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In picture one I have shown a robot arm (green) rotating to pick up a box, using a fulcrum (red). The arm after rotating is shown with black rectangle. The vertical arm on the left is attached to the horizontal green arm and goes down to make the green arm rotate.

In picture two, I have shown a robot arm which goes up and down to pick up the box, connected to a Revolute shoulder on the left which is not shown in the picture.

I have tried to modify the second picture, so I have created the first picture. I wanted to use fulcrum and related physics theorems to make the picking up easier for the robot.

Can you please tell me if I am making mistake and this is not a way to modify the arm and to make picking up easier? Does the red object act as a fulcrum?

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  • $\begingroup$ I answered the question because I saw the mod flag. If you still want the question moved, just flag it again and I'll move it. $\endgroup$ – Chuck Jan 16 '19 at 15:16
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The red object looks like a fulcrum in that it provides the pivot point for the green bar.

However, the point of a lever + fulcrum set is to generate a mechanical advantage. Mechanical advantage is essentially "trading" a displacement for a force. If the output of the lever moves half as far as the input when rotated then it generates twice the force/torque.

In your diagram, it looks like the middle of the green bar is on your fulcrum, though, so it's basically the same motion on either end, which means you're looking at a 1:1 force difference.

That is, you're not getting any more force out of your lever than you're putting in. This might be advantageous if you can only orient your actuator in a particular way, but otherwise this doesn't seem to be doing much for you. You'd want more of the green bar on the actuator side and less above the load to get a force advantage.

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  • $\begingroup$ Thank you for your answer, and yes I was talking about a condition in which lever is not placed exactly from the middle on the fulcrum although I forgot to change the pictures! $\endgroup$ – parvin Jan 16 '19 at 19:30
  • $\begingroup$ If the length on the left side is more than the right side, I as a human need to use less force to pick up a box, compared to just normally bending and picking it up from the floor. But robots cannot feel "force" as we humans do, right? it's only about energy for them, and they use same amount of energy with or without lever and fulcrum, if so, there is no change or advantages in what I have simulated compared to normal robotic arm. am I right? $\endgroup$ – parvin Jan 16 '19 at 19:35
  • $\begingroup$ @parvin - It's exactly the same for robots as it is for us. It's the same amount of energy for you because you apply a smaller force, but you apply it for a longer distance. Robots use energy, but they do so with real actuators, and actuators have ratings and mechanical limitations just like your muscles do. Your wrist isn't as strong as your ankle, your forearm isn't as strong as your calf, etc. Some actuators can supply more force than others. In using a lever/fulcrum, you can utilize a lower force actuator that has a longer stroke in place of a higher force actuator. $\endgroup$ – Chuck Jan 16 '19 at 20:05
  • $\begingroup$ To be more direct to the comment you made - a robot uses energy, but there's no such thing as an "energy actuator," so you do need to take into account peak force and speed requirements, stroke (travel distance) requirements, etc., into account when you decide how you're going to actuate a particular (sub)system on your robot. You cannot design a physical system by looking only at the total energy used for a particular maneuver. $\endgroup$ – Chuck Jan 16 '19 at 20:08

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