Ah, yes. So you have. Thank you.
I wonder why you reported this post... http://forum.arduino.cc/index.php?topic=173138.msg1285902#msg1285902
You posed the question, "Where does this belong?" The forum section is described as, "Controlling big heavy things that move, need high voltages, high current, or both". @costy35 demonstrates how to control the direction and speed of a mixer motor; which is "a thing that moves" and "needs both high voltage and high current". He uses a pair of BT138 triacs to control the motor. I believe the BT138 could be connected directly to an Arduino. (I am certainly no expert in triacs so that should be confirmed before trying it.)
In other words, @costy35 demonstrates how a cheap high-torque variable speed motor could be controlled by an Arduino with a pair of cheap triacs. Seems on-topic to me.