# How to calculate if a motor is strong enough

I am building a machine for a project that should slowly tip a screen forward about 95 degrees, hold for a couple of seconds, and then slowly return to vertical. The design I am working on uses two stepper motors connected to the screen with a belt drive. I can change the gear ratio of this drive to anything up to 2.8.

I need to select the smallest motor that will provide enough power for this application. I have the torque - speed charts for the motors, as well as the weight and moment of inertia of the screen. Is there a formula that I can use to calculate if the motor will be strong enough?

The screen will begin vertical, rotate forward about 95 degrees, and then return to vertical. The weight of the screen assembly is ~5.7 lbs. It will rotate about an axis ~2.75 inches below the center of mass. The screen assembly consists of a display surrounded on all sides by 1" t-slotted aluminum. The axis of rotation runs through the center of the bottom aluminum rail. There are two small stepper motors mounted just below this rail as well.The aluminum frame is 11.75" wide by 10.0625" tall. The motors and mounting plates extend an additional 1.66" down. Specs for the family of motors I plan to use can be found at automationdirect.com.

• What is a "screen" in this context? Are you talking about a display screen, such as an LCD monitor, or a metal mesh that's being use to separate items by size, or something else? Are there any forces acting on this screen other than gravity? Jul 1, 2015 at 17:05
• The third paragraph has been updated to include details about the screen assembly. Jul 1, 2015 at 17:26
• a picture could clarify things even further. Do you know the reduced innertia of your belt drive? Also do you know the speed at which this tipping is to happen. Jul 2, 2015 at 7:37