# Help Torque to drive robot arm

• Mfrank7143
In summary, the person is having trouble calculating the torque needed for a 700mm long robot arm that weighs 3Kg with a 6Kg mass on the moving end. The arm needs to repeatedly rotate 180 degrees and return to the starting point in two seconds. They are seeking help with this issue and have been advised to calculate the mass moment of inertia and required angular acceleration, and to define a trajectory of the desired speed and add appropriate control.

#### Mfrank7143

Hi I am trying to designing a robot arm but am having problems calculating the torque required to drive the main shoulder joint.
The arm is 700mm long and weighs 3Kg with a mass on the moving end of 6Kg. The arm is required to rotate repeatedly through 180deg then reverse back to the starting point repeatedly at a rate of one return stroke in two seconds. Can anyone help with this?

Thank you.

Mike

I don't have any practical experience with this, but your first step is to calculate the mass moment of inertia of the arm + the mass rotating about the pivot point.

Second, use your motion requirements calculate the required angular acceleration of the arm. T = I * alpha

Check out
www.electromate.com/technicalsupport/smartmotioncheatsheet.pdf

Mfrank7143 said:
Hi I am trying to designing a robot arm but am having problems calculating the torque required to drive the main shoulder joint.
The arm is 700mm long and weighs 3Kg with a mass on the moving end of 6Kg. The arm is required to rotate repeatedly through 180deg then reverse back to the starting point repeatedly at a rate of one return stroke in two seconds. Can anyone help with this?

Thank you.

Mike

Do you have a lay out of the arm? Is the arm going to drop something? It is really necessary to stop it back and forth or can it move in a continuos path?

First thing besides knowing it´s moment of intertia you need to define a trayectorie of the speed you want the arm to make. What velocity and accelertion speed are you expecting to make, then from it you can stablish the torque needed and then you add the control to make the arm follow the velocity you stablished!

Velocity curve -> Torque required -> Control (Algorithm to follow the curve speed desired) or cam.

## 1. How does Torque help drive a robot arm?

Torque is a measure of the force that can cause an object to rotate around an axis. In the case of a robot arm, torque is used to move the joints and control the movements of the arm.

## 2. What factors affect the torque needed to drive a robot arm?

The weight of the arm, the length of the arm, and the force needed to lift or move objects are all factors that can affect the torque needed to drive a robot arm. Additionally, friction and resistance in the joints can also impact the required torque.

## 3. How is torque calculated for a robot arm?

Torque is calculated by multiplying the force applied to the arm by the distance from the axis of rotation. This is known as the moment arm or lever arm. The unit of torque is typically measured in Newton-meters (Nm) or foot-pounds (ft-lb).

## 4. What role does gear ratio play in torque for a robot arm?

The gear ratio of a robot arm can affect the torque needed to drive it. A higher gear ratio can increase the torque output, allowing the arm to lift heavier loads. However, a higher gear ratio can also decrease the speed of the arm's movements.

## 5. How can torque be controlled for precise movements of a robot arm?

Torque can be controlled through the use of sensors and feedback systems. These systems can measure the torque being applied and adjust it as needed for precise movements. Additionally, programming can also be used to fine-tune the torque and movements of the robot arm.