For a car to run effectively without an electronics unit what is required? Firstly some basic data. • Power is the time rate of doing work. The unit of power is the Watt which is equal to 1 Joule per second or a force of 1 Newton operating over a distance of 1 metre in 1 second. For a motor, power is calculated by multiplying 20 torque by shaft speed (RPM). For a car the power required to drive it can be calculated by multiplying the drive force applied to the car by the cars velocity.
When the car is moving at a constant speed the retarding force is the sum of aerodynamic drag, rolling resistance which includes wheels and guides and any gravity force such as when on the hill.
- Ignoring friction losses the power from a motor can be converted into the same power at any nominated RPM by the use of gearing. (Note the torque will be altered
- For the DC motors we are using torque varies directly with motor current (amps).
- For the DC motors we are using RPM varies directly with voltage. To obtain the best performance from any car we need to take the maximum amount of energy available from the solar panel and use as much of it as possible to drive the car.
To achieve this, a high efficiency motor used in conjunction with a solar panel whose output current and voltage suits the motor characteristics is essential. A gear ratio that matches the available motor power to the power required to propel the car at the highest speed possible is just as important.
The statement above while accurate, is of little help unless we understand the implications and know what to do in order to achieve the requirements. I hope the following explanation which is broken down into each major section will make it clear.