News Micro Servos Out, Micro Steppers In?

rray Jun 19, 2022

  1. rray

    rray Staff Member

    7,706
    5,859
    128
    We previously discussed Micro Linear Servos, and the consensus was that the integrated potentiometer used for position feedback could wear out in a day, and would give jittery control.

    So I am still looking for a solution, and stumbled across Micro Stepper Motors. I had looked at them years ago when Kim had purchased a pallet of DVD players so he could harvest the laser diode's linear stepper motors, but they were about 3 inches long and I didn't know enough about stepper motors then.

    After purchasing a pair of the linear servo motors, and finding the torque low, and reliability poor, I continued looking for tiny motors, and ordered a few different micro stepper motors to experiment with. In order to be useful, I need to be able to solder wires to them, so all 3 got the treatment, and coil resistance was measured to verify they are operable. The middle one is just your basic roundy-rounder with a 0.92mm shaft diameter, and should be suitable for slow speed animations like the Union 76 Gas Station Ball, or Grist Mill Waterwheels. etc. That motor only costs $0.26 each, and for a quarter I went ahead and got 100. The other two are Linear travel mechanisms used for camera lens focusing.
    Micro Lineat Stepper 2.jpg


    I ordered a Stepper Motor Driver Board Speed Controller DC 5V-12V to test the motors with, but it STILL has not arrived from China yet. I plan on using Arduino's or similar to drive the projects, but for basic testing I plan on using this:
    Acxico 2Phase 4Phase Stepper Motor Driver Board Speed Controller DIY DC 5V-12V.jpg

    The motors should have more torque than the linear servo, and at least one of the motors has both a planetary gear head as well as metal reduction gears on a 4mm motor, so should have plenty of torque:
    Micro Lineat Stepper 3.jpg

    The reduction gear model is about the same size or slightly smaller than the previously reviewed micro linear servo motor. It is definitely built to a much higher quality standard, and 1/3 the price at $2.92!:
    Micro Lineat Stepper 4.jpg

    On this motor, I was able to solder to the linear slide nut with very little heat, so I can attach a wire to it for possible crossing gate or semaphore operation. I just cut off the flexible PC material and soldered on wires, so this one is very easy to deal with, and only cost $1.42 each.:
    Micro Lineat Stepper 1.jpg

    So I will report back when I get the tester, and as i come up with real uses for them.
     
  2. wvgca

    wvgca TrainBoard Member

    418
    218
    19
    depending on how much torque you actually need, servos are less hassle to get working, they are fairly low torque though ..
    i have run both, and light duty servos are less work and time to get working properly ..
    you will get the most torque out of a stepper in full step mode, but the resolution is on the poor side
     
  3. rray

    rray Staff Member

    7,706
    5,859
    128

    The big problem with using the tiny linear servo is their longevity. Kim Vellore (Kim's Art Shop) built several animated scenes using the small blue servo's and the position feedback trim pot inside went bad after a day of running at train shows. He would have to replace the servo the next day, because the resistive thin film in the tiny trim pot used was worn away by the contact wiper. Unless they are of a high enough quality to use optical encoder position feedback, they just wear out too quickly.

    Stepper motor drivers are super cheap at around $2-3, an Arduino Nano at around $10, a Buck Converter at $2, Micro Stepper Motors for $3, DFPlayer Mini for $2 so for under $25 it should be possible to animate Z Scale crossing gates complete with lights, sound, and motion, and have something that will reliably last a long time. These tiny motors seem to be surplus from camera lens focusing mechanisms.
     
    BNSF FAN likes this.
  4. MegaBlackJoe

    MegaBlackJoe TrainBoard Member

    38
    51
    9
    I have already built the hanlaid turnout using the linear servo motor from your previous post and the stepper motor with metal gears. I beleive the servo has more torque and less precision (for positioning the point rails) whereas the stepper motor has better precision but the torque is very low - it requires a lot of precision while building the turnout and virtually zero resistance (it shall be close to zero friction). I beleive it's possible to built a turnout using the stepper motor mentioned in the post, however since you need an incredible precision and tolerances in the moving parts to avoid friction, you can only do it using resin 3d printing for the motor mount - otherwise it doesn't work.

    Servo controlled - early prototype - I actually managed to built the entire turnout, but due to servo being too wobbly (mechanical part) and jerky (electronic part) I could not precisely position the point rails always having a gap of 0.01 inches or around so.

    https://www.trainboard.com/highball/index.php?threads/code-40-custom-turnout-drive.142718/

    The one in the video is using the stepper motor, 3d printed motor mount, however it took me around 3 prototypes to figure out the tolerances
     
    rray likes this.
  5. wvgca

    wvgca TrainBoard Member

    418
    218
    19
    i have been using servos for seven years now on turnouts, and they do function reliably ... just don't buy the cheapest ones you can get , lol ... only one servo failed, and that was the gears themselves, not the position wiper, and that one died rather quickly, within the first 3 or 4 months ..
    the speed adjustment is the feature i find the best overall ..

    on cnc plasma tables and larger stuff i use large steppers because of the torque, with gecko controllers .. on the plasma table the steppers were [ i think] rated at 1.7 volts and i drove them at 50 volts
     
    Last edited: Jun 19, 2022
    rray likes this.
  6. rray

    rray Staff Member

    7,706
    5,859
    128
    Here are a couple videos I found showing these motors being tested.

    In this one the presenter connected the motor coils directly to the low current Arduino outputs and tested his motor to determine things like how many steps per revolution the motor had:


    In this video the presenter opens up a motor to show the construction inside one of these micro steppers:


    This presenter connected one of the motors directly to an Atmel ATtiny85 chip and programmed it for forward and back motion, making a super inexpensive motor controller:


    The presenter in this video measures his micro stepper with a meter to determine the poles, then connects it to an Arduino Nano to directly drive it:


    In this video the presenter just demonstrates the positioning accuracy and repeatability, as well the metal bending torque that the mini linear gearhead stepper motor has when driven by a postage stamp sized $2 A4988 driver board. I have this motor on order from China too, due any day now:


    If you guys find more helpful stuff, please post it.
    Thanks, Robert
     
    gmorider and BNSF FAN like this.
  7. wvgca

    wvgca TrainBoard Member

    418
    218
    19
    with any stepper, if you use other than full steps [one magnet move] the torque goes down [microstepping] but resolution goes up quite a bit, i think the geckos would microstep up to about 32 increments per full step, most steppers will do 80 - 128 full steps per revolution
     
    rray likes this.
  8. rray

    rray Staff Member

    7,706
    5,859
    128

    This is good to know, but do you also need to use a driver board that supports microstepping? I have some DVR8833 motor drivers that just have 4 ins and 4 outs so are in effect just current boosters, and not like the A4988 drivers that have MS1, MS2, and MS3 but only output between 8 to 35V to the motors which is too high for these 3-5 volt motors.
     
    BNSF FAN likes this.
  9. MegaBlackJoe

    MegaBlackJoe TrainBoard Member

    38
    51
    9


    The motor I am using for my turnout. It's very low torgue - it's not even comparable to the one in the last video. I am using the Arduino to drive it as I found it very tricky to configure the current - it's either too low, or the motor overheats to the point where it can't be touched.
     
    gmorider and rray like this.
  10. SJ Z-man

    SJ Z-man TrainBoard Member

    2,915
    848
    53
    What hi saw from initial content on Amazon and eBay (after Rob notified me of the smaller ones) was the screw pitch is crazy course on several of these, meaning one or two rotations for high displacement which would lead to far less torque. Check the video “precision planetary gearbox”in post 6 that shows for example. I think you need the ‘what you normally see on a screw’ pitch.
    And some where visiably poor cut treads or already skewed connection tab.

    As MBJ said, I would hope that there is the smarts to ‘give up’ if you high current (like when the servos don’t reach/hold their angle.
     
    rray likes this.
  11. wvgca

    wvgca TrainBoard Member

    418
    218
    19
    you can safely 'over drive' the voltage on most steppers [ i have tried size 17 and up], but not the current so much... an easy way to tell is simply to hold the stepper in your hand, warm is okay, too hot to touch is not ... overdriving the voltage will -usually- speed up the response time some what , as i mentioned before the larger steppers were rated way lower than the 50 volts i drove them with ..
    i had the little ones, like what you show, but never really got around to trying them out, so i can't say too much about them ..

    ps .. the driver supports microstepping , kind of, it can be either hardware [like in the driver] which works well, or in the software, which doesn't work as well ...
     
    rray likes this.
  12. Chris333

    Chris333 TrainBoard Supporter

    2,526
    203
    48
    CNE1899, gmorider and rray like this.
  13. rray

    rray Staff Member

    7,706
    5,859
    128

    When I grow up, I want to have mad crazy skills like that! What I want to know is what kind of glue did he use. I suspect it might be some kind of UV cure resin, because it would have to be strong and cure very fast after you get the parts in place.
     
  14. wvgca

    wvgca TrainBoard Member

    418
    218
    19
    i would really like to see how you implement very small steppers there ... i didn't have a chance to test my small steppers, just the size 17 and up ones .. curiosity, lol .. i did a small cnc milling table with wee little drivers, it worked okay in full step mode [the drivers or the the software wouldn't do microstep, don't remember]
     
  15. rray

    rray Staff Member

    7,706
    5,859
    128
    I had a KFC restaurant project posted in the Z "What's On Your Workbench" thread, and someone asked if the bucket rotated, and I had to say it was not. Today however I received some DRV8833 drivers for $1.43 ea., and connected one of my tiny stepper motors to it, and connected the DVR8833 to a Digispark Attiny85 clone that I got for $4.33. This is as cheap of a micro-controller and motor driver as I can find, which, along with the $0.35 motor, is an economical way to drive something like the KFC bucket. I just have to find some watch gears to make a speed reduction mechanism, because slowing this motor causes visible stepping. There are only 20 steps per revolution with these tiny motors.

    Here is my test video:


    I just put in a simple code, and used the Arduino IDE to program it to spin 50 revolutions and stop for 2 seconds so i can see how hot the motor is:

    #include <Stepper.h>
    // steps value is 360 / degree angle of motor
    #define STEPS 20
    // create a stepper object on pins 2, 3, 4 and 5
    Stepper stepper(STEPS, 2, 4, 3, 5);
    void setup()
    {
    }
    void loop()
    {
    stepper.setSpeed(100);
    stepper.step(1000);
    delay(2000);
    }
     
    Kez, Kurt Moose, zdrada69 and 2 others like this.
  16. JoeS

    JoeS TrainBoard Member

    2,958
    719
    53
    As stone cold Steve Austin would say “can I get a hell yes!!!!”
    Nice!
     
    Kurt Moose and rray like this.

Share This Page