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Small electric vehicle project help

  1. Mar 10, 2007 #1
    I hope someone could verify/help/alter/add on my design calculation of an electric vehicle (in my case is a powered wheel barrow,3wheel, 2front wheel,1 back wheel castor, dc electric motor powered 2 front wheel).

    The specifications are:

    Speed : 2m/s maximum
    Weight : 150 max kg
    Gearbox :step down gearbox (this is compulsory, so I don’t have a choice using a speed controller)

    I started off by calculating the torque requirements for this vehicle :

    The forces are rolling resistance, acceleration and slope requirement.

    Mass Force exerted on the wheels = 1500N

    I assume the coefficient of rolling friction to be 0.1
    Rolling resistance,Fr = Cr*N
    = 0.1*1500
    = 150N

    Slope requirement,Fs = 1 on 5
    = 1500*0.2
    = 300N

    Acceleration, 0 to 2 m/s in 2 seconds
    F = m*a
    =150* (2-0)/2

    Total force required (worst possible case) =150+150+300

    Total torque require at wheel end = 600*(wheel diameter,D)
    = 600*150mm

    Before I start the motor selection, I am using a Step Down gearbox with a maximum rpm input from the motor of 2000rpm(assuming 100% transmission efficiency). The gear ratio varies from 17:1 to 68:1. I find the wheel diameter which I have use for calculating torque by using the relationship :

    Rpm = speed/phi*D

    I know the output rpm and by selecting different diameter of wheel the range of speed would vary accordingly. I have found out that a 150mm diameter wheel would give out a maximum speed of about 2m/s which is the max specification speed.

    I choose a bosch 24V 750Watt


    Nominal voltage UN 24 V

    Nominal power PN 750 W

    Nominal current IN 40 A

    Nominal speed nN 3300 min–1

    Continuous torque MN 2,2 Nm

    Breakaway torque MA 11 Nm

    Direction of rotation L

    Type of duty S 1

    Degree of protection IP 10

    Weight approx. 3,8 kg

    Part number 0 130 302 001

    The motor will be gear down about half so that it can be use for the Step Down gearbox which have a maximum input rpm requirement of 2000rpm(I realize that this will make the max speed lower than 2m/s but it will almost double the torque).

    The total torque require to overcome is 90Nm.sice the breakaway/stall torque is 11Nm, the output torque is :

    Motor torque =11*(gear ratio to Step Down gearbox)*(lowest gear
    ratio of gearbox)

    So I conclude that the motor is sufficient enough to perform the task.

    questions that i am trying to find out :
    a)Is the calculation for the total torque requirement ok? Do I need to include anything else(such as static friction, inertial body force)?
    b)Is my torque output calculation valid?
  2. jcsd
  3. Mar 11, 2007 #2
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