How to calculate inertia from deceleration time

[tryskriel]

I have a dynamometer to determine HP and Tq of cars and I am trying to setup my software and i need the inertia of my rollers to determine Tq but i have a big flywheel that will turn 1,580 revolution per each roller revolution so its very difficult to determine inertia by calculating the mass of the rollers + mass of the flywheel + gearing multiplier etc...

Someone told me that i should be able to determine inertia by turning my roller to 2000rpm and calculate the time it decelerate from 1500rpm - 500rpm

Do anybody can give me this formula or the right way to determine inertia by doing that

Thanks
Fred

 

[anathema]

Hello Fred,

Thank you for reaching out to the scientific community for assistance with your dynamometer setup. The person who suggested using the deceleration method to determine inertia is correct. This method is known as the coast-down test and is commonly used in the automotive industry to determine vehicle inertia.

To calculate the inertia of your rollers and flywheel, you will need to measure the time it takes for the rollers to decelerate from 1500rpm to 500rpm. This time, along with the known speed difference and the torque applied to the rollers, can be used to calculate the inertia using the following formula:

Inertia = (Torque x Time x Speed Difference) / (9.55 x 1000)

Where:
- Torque is in Nm
- Time is in seconds
- Speed difference is in rpm
- 9.55 is a conversion factor to convert the units to kgm² (kilogram-meter squared)

It is important to note that this formula assumes that the torque applied to the rollers is constant during the coast-down test. It is also recommended to repeat the test multiple times and take an average to ensure accuracy.

I hope this helps you in determining the inertia of your rollers and flywheel. Good luck with your dynamometer setup!

 

[ogb p]

Hello Fred, calculating inertia from deceleration time can be done using the basic formula for inertia, which is I = M * R^2, where I is the moment of inertia, M is the mass, and R is the radius. In this case, the mass would include the mass of the rollers, flywheel, and any other components involved in the system. However, since you have a large flywheel that complicates the calculation, there is another method that can be used to determine inertia from deceleration time.

To do this, you will need to measure the deceleration time of your rollers from a known speed, such as 2000rpm, to a lower speed, such as 500rpm. This can be done using a stopwatch or a data acquisition system. Once you have this time, you can use the formula I = T^2 * F / 4π^2, where I is the moment of inertia, T is the deceleration time, and F is the force applied to the system. The force in this case would be the force required to slow down the rollers from 2000rpm to 500rpm.

It is important to note that this method assumes that the force required to decelerate the rollers is constant throughout the entire deceleration time. If this is not the case, then the calculation may not be accurate. It is also recommended to repeat the measurement multiple times and take an average to improve the accuracy of your calculation.

I hope this helps. Best of luck with your software setup and calculations.