mwt UBUG 4.1 tribute PCB


     This is my layout of the classic 2-motor BEAM walker.  The circuit is a Master-Slave Dual Bicore with an added inverting multiplexer for added reverse capabilities.  Figure 1 is the "master" suspended bicore that drives the circuit.  The outputs of the master are passed through the inverting multiplexer (Figure 2) and to the inputs of the "slave" bicore (Figure 3).  When the inverting multiplexer is activated by a short between the front solder pads, the signals to the slave bicore are inverted, causing the robot to reverse.  Figure 4 is an optional Miller SolarEngine that can be used to solarize the circuit.

ExpressPCB File:  ubug_w_se_V2.pcb

For more detailed information on this circuit, see  Wouter Brok's article on the Suspended Bicore.

Associated Links:
"Junkbots, Bugbots, and Bots on Wheels" Basic 2-Motor Walker Schematic - The basis for my design
Suspended Bicore - a wonderful article by Wouter Brok on suspended bicores and the master-slave configuration
The "Miller" solar engine - Documentation of the Miller SolarEngine
mwt UBUG 4.1 tribute page - Main page for mwt UBUG 4.1 tribute robot

Figure 1

     This figure contains the circuitry for the master bicore.  The timing is set by R1, C1 and C2.  C3 is the decoupling capacitor for the 74AC240.  The indicator LEDs and current limiting resistors, D1, D2, R2, R3 are optional.  M1 and M2 are the pads for the front motor of the walker.  The two large solder pads in the upper left of the PCB are used to mount the tactile sensor to trigger the multiplexer for reverse.  When the pads are shorted, reverse is activated.

Required Components:
     1 - 74AC240
     1 - xMW Timing Resistor [R1]
     2 - .1mF Timing Capacitors [C1, C2]
     1 - .22mF Decoupling Capacitor [C3]

Optional Components:
     2 - Indicator LEDs [D1, D2]
     2 - 470W Current Limiting LEDs [R1, R2]

Figure 2

     This figure is of the inverting multiplexer for reverse.  Only one half of the multiplexer is implemented in the layout (Components C5, R7, R9, and R10 are not used but have been wired for optional experimentation).  The reversing time is set by R4 and C4.  R11 is the current limiting resistor for the reverse indicator LED, D4 and C6 is another decoupling capacitor.

Required Components:
     1 - 74AC240
     1 - xW Timing Resistor [R4]
     1 - 6.8mF Reverse Timing Capacitor [C4]
     2 - 47kW Signal Bypass Resistors [R6, R8]
     1 - .22mF Decoupling Capacitor [C6]

Optional Components:
     1 - Indicator LED [D4]
     1 - 470W Current Limiting Resistor [R11]

R5, R7, R9, R10, C5, and D3 are not used!  They make up the other half of the multiplexer and are not required for this circuit.

Figure 3

     This figure is of the slave bicore.  R12 and R13 along with C8 and C9, determine the phase shift between the front and rear motors (R14 may be used in place of R12 and R13 to form a second suspended bicore that runs independently of the one in Figure 1).  R15 and R16 are the current limiting resistors for the optional indicator LEDs D5 and D6.  C7 is the third decoupling capacitor.

Required Components:
     1 - 74AC240
     2 - xkW Timing Resistors [R12, R13]
     2 - .1mF Timing Capacitors [C1, C2]   

Optional Components:
     2 - Indicator LEDs [D5, D6]
     2 - 470W Current Limiting LEDs [R15, R16]

Figure 4

     This figure is of the optional Miller SolarEngine to solarize the circuit.  A detailed description of its operation can be found here.  Also included in this figure are the connection for the solar cell and power capacitor required for solar operation.  If solar operation is required simply connect the outer ground traces to the main board along with the two power rails (Vdd and +).

Required Components:
     1 - 1381 Voltage Detector [1381]
     1 - NPN Transistor [T1]
     1 - Discharge Timing Capacitor [C10] (~1000mF)
     1 - Diode [D7]