How to calculate operating torque and holding torque of a slew drive for a manipulator arm?

Question

Hope you are doing good and enjoying your weekend. I have a question regarding calculation of torque and tilting moment for a slew drive. Slew drive (motorised) will be used at the base of a manipulator arm to facilitate the arm rotation in 360°. image here.

For tilting moment : (the mass of each part of manipulator arm) * (perpendicular distance between CG of each part and axis of rotation) (as shown in image)

For operating torque : I am not quite sure how to calculate that because torque is also mass of each part * perpendicular distance between CG and axis of rotation. Then I thought that acceleration torque itself is the operating torque in my case (please correct me if I am wrong).

There is no existing slew drive on the manipulator so I have no reference point.

Could someone please guide me with the formula for calculating operating torque and holding torque for a slew drive based on the image shown?

Thank you for your valuable time and info. Have a great sunday :)

Answer 1

It really isn't an easy problem, since the answer depends on not only the masses and locations of each element, but also the velocities and accelerations you want to support.

When I looked into this problem myself I found precious few resources to learn from. Robotics texts tend to abstract the problem away and aren't always of much practical value.

The best starting point for me was a really ancient paper from 1975 by B.K.P. Horn who as then (and still is!) with the MIT AI Lab. I ended up writing my own primer based on Prof. Horn's to walk myself through solving gradually more difficult problems. There is a really good text book out there by Rivin on The Mechanical Design of Robots, but it is out of print.

Sorry - Not a very concise answer to your question, but maybe a starting point.