DESIGN HINTS

is simply fitted with a pulley on its output shaft , a cord is taken around the pulley and
supported on two spring balances (balance one 50 gm and balance two 100 gm). The
rotation of the pulley tends to drag the cord around thus reducing the load on one spring
balance and increasing the load on the other. To increase the load on the motor both (or
one) spring balances are moved up to increase the total load on the cord. Conversely the
load is reduced by lowering one or both spring balances. (the construction we used for
this unit moves both spring balances together initially we used a quick action clamp then
later a screw thread).The difference in tension from one side of the cord to the other
multiplied by the pulley radius gives the torque. The RPM is measured with a Laser
tachometer from Jajcar Electronics. ( Digitech QM 1448)

Power is calculated by using the formula below

Power (Watts) = Torque (mNm) × RPM × Π
30 × 1000

The standard pulley we use is 34 mm Diameter.
Multiplying the difference in tensions of the cord around the motor pulley (T1-T2) by
0.1666 gives torque in mNm.

TESTING THAT CAN BE UNDERTAKEN USING THE DYNAMOMETER

· Optimum over voltage of motors.

· Electronics package, how good is it? is it worth using?

· Panel characteristics required for best match of electronics to motor

· Motor efficiencies

· Gear and other drive system efficiencies

· Power output at car drive wheel ie. configure unit as a chassis dynamometer

simply by placing the load cord in a groove in the cars drive wheel.

· Motor characteristics for use in the Model Solar Car Mathematical Simulation

The actual Dynamometer with Laser tachometer in place is shown below.