Hi Coleman! Thank you for such a great tutorial. It was very helpful. I am designing a 6 DOF articulated robotic arm for my final year project. In this tutorial you mentioned the case in which weights are acting perpendicular to the shaft. Please tell me that how to calculate the torque for base motor, because weight of next links and motors is acting parallel to the shaft of the motor (axis of rotation). Also I want to know that how to decide the link lengths of the arm ?
@Sami Assuming the servo is oriented vertically, the load is minimal, and it really only needs to be able to overcome the inertia of the arm, which unfortunately is quite a bit harder to calculate if you’re in the design stage, so choose something around the same torque as what’s required at the elbow. Don’t rest the weight of the arm on the actuator directly. Regarding the link lengths, that’s really up to you and your application, keeping in mind that ~20" will set you back around $400 USD, a large part of which goes towards the price of the actuators. Keep in mind T=F*d, so a longer link means more torque is required by each joint.
Thanks a lot for reply. Sir! Are you sure that torque calculated for elbow will work for the base? What if I take the base torque equal to the torque calculated for the Shoulder? The address for the reference image is:
@Sami It’s just a quick estimate - without calculating the actual inertia / friction. Since it’s only one servo, choose something which should be stronger than needed (a bit overkill).
what is a pressure exerted by robot arm its lifting capacity.
@khant Pressure is a force exerted over an area. Not sure where that applies in most robotic arms. The lifting capacity is a measure of force (and most often torque at each joint).
How to calculate the torque required for motor for scara robot arm which is moving in horizontal plane and axis of motor is at Y-axis
@Praveen You can see if you can assume the arm is fairly rigid and there are no forces in z axis. As such, you need to take into consideration inertia, static and kinetic friction. We do not have the equations for these to provide, so additional research on your end is needed.
Dear Sir,
How do I calculate Rated Torque for servo motor selection for 3 Link Robotic Arm mechanism ? We able to find Stall Torque by your method but we required Rated Torque. Please provide the necessary formulas.
I am able to find Stall Torque by your method but we required Rated Torque. How do I calculate Rated Torque for servo motor selection for 3 Link Robotic Arm mechanism ? Please give the solution of the same.
@Harshal Pawar For safety, the torque calculated here should be the rated (not stall) torque. This helps take into account inertia which is not factored into the equations. You can estimate stall as 3x the rated torque (napkin math).
@Coleman Benson can u send me the formula of T3, T4, T5 and T6 ?
@Raja K It uses the same principle of torque. If you understand the first one, you’ll be able to create your own, and even more complex. You can see the equations used on the page by pressing F12 (inspection mode) and look up “DTArmCalculate()” here: https://www.robotshop.com/blog/en/robot-arm-torque-calculator-9712
Hello,Coleman Benson sir can you send me some journal and research paper to related robotic arm?
@sourabh madan Unfortunately we do not have any on hand to send. Currently working on a blog post about inverse kinematics and torque for a 4DoF robot arm.
@Coleman Benson Hi, I just want to clarify about the Robot Arm Torque Calculator. While I am reading the comments/questions here I see this answer by you.
“@Harshal Pawar For safety, the torque calculated here should be the rated (not stall) torque. This helps take into account inertia which is not factored into the equations. You can estimate stall as 3x the rated torque (napkin math).”
I just want to ask if I am right that the torque calculated in the Robot Arm Torque Calculator is the Stall Torque by using this formula:
T1 = L1*A1 + ((1/2)L1W1) (just copying the above formula of yours) which is also the Holding Torque or the Static Torque? Am I right with this one?
Then the torque calculated here that you mention is the Rated torque which uses this formula:
T=T(holding) +T(motion), am I right?
I am just confused. So if I want to calculate the required torque to accelerate the weight I can’t use the Robot Arm Torque Calculator? instead I will use the formula for rated torque which is written at the end your post. Am I right?
Thank you.
@Eugene Agustin Correct. The formula in the tool do not consider angular acceleration, largely because the user would be required to know the moment of inertial for each segment. The torque calculated by the tool is therefore the “holding” torque in static conditions, whereas you need dynamic torque. You can use the tool to get basic values for the worst case static condition max load at full extension) and knowing your arm design and moments of inertia, factor in the acceleration you want.
Hello
I am trying to do dynamic analysis of robot arm . the problem is How I can represent the moment of inertia of the mass hold by the end-effector .
@Hazim Nasir The moment of inertia calculations will depend on the design of the arm, materials chosen etc. It’s almost impossible without going deeper into the design itself. This is why dynamic calculations were omitted from this tutorial. You might try a multiplication factor to try to ensure each joint can resist / overcome inertia.