When constructing a vehicle, knowledge of physics is needed to determine what is needed to cause the vehicle to move. One such piece of this puzzle is the calculation of torque, which is the force needed to rotate an object on an axis. In the case of vehicles, torque is required to push the wheels forward or backward, causing movement. When determining torque, the builder must take into account not only the mass of the vehicle, but also the desired speed and acceleration.
Determine the acceleration needed on the vehicle and convert this number to feet per second. For example, if the required acceleration is 15 miles per hour in 10 seconds you would convert as follows:
15 mph multiplied by 5280 feet per mile is 79200 feet per hour. Take this number and divide it by the 3600, the number of seconds in an hour. The result is 22 feet per second. Now, this number is divided by the time it takes to accelerate, in this case 15 seconds. The final answer is 1.47 feet per second squared.
Weigh the vehicle to determine mass in pounds. Remember, one ton equals 2000 pounds. Divide the weight by 32 to account for friction.
Multiply the result from above and the acceleration together to determine the force. For example, if the vehicle weighed 200 pounds, then 200 divided by 32 equals 6.25. The result multiplied by 1.47 would yield 9.1875lbs/second squared. This is the force of the vehicle.
Measure the wheel radius in inches. The radius is calculated by measuring the distance from the center of the wheel to an end point on the edge. For the purpose of this guide, we'll set the radius at 7 inches.
Multiply the force and radius together. The result is the torque required for your vehicle. Using the data above, 9.1875 multiplied by 7 results in the required torque being 64.3125 pounds per inch.
