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## Main Question or Discussion Point

I would like to make a project where a dc motor will help the movement of a human arm. The motor will be at the elbow, the stationary part will be attached to the upper arm, and the moving part will be attached to the forearm, so the motor will help to rotate the forearm at the elbow.

I think the biggest torque will be when the forearm is parallel with the ground, so my calculation is something like this:

My forearm+hand+a little weight(aluminium structure, etc): m=3kg.

Gravitational acceleration: g=9.81 m/s2

The arm is a distributed load, for now let's say it is evenly distributed and the center mass is at halfway of the forearm: from the elbow it's s=20 cm=0.2m

So the Torque would be: T=3*9.81*0.2=5.89Nm.

Or going with the kg.cm: 60kg.cm.

I got a recommendation to choose a motor, for example this: https://media.digikey.com/pdf/Data Sheets/Seeed Technology/108990007_Web.pdf

But it says that the load torque is 0.55 kg.cm, so if my calculations are correct i would need hundred times more torque, which seems odd to me.

do you have any idea what i am missing, or calculating wrong?

I think the biggest torque will be when the forearm is parallel with the ground, so my calculation is something like this:

My forearm+hand+a little weight(aluminium structure, etc): m=3kg.

Gravitational acceleration: g=9.81 m/s2

The arm is a distributed load, for now let's say it is evenly distributed and the center mass is at halfway of the forearm: from the elbow it's s=20 cm=0.2m

So the Torque would be: T=3*9.81*0.2=5.89Nm.

Or going with the kg.cm: 60kg.cm.

I got a recommendation to choose a motor, for example this: https://media.digikey.com/pdf/Data Sheets/Seeed Technology/108990007_Web.pdf

But it says that the load torque is 0.55 kg.cm, so if my calculations are correct i would need hundred times more torque, which seems odd to me.

do you have any idea what i am missing, or calculating wrong?