# Geared DC Motor Selection

Hi

Disclaimer. This is my first time selecting a motor for a project. I have a DC motor in mind, but I’m not sure if the motor will produce enough torque for its intended purpose. So I need a motor that should be able to rotate horizontal disk of about 6kg at about 800rpm. I am looking at the 37D Metal gearbox motors, particularly item number 4758 with the built in encoder. Will this motor be fine?

Any help would be thoroughly appreciated.

Sincerely

Lee

Hello, Lee.

Ultimately, you will need to calculate the required torque for your system, but a 6kg disk is likely too much for our 37D gearmotors. If you are talking about connecting the motor to the center of the disk and having it oriented horizontally, the torque is given by \text{τ}=\text{I}*\text{α} , where I is the moment of inertia and α is the angular acceleration.

A disk is just a thin cylinder, so you can calculate the moment of inertia using this equation for a solid cylinder:

\text{I}=\frac{1}{2}*\text{M}\text{R}^{2}

Where M is the mass and R is the radius.

Angular acceleration is the change in angular velocity over the change in time:

\text{α}=\frac{\text{Δω}}{\text{Δt}}

You did not give the radius or how quickly you want the system to get up to speed, and ultimately those specifics will matter, but as an example for you to reference with the correct values, let’s say the disk has a 10 cm radius and you want it to take 2 seconds to reach your desired speed of 800 RPM (which is ~83.8 rad/s), then:

\text{I}=\frac{1}{2}*\text{6}*\text{0.1}^{2}=0.03\text{ kg m}^{2}