This is a very simple but accurate robot.
Step 1: Components and Tools Required -
1.bd 139 transistors-2
2. 1k and 330 ohm resistors- both 2 pieces
3. 4148 diode-1
4. 100k rheostat-1
5. indicator led-1
6. some wires
7. pcb board
8. soldering machine,soldering iron and flux
9. 100 rpm dc gear motors-2
10. 2 wheels for motors
11. plastic base
12. double sided tape for sticking the circuit
13. castor wheel
Step 2: Circuit Diagram-
You just need to follow the circuit diagram but still if you face some problem , comment , I will help you.
Step 3: Some Important Points-
1. The pinout of bd 139 that you are watching refers to the black side and not the silver side. you can also use npn transistors like 2n2222,2n3904.
2. The place where 5v is written in the diagram is positive while the earthing sign refers to negative.