Monday, April 4, 2016

Vibration Robot - Iteration 1 - Chaos

I was always fascinated with the Kilobots developed by Harvard and their amazing capabilities when operated in massive swarms of self-organizing robots. I therefore decided to build my own prototype using modules easily available locally. This was not going to be a Kilobot clone but something different based on the same principle. So recently i managed to wrangle up a few breakout boards to make a vibration robot as shown below. The modules used are as follows

Main board - Arduino Lilypad (ATMega328) from Sparkfun. The reason i chose this was due to the large number of I/O and because the PCB is circular. 50 mm diameter, 17 mm more than that of the Kilobot, which is around 33mm.

Communications - Adafruit Bluetooh EZ Serial link. This board snugly fit on top of the Lilypads serial connector. The main board could now be programmed wirelessly over the BT Serial link.

Motor Driver - A Spakrfun TB6612FNG 1A Dual H-Bridge based motor driver for the vibration motors.

Power Source - A 400mAh Li-Ion battery similar to this. (External charger)

The orange colored housing for the motors is designed in my favorite CAD tool and 3D printed on me printer. The position of the holes  for mounting the screws was calculated from the board files supplied by Sparkfun. The motors were glued in their sockets. The entire assembly was held together using M3 screws through the Lilypad holes.

The block diagram of the system is shown below. The ATMega328 operates off the 3.7 V Li-Ion battery, which also powers the BT serial. The motor driver is powered from the 3.3V regulator on the BT serial board and draws maximum 2.2 mA of supply current, which is within spec of the regulator on the BT serial board as it can source maximum 100 mA. The driving voltage for the motors comes directly from the battery. Other control and PWM signals are connected to the arduino PWM and digital I/O pins.

And the end result after all that was - Chaos - as you can see in the video below. The robot is controlled via a windows phone application that i wrote which connected over BT serial to the bot. A single 4-Byte (integer) command was sent to the bot comprising of :

Byte 0 - PWM value for motor A (0 - 255)
Byte 1 - PWM value for motor B (0 - 255)
Byte 2 - Control signals for motors: Bit 1 - Motor A CCW, Bit 2 - Motor B CCW, Bit 3 - STANDBY/STOP
Byte 3 - Reserved.

The objective was to send varying PWM values to the motors to observe a linear motion along a straight line and characterize the 2DOF aspects of the system. Not shown in the video is my phone through which i am controlling the robot by varying the PWM to the motors.

Further iterations will include several improvements over shortcomings in the current design - thinner wires, smaller or custom boards etc. Thanks for watching...

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