Week 4: February 6 to February 12, 2012

Development of Chassis and Wheel 

I already have a chassis complete with a pair of servo wheel. Unfortunately, this chassis is too big to navigate through the maze and the servo wheel did not fit with the shaft of the stepper motor. So, I have to do some modification on the chassis and the wheel. The original chassis is 160mm x 130mm. This chassis has to be cut into 90mm x 90mm to enable the micromouse to navigate through the maze without hitting the maze wall. Meanwhile for the wheel, I have to enlarge the opening to 5mm to fit the stepper motor shaft into the wheel. To do this I use a mini grinder and a calliper to grind and measure the opening.

Grinding process

The difference

Fitting the wheel into the motor shaft

Completed wheels

Mini grinder

The calliper

Week 3: January 30 to February 5, 2012

Hardware Development & Testing

I received part of the components from farnell on 30^th January while the balance arrived on 2^nd February 2012. 

1st delivery

2nd delivery

Therefore, on 31^st January I started to construct and test the motor driver with the stepper motor by using digital trainer as the input. However it didn’t work out. The stepper motor did not move at all. Then I tried to test the stepper motor directly with digital trainer. After a few attempts the stepper motor works.  This is the sequence that I used to test the stepper motor. For every 2 steps, the motor will move once. This is called two phase full driving. During this testing, the motor moved at step 1 and 3.

Step	White/Black	Blue	Yellow	Orange	Red
1	+3V	1	1	0	0
2	+3V	0	1	1	0
3	+3V	0	0	1	1
4	+3V	1	0	0	1

Testing process

The motor driver circuit

The motor

Since the motor driver did not working, I measured the voltage at the input and output of the motor driver and find out that the output voltage is different from the input. 

Input		Output
A	4.98V	A (Blue)	3.0V
A/	4.98V	A/ (Yellow)	3.0V
B	4.98V	B (Orange)	3.0V
B/	4.98V	B/ (Red)	3.0V

Basically, the input and output voltage should have the same value as this driver main function is to increase the current to drive the stepper motor. However, in this case the output voltage had the same value with the voltage supplied to the centre tap of the stepper motor (white and black wire). Why? I’m not sure. So I did searching for another schematic using SLA 7024 to compare with schematic that I used and I found one with exactly the same connection but with slightly different value.  Perhaps the motor did not work with digital trainer logic (I used 8 bits data switches as the input). As I went through the datasheet, it says “HIGH CURRENT PWM”,”DUAL PWM CURRENT CONTROL”. Perhaps this driver has to be triggered from a microcontroller. So, I decided to test the driver directly with microprocessor. Therefore I have to develop some code, probably the motor sequence to test the functionality of the driver.

Week 2: January 23 to January 29, 2012

Hardware Development & Testing

The components have been ordered from element 14 (formerly known as Farnell Components (M) Sdn. Bhd.) on 27^th January 2012. The components are:

No.	Components	Quantity	Application
1.	PIC16F877A	2	Controller
2.	Network resistor 2.2kΩ	2	Motor driver
3.	Variable resistor / Trimmer 100Ω	2	Motor driver
4.	Resistor 510Ω (1/8 watt)	10 (min quantity)	Motor driver
5.	Resistor 1Ω (1/2 watt)	50 (min quantity)	Motor driver
6.	SLA 7024M Unipolar Stepper Motor Driver	2	Motor driver
7.	Crystal 20Mhz	2	Controller
8.	Inductor 330µH	2	Voltage regulator
9.	Distance Measuring Sensor	3	IR sensor
10.	Network resistor 47kΩ	2	Motor driver

The total cost for this order is RM 287.55. I have ordered extra units for each component for testing purposes except for the motor drivers because these are the last two pieces available at element 14. Therefore, I have to come out with some back up for motor driver in case of faulty or damage. There are a few types of drivers that might be suitable to be used with Sanyo Denki unipolar stepper motor that I used. One of them is by using the SLA7062M Unipolar Stepper Motor Translator/ Drivers. This device is a complete microstepping motor driver with built in translator for easy operation with minimal control lines. This device will let you drive a unipolar stepper motor at voltages up to 46 Volts and 3A per phase. It employs an internal PWM control of motor current which is can be set by a pair of external resistors. It is designed to operate unipolar stepper motors in half, quarter, eight and sixteenth step modes. This mode can be selected by sending bits to the input M1 and M2 as below:

Input M1	Input M2	Step Mode
High	High	Half Step
High	Low	Quarter Step
Low	High	Eight Step
Low	Low	Sixteenth Step

SLA7062M

Another option is by using L297 stepper motor controller with quad darlington array ULN2075B. I am also planning to do some testing using ULN2003 to find out whether this device is capable to drive my stepper motors which has current rating of 1A/phase. 

In the meantime, I did some testing on IR01 sensor which I bought from Cytron Technologies. This sensor is an infrared sensor and is used for detecting obstacle. If an obstacle is detected, it will output logic high and the led will on. It also has a trimmer to allow adjustment of the distance the sensor capable to operate. In my testing I found out that this sensor is capable to detect as close as 8 mm (distance between sensor and the object) and as far as 10 cm. Since it has a digital output, it is cannot be used to measure the distance between the robot and the wall, therefore this sensor may be unsuitable for this project.

IR01 sensor

Reference:
http://www.micromouseonline.com/2007/07/20/motor-driver-chip/#ixzz1mI6Wj6l2

Week 1: January 16 to January 22, 2012

Hardware Development & Testing

Motor driver schematic

This is the list of components that I need for my stepper motor drivers:

No.	Components	Quantity
1.	Resistor 510Ω (1/8 watt)	1
2.	Variable resistor / Trimmer 100Ω	1
3.	Network resistor 2.2kΩ	1
4.	Capacitor 2200pF	4
5.	Resistor 1Ω (1/2 watt)	4
6.	SLA 7024M Unipolar Stepper Motor Driver	2
7.	Capacitor 470pF	4
8.	Network resistor 47kΩ	1
9.	Capacitor 220µF 25V	2

On 21^st January 2012, I went to Jalan Pasar to search for some components. However, most of the shops were closed due to Chinese New Year Celebration but I manage to get a few components as below. Meanwhile, for the rest of the components, I decided to order through Farnell. It is more convenient to order through Farnell because it has wide range of component selection and you can just ‘click’ to buy the component that you need from the comfort of your home.