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28 Bu il d Y o ur O w n Q u a d c o p t e r

Trial and Error Method
Do not be deterred by this method’s name because there is a definitive approach that is
followed in this method. The steps are:

1. Set the K and K block gains to zero.
d
i
2. Increase the K block gain until the system becomes unstable, as determined by
p
observing system oscillation.
3. Increase the K block gain to stop the oscillation induced in step 2.
i
4. Increase the K block gain to improve the system time response to an acceptable
d
value.
By following the above steps, a reasonable set of block gains should be able to be set.
These values should be tweaked to reach acceptable performances in actual operation. For
instance, it may be observed that the K block gain is set too high because the system is too
d
reactive to noise.
Ziegler-Nichols Method
This tuning method is similar to the Trial and Error method in that the first two steps are
identical.

1. Set the K and K block gains to zero.
d
i
2. Increase the K block gain until the system becomes unstable as determined by
p
observing system oscillation.
3. Note the K block gain at which oscillation starts. This will now be called critical gain
p
or K . Also note the oscillation period. This will be called P. c
c
4. Adjust all block gains per Table 2.4.
As you can clearly see from Table 2.4, control systems do not always have to contain all
three of the PID blocks. Sometimes only the P block is needed, as we saw in our thermostat
example.
Real-world PID control systems often contain an auto tuning capability in which the
block gains and response times are both detected and set to optimize system operation.
LabVIEW (LV) discussed in the next section contains a PID module that has an auto-tune
capability as well as a manual tuning capability.

LabVIEW PID Simulation
I will be using the LV 2012 student edition for my simulation platform. It is the latest student
version available at the time of this writing. Be aware that commercial, non-educational
versions of LV cost about $1200. It is not a cheap program. However, a student version is

System Type Block Gain Integral Time Derivative Time
P 0.5 K c n/a n/a
PI 0.45 K P /1.2 n/a
c c
PID 0.60 K 0.5 P P /8
c c c
Table 2.4 Ziegler-Nichols Block Gains