Robot Arm Torque Tutorial

hey, can you help me how to get the transfer function from this equations

@mohamed This article and the equations provided would not provide the transfer functions / IK directly.

Thanks for this tutorial its very help full
I just want to ask if we could contact because the robot arm is my graduate project
And i need to know more about it

@Adobe: If you have questions related to project design and challenges, we recommend that you post about it on the RobotShop forum or on our project-oriented website, Let’s Make Robots.

How do you calculate the waist rotation moment about the base ? Does the motor torque need to overcome friction (MU* Fn) ? And the inertia about the axis perpendicular to roation ?

@Vikram If the arm is balanced and frictionless (which it’s not unfortunately), the torque needed in the base would only have to overcome inertia and be able to stop the arm (decelerate). You can see if you can come up with equations, but friction and inertia at various configurations (full extension and max payload with maximum rotational acceleration) would likely need to be considered. We’ve found based on experience that the torque is not too high and in the AL5D, only a Hitec 422 is needed.

Hi , Mr Coleman Benson , the above article about calculating forces and torques is good . It is for 6 axis SCARA. Can you please explain the same for parallel kinematic robots. that would be great. Thank you

@shrishail bannigidad Although this article does not go into inverse kinematics, you can find a bit torwards the end of this guide:

Hi Coleman-i am working on a design for an arm that will have support already in place for the weight of the sample and arm and will only require the actuator to rotate the sample to the desired position; ie the only degrees of freedom are rotation about the Z axis. We will use a low friction/rolling item to support the weight of the sample and arm.When calculating the torque required by the actuator, is it correct to assume that we only need to take the inertia of the arm and sample into account and disregard the weight since it is supported? Thank you

@Thomas Fjeld So long as the mechanism is mechanically sound at the base, the torque required will need to counteract / overcome the inertia (acceleration / deceleration).

Hello Mr Coleman. First of all i want to thank you for this great tutorial.
My concern is about the “safety factor”, I’m working on the design of an arm and the first approach doesn’t require to go through the dynamics (inertia and acceleration) so the use of that “safety factor” works just fine. My question is if there’s some bibliography or references you could recommend to support the use of one or other factor (I mean numerically).
thank you!!

@Ronnie Good question; unfortunately we do not currently have any links to suggestion. You will likely ned to obtain a university physics book / robotics book regarding kinematics and dynamics.

May i know the parts available website

@Naveen Take a look on for arms and compatible parts.

Thanks For your helpful Tutorial
the last relation says : T(holding) + T(acceleration) = Ia
I think that it should be : T(acceleration) = I

@Fadi Masalmah You are indeed correct.

I found it really helpful. I want little bit more to complete my calculation. If robotic arm stops suddenly(let say from a angular velocity of x to zero) then how can I calculate jerk on joint of the link. Please give me solution.

in case of a cylindrical coordinate robot…if i place motor for linear up and down motion with the base motor(i.e motor for rotation)Then the torque of the two motors should be same or not?

@hasnid The calculations / equations would be quite different.

@Mayur Jadhav The “jerk” is a result of inertia. The inertia depends on the position of the arm, the weight of each component etc., as well as the deceleration curve as the arm stops. There’s a lot involved.