Hey guys! So I'm trying to do this pretty wide diameter in-runner engine, where the rotor is hollow (essentially trying to make a short tube within a short tube :D). After checking out the details between the different types of electric motors (and realizing that I can barely find any instructions on constructing your own AC motor, unlike the instructions to a BLDC motor) I've decided to settle for a BLDC motor. The set up is as follows - 1.7 meter radius of the stator, probably about 1.65m radius for the rotor. Rotor will be about a 5cm or so thick tube. Thus inner radius of the rotor is about 1.60m, if it's important for you guys. In any case, while I was calculating the needed voltage and amps I'll need for the motor (thus to calculate the needed battery storage and weight) I was following these two articles for the most part: http://www.instructables.com/id/Make-Your-Own-Miniature-Electric-Hub-Motor/ For the basic calcs learningrc.com/motor-kv/ for the Kv, Kt and Ke "ratings" which I would need in order to calculate the needed voltage Following along these articles, this is the progress that I had made and where my issues arose. So, taking the formula that T = 4 * m * N * L * R * i , where the values are respectively Torque, constant for BLDC, m- added teeth per phase, loops of wire per tooth, length of the magnets/motor, radius, amps. I had gotten this 101 Newton Meters (what I calced that I need to get my propeller of 3.5kg up to 3200 RPM) = 4 * 33 teeth per phase * 1 turn (6 AWG wire) * 0.02 meters "length" of magnets * 0.825 meters radius of rotor * 50 amps (borrowing from Tesla, calculated them to be running 50 apms and decided to use it as a good baseline...) At the time I was calculating the needed amps and turns of wire, at the end I settled for 50, as I mentioned above. Here comes where things get poopy. Now that I have my example amps, I need to get the voltage needed in order to start working on my battery set up. Sooo... the formula given in the second article: V = R*I + Kt * w (gamma, as in rads per second, can't write it with this keyboard :D) And the Ke = Kt = T/I0 leads me to the following calculations: Kt = 101/50 = 2.02 ; 3200 RPM (max rpm, for given torque of my prop) = 335.1 rads/s V = 0.05184 ohm (20 meters of 6 Awg *2) * 50 + 2.5*335.1 = 840V .. and that's for only ONE of the two propeller-moving motors! That... seems a bit excessive. Hell, when I was going with lower gauge wire and higher amounts of turns and could get the amps down to 2 it would skyrocket to something about 16KV+ Now, I understand I am moving a wide load, but one would imagine that the amount of teeth, the ginormous radius, small load, etc, would equal to a slightly.... lower sum. Heck, to achieve one hour of flight with this I can't even start to imagine how many what sized batteries I'd need. I have spoken to some friends who have some long-forgotten knowledge in this area and they told me that they think the formula is wrong, so if anyone can correct me on this or could give me some suggestions, I would be EXTREMELY grateful!