Fail of the Week: Photography Turntable

fotw-spinning-platform

Turntable photography has seen a rise in popularity driven by online shopping. If you can’t hold it in your hand at least you can see what it looks like from all angles. From the still image, [Petteri Aimonen's] roll-your-own turntable looks great. It’s completely enclosed and has a very nice paint job. But when you see it in action it appears to suffer from a stutter.

He isn’t just using this to capture continuously rotating video, but planned to have it rotate a set amount and then pause while an image is snapped. He used an STM32 microcontroller to drive a brushless motor which he pulled from a hard drive. It totally works, but the nature of the hard drive motor thwarted his original plan. It’s meant to run at very high speeds with low friction. But the thing was never designed to stop on a dime. So when it is directed to turn thirty degrees, it overshoots and oscillates back and forth as shown in the video.

This oscillation would go on for more than ten seconds. But [Petteri] was able to dampen it by adding some friction to the disc. He also had to tweak the original driver design, adding flyback diodes he had forgotten to include, and dealing with some issues caused when feeding a PWM signal to the coils. There are other small defeats which also ate away at him. The paint color doesn’t match the light box he’s using, there were some issues with the battery, and at one point he broke the programming header right off of his PCB. Despite these frustrating issues we still bet it was a lot of fun to work on the project.


2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.

Comments

  1. hans says:

    You can make a break for an electric motor by shorting out the leads. It’s a cool experiment too, just short out the motor and you can feel the torque increase.

    • Gdogg says:

      Yeah most h-bridges have this.

      It works by having the breakdown voltage run back through the coil itself.

    • jpa says:

      It doesn’t work that well at low RPM’s, though.

    • tekkieneet says:

      The DC brushless motor is driven as if it were a unipolar stepper. :( It
      is a quadrant I driver, so you can’t do anything except to let the motor
      run or coast. HDD motors are designed to be efficient, so they coast
      very well.

      Use 3 H-bridges and connect the motor with 3 terminals to make a 2
      quadrant driver. This configuration allows you to use dynamic brake or
      to run the motor in reverse to increase braking power at low speed.

      A closed loop control would require the speed and angle of the motor to
      to plan the acceleration/deacceleration so that the motor would stop at
      the right location.

      • Phrewfuf says:

        Ever tried shorting leads on a stepper? Those become immovable, even if there’s no power applied and/or the motor is not already rotating.

        Of course, Petteri would have to short all four leads of the motor.

  2. NiN says:

    For this job you need motor that can be controlled very precisely and stopped in place at any moment (stepper). HDD plate motor choosen for the project is exactly the opposite. This is very nice example of fail of the week.

  3. Trav says:

    why not just install a brake? When the motor is about to run, pull a solenoid in. When it completes, let the solenoid spring up against the top and hold it in position.

  4. wut says:

    Can’t one just speed it up till it looks like a standing image?

  5. Never says:

    From the video it look like it stops the acceleration right where it is supposed to position itself.
    Perhaps even some bang-bang control would have made it smoother?

  6. Dave Thunes says:

    Just a bit of nitpick: the term is “damp” not “dampen.”

  7. mojojoe says:

    I expect a high ratio gear drive would improve control here, but at that point it would probably be easier to just use a more appropriate motor.

  8. supershwa says:

    “The Website is Down” must have been a close contender for the FotW. ;P

  9. James says:

    A thin flat stepper from a scanner head on an old multifunction inkjet printer would do the job here. Such printers are plentiful and free or a couple bucks at most.

  10. RB says:

    Why steppers? If im not mistaken im pretty sure these are ran from plain old hobby motors with a worm gear and a big planetary. If he needs position add in a rotary encoder…

  11. justice099 says:

    Another way to do this would be to just continuously rotate it and have some sensors which triggered the camera at specific steps. Perhaps hall effect, or even a brush and contacts.When the revolution hits the angle you want to capture, it just triggers the camera to take a photo. Shutter speed should be plenty fast enough with enough light.

  12. dan says:

    Surely it’s be easier to let the motor run at full speed, and gear down to move the platform slowly?

    then the motor can overshoot, if you have geared for a 17,000 RPM motor to a 1 RPM motor then over shooting at the motor doesn’t make a huge difference.

    (e.g 17,000 RPM = 1RPM – slow)
    over shoot of 50 extra spins of the motor is about a 1 degree overshoot.

    which seems more than good enough -like your eyes wouldn’t even notice kind of good enough!

    1/17,000 = 5.8×10-5

    * 50 extra spins (unrealistically high) = 0.0029 extra spins *360 = 1.05 degrees.

    more realistically there is going to be a one or two extra rotation over shoot so realistically somewhere between 1/50th of a degree and 1/5th of 1 degree should be able to be achieved.

    obviously the faster you wish to spin the platform the more over shoot you need to deal with… (because the extra overshoot is not geared down to be minimal)

    given the video appears to be of a 3d printed gear… I suspect he already has the tools to do this.

  13. deadlydad says:

    FWIW, he can always go Olde School.

  14. Whatnot says:

    I see far too much instances of people saying ‘good bye’ instead of ‘goodbye’ lately.
    I wonder if that is some spell-checker fault or just one person who typed it as two words and it propagated from there.

  15. Biomed says:

    You know… you guys really still need to drop this category… or at least be HONEST and rename it “Demeaning comments from those pretending to be a God”.

    You know how many totally failed projects I’ve had? Know how many of those I want to NEVER reveal? Know how HIGHLY placed I am today in the field? ROFL…. it was cause I kept trying! It’s a passion! You can kill that passion through ridicule.

    This board is not a peer-review no matter how you struggle to make it seem so… we know whom you are because we have been you, or you will be us… take care growth is promoted without doing harm. Remember the temptation to seem godly by use of ridicule when facing a subject you could do nary a thing to succeed within. .

    We all stand on the shoulders of the giants that came before us… and we stand on those shoulders by learning from them… which means plenty of screwing up along the way. We learn more from our mistakes than our successes. Being worthwhile to the community is measured in how much you help it grow. Newspapers just report the gory bits…. what is this place?

    • dan says:

      I disagree, a failure is a failure, why call it anything other than a fail?

      and publishing failure is the best way forward, those who don’t learn from their mistakes are destined to repeat them.

      if you stop being precious about the way that you’re spoken to and realise that in general, on the internet people are pretty rude, then you look through the bile and sarcasm and you might actually find a reasonable solution to the problem that you’re facing. then you can turn your failure around and make is a success.

      there are plenty of reasonable ideas here about what the guy could have done and still could do to take the problems out of this system. -so albeit in a rude and unprofessional way, (because this is the internet and a lot of people here are not professionals) advice is sought and received, new ways of thinking are brought up, or questions are asked about new ways of thinking.

  16. Biomed says:

    FAIL of the Week.

    The title sets the tone and the masses follow suit as though given prior permission.

    Has nothing to do with the internet, its just how one was brought up. It’s been with us all along.

    You could set a more supportive tone, and should. Would take just thinking it through and changing probably little more than the title.

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