Hello, I am posting about the SMA actuator robotic arm (seen here)
that I have received so much help with. I am having some final problems figuring out torque and power consumption, and any help is appreciated.
I am using 0.006" diameter nitinol wires and about 24 inches in length, and here are their specs:
Ohms/inch = 1.4
Pull force = 0.71 pounds
Approx. current for 1 second contraction = 410 mA
When the wires contract, they pull the lower arm up from a point approx. 1 inch out from the elbow (which is my axis of rotation). The forearm is nearly straight compared to the upper arm, and the wires are inside the upper arm and pulling the forearm at about a 20 degree angle.Here is my question: how do I calculate the amount of torque one wire can produce from pulling at this point on my arm?
I was hoping to use the moment arm tutorial
, but I can't figure out how to apply it to find out the torque each of my wires can produce and with that the load they can lift when pulling that close to the rotational axis.
My arm will weigh about 3 lbs total, with 1.5 lbs each for the upper and lower arm halves. The hand weight is part of the lower arm (forearm) weight (its only about 0.05 lbs), and I was hoping to lift about 5 lbs with it.
I know this seems like a problem I should solve on my own, but I always get these calculations wrong. Any help is greatly appreciated. Thank you!