For the next iteration, I again used a treadmill, but took it completely apart. The motor is attached to an end board - using 1.5" pvc wrapped in a rubber cover (to grip and drive the tank), along with two free rollers to tumble two tanks at the same time. From the treadmill, I used the motor, AC cord, as well as the power converter and speed controller. Below is the progression of the build
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The tank tumbler stored on the wall:
A tank all cleaned and painted to be a Nitrox tank:
And Tonto who likes his box: