ATLASCAR Odometry System

ATLASCAR already has its own odometry system, the purpose of this thesis is to improve or maintain the existing system in resolution and precision and to make the system usable in most of the road vehicles.

Velocity

The velocity of the ATLASCAR is calculated with a incremental encoder installed on one of the back wheels, the encoder is enclosed in an apparatus fixed in the body of the car (figure 1). The encoder is connected directly to the wheel, so do not have any kind of multiplication. The encoder resolution is 50 PPR this means that with the wheel's diameter of 0.55 meters we can get a new value of the car's velocity every 3.49 centimeters.

Figure 1 - Velocity measurement system on ATLASCAR

Direction

The direction of the car is measured with a potentiometer connected through a pulley system directly in the steering column. This mechanism is invasive and forced modifications on the structure and devices of the steering column (figure 2 and 3). The potentiometer has a 10kohm resistance and the gear ratio through the pulley mechanism is 1:3, the data is collected by a PIC18F258 micro controller with 10-Bit analog-to-digital converter. The ADC input on the micro controller gives us a 1024 resolution, although the signal variation in this mechanism is between 0.3 an 4.4 volt, which gives us a (4.4-0.3) * 1024 / 5 = 839 resolution. The car has a 2.5 turn steering wheel so in the end we have 2.5 * 360 / 839 = 1.0727 º of final resolution.

Figure 2

Figure 3

The next step is to design a system that meets the goals of this project and choose the right sensors with which we can obtain the same or better accuracy than the existing sensors on the ATLASCAR. The final system should be able to be installed in an easy and non invasive way on most of the vehicles.