The Discount Mars Rover Project

STEP 7: SWITCH TO INTERNAL POWER

So far we have used some kind of static power supply, for the drive test we need to switch to internal power. Means: We need batteries!

The required capacity of the batteries depends on the power consumption of the rover and the time we want to operate the rover before we have to recharge the batteries. The engines are supposed to consume up to 450 mA, the average consumption will be lower, I will calculate with 300 mA. For the Arduino MEGA I googled an average of 50 mA, the raspberry pi can consume up to 500 mA when running complex calculations (and getting geometry data from a picture is a complex task). The data sheet of the HC SR-04 ultrasonic sensor tells us that they consume 15 mA. All other sensors and even the camera consume just little power.

Keep in mind that the drive motors need +/- 12V while the computers and servos need a 5V power supply. Therefore I will use two XL4015 DC/DC- step- down converters, one for the arduino and the servos for robotic arm and camera mast and one for the Raspberry Pi computer. The XL4015 is fully adjustable and can deliver any required voltage.

I have decided to use 3 2200 mAh batteries: One for the right drive system, one for the left drive system and one for the computers and servos. Each battery will have it's own main - switch to get power quickly on and - more important - off.

Which parts do I need?

3 x (11,7) V LIPO battery
3 x Switch to turn on/off the power supply
2 x XL4015 DC/DC step down converter
Many wires

What needs to be done?

Mount all LIPO batteries into the rover. Connect the batteries with the main switches.

Connect all 6 L298D directly with power supply and do not forget to connect Arduino GND with battery GND.

Connect both DC/DC converters with the batteries and adjust the converters to 5,0 V for both the Arduino and the Raspberry PI (which we will build in in one of the next steps). Make sure that all components are up and running, check that the DC converters provide 5V output voltage!

1: Main power supply switches

2: 3 x 11,1V 2200mAh LIPOs

3: Left side motor controllers

4: Right side motor controllers

5: XL4015 DC/DC converter (11,1V to 5V) for Arduino

6: Arduino MEGA

7: XL4015 DC/DC converter (11,1V to 5V) for Raspberry Pi

Your pin layout depends on you how you want to connect the L298D bridges with the Ardiono board. You need to make sure that your software definitions for the motors match with the real pin layout, otherwise the drive system will fail.

My STEP 7 SOFTWARE needs the following pin layout:

Layout of the Arduino MEGA pins for PWM motor control

A) PWM signals

PIN        Motor    Function
2          6        PWM
3          4        PWM
4          2        PWM
5          5        PWM
6          3        PWM
7          1        PWM

B) HIGH / LOW Signals for directional control

HIGH      LOW       Motor
22        23        2
24        25        4
26        27        6
28        29        1
30        31        3
32        33        5

How much do I have to pay?

2 x XL4015 DC/DC converter :  6,00 €
3 x 11,1V 2200mAh LIPOs    : 60,00 €
3 x switch:                :  3,00 €
some wires and connectors  :  1,00 €
======================================
  Total                      70,00 €