Arm length vs. torque nessisary

Lynxmotion Robot Arms
1

I have a competition coming up and was looking to build a custom robot arm similar to the AL5D. I need to be able to reach ~70 cm (around 27 inches) and lift up to 7oz. at that distance. i was wondering if the higher torque standard servo motors like the “HSR-5980SG (417 oz. in.) Digital Standard Servo” would have enough “umph” to get this done, or if not, what i could use to accomplish this. i was considering using 2 of the aluminium tubes to extend the AL5D design. will the combined weight of the arm and the 7oz. object require lots of “counterweight-ing”? i am allowed to have a fixed base so tipping over shouldn’t be an issue. I do not need super high accuracy with the heavy weights (i need to be able to drop them in a container with a ~4in x 4in square opening) but i do need relitivly high accuracy with light objects (for example putting a nail in a 1.5in circle). would this be possible with such an arm or am i expecting too much? im not terribly familiar with the physical limitations of this kind of project, sorry :blush:

thanks and sorry if im a total newb!
Ellingwood

2

The servo you’ve chosen should be fine for the job. The torque required for lifting 7 oz at 27 inches is 727=189 ozin.

3

Ok, thanks
However, will the weight of the object, arm, and motors over that distance compile to exceed the 419oz torque? I wasnt sure how to accuratlly estimate the total torque without using the center of mass, mass, and distance of each part for a rough estimate. How should I go about calculating this? is there a software capable of doing this (such as matlab?)
Thanks again,
Ellingwood

4

419oz in of torque is a stall value. This is what the servo will hold, not what it can manipulate. I would lower the stall torque by 30% and use that in your math.