Chapter 8: Robot Control with Distance Detection · Page 279
= 2 – 4
Output adjust = error
×
K
p
= –2
×
35
= – 70
Right servo output = Output adjust + Center pulse width
= – 70 + 750
= 680
By making some substitutions, the three equations above can be reduced to this one,
which will give you the same result.
Right servo output = (Right distance set point – Measured right distance)
×
Kp
+ Center pulse width
By substituting the values from the example, we can see that the equation still works:
= ((2 – 4)
×
35) + 750
= 680
The left servo and IR pair have a similar algorithm shown in Figure 8-5. The difference
is that Kp is –35 instead of +35. Assuming the same measured value at the right IR pair,
the output adjust results is a pulse width of 820. Here is the equation and calculations for
this block diagram:
Left servo output = (Left distance set point – Measured left distance)
×
Kp
+ Center pulse width
= ((2 – 4)
×
–35) + 750
= 820
The result of this control loop is a pulse width that makes the left servo turn about ¾ of
full speed counterclockwise. This is also a forward pulse for the left wheel. The idea of
feedback is that the system’s output is re-sampled, by the shadow Boe-Bot taking another
distance measurement. Then the control loop repeats itself again and again and
again…roughly 40 times per second.
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