Granular Flow Rotating Sphere using pic-microcontroller
Spring Quarter Update
This zip file contains the documentation, MATLAB code/examples, PIC code and circuit diagram.
Contact Scott McLeod for further questions.
- Brian Kephart – Electrical Engineering Class of 2009
- Jonathan Shih – Mechanical Engineering Class of 2009
- Kristi Bond – Mechanical Engineering Class of 2008
A clear sphere is filled with grains of different sizes. Our apparatus rotates this ball about two different axis based on a series of user inputs. The user inputs the specific values for things such as angle and rotational speed into Matlab. Our device takes these inputs and processes them using a series of master and slave PICs to appropriately control the motors. The motors then turn for the input duration at the desired speed causing the ball to spin correctly due to the frictional connection between both motors and the sphere or lazy susan, respectively.
This apparatus will be used for the study of granular flow and the mixing of particles within the sphere. It was important to leave the ball as visible as possible to allow for pictures to be taken of the grains within from many angles. With this apparatus we hope to aide the study of granular flow theory and allow the researches to use the device for many different applications.
The main housing, or case, for our design is composed of the following pieces.
- One 13.5” x 12” x ¾” plywood rectangle
- One 13.5” x 12” x ¾” plywood rectangle with a 3.5” diameter circle removed from the center
- Two 12” x 2.5”x ¾” plywood rectangles
The two larger rectangles form the top and bottom of the set-up with the two smaller rectangles placed vertically between to form a box with two open ends on the front and back face.
Three ball casters are placed on vertical mounts around the center circle of the top piece of the housing at equal angles. These casters prevent the ball from moving in any horizontal direction so it is only free to rotate. One of these casters is adjustable to allow the user to make sure the ball is correctly supported above the drive wheel. The force of gravity is strong enough to prevent the ball from moving up and out of the housing and also ensures a good connection with the drive wheel that is placed directly under the center of the sphere.
Main Drive Wheel
The main drive wheel is centered under the rotating sphere. The wheel is mounted onto a ¼” aluminum shaft which is connected to the Pittman motor with a flexible coupling and is also supported by a sleeve bearing on the other side of the wheel.
The main drive wheel with its corresponding motor and other components are all mounted on top of a lazy susan that is centered on the bottom piece of the housing and secured with screws. This lazy susan allows rotational motion but prevents movement in any other direction allowing the wheel to turn but always have the same center of contact with the sphere above. It is important to ensure that the drive wheel has a good connection with the sphere above because the frictional force between the wheel and the sphere must be as large as possible so that as the wheel spins the ball spins at the same rate.
Position Control Motor
A second motor is used in our design to turn the lazy susan. The motor is mounted vertically through the top plate. Another, smaller, drive wheel is mounted directly to the motor shaft and then aligned with only the top, free half of the lazy susan. A second, idler wheel is mounted on the bottom plate, so the drive wheel is sandwiched between this wheel and the lazy susan. This ensures that the drive wheel is always in contact with the lazy susan because the idler wheel exerts only a normal force. Again, this is to ensure there is no slip between the lazy susan and the drive wheel so it is automatically controlled more easily.
Complete Parts List
|Pittman GM8224 motor||—||2|
|Helical Beam Set-Screw Shaft Coupling||9861T508||1|
|Mounted Sleeve Bearing||5912K21||1|
|Flange Mount Ball Caster||5674K77||3|
|Small Drive Wheel||2471K12||1|
|1/4” Aluminum Rod||—||—|
|Aluminum Sheet Metal||—||—|
For more detail: Granular Flow Rotating Sphere