Fall 2015 RoSco: Power Budget

By Will McKinney (Project Manager/Electronics and Control)

Power Budget

Item Model Quantity Minimum Current(mA) Stall Current(mA) Voltage(V) Min Power(W) Max Power(W)
Servo(Each Track Assembly) HD 1501MG 4 500 2500 6 3000 15000
Motor(Each Track Assembly) Pololu 120:1 4 70 800 6 420 4800
Servo(Pan and Tilt) Micro 2 350 1500 6 2100 9000
Bluetooth HC-06 1 38 3.3 125.4
Arduino Uno 1 250 3.3 825
Total Tested Running Current MinCurrent Max Current Min Power Max Power
ROSCO 1A/2.5A 3268 16200 18830 97200

Above is the final power budget. The majority of our power was used by the 6 different servos and the 4 different motors. It was essential to find out how much current our rover runs off us because we needed to know if the batteries we were given were sufficient. The batteries that were given to us were 700mAh capacity, 7.2V batteries that were used on past semester’s projects. The pololu motor’s specs say that the motors run at 70mA when free run. We tested this value and found that when they were free run, the Pololu motors ran at 72 mA.

Each servo drew about 500 mA when there was no load. When we built our first prototype we were able to see how much current our rover drew when everything was running. We found that it used 1A when the motors were running and 2.5 A when the servos were lifting the entire rover. This makes sense because the motors were running with friction being applied which means they drew more current. Each motor drew about 200mA when the motors were running. When the servos were lifting the chassis, 2.5A were being used. This means that the servos were barely under any stress. The servos are rated to have 17kg/cm of torque so when the four servos lifted the 3 pound chassis, they didn’t need to consume a lot of current.

In conclusion, our 700mAh battery is sufficient for this project because this will allow us to drive at best case run the rover for 40 minutes. At worst case, the rover would be able run at 2.5A for 16.8 minutes using the 700mAh battery. This would give us enough time to complete the course when traveling at .5-.75ft/sec.