Torque required to move robot arm (special linkage)

  • #1
slkmc wwojno
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TL;DR Summary
I need to calculate a torque required for uArm type of robot arm. Servos are at the base and 2 arms are controlled by system of linkage.
I need to calculate a torque required for uArm type of robot arm. Servos are at the base and 2 arms are controlled by system of linkage.
I suppose all necessary info will be given by CAD, like weight and mass of gravity,etc..
But How would I properly size the servos? Is it the same as in classic arm where each servo is at each joint? Please see provided CAD model in the Onshape Viewer.

Here is the CAD of the arm in question:

https://cad.onshape.com/documents/e...renderMode=0&uiState=655cc9f611f8d44e40ff0e2c

I changed the colours on the example assembly to make it more recognisable. Right servo is connected to the blue arm only. Left servo is connected to the purple arms. The green arm that holds the gripper is not connected to any servo, just to the base.

Thanks!
 
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  • #2
You will need to ascertain which geometry of the system will produce the maximum load on the operation of a given servo. From there it should be a simple exercise to solve for the moments and torques (as required for a desired acceleration). The other way to proceed involves exact solution of the system, probably using Lagrange multipliers (?) I presume there is software on the shelf that will do this.
 
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  • #3
Welcome to PF.

You will need to reduce the design to straight line link lengths, between pin positions, and then the angles between the pins. Think of the links as a chain of 2D vectors, stretching from the base to the load, via the pin position points.

You then apply the maximum load to the virtual structure, and follow how that force flows back through the link structure, to become a torque at the servo. Since it is a 2D linkage, I would solve it numerically.

By sweeping the servo angle/length in small steps, through all possible combinations of geometry, you search the range for the maximum servo torque. Look closely near the maximums, to make sure that the torque is bounded, not infinite.

Check that the axial tension or compression in each link is within design bounds, and that the pins and bearing surfaces are sufficient for the loads involved.
 
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  • #4
can you provide the calculations by assuming the the links lengths and weights?
 

What factors determine the torque required to move a robot arm?

The torque required to move a robot arm is primarily determined by factors such as the arm's weight, the load it carries, its geometry, and the friction in the joints. Additionally, the acceleration and speed at which the arm needs to move also significantly influence the required torque.

How do you calculate the torque needed for a robotic arm with a special linkage?

To calculate the torque for a robotic arm with a special linkage, you must consider the mechanical advantage provided by the linkage design. The calculation involves determining the force needed at each joint to perform the desired movement and then using the arm's geometry to convert these forces into torques. This typically requires knowledge of vector mathematics and dynamics.

What is the role of gear ratios in determining the torque in robot arms?

Gear ratios play a crucial role in determining the torque output in robotic arms. A higher gear ratio can increase torque output at the expense of speed, allowing the motor to move heavier loads more effectively. Conversely, a lower gear ratio increases speed but decreases torque, suitable for lighter and faster operations.

Can software simulations help in optimizing the torque requirements for robotic arms?

Yes, software simulations are extremely useful in optimizing torque requirements for robotic arms. They allow engineers to model different scenarios and configurations, assess the effects of various loads and forces, and make adjustments before the physical prototype is built. This can lead to more efficient designs and better performance of the robotic arm.

What are common challenges when designing torque requirements for robot arms with special linkages?

Common challenges include accurately predicting real-world loads and interactions, dealing with the non-linear behavior of materials under stress, and ensuring the arm can handle unexpected loads or impacts. Additionally, achieving the desired precision and repeatability in movements while maintaining efficiency and minimizing wear and tear on components can also be challenging.

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