Turntable VII: Motorized!

The stack is in place and wired up.

Initially I had some issues loading the code into the Arduino, and finally worked it out with my brother-in-law’s guidance. I’d been loading it correctly, but a command was missing that caused the motor to remain unresponsive. Once that was sussed out the turntable started working without much of a problem, at least while it was powered via USB.

An issue arose when I powered the Arduino with 12V DC. When the motor was running on that voltage, it got sizzling hot and moved erratically when activated. However, when I switched back to the USB cable (which is regulated at 5V) it worked perfectly fine.

We are working on that, and then we will be keying in a slower speed. Ideally the deck will rotate at 1 rpm, but it is currently closer to 4-5 rpms. Overall, though, I am very excited and relieved that it is able to run!

Here’s a video of the turntable in action. You can see both the 180-degree rotation as well as the 0.9-degree nudge (just in case the deck goes out of alignment).

Edit: I think I’ve pinpointed the issue with the DC supply. While the motor indicates that it is a 12V motor, to be safe we should have calculated Ohms Law, which tells us that a  source should never exceed I=V/R (or “Current” equals “Voltage” divided by “Resistance”).  Any more than that and the motor will draw too much when idle (it draws the most voltage while holding). My brother-in-law and I both assumed that the motor shield would regulate the voltage.

For my motor (as per the specs listed on the packaging):

V=0.5A
R=17 ohms
I=0.5×17
I=8.5 volts

Thus, according to Ohm’s Law we don’t want the voltage to exceed 8.5 volts. I guess that is what the motor specs mean:

“Each phase draws 500 mA at 8.5 V, allowing for a holding torque of 7Ncm (10oz.in) … Rated Current/phase: 0.5A … Phase Resistance: 17 ohms.”

To be honest, that’s mostly Greek to me, but the numbers align with my math.

I’m not too concerned with torque (because there isn’t much weight or resistance on the turntable) so 5 volts should be plenty. The motor has been working just fine on the 5V USB, but I would prefer a straight DC supply because I may decide to add a USB extension between the USB port and the fascia.

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