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Stepper Motors: Someone feel like helping me out with a loudspeaker turntable design for measurement purposes?

Hey, everyone. I’ll try to keep this OP brief and to the point, especially since I know not everyone here is “up” on what loudspeaker testing consists of. But I want to give a little background so you understand why I am asking this question…

I test loudspeakers to gauge their accuracy and determine what is likely to be a good buy and what is not. This involves simply placing the speaker on the ground, placing a microphone at a distance and sweeping a log sine signal through the speaker and capturing the result. As part of this, I take measurements with the loudspeaker at different axes. I capture data in 10 degree increments, up to 360 degrees.

For the rotation, I have gone the traditional DIY route of purchasing a lazy susan bearing and sandwiching it between two sheets of 2x2 foot plywood. Here’s an example of the turntable with a speaker on top:

You can find a gif I made showing this in action here to give you an idea of what I am doing:

The place where a remotely controlled stepper motor would come in handy is…
Right now taking my measurement process is: sweep the signal through the speaker, walk to speaker, rotate speaker 10 degrees, walk back to computer, sweep, rinse, wash, repeat until I have collected all the data I need. The speaker is about 40 feet away. And I’m taking 20+ measurements. That takes a decent chunk out of my testing time. Not to mention leaning over to align the speaker at the right angle. I have a bad back as it is.

The tic USB controllers from Pololu would solve my issues about remotely controlling the spin. Perfect!

So that brings in to question what motor to purchase:
What I would like is to have the motor support the platform directly. Literally, purchase a motor adapter, bolt it to the adapter, done. I just don’t know if there is a motor that will support this and I would rather have an adapter that would support the spinning platform better than the universal adapters I’m seeing.

What I need is:

  • Motor/Platform must be able to support 100 lb speaker BUT located off center (making the front of speaker the center of rotation)
  • Speaker would be on a platform like in the above
  • Ability to set increments of rotation in 10 degrees so I don’t have to walk back and forth 40 feet to the speaker/computer.
  • I would like to avoid using a motor driven belt with two ‘gears’ because the turntable top needs to be flush with the ground plane. That way the speaker is on the same level with the ground and not raised above it (this is important in measurements). I dug a 1.5” pit today so I could sit my current turntable in the ground and make the spinning portion flush.

Can anyone tell me if what I want to do is possible? Will a NEMA 23 motor do the trick (I don’t think so)? Will a NEMA 34 motor do the trick (I think possibly) and if so, will the tic controller work with a NEMA 34 (I only see NEMA 23 as max here)?

Thanks in advance for any help. It is truly appreciated.

  • Erin

To select a motor you must determine the torque required to accomplish the mechanical action. Of course the motor, motor driver and motor power supply must all be chosen to match.

You can make the torque measurement with a simple setup. Start by reading up on force and torque here: https://www.pololu.com/blog/10/force-and-torque

A popular way to drive a turntable is with a rubber wheel mounted on the motor shaft, pressing directly down on the turntable surface at the outer edge. Example; https://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2012/jeb373_jpw97/WEBSITE_HTML_HELIOWATCHER/HelioWatcher.htm

Note: the designations NEMA 23 and 34 tell you the size of the motor mounting faceplate, and nothing about the motor itself. Hundreds of variations are available in most common NEMA sizes.