Z Scale Motor Life

shortpainter Nov 6, 2019

  1. shortpainter

    shortpainter TrainBoard Member

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    Some of you may know I design 3D printed locomotives and frames that mount Rokuhan motors and trucks. I'm curious about the life span of those motors and all other z scale motors. Has anyone ever used a locomotive to the point the motor died from usage? How long did it take? I have seen some third party micro motors for drones for sale on Amazon, Ebay and sources from overseas. How do these motors compare to the ones used in AZL, MTL and Rokuhan locomotives? How do you know the life span of a motor(other than running one until it dies)?

    I'm interested in designing new types of locomotives using motors that are not from the big three in Z.
     
  2. southernnscale

    southernnscale TrainBoard Supporter

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  3. SJ Z-man

    SJ Z-man TrainBoard Member

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    Many of the smaller motors are reliable enough. However, the smaller ones tend to be lower voltage, like 3, 5 or 6 volts. That fine if the power pack is reasonably controlled. Its more about the loading. If you put one of the tiny 'can' motors in something heavy, say and MTL GP-35 or and AZL diesel, you will need a higher speed motor with gear reduction (more than you see with the typical worm gear to get enough torque to easily move the loco at reasonable speed and 5-25 cars.

    Heat, is your enemy. once you push the motor to where you don't see any perceivable increase in the speed, the heat factor will begin to significantly increase.
     
    ddechamp71 likes this.
  4. shortpainter

    shortpainter TrainBoard Member

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    If a motor says it can handle up to 3 volts, will it last longer if it is fed 1.5 volts its whole life? Is reducing the voltage input a way to eliminate the heat problem?

    My goal is to put a 6mm motor in a frame for a GE 44 Tonner using the trucks from a Shorty. I found some plastic worm gears from a source in China that is very close to the Rokuhan shorty's metal worm gear. I hope to get good results using the worm, shorty trucks, a 6x14mm motor and a 3D printed frame. My concern is obviously the motor and its life span. I can find many 6mm (and smaller) motors but I cannot find a way to determine the quality.
     
  5. LWR21

    LWR21 TrainBoard Member

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    I think your project will pique a lot of interest. Thank you for pursuing this.
     
  6. rvn2001

    rvn2001 TrainBoard Member

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    I have burned out a motor in all of the manufacturer's locos. I run my trains almost every day and for extended periods at train shows. I still have some of my original Marklin locos that have only needed cleaning, lubrication and new brushes. I started in Z scale in 1972 when it was first introduced in the states.

    I really like your work and look forward to your next project.
     
  7. z.scale.hobo

    z.scale.hobo TrainBoard Member

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    John tested the shorty, which is what you might be searching for ... https://www.raildig.com/raildig-build-projects/shortytown-in-z-scale/

    Money Quote: I received my Shortys ... a few weeks ago and I’ve since been running the legs off of this chassis, easily 10 hours per day for several weeks now and it’s still running smooth and quiet.

    Seems that he never added on to this story, so we don't know how much longer it went. Of course, adding mass such as a brass shell will definitely load the motor more leading to more heat generation.
     
  8. minzemaennchen

    minzemaennchen TrainBoard Member

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    Hi Rudy, I wouldn't be that concerned: you are selling a kit, so if somebody can assemble you creations they will be also able to replace an inexpensive motor if it blows up. And due to brass shell no meltdowns either.
     
    southernnscale, LWR21 and Kez like this.
  9. tracktoo

    tracktoo TrainBoard Member

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    With really small motors high gear reductions are an imperative. 75:1 minimum and up to 150:1 and more depending on motor specs, wheel diameter (an often overlooked piece of the final drive reduction), and desired scale top speed. If you expect any performance in either pulling power or speed control those need to be accomplished while allowing the motor to run reasonably close to its rated operating range. Miniature motors accomplish their power with RPM's, not torque. It's all in the HP calculation formula (Torque x RPM/ 5252), worth a search and an understanding if you're not familiar.

    Also, for motor life, don't use a supply voltage that exceeds the motor rating. Pulse power controllers are great for speed control but must not be used for limiting peak voltage. You will have brush trouble if you try to limit top voltage with PWM.
     
  10. shortpainter

    shortpainter TrainBoard Member

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    Thanks for all the feedback. My first experiments will be with a 45000 RPM 3.5 volt 6x14mm motor. I don't have much faith in that setup but I found a better alternative. There is a place that sells 6x21mm motors with a 700:1 speed reduction that rotates at 90rpm. It accepts up to 6 volts which I imagine is much more compatible to most of our layouts. The worm gears I have will not fit the shaft but it may still work. If I power it with four AA batteries it stays within operating limits and runs at a nice pace with good torque. Of course, everything depends on how well the shorty trucks will accept those kind of power sources. We'll see.
     
  11. tracktoo

    tracktoo TrainBoard Member

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    700:1 primary reduction is way too much especially running through a final worm drive. The primary reduction is the multiplier for each following reduction. Assuming about a 14:1 final worm reduction the primary reduction should only be about 10:1. That's a 140:1 final drive. With 15:1 primary that would be 210:1. Those are probably the ranges you will want unless you're running a monstrous set of drivers.

    With a primary reduction of 700:1 that will be 9800:1. Without any other info on wheel diameters it's safe to say that will be way too much. Hope that helps.
     
  12. shortpainter

    shortpainter TrainBoard Member

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    Good to know. There is a 136:1 and a 26:1 motor available, too. Ill try those out.
     
  13. tracktoo

    tracktoo TrainBoard Member

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    Both of those are probably too high, too. The 136:1 will definitely be too high but the 26:1 will run awfully slow, too. That's still 364:1 assuming a 14:1 final drive ratio.

    I have used 33" Z wheels (.150") with a final drive of a 14:1 worm gear (120DP or approximately .2 mod) which was as large as would fit with that wheel diameter without hitting the rails at turnouts and crossings. Even with 42" drive wheels (.191") the max final drive you are likely to want is about 200:1 which is still measurably higher than the 364:1 accomplished with the 136:1 primary gear with a 14:1 final gear. This is the source of my speculation that the primary gear you'll likely want is about 10:1 with 15:1 being absolute tops.

    Do you know what wheel diameter you'll be interested in using and what final gear set you're planning?

    To help envision all of this, here's a real world example that I have posted on this board in the past. It's one of my prototype test chassis with 33" Z wheels (.150") and approximately 145:1 final drive ratio running at full speed. This might help you to see what I'm talking about. And the motor is nominally in the RPM range you're talking about, if anything, even faster. It's from these experiences that I make these suggestions with such conviction. :)

     
  14. tracktoo

    tracktoo TrainBoard Member

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    In this sentence quoted from the above post, the highlighted word should read "lower" as this edit shows. Sorry for the error.

    Even with 42" drive wheels (.191") the max final drive you are likely to want is about 200:1 which is measurably lower than the 364:1 accomplished with the 136:1 primary gear with a 14:1 final gear.
     

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