Well done on a simple and effective dyno! I might well make something similar myself to compare some of my motors Observing the question about tacho calibration, this is simple as an ordinary fluorescent strip lamp actually is flashing with each peak in the cycle of the mains. Therefore the lamp will flash 6000 times per minute. With the tacho pointed at the lamp and set for 2 bladed props will therefore read 3000 rpm. As for the absolute accuracy of the mains 50 cycles/sec, well, that's another question Btw, in my experience clamp type ammeters are not always that accurate, particularly for dc. Measuring high currents accurately for the DIYer without introducing what could be a significant voltage drop isn't easy so I don't have a better suggestion All in all another well done from me!