Methods of Transmission of Mechanical Power through Gears and Belts - Lab Report Example

Transmission of power is a common requirement in most mechanical devices. The most common methods of transmission of mechanical power are through gears and belts. Though gears are more efficient, they can only work with fixed gear ratios. Various in-case belts can work with continuously varying sizes of the pulleys, thus enabling usage at all levels. Belts are used in applications from kitchen grinders to cars. While belts can transmit power, they are generally considered inefficient because of the slip between the pulley and the belt. This also results in an ineffective transmission ratio and hence the speed.

The slip of a belt depends on the coefficient of friction between the two, the shape of the belt, and the torque transmitted. Belts used can be flat belts which are supposed to have a higher slip compared to the vee belts. Originally, belts were made of leather and rubber but today several synthetic materials and steel-based belts are available that reduce wear and tear.

2. Theory
The relationship between the tensions in the slipping pulley is studied and recorded by Grosjean1 and Fawcett and Burdes2 using the apparatus shown in figure 1. The details are shown in the calculations below:
T2/T1= /in
For a flat belt or a string, the angle  is 900
The torque transmitted by the belt is :
Torque = (T2 – T1) x R
The power transmitted is given by the equation:
Power = Torque x 

3. Apparatus
The experiment has the following apparatus in place as shown in figure 1.
1. There is a variable speed DC electric motor driving pulley of a fixed radius.
2. The pulley has on one end a series of weights which is variable from 0 N to 10 N.
3. On the other end, the string running over the pulley supports a spring balance which helps in measuring the tension on the other side.
4. The angle of contact between the pulley and the string can be set to four different values
5. The motor voltage and current are measured using digital meters and the rotational speed of the pulley is measured using a digital tachometer.

4. Procedure
The following procedure is followed during the experiment:
1. The motor voltage is set at 10V and the angle of contact between the pulley and the string is made 90 degrees. The pulley direction is maintained such that the weight tension is more than the spring tension at the spring balance end.
2. Load T2 is varied by hanging a range of weights on the string. For each weight, the string tension along the spring balance is measured and recorded.
3. The load is varied until the motor stalls and the red current control light starts flickering.
4. This operation is repeated for various string contact angles of 180, 270, and 360 degrees.
5. For one contact angle alone, in addition to measuring the tensions, the pulley speed, the voltages, and the current at the motor end are also measured and recorded.

The efficiency curve we notice tapers off after the initial steep gain and then starts to come down. This happens with every system and they operate efficiently at a specific load. Read More