Help design torque, power needed

In summary: The average torque is not necessary to calculate the rate of acceleration. However, you can find the average torque by taking the average torque throughout the rpm range.
  • #1
tebrown3
5
0
I am designing a transmission for my class but i have a couple of concepts i kinda confused, i have a 550lbs load, and i want to move 35mph=15.64m/s at a constant speed, assuming the drag coefficient to be Cd=.55 and the coefficient of rolling resistance to be Crr=.3 (tires on sand), i found out the two frictional forces going against a rigid body(my off road car) which are the sum of the Rolling resistance force and the force of aerodynamic drag which turned our to be F=815.21 N, i want to like to learn how to find the torque necessary to move it and the power required, do we keep power constant?, and does the power depend on torque or vice versa? Thanks in advance
here are the eqn used

http://upload.wikimedia.org/math/2/8/5/28560fb9ccae7b5f811de11f965d5478.pnghttp://upload.wikimedia.org/math/9/a/b/9ab71e6e4f97b6a9d63cfa5aded81f1a.png
 
Last edited:
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  • #2
Note that:

Work = Force X Distance

Power = Work / Time = Force X Distance / Time

Velocity = Distance / Time

Thus,

Power = Force X Velocity

You can compute your power from the 815 N force you figured and your 35 mph velocity.

Then the power and torque are related as:

Power = Torque X Angular velocity

And you can find the angular velocity from linear velocity and gear ratios.
 
  • #3
thank you that cleared up alot, but how do you calculate the power and torque needed when the car is at rest to 35 mph?
 
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  • #4
Compute Power = Force X Velocity from your numbers above.

Then look at your engine rpm at 35 mph. Use the transmission gear ratio to find the transmission rpm. Using this power and rpm, figure the transmission torque.
 
  • #5
edgepflow said:
Compute Power = Force X Velocity from your numbers above.

Then look at your engine rpm at 35 mph. Use the transmission gear ratio to find the transmission rpm. Using this power and rpm, figure the transmission torque.

To calculate the rate of acceleration don't we need to know the average torque? That is from rest (to get the load moving) through the engines rpm range to 35 mph. Which would be calculated as a function F(x) torque (or maybe F(x) power)?

Willy
 
  • #6
To calculate the rate of acceleration don't we need to know the average torque? That is from rest (to get the load moving) through the engines rpm range to 35 mph. Which would be calculated as a function F(x) torque (or maybe F(x) power)?

Willy
 

1. What is torque and why is it important in design?

Torque is the measure of a force that can cause an object to rotate around an axis. In design, torque is important because it helps determine the amount of power needed to rotate or move a certain object. It also affects the strength and stability of a design.

2. How do you calculate the torque needed for a design?

The formula for calculating torque is torque = force x distance. First, determine the force needed to move or rotate the object. Then, measure the distance from the force to the axis of rotation. Multiply these two values together to calculate the torque needed for the design.

3. What factors influence the power needed for a design?

The power needed for a design is influenced by several factors, including the amount of torque required, the speed at which the object needs to move, and the efficiency of the design. Other factors such as the weight and friction of the object can also impact the power needed.

4. How can I ensure that my design has enough power?

To ensure that your design has enough power, it is important to carefully consider all the factors that influence power, such as torque, speed, and efficiency. Additionally, conducting thorough testing and analysis can help determine the power needed for a design and make any necessary adjustments.

5. What are some common mistakes to avoid when designing for torque and power?

Some common mistakes to avoid when designing for torque and power include underestimating the amount of torque needed, neglecting to consider the speed of the design, and not accounting for potential inefficiencies. It is also important to consider safety measures and potential risks when designing for torque and power.

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