Best Of *Science* of solving N scale diesel mechanism drivetrain vibration noise?

[mecgp7]

The motors that are noisy are not balanced.  If you balance these motors/flywheels you would be surprised how smooth and quiet the will run. I have done this to several Atlas motors and flywheels. Learned this back in the 1960s with Aurora slot cars, a balanced armature reduced the noise with the three brass gears.

I'd be in your debt if you could explain how to balance them. You'd probably put more than a dozen motors back into service.

[atsf_arizona]

OK, here's my discovery on the Intermountain SD45-2 noisy mechanism.

The problem I was experiencing on these mechanisms, appears to be a missing mounting tab on some of the Intermountain SD60-style HTC trucks.

Specifically, I realized after doing the "vertical up/down test for gear tower hitting the worm", that:

• One of the two Intermountain SD45-2 trucks is missing the 'mounting tab' that the IM chassis is supposed to sit on
• Thus that end of the mechanism, with nothing holding/preventing the gear tower to keep it separate from the worm, the top of the gear tower gear teeth thus bottom out in the worm.... thus squealing continuously.  See the photos below.
• After replacing the 'missing tab' truck with a 'proper tab' truck.... the IM SD45-2 mechanism with two "good trucks with mounting tabs" now runs practically silently

Wow.

What was messing me up in the months previously: I had two noisy IM SD45-2 mechs'....... each had one 'good truck' and one 'missing tab  truck'.   I was not aware of this small tab before nor the "gear tower bottoming out in the worm gear" issue..... and also had never tried swapping the trucks in such a way that "two good trucks" ended up on the same mechanism.

Intermountain SD45-2 truck with the proper mounting tab:


IM truck missing the mounting tab:   

(maybe this is a manufacturing defect, "wrong part" somehow got into IM locos at factory?)   
(JS:  CORRECTION:  this "mounting tab" is easily broken off.  See replies #79, #83, #86, #89 below).




Here's another shot, this one from from Andre Kitzinger's website, showing a SD50/SD60 truck with the "mounting tab" in place:



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This is a the former noisy IM SD45-2 mechanism, this mechanism with out any modifications, i.e., no "spring in universal joint".
YouTube: 

/>
See the difference from original very noisy mechanism here (TubeChop):  http://www.tubechop.com/watch/8728407

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NOTE:  I then tried two of these "proper trucks" in the Intermountain "spring in the universal joint" modified mechanism.
 
Result:  That modified-with-springs-in-universal-joint mechanism was *louder* than the one shown in the YouTube above. 

I will to go in, remove those springs, then move the "good trucks" to that mechanism, and see if it is quieter.

Conclusion:  So, as Ron Bearden has said multiple times, putting the "spring in the universal joint" is *not* a cure-all.... it's a possible cure if (and ONLY if) the worm gear lateral play needs to be restricted.... and the amount of spring tension he says is key. 

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See if the "replace missing mounting tab truck with proper truck with mounting tab" solution,  resolves Intermountain noisy mechanisms, first.

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HYPOTHESIS and RESEARCH REQUEST:   

If you have a very noisy Intermountain mechanism, take a flashlight and see if your trucks have this mounting tab, or are missing the mounting tab.

Then share with us here....  does:

* Intermountain SD60-style HTC trucks "MISSING the mounting tab"  equate to a NOISY Intermountain mechanism ?

* Conversely, do SD60-style HTC trucks "WITH the proper mounting tab"  equate to quasi-SILENT Intermountain mechanism ?

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Awaiting your comments/responses.

[tehachapifan]

Wow, interesting find! Does this look like something that might've broken off of, or fell out of, the truck tower or is it clear that it was never there to begin with? I ask because there appears to be a slightly uneven bottom edge just above where the missing tab would be in the above photo.

[atsf_arizona]

Wow, interesting find! Does this look like something that might've broken off of, or fell out of, the truck tower or is it clear that it was never there to begin with? I ask because there appears to be a slightly uneven bottom edge just above where the missing tab would be in the above photo.

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(JS:  CORRECTION:  My original reply below incorrect, this "mounting tab" is easily broken off. 
See replies #79, #83, #86, #89 below.  I am leaving my original text here to document how our conversation flowed)
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Hi, Otto,

Nothing has been broken off - it looks like the truck frame was molded that way, without the mounting tab.    Nothing was broken off (that's probably just the photo angle... it was difficult to get a photo that would show you all what I have discovered). 

There's no pilot hole or anything there that I could think is the place where a rod or retaining tab was "supposed to have been put there" - it was never there to begin with. I had two different noisy IM locos..... both with 'one good truck, one bad truck'.      (When I get time I will go back and take a better photo)

I suspect that a different mold or part was accidentally used....

All, looking forward to hearing your experiences: 

Does:

* Intermountain SD60-style HTC trucks "MISSING the mounting tab"  equate to a NOISY Intermountain mechanism ?

* Conversely, do SD60-style HTC trucks "WITH the proper mounting tab"  equate to quasi-SILENT Intermountain mechanism ?

* What do the trucks on your noisy Atlas SD50/SD60 mechanisms look like, does the same two possible relationships above also apply?

We are still in the research phase, I don't know how many of you out there will find if you have Intermountain or Atlas locos with SD50/SD60 HTC trucks with a "missing mounting tab".  Thx in advance for reporting in.



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JS: Many others subsequently report below that "missing mounting tabs" definitely equates to noisy Atlas SD50/SD60 and Intermountain mechanism
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[Big Train]

I had one IM SD45T with that same issue. On one truck the pin on one side was missing and was not only causing excessive gear noise but a wobble under certain conditions. An email to IM (whose customer service is AWESOME, BTW...) sent me replacements and the new ones solved the issues.

Perhaps when they were assembled initially, or maybe at some other point, the trucks jammed up into the chassis too far and the frame screws tightened. Then really tightened because the trucks refused to stay installed in the chassis, crushing or otherwise destroying them.

I cringe every time I see somebody try to jam a truck back into position without loosening the frame screws and seating them properly.

Wow, Aurora slot cars.....this was one of my hobby experiences before N Scale. Yes, I remember balancing the armatures....something about two parallel razor blades?

Great....something else to tune.....

[rrjim1]

I'd be in your debt if you could explain how to balance them. You'd probably put more than a dozen motors back into service.

Do a search on how to balance a slot car armature. I'm sure there are lots of videos out there. I use a Magnetic Balancer. 

[peteski]

Do a search on how to balance a slot car armature. I'm sure there are lots of videos out there. I use a Magnetic Balancer.

The fly in the ointment is that in order to balance the armature, it has to be removed from the motor.  Which means that both flywheels have to be removed, and then the motor completely disassembled.  Afterwards the flywheels have to be pressed back on.  Without special tools in a home workshop you can slightly bend the motor shaft during this process. At that point all the balancing you just did is wasted.

[BCR751]

Also, already mentioned, if there is a "scientific" tool that's useful, it's a milliamp meter.  It is one of the handiest tools ever when working on these things as it monitors pickup as well as any and all changes in load (which binding mechanisms will introduce).  And it reads pretty small changes.  If you can see it or hear it, it will show up in the amp draw.  Again, a mark on a wheel with an amp meter needle bouncing (use an analog meter, not digital) can point to a problem and also because of the occurrence relative to a mark, can help to pinpoint the very spot in the mechanism where the problem is located.  If it's occurring at wheel speed, it's in those final components that are operating at that speed.  If it's in multiples, it's back in the gear train.  Things like that.  If it's a drop in the meter, it's a pickup problem.  If it's a spike in the meter, it's a mechanism binding problem.

I hooked the Atlas C-630 motor, in the frame but sans drive linkage, to both a volt meter and a milliamp meter.  As I advanced the throttle:

Motor started at about 1.25 volts    mA meter reading - bouncing between 0 and 20mA. 

at 2 volts      mA meter bounced between 40 and 60 mA. 

at 3 volts       mA meter bouncing between 70 and 80 mA.

at 4 volts       mA meter steady at 80 mA

from 4 - 12 volts      mA meter increased from 80 to 90mA at about 4.25 volts and remained there, no bouncing

It's hard to tell but I think I can see the motor slowing a bit during a revolution at the lower voltages, almost like it is rubbing on something as it turns.  If I can figure out how to do it, I'll try and post a video of it.  When I hooked up the drive train, the setup produced almost the same results as above, just a bit more current draw but hardly noticeable. 

I painstakingly examined the motor, the plastic cradle the flywheels and I just can't see what could be causing the rubbing, if indeed that's what's happening here.  I checked the flywheel shafts as the motor turned slowly and they don't appear to be out of alignment.  By the way, the motor didn't make any objectionable sounds during these tests nor when the drive train was connected.

I hooked up the other C-630 I have with the same setup and got virtually the same readings.  Hopefully, I can find the cause(s) of these issues.  Lots of good suggestions here in this thread.

Doug

[jagged ben]

Hi, Otto,

Nothing has been broken off - it looks like the truck frame was molded that way, without the mounting tab.    Nothing was broken off (that's probably just the photo angle... it was difficult to get a photo that would show you all what I have discovered). 
...

John, the pins broke off.  Trust me.  I've seen it a whole bunch.  Another horrible feature of those Atlas trucks.  Those little pins are super fragile and break all the time.  Probably some break on the way from the factory, they are so fragile in some cases.   I've ordered a dozen extra of those truck tower parts from Atlas because I just know that those pins will break again on my fleet of SD50s/60s/60Ms/40T-2s/45T-2s/45-2s.    To anyone who owns one of those models and notices that it's leaning to one side... it's because one of those pins broke off.    And yes, for sure, once they break off then the worm is no longer sitting in proper relation to the worm gear, height wise, and you'll get noise/performance issues.  Not to mention coupler height issues, if you had them properly elevated beforehand.   

[peteski]

It's hard to tell but I think I can see the motor slowing a bit during a revolution at the lower voltages, almost like it is rubbing on something as it turns.  If I can figure out how to do it, I'll try and post a video of it.  When I hooked up the drive train, the setup produced almost the same results as above, just a bit more current draw but hardly noticeable. 

Does the cyclical slowdown correspond to each revolution of the motor shaft or in-sync with each revolution of the wheels?  Whatever it is in sync with that usually indicates that this rotating component which has an off-center point of rotation, out of round or skewed on its center of rotation.

[John]

Maybe drill a little hole and put in a metal post with superglue?

[bman]

Hi, Otto,

Nothing has been broken off - it looks like the truck frame was molded that way, without the mounting tab.    Nothing was broken off (that's probably just the photo angle... it was difficult to get a photo that would show you all what I have discovered). 

The pins are a  molded on part of the gear case and get broken off easily if care is not taken.  I cringe when I see club members put an Atlas SD50/60/60M chassis on the track  and then proceed to press the shell on from there.  This is one way i've seen them get broken off.  Pushing the trucks into the mechanism without loosening the frame screws is the other way.  I've seen this too many times. I've broken a couple my self but usually gravity and a vertical drop is my story.   I usually just order the gear case and keep on hand in my parts box.  Modeling Conrail I've a fleet of SD50's and a couple of SD60/60M's and working on a SD60I using a Kato 80MAC cab.  While they run well,  I'm not a big fan of this design.  I've often toyed with the idea that the next one I get that's broken I'll try to make a pin with some of the wire we use for the throws for the Tortoise machines on our club layout.  Might be a little more robust and take all the handling that these go through at times.  Time will tell.  Stay tuned.

[u18b]

You know.  This is great research.  A great example of working together to share knowledge.

When I did a lot of research on the HTC truck problems I only had my 2 locos to go by. 
The clicking Daniel referee to is from the gears cogging when the axles float too much.  That I observed and was able to solve. 

What I was unable to solve conclusively was what a couple of people called hopping.  They said their SD50 would actually hop.  I was unable to reproduce this problem.   The closest I could guess was the main double gear coming out of position. 

But now I'm wondering if one if these pins might have been broken and contributing to the problem.

By the way.  Funny and true story.  I told the guy with a proven hopper SD50 to send it to me to study.  I heard these complaints out there, but no one but this guy said they currently had one. 

So he boxes it up and sends it to me.
But the shipper dropped the box and it got run over!!!  Lol

I guess the guy could have been lying, but that was not his nature.   I think it really happened.

So I STILL have never documented a hopping HTC loco.


 

[peteski]

By the way.  Funny and true story.  I told the guy with a proven hopper SD50 to send it to me to study.  I heard these complaints out there, but no one but this guy said they currently had one. 

So he boxes it up and sends it to me.
But the shipper dropped the box and it got run over!!!  Lol

I guess the guy could have been lying, but that was not his nature.   I think it really happened.

So I STILL have never documented a hopping HTC loco.

I've seen locos hopping. When there is too much vertical play at the truck pivot, under load the worm will ride over the worm gear's teeth and make the chassis lift as that worm skips over the teeth.

[atsf_arizona]

John, the pins broke off.  Trust me.  I've seen it a whole bunch.  Another horrible feature of those Atlas trucks.  Those little pins are super fragile and break all the time.  Probably some break on the way from the factory, they are so fragile in some cases.   I've ordered a dozen extra of those truck tower parts from Atlas because I just know that those pins will break again on my fleet of SD50s/60s/60Ms/40T-2s/45T-2s/45-2s.    To anyone who owns one of those models and notices that it's leaning to one side... it's because one of those pins broke off.    And yes, for sure, once they break off then the worm is no longer sitting in proper relation to the worm gear, height wise, and you'll get noise/performance issues.  Not to mention coupler height issues, if you had them properly elevated beforehand.   

You're right.  Now that I know what to look for, clearly yes, I could see that once upon a time, there were plastic protruding mounting tabs on these two trucks.... but no longer.

* What is the Atlas part number (or Intermountain part number) to order for replacement?   
* Is it worth it to just get the replacement case and easy enough to transport the gears into the new gear case?
* Or is that difficult enough, that one should just order replacement trucks?

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And by the way, I haven't forgotten about the other Atlas B40-8 mechanism, and the need to shim it to keep the gear tower from bottoming out.
I'll get back to that one too with experiences to share.

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Cool inputs.... thx all.... keep the input coming.