Written By: Adham Ibrahim, Project Manager
The Micro-SegBot is a self-balancing two-wheeled robot that was built as a toy for hobbyists and children. It was designed to emulate a full size Segway. As the name suggests, the Micro-SegBot will be considerably minuscule in size when compared to the Segway. The Micro-SegBot will be remotely controlled via Bluetooth by any Android phone that is equipped with the Arxterra mobile application. The base of the robot houses all of the electronic components that are necessary to successfully operate it.
- The Micro-SegBot must be capable of traveling forward and making right and left turns.
- The total cost of the project must remain below $600.00.
- The form factor of the Micro-SegBot must resemble that of a full size Segway.
- Must successfully navigate a figure 8 course on carpet and tile surfaces.
- Must be capable of ascending a six-degree ramp.
- Must be remotely controlled via Bluetooth by an Android phone through the Arxterra interface.
Major Project Features:
The Micro-SegBot features a compact design with dimensions of 6x3x6, which make it ideal for a portable kid’s toy that can easily be transported in a backpack or small duffle bag.
The Micro-SegBot is equipped with an electronics case that houses the printed circuit board (PCB) and the battery. The addition of the electronics case eliminates unsightly wires and provides a neat and stylish design.
The Micro-SegBot can be remotely controlled via the Arxterra remote control panel in the Arxterra mobile application, which can be downloaded on any Android phone or tablet.
Completely 3D Printed Body:
The base of the Micro-SegBot is completely 3D printed with PLA plastic. PLA plastic is a very durable and affordable material. The Micro-SegBot can be customized to any color and printed from any 3D printer that is capable of printing PLA plastic by using the SolidWorks model in this document.
System Block Diagram:
The system block diagram begins with the 7.4 V battery that is powering the device. The battery is directly connected to the Arduino Nano and the L298P motor driver. The 3.3 V output of the Arduino Nano is used to power the HC-06 Bluetooth module and the MPU-6050. A detailed description of the system block diagram can be found here.
The interface definitions were created to map out the connections that need to be made between the various devices on the PCB of the Micro-SegBot. The pins for the Atmega328, Arduino Nano, MPU-6050, and HC-06 Bluetooth module are listed in the interface definitions. The pins that are in the same row are connected to each other. Click HERE or more details on the interface definitions.
The L298P motor driver consumes the majority of the power that is supplied to the Micro-SegBot to drive the brushed DC motors. As specified in the system block diagram, the L298P motor driver and the Arduino Nano are powered by the 11.1 V from the battery, while the HC-06 Bluetooth module and the MPU-6050 are powered by the Arduino Nano. The currents listed in the chart below are the maximum currents for each device. However, the operating currents will be less than the current listed, especially for the L298P and Arduino Nano. Therefore, these two currents have a significant tolerance while the tolerances for the other two devices are much less. More information on the power consumption of the Micro-SegBot can be found here.
The Micro-SegBot was designed to be as light as possible to make it easier for transportation without sacrificing performance. This feat was successfully achieved. The total mass of the Micro-SegBot is only 0.368 kg, or 0.81 lbs. More details on the mass of the Micro-SegBot can be found here.
The estimated total cost to recreate this project is approximately $335.00. However, we paid over $100.00 less than the cost estimate because we were able to use motors, motor mounts, and wheels from toys that belonged to different members in the group. The battery, motors, and the PCB fabrication (which we contracted out to OSH Park) will likely be the most significant costs for this project. More details on the cost of the Micro-SegBot can be found here.
A schedule was developed to provide a timeline to ensure that the Micro-SegBot will be complete by May 8, 2015. The schedule includes an overview of the major activities that are required to complete the project and provides a timeline for each activity. There are three milestones, which are critical items that need to be completed by the date provided. The three items are the preliminary design, completion of the final design, and the demonstration of the project. The dates by which the milestones must be complete are 3/13/15, 5/4/15, and 5/15/15 respectively. The duration of the tasks in each section may fluctuate, but a delay in one task will result in the acceleration of another to ensure that the milestones are on schedule. The schedule is displayed in the images below.
- Manufacturing Material:
- A trade off study was conducted to determine the material that would be used to construct the body of the Micro-SegBot. The materials that we examined were PLA, Aluminum, Steel and ABS. The Trade-off study showed that for PLA was the most ideal in terms of cost and availability because of our readily available 3D printers.
- A trade off study was conducted to determine the current output that would be most ideal for our battery and the C-Rating that we need. The trade off study examined different types of batteries such as Lithium Ion, Nickel metal hydride, and lithium iron phosphate batteries and compiled a list of advantages and disadvantages for each type. More details about the results of the trade off study can be found here.
- A trade off study was conducted to determine the type of motors that should be used for the Micro-SegBot. Due to the small scale of our robot, we only considered mini and micro-sized motors. The different types of motors that we examined were DC motors, Stepper motors, and Servos. We ultimately determined that the DC motors were the ideal choice for our robot because it offered the best combination of RPM and torque. More information on the motor trade off study can be found here.
A prototype made out of wood was designed and built in order to begin testing the software that would eventually be used on the Micro-SegBot. It was composed of toy motors and wheels with tread that were designed to run on multiple surfaces. The goal was to make the rapid prototype resemble the design of the Micro-SegBot as much as possible while remaining on schedule for the project. More details on the rapid prototyping for the project can be found here.
The components of the Micro-SegBot were all tested individually to ensure that they were functioning properly prior to being assembled. The tests for the MPU-6050, HC-06 Bluetooth module, L298P motor driver, and the Arduino Nano can all be found in the appropriate links below. MPU-6050 Testing Bluetooth Module Testing L298P Motor Driver Testing Arduino Nano Testing Tests were also conducted to observe the Micro-SegBot operating remotely via Arxterra. The video can be found here.