# Motor Sizing for Wheel Endurance Testing

• SR71
In summary: If so, the motor would only need to generate enough torque to overcome the resistance of the belt or VFD at the angular velocity(s) of interest. In summary, the engineer would need to size the motor to have enough torque to overcome the wheel friction at the desired angular velocity.
SR71
TL;DR Summary
Motor sizing for wheel endurance testing
I am working with a wheel endurance testing application. I am trying to size a motor for the system. Basically, I have a drum which has to be rotated by the motor. I have different size wheels that I have to test. The motor is supposed to rotate the drum and then the wheel is pushed onto the drum with a force.

My question is when I want to find the torque (Fx perpendicular distance) do I use the radius of the drum or the radius of the wheel being tested? Currently, I am using the radius of the drum as the wheel is being pushed onto the drum but this gives me huge numbers as the wheel is pushing with 1000-2500 lbs of force.

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If the motor is on the drum then use the drum radius. If it is on the wheel then use the wheel radius.

Torque will be different in both cases but so will be the angular velocity. In both cases, the power will always be the same.

SR71
SR71 said:
My question is when I want to find the torque (Fx perpendicular distance) do I use the radius of the drum or the radius of the wheel being tested? Currently, I am using the radius of the drum as the wheel is being pushed onto the drum but this gives me huge numbers as the wheel is pushing with 1000-2500 lbs of force.
How is the radius of the drum or wheel relevant for this? The force is aligned with the axles so it's got no leverage. Am I misunderstanding the drawing? Or are you obtaining the tangential component due to the friction?

Since the angular velocity is constant during the test (or so I think from the video), I would say to size the motor you just need it to have enough torque to overcome the friction from the bearings and the friction due to the deformed wheel rolling.
I guess the second one should be the greatest one but I don't know how to derive it yet.

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Juanda and Lnewqban
Welcome, @SR71 !

Due to the different diameters of wheels to be tested, I recommend to engineer a variable velocity connection between motor and drum.
It could be a variable pulley-belt system, or a VFD (variable frequency drive), for example.
I assume each test has one or several specified angular velocities for the wheel.

Juanda and Tom.G

## 1. What factors should be considered when sizing a motor for wheel endurance testing?

When sizing a motor for wheel endurance testing, consider the following factors: the required torque and speed, the load characteristics, the duty cycle, the thermal capacity of the motor, and the environmental conditions. Additionally, ensure that the motor can handle the peak loads and has a suitable safety margin for long-term reliability.

## 2. How do I calculate the required torque for wheel endurance testing?

The required torque can be calculated by considering the wheel's rolling resistance, the friction in the test setup, and any additional forces such as aerodynamic drag or incline resistance. Use the equation T = F * r, where T is the torque, F is the force, and r is the radius of the wheel. Summing all contributing forces will give you the total required torque.

## 3. What is the importance of the duty cycle in motor selection for endurance testing?

The duty cycle is crucial because it defines the proportion of time the motor will be active versus inactive. For endurance testing, the motor often runs continuously or for extended periods, so selecting a motor rated for continuous duty (S1) is essential. This ensures the motor can handle the thermal load and operate efficiently over long durations without overheating.

## 4. How do I ensure the motor can handle peak loads during wheel endurance testing?

To ensure the motor can handle peak loads, you should look at the motor's peak torque rating and compare it with the peak loads expected during testing. It's advisable to select a motor with a peak torque rating at least 20-30% higher than the maximum expected load to provide a safety margin and account for any unforeseen stresses.

## 5. What role does the environment play in motor selection for wheel endurance testing?

The environment can significantly impact motor performance and longevity. Factors such as ambient temperature, humidity, dust, and exposure to corrosive substances must be considered. Choose a motor with appropriate IP (Ingress Protection) ratings and thermal management features to ensure it can withstand the environmental conditions of the testing setup.

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