Fine-tuning loco to degrade performance

Discussion in 'HO Scale Model Trains' started by scottcn, Jul 10, 2007.

  1. scottcn

    scottcn Member

    Well, that wasn't really my goal, but that's what happened. I put a DCC decoder in an old blue box Athearn GP38-2 loco - no problems there. I then had the bright idea to try and tune up the engine to improve it's performance, especially at lower speeds. Previously (i.e., ~15 y ago) I used this loco with a toy set power pack and I could only coax three speeds out of it: off, unrealistically fast, and even faster. So, I took apart the power trucks and gear assemblies, filed off a bit of flash from the gears, reassembled everything, and then turned on the power and ...

    (sorry, but nothing blew up, sparked, or made a big noise)

    ... found a problem that I either didn't have before or didn't notice.

    The truck assemblies (generally the front, but sometimes the back) shake from side to side (at several times per second) when the motor is turning at low speed. At higher speeds, this shaking disappears. Oh, when I am noticing this, the engine is held/balanced so the wheels are not on the tracks. I suspect that the rails and the weight of the engine would keep this from happening if the engine was placed on a track but that seems like covering up the problem rather than fixing it.

    To wrap up what is becoming a long-ish story, I disassembled/reassembled the power trucks many more times to check/clean/file the gears but the shaking did not go away. Eventually, I assembled the trucks without any of the gears except the worm that is attached (via couplings and shafts) to the motor/flywheels. The shaking still occurs. If I disconnect the motor and flywheels from the worm, there is no shaking so there's got to be a problem with the worm itself or the connection between the worm and motor/flywheels. This is getting frustrating!

    Does anyone have any ideas for specific things I should be looking for? Would lubrication help? Is trying to fix this shaking even something I should worry about?

  2. green_elite_cab

    green_elite_cab Keep It Moving!

    I get shaking like this sometimes. My best guess is either the pin the trucks are attached to are sheered off, creating loose trucks, or that there is something being bumped by the motor.
  3. sumpter250

    sumpter250 multiscale modelbuilder

    Old bluebox Athearn. Most probably, the cause of the shaking is the universal coupling between the motor, and the wormgear. Yes all, or some part of it. The cup/ ball at the motor, the spline coupler, or the cup/ ball at the worm gear. These are cast delrin, and occasionally you will get one that is slightly eccentric. This is also the cause of noise from vibration, at speed. You can try a different universal drive, or find some replacement drive parts.
  4. doctorwayne

    doctorwayne Active Member

    It sounds to me as if this is simply the motor "cogging". While Athearn motors are almost indestructible, they're not great runners at low speeds. At low speeds (and low current to the motor), the poles on the armature tend to be momentarily held from turning by the magnetic forces of the field part of the motor. In effect, the motor is stopping and restarting: as you increase the power (and the speed) these forces are overcome, and the loco runs more smoothly.
    You could replace the motor with a good quality can motor. NorthWest Short Line, which sells motors, gears, and drivetrain parts, contends that neither the gears nor the drivetrains in Athearn locos are the cause of poor operating characteristics of Athearn locos: rather the problem is the low-cost motor.

  5. scottcn

    scottcn Member

    Thanks, everyone for your thoughts and ideas.

    green_elite_cab: Perhaps there is some extra play where the trucks rotate around the pin, but I know the pin is still there. Actually, it seems like the shaking is a back-and-forth rotation around this pivot point. I haven't noticed anything rubbing against the motor or drivetrain, but will double-check that tonight.

    sumpter250: When I get home tonight, I'll take a look at the drivetrain and universal couplings. That's something I haven't checked before and could be the problem since the shaking doesn't start until the motor is connected to the trucks.

    doctorwayne: I have also read what Northwest Short Line says about the quality of the Athearn gears/drivetrain versus the motor and have considered installing a new motor in this loco. Undoubtedly, a new motor would improve slow speed performance but that seems (to me) to be a separate issue from the shaking since I don't notice the motor itself shaking unless it is connected to the trucks. I may go ahead and buy a new motor anyway - my wife is away on vacation and surely she won't notice a new motor among her many vacation expenses when the credit card bills come :). (or maybe that should be "credit card bills :eek: :shock:")

    Thanks for the good ideas. I'll check these things out tonight in the hopes that I can definitively solve - or at least identify - the source of the problem. Of course, if anyone else has other ideas, I'm all ears.
  6. thedowneaster

    thedowneaster Brakeman

    Adding to DoctorWayne's comments...You might be able to improve motor performance and life by adding a resistor/capacitor pair to the positive and negative terminals of the motor. The R/C crowd has done this for years and years to help cancel "radio noise" from the motor.

  7. brakie

    brakie Active Member

  8. green_elite_cab

    green_elite_cab Keep It Moving!

    I have a brand new RTR GP38-2, and a not often used AC4400CW that still give similar problems. the other blue boxes work better.
  9. brakie

    brakie Active Member

    I have several of the newer RTR units and all run better then my tuned up BB units.My 2 GATX GP38-2s draws less then a 1/4 amp while in consist.Far better then my older BB units at 1/2 amp for a 2 unit consist.
  10. green_elite_cab

    green_elite_cab Keep It Moving!

    Perhaps i need to tinker more with it then. I can find no problems. no DCC or extra stuff is installed. the GP38 is new, but its been EXCESSIVELY noisy and shaky since day one. The AC4400CW on the other hand only started after few weeks. attempts to clean the AC4400CW haven't seemed to help, although i should probably take a look at the GP38 again.
  11. doctorwayne

    doctorwayne Active Member

    As brakie suggests, the Athearn motors can be "tuned" to improve their performance. I just went into the layout room and tested some Athearn locos: neither my SW1200RS switchers, nor my GP7/GP9 displayed any shaking with the trucks not touching the tracks. Even though all have had can motors installed, your problem may lie with the electrical collection system used on Athearn locos. The system of steel straps is not very reliable at best, and should be replace with wires. With the straps, when your loco is not on the tracks, "play" in the drivetrain, coupled with the limited low speed capabilities of the motor and the altered position of the straps (due to the trucks "hanging") may cause intermittent contact, causing the motor to cut-out. Soldering wires to both pick-up points on both trucks and both contact strips on the motor will eliminate this part of the problem. I discard the long top strap, soldering the wires directly to the copper strip below it and to the copper strip on the bottom of the motor: remove the copper strips (don't lose the brushes and springs!) before soldering.

  12. scottcn

    scottcn Member

    Any guidance on what, exactly, should be done to tune-up Athearn motors and drivetrains? At one time, I found a website that ran through the process, but must have forgotten to bookmark the site.

    Wait ... a quick Google search found:
    Athearn tuneup and
    Athearn model train. Stuff to read and try tonight.

    Actually, I have already discarded the metal straps. I'm using one of the Digitrax decoders that comes with a no solder Athearn harness. With this harness, the metal straps are replaced by wires that attach quite securely to the pick-up points on the trucks. Next time, I'll save a few bucks and just solder the wires to the appropriate spots, but I didn't have a soldering iron when I bought this decoder.

    I didn't get a chance to work on the engine last night -- I found that I was unable to watch the baseball All Star game and do some work on my computer and work on the engine at the same time. Hopefully tonight I'll be able to devote some time to it. If I don't find any obvious problems in the drivetrain or elsewhere, I'm going to reassemble the engine and see how well it works when on the tracks. If it runs reasonably well, I may just ignore the fact that the trucks shake when the engine is off the tracks - hopefully the engine will never encounter a situation on the layout where it is suspended in mid-air because then I've got bigger problems than shaking trucks!!
  13. doctorwayne

    doctorwayne Active Member

    Hey, back in the '50s and '60s they kept telling us that we'd soon all be driving flying cars! :rolleyes: :-D :-D At least with a flying train, you wouldn't have to worry about track cleaning. :lol:

  14. scottcn

    scottcn Member

    Actually, my next question was going to relate to flying trains ... does anybody know how to fix an HO scale anti-gravity unit? Mine seems to be broken (and the guy I bought it from on eBay *promised* that it would work) :) :-D.
  15. green_elite_cab

    green_elite_cab Keep It Moving!

    lol, thats why we need Maglev trains....

    $10,000 fee. of course, you get free shipping. I'm not responsible for any damages caused by mini black holes or other malfunctions that are beyond the warranty.
  16. trainnut65

    trainnut65 Member

    Drive shafts. And that is all i am going to say. Bye now
  17. scottcn

    scottcn Member

    Ah yes, trainnut65, the psychic. How did you know that I broke the driveshaft tonight? Just squeezed one of the couplings a little too hard and I heard a tiny snap. :eek: Regardless, I reinstalled the engine, slightly-broken driveshaft and all, and guess what - there's no more shaking. :thumb: This, of course, demonstrates the little known corollary to "If it ain't broke, don't fix it" which is "If it don't work, break it. That'll fix it." Well, it worked for me this time, but your mileage may vary.

    Actually, I now think that the shaking was an artificial problem. I only ever noticed the problem when I ran the motor with only 1 truck attached. With both trucks, no shaking. Maybe having both trucks installed balances out the system and therefore there's no shaking? Just a working hypothesis, but now that the shaking is gone, I have no plans to disassemble everything to try and make the problem come back!

    Thanks, everyone for your suggestions and help!
  18. scottcn

    scottcn Member

    I'm no electrical engineer but ...

    So after reassembling the engine, I was checking the wheels using my handy dandy NMRA standards gauge when I noticed that my NCE PowerCab was turning off and restarting itself. A quick check of the wiring inside and outside the loco didn't reveal any obvious spots where a short circuit could be occurring. Crossing my fingers that my PowerCab wasn't breaking I went back to checking that the wheels on the engine were in gauge.

    ... and did you realize that those NMRA gauges are metal?? :lol:

  19. green_elite_cab

    green_elite_cab Keep It Moving!

    All i know is that NMRA guages are also half chameleon, because i can never find it half the time.

    AS far as the noise problem, i've come up with a different solution. Run your train full speed in both directions for a few minutes each way, if you have an oval of track or something. It seems to wear down the motor brushes, or whatever is causing the major noises if it isn't loose parts.

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