Torque estimate ?

Hi,

I know this isn't a mechanical eng. forum, but I wanted to ask because many of you surely have a lot experience in using servos/motors in your projects.

I have a solar panel screwed onto a shaft which connects directly to a servo motor shaft. How much should the torque rating of the servo be to be able to rotate it ? I mean an estimate of the minimum torque required. The panel weighs 0.8kg plus a few grams for the solar panel holder (made of perspex). No gears are used.

I would need the servo shaft to rotate a total of about 135 degrees, rotating a few degrees every hour for eight hours (It will operate like a stepper, stepping during each hour). The speed of rotation is not important, as long as it rotates. The panel's length is 32cm and height is 18 cm. It is a solar tracker.

There will also be another servo to rotate the round base.

A rough diagram is attached below.

Thanks.

There are two equations that you will find useful

1. T = I * alpha

This is the rotational equivalent of Newton's second law ( F = ma ). In this case T is torque, I is the moment of inertia, and alpha is the angular acceleration in radians per second squared.

2. T = Kt * i

This relation says that a motor will produce an amount of torque equal to some constant Kt which is a property of the motor times the current going through the windings.

It should be reasonably easy to find the formula for the moment of inertia of a disc,

https://en.wikipedia.org/wiki/List_of_moments_of_inertia

which will of course be an approximation of your system. Looks like Iz = (mr²)/2 After that you need to find the Kt for your motor and then you can pick a current that will give you an alpha that you require to move the platform.

Papabravo said:

There are two equations that you will find useful

1. T = I * alpha

This is the rotational equivalent of Newton's second law ( F = ma ). In this case T is torque, I is the moment of inertia, and alpha is the angular acceleration in radians per second squared.

2. T = Kt * i

This relation says that a motor will produce an amount of torque equal to some constant Kt which is a property of the motor times the current going through the windings.

It should be reasonably easy to find the formula for the moment of inertia of a disc,

https://en.wikipedia.org/wiki/List_of_moments_of_inertia

which will of course be an approximation of your system. Looks like Iz = (mr²)/2 After that you need to find the Kt for your motor and then you can pick a current that will give you an alpha that you require to move the platform.

Click to expand...

You forgot to mention the influence of wind!