then I have no answer for you.  By doing these two procedures I cured the two speed problem in my motors.


Fred Younkin

#3 DavidR

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Posted 21 November 2017 - 03:31 PM

oil the motor bushings with a good 20-30 weight non detergent oil, best done after running them awhile to heat them up so oil gets sucked into the oilite type bushings, fixed a few of mine this way


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#4 dalek

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Posted 21 November 2017 - 06:30 PM

Back some time ago, when I discovered the inherent two-speed symptom, I figured it was most likely an arm shaft to bushing issue.  

 

The clearance between shaft and bushing of the H7 and HR seems near zero -- I can't detect any side play.  When I try to oil the bushings (I've used GetSome 1000 and Glidex), even with magnification, I've never seen evidence that any oil has been drawn into the bushing.

 

When I get a chance, I'll try getting the bushings warmer before I oil them to see if that cures a motor.  

 

If that doesn't make a difference, I think I'll take the arm out and reduce the shaft size a tiny bit where it rides in the bushings to see what that does (will spin the arm with a drill and briefly wet sand with 1800 grit).  


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#5 crazyphysicsteacher

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Posted 30 November 2017 - 06:57 AM

I have found an issue that may fix your problem. I have found that the new batch(since tim took over) has some hot glue applied to the brush/spring arm in at the base where it passes through the endbell and the plastic endbelly thingie.( sorry no real words for it) Some motors have had too much glue used during build and the glue holds the brushes off the comm after a small amount of wear. I found this on a retro hawk that was great that then slowed for no reason while on track. I autopsyed it and found the brushes were being held off the comm by the glue. A little slice and the stuck brush smacked the other one. I have since started looking at the amount of glue at the inside when picking motors. A new tip for all you out there.

Chris Wendel
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"Failure teaches way more than success. It shows what does not work and what to never do again, again..." 🙊🙈🙉  


#6 dalek

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Posted 30 November 2017 - 10:20 AM

A few months ago, I became aware of the "hot glue applied to the brush/spring arm in at the base" and the potential of it now allowing the brush arm to apply all of the pressure it can.  I assumed it was silicone rather than glue, but I guess it doesn't matter what the material actually is.

 

I don't see any reason to have it there as far as sealing, so I tend to think it's there to dampen out vibrations in the brush/spring arm.  Maybe not -- but I'll be keeping it in mind when I have a chance to do more troubleshooting of the Hawk 7 & Retro issues.

 


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#7 dalek

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Posted 02 December 2017 - 11:26 AM

Last night at the local raceway, one of the drivers had a Hawk 7 doing the two-speed thing.
 
The motor brushes were fully seated, however, the gear lash was, what I consider, excessive.
 
The motor was soldered in (flexi chassis), so in order to reduce the gear lash, the driver replaced the 35T Cahoza spur gear (straight, plastic) with a 36T metal gear.  The lash was less, but was still what I would call excessive.  With the metal spur, the car quit being a two-speed but was slower than an average Hawk 7.
 
He then replaced the spur gear with a brand new 36T Cahoza 16 degree angled spur.  This reduced the lash considerably.  
 
As it turns out, the motor was not bad.  With the new gear, it performed as an average Hawk 7 and was no longer a two-speed.
 

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#8 dalek

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Posted 11 December 2017 - 10:33 AM

I discovered that changing the spur gear can cause the slow-when-cold problem.

 

Yesterday I did some Hawk 7 motor testing at P-1 Raceway. 

 

Summary:
Angled Cahoza spur = best performance
Straight Cahoza spur = slow-when-cold, also slower overall
Straight other spur = slower always
 
 
The details:
 

The motor was in my JK Indy car, geared 10T ARP straight pinion and 37T 16 degree angled Cahoza spur.

 

When I replaced the angled spur gear with a 37T straight Cahoza, the car then became slow-when-cold. 

 

It took about a minute of running laps for the car to get up to full speed.  But even then, the best lap time was a full half tenth slower than I was able to run with the angled spur.  I experimented with gear lash regarding all of the gear combinations, in order to get the best lap times. 

 

Side note:  Regarding lap times, gear lash can make more of a difference than I used to think -- and near-zero is not always best.

 

I then replaced the Cahoza straight spur with a different brand 37T straight spur.  I don't know what brand it was b/c I bought it a long time ago and it was just in with my other spur gears, not in its package.

 

Again, the car was slow at first, but it remained slow.  It wouldn't speed up as I ran more laps, like when the Cahoza straight spur was installed.

 

I wonder if the plastic that the Cahoza gears are made of gets more slippery when it gets warm.

 

Anyway, I put the Cahoza angled spur back on the car, and the lap times were back to normal.  Good motor, good lap times and seemed to be running at full speed right from the first lap.

 

This was a new motor that had been installed in a car and the racer said it was "bad" so returned it to the raceway owner.


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#9 Rob Voska

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Posted 11 December 2017 - 01:09 PM

If you have a spec gear ratio you are out of luck.  How can one afford to go to a new track, learn the track & fight equipment at the same time when everything seems to be hit and miss.


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#10 CoastalAngler1

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Posted 11 December 2017 - 01:31 PM

When is P-1 going to change that jk indy car?  Even after Doc pushed so hard for the Florida class, he doesn't even run them. 

 

Dennis and Terry like the lightweight drag pinion, I think you might find another .05, and it likes all the spurs.  I recently discovered noticeable differences in spurs from one manu to another, and I agree most times the angled cahoza is fastest - in my Mossetti Defenders.  It's hard to find quality slot car parts, that is for sure.  Thrashing 3-5 of everything is about right to hang up front with the Florida thugs.  Some racers can build rockets with used parts I throw away, go figure.  I now have a trash bin to find fast parts haha.  I'll give you a couple 2 speed motors next time I see you.

 

Dale, will you save me some good gears after you find the fast ones?


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#11 W. J. Dougherty

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Posted 11 December 2017 - 02:21 PM

Dale, Next time you test try an angled pinion. Several years ago when I raced wings we used 10t 5* angled pinions with 44t 2* spurs. They were very fast...
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#12 swodem

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Posted 21 December 2017 - 06:49 PM

Read the response just posted up on JK's facebook page
 
They have done an analysis of two motors sent back to them,
 
and some fresh testing on new motors running them in, in Simple Green
 
It may be, actually, that the relatively new phenomenon of poor performing 2-speed or hot and cold motors is directly related to the relatively new practice of running motors in submerged in impure liquids, and then subsequently also running them before they are both flushed perfectly clean, and having ensured the comm slots are not gummed up.
This filling of the comm slots is very hard to avoid when running in motors in suspension, unless the 'paste' disperses thinly throughout the solution.
 
Thats why I use water, you can see the brush dust dispersed in the water, and there is no residue to burn 
 
But I dry the motors fully before running them (20min in the clothes dryer, in a sieve on the shoe rack)
 
I'm not saying its the situation in every case, but those posting complaints about their motors would be beneficial if you can also post pics of your comms!!!
 
Just sayin...
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#13 Shiggy

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Posted 31 December 2017 - 02:14 AM

I have two Hawk 7 motors exhibiting the slow-when-cold deal. One dry break in on a power supply. One with in-car on-track break in.
Ran a bunch of track testing today with many different ratios.
Short story:
Running 12/36, .700 they are ~0.5sec slower than "normal" and take 25 laps to slowly get up to speed. A stop of more than ~45sec and the "2-speed" affect starts over.

Using my old ratio, 13/37, .700, the same motors are up to speed in 2-3 laps. BUT the reason I do not want to use this ratio is the motor heats up quickly and late in a race it slows by 0.2-0.3sec.

These motors will be returned to Tim with the full testing details for evaluation.

I finished by installing a 3rd, new, motor with a 12/35 ratio. In-car, on track break-in. Up to speed in 15 laps.
After 100 laps cooled for 5 min.
Up to speed in first 2-3 laps, and then lapped 0.05 sec quicker over next 25 laps.
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#14 dalek

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Posted 31 December 2017 - 11:17 AM

 

Short story:
Running 12/36, .700 they are ~0.5sec slower than "normal" and take 25 laps to slowly get up to speed. A stop of more than ~45sec and the "2-speed" affect starts over.

These motors will be returned to Tim with the full testing details for evaluation.
 

 

Shiggy,

 

I found (explained in post #8 above) that, in my case, the ratio wasn't the culprit, it was the gears themselves that caused the slow-when-cold symptom.

 

I'm doubtful that Tim will be able to duplicate your problem.  Not only can gears make a difference, but even the chassis itself might make a difference if harmonic vibrations are involved.

 

To really nail down the cause, if you would try different brands and types (angled and straight) of 12t pinions and 36t spurs, it could either confirm or eliminate gears being the cause (as was in my case).

 

I've also found that gear lash can make a significant difference in lap times.  I tested and found that some gear combinations give the best lap times with near-zero lash, and some like it looser.

 

If you send the motors to Tim, he might need the gears also.


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#15 Shiggy

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Posted 31 December 2017 - 11:45 AM

Shiggy,
 
I found (explained in post #8 above) that, in my case, the ratio wasn't the culprit, it was the gears themselves that caused the slow-when-cold symptom.
 
I'm doubtful that Tim will be able to duplicate your problem.  Not only can gears make a difference, but even the chassis itself might make a difference if harmonic vibrations are involved.
 
To really nail down the cause, if you would try different brands and types (angled and straight) of 12t pinions and 36t spurs, it could either confirm or eliminate gears being the cause (as was in my case).
 
I've also found that gear lash can make a significant difference in lap times.  I tested and found that some gear combinations give the best lap times with near-zero lash, and some like it looser.
 
If you send the motors to Tim, he might need the gears also.

I used the same type pinion (angled) and spur (JK narrow) for all the testing. Yes, the lash can affect performance, and I did need to adjust that a couple of times. Did not include the poor setup results.

I also have the same 12/36 setup in an identical car with a different H7 and it runs fine.

IME if I change spurs from straight to angle or to a different brand, all the same tooth count, I also need to reset the lash. Never have had it cause the "2-sp" or "slow-when-cold" affect. Just slow, tight or noisy.
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#16 dalek

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Posted 01 January 2018 - 11:10 AM

I also have the same 12/36 setup in an identical car with a different H7 and it runs fine.

 

 

Keep in mind that the supposedly same setup, but in a different car, is not always a conclusive measure.  
 
I bought five Sonic 10t pinion gears.  
 
I've had mixed results with them.  
 
After looking at them with 3x magnification, it's no wonder.  I can see that the tooth profiles are not all the same due to variations from the machining process. 
 
Of course, wear could also cause variations in gear performance.
 
Considering that, at 30,000 RPM, a pinion is spinning 500 times per second, it's easy to believe that only a slight variation from optimum, could have a significant negative result.

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#17 Shiggy

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Posted 01 January 2018 - 12:30 PM

I use the same brand and type pinions and spurs.
The 12T and 13T in the test had been used with success before, as had the 12T in the second car.
All the spur gears had been used previously. If I had multiples of the same size I tried each one and tested with the best one.
The 11T pinion was new.
Did my best to minimize the variables.
D. "shiggy" Person

#18 dalek

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Posted 08 February 2018 - 01:46 PM

Two weeks ago, while running practice laps just before a race, I had a fast Hawk 7 but it suddenly started "2-stepping".  
 
I didn't use it that night but last week at home, I put the motor on my power supply and, as expected, it 2-stepped much more than normal.
 
I was able to fix the motor by flooding the bushings with Glidex -- especially focusing on the bushing in the endplate. 
 
You can't really see the bushing, but I wanted to fill up that blind area between the bushing and the can, with oil so I held the motor with the shaft vertical then put the oil on deep -- as much as surface tension would allow.
 
Then I rotated the arm and worked it end to end for several minutes.
 
Eventually, I could see oil on the inside of the endplate (behind the comm) but by then I had mopped up the excess oil on the outside and turned the motor on its side so oil didn't get on the comm (if it had, I would have used contact cleaner or Voo Doo to clean it off).
 
When I ran the motor on my power supply, it was much better -- in other words, it had the "normal" amount of 2-step.
 
Last Friday I put it back in a car and it was fine.  I raced it and it did very well.
 

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#19 dalek

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Posted 14 February 2018 - 08:14 AM

Yesterday, while doing test and tune, I had a Hawk 7 go 2-step on me when I changed spur gears.  
 
Both gears were 64 pitch, 36 tooth and 16 degree.
 
The original gear was an S&K, the replacement was Cahoza.  Both gears were used.  I looked at the Cahoza gear teeth with magnification and couldn't see anything unusual.
 
Note:  I had previously filed off the built-in spacer of the Cahoza so I can tweak gear mesh by moving spacers.
 
I was able to stop the Cahoza 2-step by removing all axle spacers (about .035" total) from behind it so all there was left was one .005" spacer.  Of course I had to unsolder the motor and reinstall it to get correct gear lash.
 
As I continued to test, I also had unexpected occurrences, to one degree or another, of some of the slow-when-cold and total-slug issues when I tried various combinations of straight and angled spurs and pinions.
 
Due to time and money (buying new gears to compare to the used ones), my conclusions are incomplete but I wanted to post what I discovered so far as a heads-up and to encourage experimenting with gears when anyone has a Hawk 7 or Hawk Retro that seems like a bad motor.
 
 

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