||We took a bipartite approach to the
design: mechanical and electrical. The mechanical section involved
the actual apparatus and the efforts to reduce the weight and remove the
transverse stress on the motor screw. The electrical section
involved the coding of the hardware and software so that the computer
could be used as a valuable tool to help make students' learning
On the mechanical engineering side, we reduced the weight of the base plate by over 50% by using an acrylic material as opposed to aluminum. We also reduced the weight of the friction plane by over 75% by making the plane a frame and reducing the outer dimensions of the plane. In removing the unwanted stress on the motor shaft, we used a system of two rollers and a crossbar.
The rollers support the entire weight of the friction plane and are connected to the motor screw only in the transverse direction. This difference of axis (i.e. horizontal versus vertical) results in the removal of transverse force on the screw, and subsequently results in a longer motor life.
All Pro/ENGINEER source files are located here. The next two pictures show the total assembly at an angle; click for a larger picture.
Here are two more pictures, both from the side and underneath views. Click them for a larger picture.
On the electrical engineering side, we wrote an entirely new Visual Basic program to operate the motor and to determine the needed coefficients from the data. The user manual, documentation, and executable code is available here. With this software, the user can control all aspects of the lab through the computer. A computerized motor makes movement much more smooth and accurate and not potentially jerky, if done by hand. Additionally, limit switches were added at the ends of the motor track to prevent the motor sled from 'bottoming' out and causing damage to the motor.
To use the FrictionLab software, first, users will have to change the material on the friction plane (hung on two screws) to the desired test material. In the case of testing for static friction, the user raises the incline of the plane until slippage (or tippage) occurs. The user can find the angle using the magnetic protractor, shown below, and calculate the coefficient.
In finding kinetic friction, the test block is placed so that it will fall through the photo gate. The photo gate timer, shown below, is set and the plane is inclined. The test stops when the block slides through the photo gate and a time is recorded.
The user can then calculate the coefficient of kinetic friction.