constant torque springs 1

[jonboy999]

hi,
i am currently working on a project involving constant torque springs. i have been looking for formula or methods of calculating the release speed of this type of spring. i need to calculate a value for number of turns per second. calculating output torque etc has not been a problem, but i cannot find any information on calculating release rate.

any information would be appreciated!

thanks

jon

 

[israelkk]

I assume the spring is connected to something that has a weight, mass and inertia. The spring probably is not alone by itself. Therefore, when you talk about the release time you actually mean to calculate the time to unwind the spring and accelerate the inertia both together.

 

[jonboy999]

ok, but before i start adding resistance to the un-winding i would like to calculate the time to un-wind the spring on its own. the feasibility of using a constant torque spring depends upon this un-winding rate. i assume it would be best calculate the rate in free form then add the resistance to the calculation?

 

[israelkk]

Usually the added inertia is much larger than the spring's own inertia. Therefore, you can neglect the spring and just calculate the acceleration as of the torque that the spring creates (take the springs as a massless motor). Otherwise you will need to create/write the differential equation of the spring spiral and numerically integrate infinitisimal parts of the spring strip combined with the accelerated inertia. You can not separate the spring from the added inertia if you want quite an exact solution.

 

[jonboy999]

ok thanks, so ignore the interia of the spring and use the interia of the mass im turning with the kinetic energy to work out the angular velocity. thanks for the help! i only need a rough estimate so this method should be good! cheers!