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- Selection of a torsion spring to open a hinged lid

Hi,

I'm designing a small container with a spring loaded hollow rectangular lid. I want the lid to open when a button is pressed, so I have a torsion spring at the hinge. I want to know if the spring I selected is able to open the lid and also how long it would take to open 90°.

Below is a diagram of the hinge, spring and the center of gravity (COG) of the lid. The mass of the lid is 0.005 kg.

Torque needed to open lid:

Torque = weight * distance to COG * Cos(33)

= 0.005 kg * 9.8 m/s^2 * 0.0226 m * 0.8386

= 0.0009 Nm

I'm going to design a custom spring, but for the sake of this question let's assume this torsion spring from McMaster which has a max torque of 0.117 in-lbs (0.0132 Nm).

I also want to know how fast the lid will open in seconds given this spring.

I'm getting the center of gravity MoI from CAD, which I think I need:

I know that: Torque = Moment of inertia * angular acceleration

So: Angular acceleration = Torque/MoI

Using the spring torque and the Z MoI:

Angular acceleration = 0.0132 Nm/9.371e-007kg*m2

= 14087 rad/s^2

Thank you for your time!

I'm designing a small container with a spring loaded hollow rectangular lid. I want the lid to open when a button is pressed, so I have a torsion spring at the hinge. I want to know if the spring I selected is able to open the lid and also how long it would take to open 90°.

Below is a diagram of the hinge, spring and the center of gravity (COG) of the lid. The mass of the lid is 0.005 kg.

**This is what I have so far:**Torque needed to open lid:

Torque = weight * distance to COG * Cos(33)

= 0.005 kg * 9.8 m/s^2 * 0.0226 m * 0.8386

= 0.0009 Nm

I'm going to design a custom spring, but for the sake of this question let's assume this torsion spring from McMaster which has a max torque of 0.117 in-lbs (0.0132 Nm).

**Question #1:**Since this spring is able to provide 0.0132 Nm and I only need 0.0009 Nm, the spring should work. Is this correct?I also want to know how fast the lid will open in seconds given this spring.

I'm getting the center of gravity MoI from CAD, which I think I need:

I know that: Torque = Moment of inertia * angular acceleration

So: Angular acceleration = Torque/MoI

Using the spring torque and the Z MoI:

Angular acceleration = 0.0132 Nm/9.371e-007kg*m2

= 14087 rad/s^2

**Question #2:**Is this correct? This 14087 rad/s^2 answer seems way too fast to me.**Question #3:**How do I convert this angular acceleration to the number of seconds it will take the lid to open 90°? I would like it to open in less than 1 second.Thank you for your time!

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