Spring 2016 Pathfinder: Current Drawn Test
by:
Tuong Vu (Electronics & Control – Sensors, Actuators and Power)
Table of Contents
Introduction:
This blog post will be explaining the total current drawn from the batteries by the motors. The amount of currents drawn from the batteries are resulted of the wheels experiencing at different friction forces. Different friction forces correlated to different terrains that the pathfinder traveled on. For example, rocky or sandy terrains required the pathfinder to exert more torque on its wheels in order to move which corresponds to more current being drawn from the batteries. The friction force is much larger on sandy or rocky terrains compare to smooth cement terrains. The more currents being drawn by the pathfinder lead to shorter batteries life (refer the previous blog post about batteries life).
Test procedure:
Components:
- R.S.E.717 Multimeter
- Samsung S7 cell phone
- Motors : Pololu motors
Using the DMM in series with the motors shield would allow currents drawn from the batteries by the motors to be observable. As the pathfinder conducts its route, collecting the currents being drained from the batteries is an issue. A smartphone was attached in the back of the pathfinder to record the currents being drawn from the batteries as the pathfinder goes through its route.
Current drawn:
- Moving back and forward do not require high amount of pressure on the wheels which current was drawn was the low, refer to figure.1.
Figure 1
- Turning left and right required more than the average current drawn,so the battery life is shorter, refer to figure 2.
Figure 2
Different load & road environment :
Torque is the ( N*M) as N is the force and M as mass of the total load. Amps is the current drawn by the motors. As the pathfinder undergoes a route through rocky terrain, more torque is required to turn its wheels. Travelling on rocky terrain deplete the batteries much faster than travelling on smooth surface, current drawn from the motor is linear proportional to the motor torque, refer to figure 3.
Figure 3
Conclusion:
The amount of currents drawing from the batteries is related to the terrains that the wheels of the pathfinder travels upon. Rocky and sandy terrains require the pathfinder to exert more torque on its wheel in order to move which corresponds to more current being drawn from the batteries,so turning left and right draw more current than going forward and backward.
Sources: