Both motors are rotating forward:The kart will move forward.
Both motors are rotating backward:The kart will move backward.If motor L is moving backward and motor R is moving forward:The
kart will make a left turn.
If motor L is moving forward and motor R is moving backward:The
kart will make a right turn.In order to change the direction of the motors, you need to change the direc-
tion of the current flowing through the motor windings. A circuit called an H-
bridgeflips the direction of the current through the motors. In the receiver
schematic (refer to Figure 11-3), IC3 contains two H-bridges. (You can’t see
the H-bridges in the schematic, but trust us: They’re in there. You’ll see
where they go when you get to the steps for assembling the go-kart.)To control the motors, the H-bridge needs the following inputs, as shown in
Figure 11-3:Pin 16:+V to power the IC.Pin 8:A separate +V to power the DC motors.
This is why you need to use a second battery pack; it helps isolate the
ICs from electrical noise generated by the DC motors that can cause the
circuit to stop functioning intermittently. Read about this in the upcom-
ing parts list section for this project.Pins 1 and 9:The signal, supplied from Pin 7 of the decoder (IC1), goes
to Pins 1 and 9 of the H-bridge in IC3. If Pin 7 (IC1) is at +V, both DC
motors turn on. If Pin 7 of IC1 is at ground, both DC motors turn off.
Pins 2 and 7:Pins 2 and 7 of the H-bridge determine in what direction
motor L rotates. To rotate motor L, the H-bridge requires +V at Pin 2 and
ground at Pin 7 in order to go in one direction, or the opposite to go in
the other direction. In order to establish the +V and ground connections
for motor L, you connect Pin 6 of the decoder to Pin 2 of the H-bridge
and also connect Pin 6 to IC3. IC2 inverts the signal so that +V becomes
ground or ground becomes +V. You then connect the inverted signal to
Pin 7 of the H-bridge; this gives you both the +V and ground you need to
control the direction of motor L.Pins 10 and 15:These control the direction of motor R in the same way
that Pins 2 and 7 control motor L. To rotate motor R, the H-bridge requires
+V at Pin 10 and ground at Pin 15, or the opposite to go the other way.
Connect Pin 5 of IC1 to Pin 10 of the H-bridge and also connect Pin 5 of IC1
to IC2. IC2 then inverts the signal so that +V becomes ground or ground
becomes +V. That signal now goes to Pin 15 of the H-bridge.244 Part III: Let There Be Light