Minibot
Published by: admin
Using 2 mini dc motors, 2 mini lithium cells, zigbee trasceiver, pic microcontroller …………..
The idea of this MiniBot comes to my mind after i read this article (http://www.instructables.com/id/Building-Small-Robots-Making-One-Cubic-Inch-Micro/) about an 1 inch cube micro sumo robot. to enter this micro sized robotic world, i start my mini robot with the size 1.5inch x 1.5inch x 2inch cube. maybe next time i will try smaller one called MicroBot, so for now, lets discuss about this MiniBot i am currently developing.
finding suitable component
A) motor
the motor must be very small in size, small current consumption (due to small size of battery), and powerful enough to drive the MiniBot. the first motor i found is a vibrator motor from my old nokia 3310 phone. its small, and i believe it is also small current consumption, but the problem is i dont think its powerful enough to drive MiniBot, because it doesnt have gear box (this mean the gear ratio is 1:1), and another reason is i only have 1, i need to find another for left and right wheel. at the end i decided to use Pololu 30:1 Micro Metal Gearmotor.
B) battery
as for the battery, of course the size need to be small and light, as it need to be fitted in the small size robot. “small and light”, the first thing that comes to my mind is lithium polymer battery. li-po is very popular for gadget like handphone, mp3 player, camera, and laptop. its popular due to its high capacity to size ratio, in the other words, its smaller compare to other types of battery with same capacity. so, i found two cell of li-po from some old mp3 player with build in battery. beside from mp3 player, you can get it from sparkfun, single cell li-po. You can always contact cytron sales to place special order on the battery for you. For li-po battery, its advised to charge it using li-po charger. overcharging li-po will cause this battery to explode. be ware of that! We don want you to burn your house down…
li-po from mp3 player
li-po from sparkfun
C) controller
for this minibot, the controller i use is dspic30F4012 from microchip. its actually up to you, any microcontroller will do, but still it need to be small, and also make sure that you have enough I/O for your motor and also sensors. for my case, currently i dont have any sensor, only 2 dc motors, 2 switches, 2 leds, 1 buzzer and a zigbee module. so, i use only 11 I/O; 6 for motors (3 for each motor including pwm control), 2 for switches, 2 for leds, 1 for buzzer and 2 for zigbee (uart). for dspic30F4012, there are 19 I/O (not including mclr and osc pins). i used 11, so i still have 8 I/O, for maybe i can add in sensors.
D) Etc
besides those listed hardware for A, B and C, you will still need donut board, switches, leds, buzzer, and motor driver. motor driver that i choose is L293D that can drive 2 dc motor, with pwm input. for other hardware, i think its quite easy to find. just bare in mind that you are building a 1.5inch x 1.5inch x 2inch cube robot. all components must be very small and light.
building process
In the process of building minibot, you have to always remember that you are building a very small size robot, and you have to squeeze all the components into the predefined size of your robot.
cut the donut board into the size of the minibot.
to make the robot as small as possible, the motor will be place in the “half standing” position, with one a bit to the front and another one a bit to the rear. to “stick” the motor to the donut board, i simply solder some part of the motor gear box to the donut board. you have to be very careful about the alignment of the motor on the donut board.
the 2 wheel is not side by side. one is a bit to the front, and another, a bit to the rear. this is what you have to pay to reduce the size of the robot.
wheel i use for this robot is something like a rubber wassher that normally come together with servo motor.
the size of the rubber wassher fit perfectly to the Pololu 30:1 Micro Metal Gearmotor.
after mounting the motor to the board, i solder 2 small multilayer capacitor at the bottom of the donut board that will play the roll as the castor of the robot.
completed with the hardwares, now the circuitary. lets start with the motor driver. i use L298D as the motor driver for Pololu 30:1 Micro Metal Gearmotor. L293D support up to 800mA current, and i think that is more than enought for the tiny motor. i solder L298D directly to the donut board as there is no extra space for the ic socket.
continue with the battery connector.
on/off switch.
voltage regulator and capacitor.
i use plastic pcb stand to support the upper circuitary. the reason of using plastic type is to reduce the weight of the robot. (sorry for the blur image)
the lower circuitary consist of voltage regulator, motor driver, on/off switch, battery connector, and leds. for the upper circutary, it will consist of the microcontroller, switches, and zigbee.
for switches at upper circuitary, i use small limit switch that i desolder from a broken cdrom.
now complete with the zigbee module.
Song! Damn song!
Nice Minibot!
When you want to continue the article…?
Madi, thanks for commenting on our blog….. Our engineer will continue to update the blog once there is time. But time does not seem to be with us. It always fly…..
ober: no worries…
very cool robot!!! can you post your code? how did you setup your base w/ the zigbee? great project. thanks.
Cool…
Not really automated though, without the sensors…
But it is so small, its hard to fit in more stuff…
i would like to know how much would a small lipo battery cost if i go to cytron and place special order for it ?
Nice blog here.
What is special order? how special?