Here are the details: Weight (skateboard + rider) = 75kgs
Required cruising speed = 25kmph
Required range = 15km
Here are my calculations:
To keep a comfy window, assume speed is 30kmph, and since wheel circumference is 23cm, RPM = 2174.
Here is the motor I plan to use: Turnigy Aerodrive SK3 - 4250-350kv Brushless Outrunner Motor (https://hobbyking.com/en_us/turnigy-aerodrive-sk3-4250-350kv-brushless-outrunner-motor.html)
Thus at 2174rpm, the voltage required to run the motor is 6.2V.
Question 1: Does this mean I cannot go above say 11.1V of LiPo voltage?
Power = (Voltage)x(Current)
Thus this means that at the motor rating of 1000W and our voltage of 6.2V, the current draw will be 161.2A, which is insanely high!
Question 2: What is going wrong in the above calculation?
At the cruising speed of 30kmph, and the corresponding current draw of 161A, the travel time required (to finish travelling 20km) would be 2/3 hours, and therefore the required battery would have to be 108mAh.
Thus, according to my calculations, I will need a 180A ESC and a 2S 110mAh LiPo.
I think I have made a mistake in the fact that I am using a belt drive drivetrain with a 1:3 reduction and I have not accounted for this. Is this the case?
Question 3: Why is the system mass not coming into the picture??
Question 4: How would you design the power system for this project?
It is not necessary to answer all questions, any help will be much appreciated.