Powering a Mobile Robot

This blog post on powering a mobile robot is an excerpt from Lesson D-9 of our Intro to Robotics   program. Intro to Robotics consists of four levels that start at the beginning and systematically teach you to build circuits, use a Raspberry Pi, and write code in Python. In the final level, you will take all the skills you've learned and build a mobile robot of your own. The full Intro to Robotics course contains 72 detailed lessons with 200+ projects and activities. Sample lessons and  full scope and sequences for all four levels can be found here.

 

Throughout Levels A, B, and C, your projects will be powered via an AC wall adapter that supplies 5-volts to the Raspberry Pi. This power source is very stable, but the cable required for this connection makes it a poor choice for a mobile robot. In Lesson D-9, we teach you how to power the robot using on-board batteries, which will enable the robot to be fully mobile.

 

Power Conversion

The battery pack on the robot will use 6 AA cells in series, for a total voltage of 7.2 to 9.6 volts, depending on whether alkaline or NiMH cells are used. The micro USB power input connector of the Raspberry Pi requires 5-volts, so a voltage regulator must be used to lower the battery pack voltage down to a level that can safely power the Pi.

Six AA Batteries Connected in Series 

The voltage regulator module in the Level D kit is built around the LM2596 voltage regulator. The LM2596 can take in voltage levels from 40-volts down to 6-volts and output a stable 5-volts that can be used to power the Pi. To the right are the connections to the voltage regulator module.

Voltage Regulator 

Input power comes into the module from the 9-volt input that connects to the battery pack. The input power from the battery pack is also connected to two jumper-wire connections that are used to power the motor drive IC that will drive the motors. The output from the voltage regulator module is a right-angle micro USB connector that connects to the power connector of the Pi.

There is no power switch for the voltage regulator. As soon as you connect the battery pack to the voltage regulator, the motor drive IC will be powered, as well as the 5-volt input to the Pi.

Always use caution with the motor drive power wires when the battery pack is connected. The motor drive power wires will have full battery pack voltage and current available on those wires. If they’re improperly connected or shorted, damage to components or fire could result.

 

Installing the Power Pack on the Robot

During the activity portion of Lesson D-9, we walk you through several steps including:

Connecting the motor drive power wires to the breadboard:

Connecting motor drive power to breadboard 

Placing the batteries in the battery pack and sliding the battery back into place on the lower chassis of the robot below the Raspberry Pi.

Side view of robot power pack sitting below Rasbperry Pi 

The power pack is secured with strong velcro so it won't slip out, but it can also be removed when it's time to change the batteries.

Rear alignment for robot battery back

 

This blog post on powering a mobile robot is an excerpt from Lesson D-9 of our Intro to Robotics   program. Intro to Robotics consists of four levels that start at the beginning and systematically teach you to build circuits, use a Raspberry Pi, and write code in Python. In the final level, you will take all the skills you've learned and build a mobile robot of your own. The full Intro to Robotics course contains 72 detailed lessons with 200+ projects and activities. Sample lessons and  full scope and sequences for all four levels can be found here.

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