I was helping my son with his kitchen renovation. We were working with a cement type backer board which incredibly dense (and heavy).
I had taken along my Makita cordless and figured we'd work together drilling down the flooring.
My son's latest purchase was this Dewalt 895 driver. In typical fatherly fashion I was ready to tease him about such an expensive purchase since I knew he already owned a cordless drill. My opinion changed abruptly when I actually used this powerhouse.
My poor Makita just couldn't hack driving screws through cement board. I ended up putting it back into its case. Considering each 3 foot by 5 foot board requires enough screws to be spaced 8 inches apart, it kept going and going. I finally asked when the battery was going to run flat (as they say in England).
I was intrigued by the fact that this uses a brushless motor. I couldn't fathom how you can get a direct current motor to work without brushes. I guess I haven't been paying attention to technology advances in the last few decades.
I grew up in an era where the kitchen mixer, electric drills and blenders would send out a stream of sparks as the brushes would rub against the commutator, reversing the current flow, reversing the magnetic field of the armature and creating the torque of the device. These appliances and tools used series motors which have their greatest torque when stalled. Just the thing when you are trying to mix up some thick cookie dough or drill through a brick. The brushes eventually wear out and I've actually changed a few in my time.
The brushless direct current motors are actually being powered by alternating current produces by electronic circuitry, since all electric motors require a switching of the magnetic field.
I found a flash animation that demonstrates this.
The subfloor is down, it is not going anywhere since it is set in cement and screwed in place. My knees ache even with the knee pads and we still have the tiling to do. I wish there was a tool to make that easier.