Torque and Rolling Resistance

In summary, the conversation discusses finding the torque required for an electric vehicle to pull a 1000kg trolley on four Nylon Wheels on smooth concrete. The rolling resistance and normal force are calculated for both the trolley and the vehicle, and the total rolling resistance is determined. The equation for torque is then used to find the minimum required torque to get the trolley and vehicle rolling, which is 9.32 N.m. The conversation also discusses finding the torque needed for the system to reach a maximum velocity of 5km/h and includes a calculation for determining when the drive wheels will slip based on the static friction force.
  • #1
tcitizen
4
0
Hello.

I'm trying to find the torque required of an electric vehicle to pull a 1000kg trolley on four Nylon Wheels on smooth concrete. The trolley fully supports its own weight. The vehicle has 2 rubber drive wheels of Radius( r = .125m). Now I'm not sure if am on the right track because i can't find much information on Rolling resistance.

Using Fr = Crr * N to find the rolling resistive force.
Where Fr = Rolling resistance force
Crr = coefficient of rolling resistance
N = Normal force

Rolling resistance of trolley
Assuming Crr = .004
N = 1000kg * 9.81 m/s^2
Ft= (.004*9810) = 39.24

rolling resistance of vehicle
Fv = (45kg * 9.81 m/S^2 * .08)
Fv = 35.316
Ftotal = Fv +Ft
Ftotal = 35.316 + 39.24 = 74.6N

So if I use the equation for toque
T = F * r
T = 74.6 * .125
T = 9.32 N.m

This should give me the minimum required torque to get the trolley and vehicle rolling on a smooth horizontal surface. Yes/No?


Also if my system were to reach maximum velocity of 5km/h (1.389m/s) how do I find the torque needed.


Regards
tcitizen

PS I've tried to include as much information as possible.
 
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  • #2
tcitizen said:
Hello.

I'm trying to find the torque required of an electric vehicle to pull a 1000kg trolley on four Nylon Wheels on smooth concrete. The trolley fully supports its own weight. The vehicle has 2 rubber drive wheels of Radius( r = .125m). Now I'm not sure if am on the right track because i can't find much information on Rolling resistance.

Using Fr = Crr * N to find the rolling resistive force.
Where Fr = Rolling resistance force
Crr = coefficient of rolling resistance
N = Normal force

Rolling resistance of trolley
Assuming Crr = .004
N = 1000kg * 9.81 m/s^2
Ft= (.004*9810) = 39.24

rolling resistance of vehicle
Fv = (45kg * 9.81 m/S^2 * .08)
Fv = 35.316
Ftotal = Fv +Ft
Ftotal = 35.316 + 39.24 = 74.6N

So if I use the equation for toque
T = F * r
T = 74.6 * .125
T = 9.32 N.m

This should give me the minimum required torque to get the trolley and vehicle rolling on a smooth horizontal surface. Yes/No?


Also if my system were to reach maximum velocity of 5km/h (1.389m/s) how do I find the torque needed.


Regards
tcitizen

PS I've tried to include as much information as possible.

Where does this come from: Fv = (45kg * 9.81 m/S^2 * .08)?
What is the 45kg? the .08?
 
  • #3
That is the equation for the rolling resistance of the vehicle.
Fv = Crr * N
Fv = rolling resistance of vehicle
0.08 = coeff of rolling resistance of vehicle
45kg = mass of vehicle
 
  • #4
Looks like what you have is OK, now that you have identified your additional calculations. Why do you doubt it?

If you are going forward at a speed V, then the power required (at steady state) is
P = Ftotal * V = Torque * omega_wheel

Solve this for the torque required after you get the drive wheel speed.
 
  • #5
Given a cart and concrete floor at my disposal, I would load the cart and measure the force required to pull the cart. That's what I did. But depending upon application, I might be more concerned about the force required to overcome surface irregularities from a standing start or low speed.
 
Last edited:
  • #6
tcitizen: Wouldn't you need to also include axle bearing friction as an additional term in your torque equation? The resistance due to axle bearing friction depends on bearing radius and bearing coefficient of friction. Also, to try to model the surface irregularities mentioned by Phrak, you could perhaps estimate the effective incline (slope angle) of the surface asperities, and work your problem on an inclined plane having that upward slope angle.
 
  • #7
And this can go one without end, this inclusion of additional effects. Besides the axle friction torque, we can include the friction in the transmission, the motor friction, etc. But that really goes beyond the original question which was the relation between the rolling resistance (only) and the torque required to overcome rolling resistance. This is a case of "problem creep."
 
  • #8
Yes, there are many many factors to consider, the loading case of 1000kg is the absolute maximum that could be applied in ideal situations, realistically loads of <500kg will be more commonly used.

I've got a query, What, if any, is the difference between friction force and traction force?
Because I would like to determine whether the drive wheels will slip in this situation.

Regards
 
  • #9
I think I just figured it out.

I just use the equation for static friction of the drive wheels and the surface.
Then use the torque equation to determine the maximum torque before slipping.

Fs = us * N

where Fs = static friction force
us = coeff of static friction
N = normal force

Fs = 1 * 45 *9.81
= 441.45

T = Fs * r
where T = torque
r = radius of wheel

T = 441.45 * .125
T= 55.18 n.m
therefore when 55.18 n.m of torque is applied wheels will slip.
 

1. What is torque and how is it related to rolling resistance?

Torque is a measure of the twisting force that causes an object to rotate. In the context of rolling resistance, torque is the force that is applied to the wheels of a vehicle in order to overcome the resistance caused by the contact between the wheels and the surface they are rolling on.

2. How does the weight of a vehicle affect its rolling resistance?

The weight of a vehicle has a direct impact on its rolling resistance. The heavier the vehicle, the more force is required to overcome the resistance of the surface it is rolling on. This is because a heavier vehicle exerts more pressure on the surface, creating a larger contact area and thus increasing the resistance.

3. What factors contribute to rolling resistance?

There are several factors that contribute to rolling resistance, including the type of surface the vehicle is rolling on, the weight and design of the vehicle, the type of tires and their inflation pressure, and the speed at which the vehicle is traveling.

4. How can we reduce rolling resistance in vehicles?

There are several ways to reduce rolling resistance in vehicles. One of the most effective methods is to use tires with low rolling resistance, which are specifically designed to reduce the amount of force needed to overcome resistance. Additionally, reducing the weight of the vehicle, maintaining proper tire inflation, and choosing smooth and flat roads can also help to reduce rolling resistance.

5. What are the practical applications of understanding torque and rolling resistance?

Understanding torque and rolling resistance is essential in the design and operation of vehicles, especially for fuel efficiency. By minimizing rolling resistance, we can reduce the amount of energy needed to move a vehicle, resulting in less fuel consumption and lower emissions. This knowledge is also important in industries such as transportation and logistics, where efficiency and cost savings are critical factors.

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