The door is made out of 1/2" plywood and its dimensions are about 9cm W x 38cm H. The force is applied to a point on the door that is about 11cm down from the hinge point. I dont really know how to calculate torque. Do I need a large servo? The next size up is 35kg/cm. Or should I tree to connect it to 6.8V? OR does it seem fine to you guys?
Scratch that, I can't find a 7V power supply, so I will get a 12V power supply for the Arduino and use a buck converter to step it down to 6.8V for the motor. If there is a better way to do that please let me know.ThanksIan
That wasn't so difficult, was it? BUT.... did you use the scale to measure the "weight" when you first began to raise the door?Paul
Thanks everyone for all the input. I finally bought a scale and measured the weight of the door as Paul suggested. It is about 2.2lbs, plus I will be adding about 0.3lbs of insulation so, to round up, I will assume 3lbs. The radius from lift point to the motor output shaft is about 6inches, so it will require about 18in-lbs of torque which is 20.7kg/cm
No, torque is still not a ratio, its a product of force and radius.If your door is 9cm x 38cm, then the mass of about 1.3kg acts 38/2 = 19cm from the hinge, so the torqueis 1.3 x 9.8 x 0.19 = 2.4NmAt 15cm from the hinge the force needed is thus 2.4 x 0.15 = 0.36N. Again without details of the linkagegeometry between door and servo there's nothing more to say. The linkage turns the servo's torque to a force, and is essential to any calculation relating the servo's requirements.BTW your 9cm x 38cm x 1/2" 'plywood' has a calculated density about 2.3g/cm^3, so its definitely not plywoodif your dimensions and mass are correct.Can you provide a good diagram and check all the numbers?
Hi Mark, thanks for the response.I am not really sure what you mean when you say torque is not a ratio, did I imply it was? I multiplied the weight in pounds to the radius in inches to get 18inch-pounds of torque. Is that incorrect? I understand the linkage might make things more complicated but I am trying to get a ballpark.
The plywood door is definitely plywood… see pictures if you don't believe me. Also see attached photo with the scale where I measured about 2.2lbs. The door itself doesn't weight 2.2lbs, just at the point where I'm lifting from which is in-between the hinges and centre of gravity.
I rounded 2.2lbs to 3lbs, and I measured 6 inches away from the motor centre of rotation, so I multiplied to get 18 inch-pounds of force.
I didn't draw up a diagram but annotated the images with dimensions. Also, apologies I said the door was 9cm wide originally, i meant 19cm. Let me know know if there is any info still missing.