Torque calculation for Louvre blind tilt motor (re-post) 2

[logikman]

Reposted to show correct image file address.

I am trying to find out how to calulate the torque of minature stepper motor to operate louvered blinds (venetian blinds). The attached GIF shows the principle. Basically a rod has 3 control threads attached by winding the threads about 3 truns around the spindle. The ends of the threads are sequentially attached to the vertical louvers of the blind at the front and rear of the blades. As the rod rotates anticlockwise the thread at the rear allows the back edges of the attached blades to fall downward (under their own weight) The thread at the front winds upward and pulls the louvre blades with it to tilt the blades. The thread and the turns are set to allow about 90° of rotation allowing the blind to closed or open. We want to achieve this using a small electric motor but to get a sample we need to calculate the torque required. How do we go about determining this ??

 

[tinfoil]

Have you considered getting empirical measurements by actually measuring a real blind?

 

[sreid]

Most of the torque required will be be in the rod bearings. Automation Direct

http://web2.automationdirect.com/adc/Shopping/Catalog/Stepper_Systems

is selling stepper systems at excellent prices.

 

[UKpete]

If you mean how do you measure it, well you can rigidly attach a beam across the spindle at right angles to it and so that the centre of the beam is on the spindle (to cancel out gravitational effect on the beam). Then with a spring balance on the end of the beam (at the right hand end if it were shown on your diagram) lift the beam so that it just starts to rotate the spindle.

Torque = d x g x w (Nm)
where
d = distance from point of connection of spring balance to the spindle (in metres)
g = accel. due to gravity (9.81m/s²)
w = weight recorded on spring balance (in kg)

 

[logikman]

Many thanks to
Tinfoil - for the idea
UKPete - for how to do it
SRIED - for the usefull link.

Logikman