question about how much weight a motor can have sitting on it before it stops

Posted by: @ncc1701d

Anyone know the math for figuring how much weight it an take?

There is no single formula that would work for all motors.   You'll need to look up the specifications for the motor in question.   Some motors are not designed to be used with a lot of force in the direction parallel to the output shaft.   Other motors are designed specifically for that type of supplication and would be sure to have specs called out.

The amount of force they can handle in the direction you indicate will depend on what type of bearings are used within the motor.   Typically turntables that have a lot of downward force (or weight) are often built on a special shaft that is separate from the motor, and the motor is just used to turn the table rather than support it.

In any case, there is no single equation that can be applied to just any motor.  You'll need to look up the specs for the motor you have.

@ncc1701d

I can only echo @robo-pi's comments and add that if you do stop the shaft of the motor under power it can burn the insulation and cause an internal short circuit, thereafter you can throw the motor away and buy a new one.

Locking the shaft of an electric motor for a short period is actually one of the standard tests performed during Factory Acceptance Testing. I have added a description below if you want to know more!

@pugwash

Interesting. Thank you for the pdf

@ncc1701d

I too echo the comments from @robo-pi and @pugwash, as there are two major loads to be considered and researched if taking this rout:

1) Axial load capacity of the bearing
This is the type of load the bearing will experience when you orient the motor shaft in the vertical position, as opposed to a radial load when the motor shaft is oriented in the horizontal position. As far as I am aware, most motors are not generally designed to take axial loads, and if they are, will probably be specifically built for such loads in mind.

2) Torque load capacity of the motor
The weight (mass) of the object will have a profound effect on torque due to its inertia... the greater the weight, the greater the inertia and power required to make the thing spin - Such inertial loads can draw enormous amounts of current, hence the reason for industrial contactor's and their associated circuitry.

As @robo-pi's mentioned... there's a good reason why:

    "turntables that have a lot of downward
      force (or weight) are often built on a special shaft"

...so such loads are not focused on the motor/spindle bearings, but rather on dedicated bearings than can handle the load.  Such a design also offers the use of different ratio's of pulleys and gearing to accomodate the design.

Cheers!