DC Motor Questions -- Building my own motor

[nryan34]

Hi, I am attempting at making a simple device that will run on dc power that just spins a item i place vertically in the air. I am trying to do it without having to by any of the parts being i could just buy a new one for around 250 bucks.

My first question is how to you determine the amount of torque i need to turn the object with a given motor? (trying to decide between a 6V or 12V motor)

What is the simplest (and cheapest) way of regulating the speed of the motor? (i only need to run the motor from 5-15 rpm unless i use gears to reduce the rotational speed of my object)

I also have roughly 8 6V 4.5aH rechargeable batteries to use, is it possible to hook those in series and run the 6V motor off of them? If so, what would be the potential drawbacks to doing so as opposed to buying a higher capacity battery?

 

[berkeman]

My first question is how to you determine the amount of torque i need to turn the object with a given motor? (trying to decide between a 6V or 12V motor)

The torque required will be determined by the bearing friction and the moment of inertia "I" of your setup, and the required angular acceleration for your setup. Do you have any of those numbers yet?

What is the simplest (and cheapest) way of regulating the speed of the motor? (i only need to run the motor from 5-15 rpm unless i use gears to reduce the rotational speed of my object)

The simplest might be to use a mechanical rotating speed regulator (like you saw on old steam engines). Otherwise, you can sense the output speed and use pulse-width modulation (PWM) of your DC voltage to the motor to regulate its speed.

I also have roughly 8 6V 4.5aH rechargeable batteries to use, is it possible to hook those in series and run the 6V motor off of them? If so, what would be the potential drawbacks to doing so as opposed to buying a higher capacity battery?

Hooking them in series will give you a higher voltage with the same Ahr rating as an individual battery. Putting batteries in parallel is not recommended unless they are specifically matched for output voltage and previous use (they need to be matched from initial manufacture, and always used in parallel together so they share the same discharge/charge history).