Motor Design

[kburrie1]

I am trying to design the components of a mechanism that will allow me to precisely rotate a vertical, axial load. The motor and its components will need to support an axial load of 125 lbs, and be able to rotate (in both directions) in increments of about one-tenth of a degree. The shaft is made of steel and about three inches in diameter. I have considered connecting the shaft to the base using some type of bearings, to support the load and eliminate friction, and then connect a stepper motor to the shaft underneath the bearings. I don't have any experience with this type of thing so if anyone has any ideas or suggestions I would greatly appreciate it. Thanks.

 

[MotorVib]

Talk to the motor vender. They know more about the motor and the bearings. This is the type of question that the motor manufactures get all of the time.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[zekeman]

The bearings are the easy part. You have to specify ( not necessarily in this order)the accuracy of the angular position, the allowed overshoot, the speed of response and the the moment of inertia ( or the geometry )of the rotating mass. A simple stepper usually is nor the answer.

 

[MintJulep]

Why make when you can buy?

Companies like Camco-Ferguson, Sumitomo, CDS, Rotomation and many others have a plethora of fully-developed commercial products to rotate things precisely.

 

[MotorVib]

By zekeman is right bearing are simple. With this small of a motor ball bearing might work. If it do then you can stay with a std motor. Over overshooting will be harder if it is to tight of angle.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[FILGUEIRAS]

To buy the thing is certainly easier, but to build it is funnier.
I´d use a Geneva wheel, with the suitable gear train. When loads are small, it´s precise enough to be used in movie projectors.

 

[kburrie1]

Thanks for the posts everyone. My problem right now is calculating the torque. Do any of you know how to calculate torque with a purely axial load?

 

[j8715]

Is this homework or something you are actually building?

If you want to position with this accuracy you need a resolution of 3600. Among other reasons, this rules out geneva wheel.

I think your main question is "how do I size a motor?"

http://www.as-automation.com/cheat_pre_reg.html

This should answer all you need to know about torque.

Second is control. If you have a load inertia that is wildly above the motor inertia you are going to have trouble controlling your movements.

Read:

http://www.motioncontrolonline.org/files/public/Load_Inertia_Motor_Selection.pdf

Once you get the loading figured out, picking a bearing should be easy.