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Slow walker - explorer v.1.20

Its name comes from its maximum speed. It is my first remote controlled robot. Since I was kid I liked that kind of toys, but I grew up in 80's, 90's when remote controlled cars and tanks were not easily available for all kids. Then I become a teenager and it wasn't proper to play with such toys. Fortunately, when you are an electronic engineer you can build it by your own.


In this model I put a pressure on the biggest simplification of the design. That cause, that it can only drive forward, backward, turn left, turn right and turn in a place. It was impossible to realize additional features like e.g. turn on and off some lights. Other assumption was to use old radio modules that didn't want to work with microcontrollers. That is why it designed with only simple digital devices (gates). The most sophisticated devices are coder and decoder in transmitter and receiver. They are perfect to use with those radio modules.


Transmitter

Schematic:





It can be divided on three parts:

  • keyboard
  • coder
  • radio module


Keyboard is a simple four microswitch buttons:

  • PL – forward left
  • PP – forward right
  • TL – backward left
  • TP – backward right


When pressed it short circuit coders input to the VCC what gives logic one. Capacitors 100nF connected parallel to switches, eliminates bounce side effect. Resistor connected between switch and ground defines logic zero on input of encoder when button is not pressed.


Combination of pressed buttons and states of lines A1-A5 are constantly sent with frequency defined by elements R5, R6, C5. Data is sent in series on output Q.




Receiver

Schematic:





It can be divided on three parts:

  • radio module
  • decoder
  • simple logic


Data from radio module is delivered to decoder input Din. Incoming data is shifted according to oscillator frequency into its internal shift-register. Of course, frequency in transmitter and receiver must be exactly the same. When whole data arrive, then address bits are compared. When they are the same, then data lines are copied to D6-D9 lines and on line VT appear logic one.


Logic gates protects motor control device before combination of two logic ones on theirs inputs (this can cause damage of them). This combination can be interpreted as turn motor left and right in the same time. Of course this is impossible, but will turn on all transistors connected in circuit of H-bridge. This is bad.
NAND gates acts as supervisors on data lines. As soon as forbidden combination appear, their output will become a logic zero and this will disable further data flow. In any other cases gates U3A, U3B, U4B, U4C transmits data to motor controllers. When data is invalid and VT remains zero, data is also not transmitted. This will cause engines to stop.


Series of capacitors on the top of schematic are dedicated for logic semiconductors and assure energy for them during switching process.


Model construction

As a base I used plastic tank from shop with cheap toys. It wasn't easy to find toy with moving , rubber tracks. When I bought it and disassembled, it turned about that it has only one motor common for both sides. It was enough for me, so I replaced it with two, very old gear box. Gear made from a few tooth wheels is incredibly strong. Unfortunately original engines has died, so I replaced them with motors from CD-ROM. Fortunately, they are strong enough.


All parts are made from plexiglass Details can be seen on pictures. As a power supply, I used battery from very old and big Nokia mobile phone. It gives 6,8V voltage what is enough for this electronic. However I think about changing them into small accumulators. They are heavy enough to make this robot more stable.





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