RoboteQ AX2850 - Manual (Page 102)

Closed Loop Speed Mode
102 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007
PID tuning in Speed Mode
As discussed above, three parameters - Proportional Gain, Integral Gain, and Differential
Gain - can be adjusted to tune the Closed Loop Speed control algorithm. The ultimate goal
in a well tuned PID is a motor that reaches the desired speed quickly without overshoot or
oscillation.
Because many mechanical parameters such as motor power, gear ratio, load and inertia are
difficult to model, tuning the PID is essentially a manual process that takes experimenta-
tion.
The Roborun PC utility makes this experimentation easy by providing one screen for chang-
ing the Proportional, Integral and Differential gains and another screen for running and
monitoring the motors. First, run the motor with the preset values. Then experiment with
different values until a satisfactory behavior is found.
In Speed Mode, the Integral component of the PID is the most important and must be set
first. The Proportional and Differential component will help improve the response time and
loop stability.
In the case where the load moved by the motor is not fixed, tune the PID with the mini-
mum expected load and tune it again with the maximum expected load. Then try to find
values that will work in both conditions. If the disparity between minimal and maximal pos-
sible loads is large, it may not be possible to find satisfactory tuning values.
Note that the AX2550 uses one set of Proportional Integral and Differential Gains for both
motors and therefore assumes that similar motors, mechanical assemblies and loads are
present at each channel.