Small electric vehicle project help

[akueddy]

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
=150N


Total force required (worst possible case) =150+150+300
=600N





Total torque require at wheel end = 600*(wheel diameter,D)
= 600*150mm
=90Nm

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

http://www.boschmotorsandcontrols.co.uk/elektromotoren/produkt/0130302001/index.htm


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)
=11*2*17
=374Nm>90Nm

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?

 

[P.Ramesh]

A fantastic formula for motor torque, speed and power calculation. It is for hydraulic motor-- but u can use it for electric if you want.

page 21st of the link http://hydraulics.eaton.com/products/pdfs/E-MOLO-MC001-E3.pdf

dont miss it. download it now.

 

[ravenprp]

Hello,

Thank you for sharing your design calculations for your small electric vehicle project. It seems like you have put a lot of thought and effort into your design, and I appreciate your attention to detail.

To answer your questions, I would say that your calculation for the total torque requirement is generally correct. However, there are a few things I would suggest considering:

1. In addition to rolling resistance, acceleration, and slope requirement, you may also want to consider other factors that could affect the torque requirements, such as air resistance and inclines or declines in the terrain.

2. Depending on the type of terrain your electric vehicle will be used on, you may also want to consider the static friction of the wheels. This could affect the torque requirements and should be taken into account in your calculations.

3. In terms of your torque output calculation, I would suggest double-checking your gear ratio calculations. It seems like you may have used a gear ratio of 2 in your calculation, but the gear ratio for your motor is actually 17:1. This may affect your final torque output and should be adjusted accordingly.

Overall, I think your design is well thought out and your calculations are on the right track. I would suggest double-checking your gear ratio calculation and considering any additional factors that may affect the torque requirements. Best of luck with your project!