RoboteQ AX2850 - Manual (Page 100)

Closed Loop Speed Mode
100 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007
7. Move the cursor of the desired motor to the right so that the motor starts rotating,
and verify that a positive speed is reported. Move the cursor to the left and verify
that a negative speed is reported.
8. If the tachometer or encoder polarity is the same as the applied command, the wir-
ing is correct.
9. If the tachometer polarity is opposite of the command polarity, then either reverse
the motor’s wiring, or reverse the tachometer wires. If an encoder is used, swap its
CHA and ChB outputs
10. If a tachometer is used, proceed to calibrate the Max Closed Loop speed.
11. Set the controller parameter to the desired Closed Loop Speed mode using the
Roborun utility.
Adjust Offset and Max Speed
For proper operation, the controller must see a 0 analog speed value (2.5V voltage on the
analog input).
To adjust the 0 value when the motors are stopped, use the Roborun utility to view the
analog input value while the tachometer is not turning. Move the 0 offset potentiometer
until a stable 0 is read. This should be right around the potentiometer’s middle position.
The tachometer must also be calibrated so that it reports a +127 or -127 analog speed
value (5V or 0V on the analog input, respectively) when the motors are running at the max-
imum desired speed in either direction. Since most tachometers will generate more than
+/- 2.5V, a 10kOhm potentiometer must be used to scale its output.
To set the potentiometer, use the Roborun utility to run the motors at the desired maxi-
mum speed while in Open Loop mode (no speed feedback). While the tachometer is spin-
ning, adjust the potentiometer until the analog speed value read is reaching 126.
Note: The maximum desired speed should be lower than the maximum speed that the
motors can spin at maximum power and no load. This will ensure that the controller will be
able to eventually reach the desired speed under most load conditions.
Important Warning:
It is critically important that the tachometer and its wiring be extremely robust. If the
tachometer reports an erroneous voltage or no voltage at all, the controller will con-
sider that the motor has not reached the desired speed value and will gradually
increase the applied power to the motor to 100% with no way of stopping it until
power is cut off or the Emergency Stop is activated.
Control Loop Description
The AX2550 performs the Closed Loop Speed mode using a full featured Proportional, Inte-
gral and Differential (PID) algorithm. This technique has a long history of usage in control
systems and works on performing adjustments to the Power Output based on the differ-