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### Author Topic: torque to rotate around vertical axis?  (Read 1480 times)

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#### davidc

• Beginner
• Posts: 4
##### torque to rotate around vertical axis?
« on: December 07, 2009, 06:11:30 AM »
How much torque would the motor need to rotate 2x1 m long arm if it rotates around vertical axis?
Weight is around 5kg

Weight--------Motor-------Weight
|
---------------ground----------------

It is not really weight dependent, right?

#### waltr

• Supreme Robot
• Posts: 1,944
##### Re: torque to rotate around vertical axis?
« Reply #1 on: December 07, 2009, 08:27:39 AM »
For a steady motion, no acceleration, the torque only needs to be enough to over come friction in the bearings.

But, to go from stopped to some speed, acceleration, the torque needs to over come the mass inertia of the weights and the same torque but opposite, to stop the motion.

If each mass 5kg and the total arm length is 2m. Then the torque required = length * mass * acceleration(tangential) + bearing frictional force * bearing radius.

The equations can be found in any first year physics text.