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MDC/Roundhouse Prairie Kit: Building a SP 2-6-2 (formerly MDC/Roundhouse Atlantic Kit)

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Posted by richg1998 on Friday, July 25, 2008 5:47 PM

 New Haven I-5 wrote:
 TwinZephyr wrote:
The motor mount hole (actually a rectangle) is right there between the second and third driver axle slots.  The kit instructions should show the motor and idler gear being installed on the mounting plate.  Then that assembly is attached to the frame with one screw.  The rectangular hole is intended to allow for fore-aft adjustment the idler and axle gear mesh.
Let me get this straight, a screw is supposed to go the that rectangle? That is not in the instructions.

 

That is what is in the PDF link I posted at 4:12 PM today. Take a look.

Rich

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Posted by New Haven I-5 on Friday, July 25, 2008 7:07 PM
 richg1998 wrote:

 New Haven I-5 wrote:
 TwinZephyr wrote:
The motor mount hole (actually a rectangle) is right there between the second and third driver axle slots.  The kit instructions should show the motor and idler gear being installed on the mounting plate.  Then that assembly is attached to the frame with one screw.  The rectangular hole is intended to allow for fore-aft adjustment the idler and axle gear mesh.
Let me get this straight, a screw is supposed to go the that rectangle? That is not in the instructions.

 

That is what is in the PDF link I posted at 4:12 PM today. Take a look.

Rich

My instructions are different. I guess its time to bring out the drill......   

 

 

 B.T.W, the loco is finished, only need to drill a hole for the screw.

- Luke

Modeling the Southern Pacific in the 1960's-1980's

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Posted by New Haven I-5 on Friday, July 25, 2008 9:18 PM
 How would I remotor this? How much would it cost?

- Luke

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Posted by richg1998 on Friday, July 25, 2008 9:19 PM

I cannot see the problem. Does the motor and gears look like  the loco you have, look like the PDF document? The photos of your present frame are the same as the PDF document I posted. The motor attaches to the mounting plate with the gear. A little shimming might be needed for proper worm/gear mesh.  Another screw goes up through the small rectangular hole to the bottom of the motor and gear mounting plate. The small rectangular slot allows you to move the motor and gear plate slightly for proper gear alignment and mesh.

Rich

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Posted by New Haven I-5 on Friday, July 25, 2008 9:41 PM

How do I remotor it because the motor is J-U-N-K? What parts do in need & how do I do it?

- Luke

Modeling the Southern Pacific in the 1960's-1980's

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Posted by richg1998 on Saturday, July 26, 2008 10:07 AM

NWSL has re-gear kits for MDC locos. 

You can also pull the worm and install it using a sleeve on a 16X20mm motor from NWSL. Put bathtub caulk under the motor and press the motor in slightly for proper gear mesh. I and others have done that. With a double shaft 16X20mm motor, there is enough space for a flywheel. There is a fellow who sells can & coreless  motors in the HO section of ebay that I have bought from.

The new Athearn/Roundhouse now sells parts the might fit your loco such as the motor. The new style motor snaps into a plastic assembly that is attached to the frame with a couple screws. I can send you photos of the new Roundhouse locos instructions that have part numbers. I do not know if the MDC worm is the same as the worm on the new motors. I will check when I get home tonight.

I am sure others will have suggestions. Dan Bush of Yardbird Classic Trains might be some help. I have bought from him.

Sorry no URLs for links as Trains.com has whacked me once for posting a commercial site, removed the post and warned me in a PM about doing that. Others can post the links.

Cheers

Rich 

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Posted by New Haven I-5 on Saturday, July 26, 2008 10:12 AM
 What are the numbers for NWSL kits, and would any of these http://yardbirdtrains.com/YBHHindx.htm work?

- Luke

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Posted by richg1998 on Saturday, July 26, 2008 4:11 PM

 Make sure you have a set of dial calipers. Very useful.

Useful information

http://www.modelrailroadforums.com/forum/archive/index.php/t-2548.html

You can contact Dan Bush. He is very helpful

 Rich

 

 

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Posted by fwright on Saturday, July 26, 2008 5:53 PM
 New Haven I-5 wrote:

How do I remotor it because the motor is J-U-N-K? What parts do in need & how do I do it?

I have to question the "junk" adjective.  Are there reasons for saying that the motor is junk?  Or are you saying that because it's an open frame motor that it's inherently inferior?  There are only 3 thngs that typically go wrong with open frame motors over time.

1) The bearings become worn and sloppy.  Happens to can motors, too.  The bearings in an open frame motor are accesssible for cleaning and lubing.  Often noise comes from dry bearings.

2) Brushes wear.  Happens to can motors, too.  Brushes in an open frame motor are replaceable (you can replace brushes in some can motors, others you can't).  Finding new brushes for any motor can be an exercise in frustration.  Luckily, brushes take a long time to wear.

3) Old Alinco magnets used in open frame motors become weak with time, especially time with heat.  Removing the armature weakens an Alinco magnet.  Open frame magnets are easily replaced with rare earth stacked magnets for no more than $5 per motor, and really improve the slow speed performance of an open frame motor. Remotoring seems to be a lot more in vogue on this forum, rather than the simple magnet upgrade - for reasons I have not been made aware of.

Remotoring typically costs $20 and up, depending on whether the gearbox is going to be reused.  New can motors typically have smaller shafts than the old open frame motors did, so the shaft may have to be bushed to use the same gearbox.

An easy check is to apply power to a (any) motor as it sits in your open hand.  The vibration and noise level of the motor will quickly tell you if the motor is reasonably balanced.  While an open frame motor can have its armature balanced, at that point it may be easier to remotor.  At the same time, you can check the bearings for play.

Many. many sins of the gearing and drive are blamed on the motor - and simple remotoring does nothing to help.  As you assemble the kit, ensure free running at each step.  Check to see if the model rolls freely on a flat surface without the motor and worm - plate glass is ideal.  If it doesn't roll freely, then it needs more work.  Check after you put each set of drivers in their bearings.  Check after installing side rods and valve linkage.

If you have a free running chassis, and the motor checks good, you are probably in for regearing unless you can fix the flaws in the gearbox.  NWSL regear kits should be considered if it won't perform right even after cleaning any and all flash from gears and adjusting gear mesh.

When building locomotive kits, I took the advice of some mentors and use a known good open frame motor during tuning and testing of the chassis.  A can motor is more susceptible to burning up when I manage to introduce a bind in the mechanism during construction.  Only when I am satisfied the chassis is running right will I insert a can motor that takes less space in my small locomotives.

my thoughts and experiences, your choices

Fred W

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Posted by New Haven I-5 on Saturday, July 26, 2008 5:59 PM
 fwright wrote:
 New Haven I-5 wrote:

How do I remotor it because the motor is J-U-N-K? What parts do in need & how do I do it?

I have to question the "junk" adjective.  Are there reasons for saying that the motor is junk?  Or are you saying that because it's an open frame motor that it's inherently inferior?  There are only 3 thngs that typically go wrong with open frame motors over time.

1) The bearings become worn and sloppy.  Happens to can motors, too.  The bearings in an open frame motor are accesssible for cleaning and lubing.  Often noise comes from dry bearings.

2) Brushes wear.  Happens to can motors, too.  Brushes in an open frame motor are replaceable (you can replace brushes in some can motors, others you can't).  Finding new brushes for any motor can be an exercise in frustration.  Luckily, brushes take a long time to wear.

3) Old Alinco magnets used in open frame motors become weak with time, especially time with heat.  Removing the armature weakens an Alinco magnet.  Open frame magnets are easily replaced with rare earth stacked magnets for no more than $5 per motor, and really improve the slow speed performance of an open frame motor. Remotoring seems to be a lot more in vogue on this forum, rather than the simple magnet upgrade - for reasons I have not been made aware of.

Remotoring typically costs $20 and up, depending on whether the gearbox is going to be reused.  New can motors typically have smaller shafts than the old open frame motors did, so the shaft may have to be bushed to use the same gearbox.

An easy check is to apply power to a (any) motor as it sits in your open hand.  The vibration and noise level of the motor will quickly tell you if the motor is reasonably balanced.  While an open frame motor can have its armature balanced, at that point it may be easier to remotor.  At the same time, you can check the bearings for play.

Many. many sins of the gearing and drive are blamed on the motor - and simple remotoring does nothing to help.  As you assemble the kit, ensure free running at each step.  Check to see if the model rolls freely on a flat surface without the motor and worm - plate glass is ideal.  If it doesn't roll freely, then it needs more work.  Check after you put each set of drivers in their bearings.  Check after installing side rods and valve linkage.

If you have a free running chassis, and the motor checks good, you are probably in for regearing unless you can fix the flaws in the gearbox.  NWSL regear kits should be considered if it won't perform right even after cleaning any and all flash from gears and adjusting gear mesh.

When building locomotive kits, I took the advice of some mentors and use a known good open frame motor during tuning and testing of the chassis.  A can motor is more susceptible to burning up when I manage to introduce a bind in the mechanism during construction.  Only when I am satisfied the chassis is running right will I insert a can motor that takes less space in my small locomotives.

my thoughts and experiences, your choices

Fred W

The motor is 30 + years old. So if I put a magnet on the motor, it will work?

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Posted by fwright on Saturday, July 26, 2008 6:51 PM

 New Haven I-5 wrote:

The motor is 30 + years old. So if I put a magnet on the motor, it will work?

Try powering the motor sitting on your open hand.  It will probably run as is.  May need a drop of light oil (I like Labelle) on the bearings to reduce bearing noise.  Does it vibrate heavily or is it reasonably smooth?

If it's reasonably smooth, it may work fine as is. The new magnets can be added when you choose.  If it's rough, and stings your hand, then you can spend effort and some money trying to fix the motor, or replace it with an inherently better motor.

Next step is your chassis.  Does it roll freely after being nudged (without the motor and worm installed)?  Or does it stop the instant you stop pushing it?  Or does the effort to roll vary as the wheels turn?  Don't settle for believing that a little running in will cure binds.  Fix the cause of the binds.

The final check of motor, magnets, and chassis is current draw. This measures the actual load and efficiency of the motor.  The problem with current measurements is that a high current can come from problems in the motor, motor magnets, or chassis - and you don't know which until you have checked each individually.  You need a DC power supply and an ammeter measuring to about 0.5 amps.  A decent condition open frame motor with a good chassis should draw less than 0.5 amps running the locomotive by itself.  New magnets for an open frame motor will probably cut the current to 0.35 amps or less.  A can motor should be in the neigborhood of .25 amps or less.  A very free chassis with a coreless motor could be as low as 0.1 amps.

I also recommend you do a web search for various other references on remotoring by people who do it frequently.  Look for objective reasons for using certain motors and/or gears.  There is a lot of misinformation on motors bandied about based on advertisements or hearsay or personal bias or other less than reliable sources.

My personal bias is to avoid tossing out perfectly good components that produce 90% of the performance of the touted "gold standard".  Others may want that 100% performance no matter the cost.  The problem is that the whole model must be up to that level to get the benefit of the superior motor.

Hope this helps

Fred W

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Posted by twhite on Saturday, July 26, 2008 7:00 PM

New Haven--

FWright has some VERY good ideas.  However, if your open-frame motor is 30+ years old and this is a kit, do yourself a favor and run the motor IN.  It probably hasn't had any running since the factory, and needs to be 'tuned'.  One way of 'tuning' an open-frame motor is by lightly applying some alcohol with either a Q-tip or a very soft toothbrush to the brushes while the motor is running, to clean the contacts.  Those MDC open-frame motors, combined with the reduction gear in the mechanism usually work quite nicely.  I've several MDC 2-8-0's with the original small open-frame motors, and they run quite well.  But open-frame motors have to be run IN for a period of time before they reach their full capacity, they're not like Cans, which just take off immediately. 

Hold the motor between your thumb and forefinger and apply power.  Wait while the motor stops jerking (this might take about three to four minutes as it breaks in) then mount the motor to your loco frame with just the MAIN RODS connected.  When the mechanism is running smoothly, then connect the cylinder rods and slowly work the motor in both directions to full capacity.  If that's running smoothly, just let the motor run for about two to three minutes in each direction.  Make sure you've greased the reduction gears, of course.  I use LaBelle gear grease, it's perfect for any gears, and a couple of drops does the job.  Your motor should then be working very smoothly. 

Just a thought. 

Tom Smile [:)]

 

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Posted by New Haven I-5 on Saturday, July 26, 2008 8:28 PM
 twhite wrote:

New Haven--

FWright has some VERY good ideas.  However, if your open-frame motor is 30+ years old and this is a kit, do yourself a favor and run the motor IN.  It probably hasn't had any running since the factory, and needs to be 'tuned'.  One way of 'tuning' an open-frame motor is by lightly applying some alcohol with either a Q-tip or a very soft toothbrush to the brushes while the motor is running, to clean the contacts.  Those MDC open-frame motors, combined with the reduction gear in the mechanism usually work quite nicely.  I've several MDC 2-8-0's with the original small open-frame motors, and they run quite well.  But open-frame motors have to be run IN for a period of time before they reach their full capacity, they're not like Cans, which just take off immediately. 

Hold the motor between your thumb and forefinger and apply power.  Wait while the motor stops jerking (this might take about three to four minutes as it breaks in) then mount the motor to your loco frame with just the MAIN RODS connected.  When the mechanism is running smoothly, then connect the cylinder rods and slowly work the motor in both directions to full capacity.  If that's running smoothly, just let the motor run for about two to three minutes in each direction.  Make sure you've greased the reduction gears, of course.  I use LaBelle gear grease, it's perfect for any gears, and a couple of drops does the job.  Your motor should then be working very smoothly. 

Just a thought. 

Tom Smile [:)]

 

Thanks, but the problem is the motor DOESN'T work. Its one of the Sagami Open frame motors( it is round.).

- Luke

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Posted by twhite on Saturday, July 26, 2008 8:51 PM

New Haven: 

Oboy--I thought it was one of those smaller open-frame motors that came with the MDC kits back when I was building them.  My bad, I apologize. 

I'll be frank--I've never liked Sagami's, they have always proven to be too 'delicate' and WAY underpowered.  I usually replace them with NWSL's ASAP, when I get a brass lokie with one.  What I would do is take it down to your LHS, look for a NWSL (or any other brand than Sagami) that is the same size and has the same diameter shaft.  You should be home free, after that.  If the Sagami is what came with the kit to begin with, then there should be instructions on how to mount it on the frame--the NWSL (or whatever replacement can you get) should fit the same way. 

Man, I hate to say it, but this is sounding COMPLICATED.  Does your instruction sheet show ANYTHING about mounting a 'can'?  Or is the sheet geared toward an open-frame motor? 

Tom Confused [%-)] 

 

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Posted by fwright on Saturday, July 26, 2008 9:32 PM
 twhite wrote:

New Haven: 

Oboy--I thought it was one of those smaller open-frame motors that came with the MDC kits back when I was building them.  My bad, I apologize. 

I'll be frank--I've never liked Sagami's, they have always proven to be too 'delicate' and WAY underpowered.  I usually replace them with NWSL's ASAP, when I get a brass lokie with one.  What I would do is take it down to your LHS, look for a NWSL (or any other brand than Sagami) that is the same size and has the same diameter shaft.  You should be home free, after that.  If the Sagami is what came with the kit to begin with, then there should be instructions on how to mount it on the frame--the NWSL (or whatever replacement can you get) should fit the same way. 

Man, I hate to say it, but this is sounding COMPLICATED.  Does your instruction sheet show ANYTHING about mounting a 'can'?  Or is the sheet geared toward an open-frame motor? 

Tom Confused [%-)]

Same for me, I apologize for assuming it was the standard MDC open frame motor that came standard with their kits before the 1990s.

I don't know when Roundhouse/MDC started using nickel plated drivers.  Most of my kits have nickel plated drivers because I looked for that before I would buy.

The change to can motors from open frame was very late for Roundhouse - I believe it was in the '90s.  A few late kits (post 2000?) even got improved gear boxes.  But there were (and are) many unstarted kits from the open frame motor era still available.  Roundhouse was very poor at updating their kit instructions to reflect these changes.  At best, there would be an errata sheet reflecting the changes for the new components.

Tom has given you good advice about locating a new motor.  If I had any spare open frames, I'd ship you one to try for fit.  One downside to a can motor is that very few are user repairable.

A common method of mounting a can motor is to install a plate for the motor to rest on, and then use a layer of silicone rubber for the final location and adhesive.  This also insulates the motor from the frame, so ensure both wires from the motor are used (good for later DCC conversion).  Adjust the motor in the silicon rubber for optimum gear mesh while the rubber is setting.

Removing and remounting the worm will be the most difficult part of the new motor.  If you can't move the worm (the spiral gear) to the new motor, then you are looking at regearing.  The worm should be a press fit.  Getting the right size shaft or a bushing on the new motor will be important.  If there is space, a double shaft on the new motor with a flywheel on the back side will smooth performance.

The above is based on the assumption that the worm is mounted directly on the motor shaft.  An improved drive is to separate the motor from the worm shaft with a universal linking the 2 shafts.  This causes less stress on the motor bearings, which are not set up for it.  But the improvement requires a different gear box with bearings for a separate worm shaft.

just my thoughts

Fred W 

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Posted by TwinZephyr on Saturday, July 26, 2008 10:12 PM

How about posting a photo of the motor in question and a photo of the motor mounting bracket?

BTW, MDC did sell locomotive kits with a Sagami can motor and brass drivers.  In regards to the Harriman engines, a kit with a can motor is more likely to have brass drivers than nickel plated drivers.

Also, the motors used in MDC old time 2-6-0 and 2-8-0 kits and the new Roundhouse old time RTR locomotives are noticably smaller than the motors supplied with the Harriman series 2-6-2, 4-6-0, 2-8-0 and 4-4-2 kits.

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Posted by New Haven I-5 on Sunday, July 27, 2008 12:10 PM
 TwinZephyr wrote:

How about posting a photo of the motor in question and a photo of the motor mounting bracket?

BTW, MDC did sell locomotive kits with a Sagami can motor and brass drivers.  In regards to the Harriman engines, a kit with a can motor is more likely to have brass drivers than nickel plated drivers.

Also, the motors used in MDC old time 2-6-0 and 2-8-0 kits and the new Roundhouse old time RTR locomotives are noticably smaller than the motors supplied with the Harriman series 2-6-2, 4-6-0, 2-8-0 and 4-4-2 kits.

Thanks everyone. The loco came with brass drivers. I'll have to go to my LHS next weekend and see what motors they got.

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Posted by richg1998 on Thursday, July 31, 2008 3:40 PM

I  just received a set of brass driversfor a MDC 2-8-0 that I plated for $24.00 including shipping. The company is Sierra Scale models.

Rich

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Posted by Autobus Prime on Thursday, July 31, 2008 4:25 PM
 New Haven I-5 wrote:
Thanks, but the problem is the motor DOESN'T work. Its one of the Sagami Open frame motors( it is round.).


NHI5:

Can you take a ruler and measure that motor in millimeters? Case diameter, case length, shaft diameter, and shaft length are what is needed, and the width across any case flats.

Jameco sells some very nice automotive can motors, similar to the ones used in the Helix Humper, for a very low price...only a few dollars each, I think.
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Posted by Attuvian on Thursday, January 20, 2011 2:14 AM

Fred, are you still out there somewhere?  I ran across this old string from New Haven I-5 while researching issues with an MDC Prairie upgrade that I'm considering.  IYour observations above on motor and gear issues is quite helpful.  I think that what I've got in hand is an old "Phase II" geared unit as there is an idler on the motor mount that mates the shaft worm to the driver axle gear.  I have lubed the motor (it sat in storage in this loco for about 25 years) and given it your hand-held test.  It has some vibration on low to mid range which, of course, disappears progressively as I crank up the juice.  Although the armature has a small amount of front-to-back play at rest, I don't think this is a factor as the low speed vibration issue isn't noticeably reduced when I hold it vertically for a full-range test.  Perhaps lower speed vibration is an inherent liability with these motors (don't know who made it).  I don't think it's the bearings - unless they were bad from the factory - as there's probably less that an hour on the motor in its lifetime and I have always insured that it was properly lubed.  (BTW, are the skew-wound motors that I'm seeing advertized in some of the new RTR engines specifically designed to smooth out low rev operation?).  Your comments above indicate that uneven low speed operation might also be due to a wimpy Alnico magnet.  I can't imagine that this one has ever been subject to excessive heat, and how would I test its strength to find out?  But this may be a secondary issue as the engine creeps pretty well when it's fully assembled.

If I can get this thing to run both smoothly and relatively QUIETLY, I may invest in not only the time and bucks to superdetail it, add more prototypical trucks (the trailer is really goofy in appearance, maybe kitbash a more realistic firebox and even think about installing DCC sometime in the dim future. 

Actually, noise may be the biggest issue.  I guess I'm presuming it's due to engine vibration.  The assembled frame rolls quite freely but there is a very slight clunk once on every rotation of the drivers when testing.  The clunk is not speed or load dependent and I might be able to live with it - I still remember some of the clanking of old NYC steamers from the early 50s that passed my house in southern Michigan when I was a boy.  What I've really got to work on, though, is the noise both from the open frame motor and the open portions under the boiler.  There are no burrs on any of the gears, the worm is meshed about half way in the idler and the idler doesn't seem to be binding in the gear box.  I have already placed a thin layer of cushioning material between the motor mount and the driver framing to reduce vibration noise that may transferred to the drivers and amplified by the weight of the engine on the rails.  Can't tell if it helps much because of the noise radiating directly from the open spaces.  Noise must be kind of a relative issue and I should probably find an expert to give it a spin.  Being a newby, I hope I don't run into someone inclined to look down their nose at my gear - and me!

Got any thoughts? 

John B       P.S. - I can see why guys just pony up the bucks and buy the spiffy new stuff with everything already done!  But somehow that's not really the point, is it? 

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Posted by richg1998 on Thursday, January 20, 2011 8:41 AM

Get the MDC 45 to 1 regear set from NWSL.

http://shop.osorail.com/category.sc?categoryId=62

Get the motor that is now used in the new Roundhouse locos that still uses the same type of gear set. Get the flywheel from NWSL.

http://tinyurl.com/4k7kmcb

1998 MDC and 2008 Roundhouse locos motors. You have pre-1998 which also uses the same compound gear drive.

From Athearn, You can get the plastic fixture that holds the motor or use bath caulk.

I did something like this some years ago using a Tyco ten wheeler. I made my own compound gear drive using the NWSL gears and used a 1620 double shaft Sagami can motor with flywheel. What a beautiful runner. I was using a home made power pack with pulse power. The motor is sometimes on ebay.

I bought the NWSL Quarterer to make sure the drivers and side rods ran just fine.

Rich

 

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Posted by richg1998 on Thursday, January 20, 2011 8:52 AM

Below is a link to HO Seeker with many Roundhouse steamer diagrms. I sent him the diagrams for my new Roundhouse locos. I emailed Athearn and they have many of the parts. Screws to mount the plastic motor holder.

http://www.hoseeker.net/mdcinstructions.html

Rich

 

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Posted by Attuvian on Tuesday, February 1, 2011 5:31 PM

If you're still out there, what did you do with your trailing trucks and fireboxes on your upgraded Pairies?

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Posted by fwright on Wednesday, February 2, 2011 5:13 AM

Attuvian

....I have lubed the motor (it sat in storage in this loco for about 25 years) and given it your hand-held test.  It has some vibration on low to mid range which, of course, disappears progressively as I crank up the juice.  Although the armature has a small amount of front-to-back play at rest, I don't think this is a factor as the low speed vibration issue isn't noticeably reduced when I hold it vertically for a full-range test.  Perhaps lower speed vibration is an inherent liability with these motors (don't know who made it).  I don't think it's the bearings - unless they were bad from the factory - as there's probably less that an hour on the motor in its lifetime and I have always insured that it was properly lubed.  (BTW, are the skew-wound motors that I'm seeing advertized in some of the new RTR engines specifically designed to smooth out low rev operation?).  Your comments above indicate that uneven low speed operation might also be due to a wimpy Alnico magnet.  I can't imagine that this one has ever been subject to excessive heat, and how would I test its strength to find out?

Actually, noise may be the biggest issue.  I guess I'm presuming it's due to engine vibration.  The assembled frame rolls quite freely but there is a very slight clunk once on every rotation of the drivers when testing.  The clunk is not speed or load dependent and I might be able to live with it - I still remember some of the clanking of old NYC steamers from the early 50s that passed my house in southern Michigan when I was a boy.  What I've really got to work on, though, is the noise both from the open frame motor and the open portions under the boiler.  There are no burrs on any of the gears, the worm is meshed about half way in the idler and the idler doesn't seem to be binding in the gear box.  I have already placed a thin layer of cushioning material between the motor mount and the driver framing to reduce vibration noise that may transferred to the drivers and amplified by the weight of the engine on the rails.  Can't tell if it helps much because of the noise radiating directly from the open spaces.  Noise must be kind of a relative issue and I should probably find an expert to give it a spin.  Being a newby, I hope I don't run into someone inclined to look down their nose at my gear - and me!

Rich gave you some great advice, and he's got more experience with MDC mechanisms than I do.

Issues which I picked up on in your text:

  • gear mesh should be a lot tighter than you seem to think.  The old timer method was to use a very thin piece of paper as the spacer between the gears.  They would push the gears tighter until they just remove the thin paper.  Basically a paper feeler gauge set to around 0.003" or so.
  • if the worm is mounted on the motor shaft, any longitudinal slop in the motor will cause the gear mesh to change.  The old fix was to add washers in the gearbox to prevent the worm moving from the correct position.  Adding washers inside the motor is not a good idea because removing the armature from an Alinco magnet motor causes some permanent loss of magnetism.
  • the clunk in the mechanism should be located and eliminated.  If it is a clunking noise, it's probably coming from the rods striking something on their rotation.
  • finding the noise requires detective work.  I've sometimes used a rubber hose on the end of a small funnel to better locate the source.  It's a trick I learned working on old British sport cars, and is similar in principle to a doctor's stethoscope.
  • Cogging is an inherent phenomena of permanent magnet motors with iron armatures.  Cogging is the acceleration/deceleration of rotation caused by the varying intensity of the magnetic attraction/repelling of the armature pole as the motor rotates.  It can be felt as an impediment to rotation at several points as you rotate the motor shaft by hand.  Strong cogging prevents smooth motor operation at low RPMs.  You counteract cogging through improved motor design.  Skewed armatures, increasing the number of poles, and widening the magnetic field band all are ways to reduce cogging.  A can motor uses circular magnets wrapped around the armature to increase the magnetic field band.  A 3 pole open frame motor will be worst case cogging. 
  • I can't tell from words whether the low speed vibration of the motor is from cogging.  You would have to compare several motors turned by hand, and at low voltage to get a better feel for what is happening.  With minimal vibration at higher RPMs, it sounds like the motor is pretty well balanced and the bearings are decent.
  • Alinco magnets will lose magnetism slowly over the decades.  Rare earth magnets have a much denser and longer lasting magnetic field, and therefore can improve an open frame motor where the magnets have weakened.  Can motors usually use ceramic magnets (a few use rare earth), which are also better than Alinco.

Rich's suggestions for regearing and remotoring are an excellent path to improved performance.  The mechanism still must be freed from any binds and clunks.  If quartering is off, there will be rotational bind in the mechanism, hence Rich's suggestion to check quartering.

my thoughts, your choices

Fred W

  • Member since
    December 2010
  • From: Portland, Oregon
  • 658 posts
Posted by Attuvian on Wednesday, February 2, 2011 9:23 AM

Thanks, Fred.  Your explanation of cogging cleared up a lot.  I took the motor into my hobby shop and a guy at their repair bench gave it his own hand-check.  As another older guy I granted him an immediate extra level of credibility.  He said it was one of the better running open frame motors that he had run across in a long time.  I'm presently inclined to see if I can reatin it by redoing the gear mesh, experimenting with a thin rubber or stiff foam pad (like the double-sided sticky stuff for mounting things on walls) between the motor mount and chassis, and maybe some inserting some sound-absorbing material in the cavernous boiler.  Fixing is good; learning something in the process is better.  I'm certainly without a deadline here.

As far as the clanking is concerned, I like the tubing and funnel idea.  Indeed, the side rods might be the issue - I just reviewed the exploded diagram that came with the kit and noticed that in a copuple of cycles of tearing her down and reassembling I've left off reinstalling the #2 washers between the wheels and the rods.  Another thing I should check is how that noise might change by running the chassis around the circuit without the boiler.

John (who went by my middle name Fred prior to Jr. High - family still uses it)   ; )

  • Member since
    November 2002
  • From: Colorado
  • 4,075 posts
Posted by fwright on Wednesday, February 2, 2011 11:13 AM

A few additional thoughts about cogging.  External to the motor, methods to improve slow speed running are:

  • higher ratio gearing.  Using a higher ratio gear set raises the motor RPM above stall for a slow loco speed.  The trade-off is reduced top speed on 12v.  For steam lovers, switching engines benefit from the higher gear ratio, while you may want road power to run a little faster.
  • adding a flywheel.  The flywheel smooths out the cogging by storing and releasing rotational energy.  A flywheel can mask hitches and binds that are not inherent to the drive.  So I like to get a mechanism running as smoothly as I can before adding the flywheel.  The experts in steam mechanisms suggest that if a new motor has a shaft diameter of less than 2mm, the flywheel should be separated from the motor by universals - the bearings on the very small shafts are too wimpy to support flywheel loads.
  • using pulse power/BEMF.  Pulse power and feedback loops can help the motor power through the cogging.  These can be so good that some would say a flywheel gets in the way.  Again, like flywheels, pulse power and BEMF can mask issues in the mechanism, so I like to test and get the mechanism right before tuning for even better performance with pulses and feedback.

my thoughts, your choices

Fred W

  • Member since
    December 2010
  • From: Portland, Oregon
  • 658 posts
Posted by Attuvian on Wednesday, February 2, 2011 11:43 AM

All the information about cogging is excellent.  But I may be fortunate with this particular motor.  Although I notice the cogging when turning the armature with my fingers, it dosen't seem to have much effect when installed on the chassis and run on low speed.  There is no obvious jerkiness at creep speeds, whether hauling a string of cars or not.  Current power is my old MRC Tech II pack.  In momentum mode there is some slight hesitation when it first moves (easily less than the first quarter inch) but I get the same with my old Athearn blue box GP9.  Should there ne none at all?

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