# Motor selection for a small city runner



## TheKid (Mar 10, 2017)

Greetings everyone, 

I am trying to understand motor selection (AC in particular) for my mini project. They vehicle I have in mind will be small in size similar to the smart car or the g-wiz, it's purpose being to get you around town/city which is why I was leaning towards AC motors to make use of the regenerative braking. I created an excel spreadsheet based on my estimated final vehicle weight (including two passengers and an extra load of 110lbs) and came to a value of 1480lbs. The spreadsheet is similar to the one found in Seth Leitmans "Build Your Own Vehicle". 

Basically, based on the vehicle weight and all that other good stuff (rolling resistance, aerodynamic drag forces etc) I have reached a value of 50.2lbs for my 'total drag force' (level surface). Multiplying this by the torque multiplier (based on the wheels I chose) I get a value for the 'total drag torque': 47.68 ft-lbs. I should say that my design centre speed is 30 mph and the values I have mentioned are for 30 mph vehicle speed.

From here I calculated the required hp of a motor:
hp(motor) = (torque(wheel) x mph x revs/mile) / (315120 x n) and reached a value of 4.47. 

I am getting to my question I promise. Now my job is to find a motor rated at 5hp, and find the RPM at which the motor delivers this hp from the torque-speed curves. This is where I get completely confused and any help in deciphering the curves will be so helpful to me. I have looked at the HPEV AC-23 motor, and the corresponding curves. However there are two different type of curves to look at: peak and continuous. I have looked at the continuous curve for the AC-23 motor at 72 Volts, from my understanding 5 hp is produced at 2700 RPM at 98 ft-lbs of torque at 60 amps. Can anyone hint at whether or not I am reading the graph correctly? And what is the difference in the peak and continuous curves from a designer perspective? The DC curves seem much more intuitive to me. The AC ones are throwing me off, and as a result I have spend over 3 days staring at different curves trying to reach a eureka moment where it suddenly clicks, to no avail. I thought this would be a good place to get some information for my specific case. Any help is really appreciated!

link to the AC-23 curve:
http://www.hpevs.com/Site/power_gra...3-72-volt- 650 amp imperial continuous FC.pdf


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