RoboteQ AX2550/2850 Connecting Tachometer to Analog Inputs, Potentiometer wiring in Position mode

Connecting Sensors and Actuators to Input/Outputs

Connecting the potentiometer to the controller is as simple as shown in the diagram on Figure 29.

+5V 14

Input Pos 1 11 or Pos 2 10

10kOhm

Ground 5

FIGURE 29. Potentiometer wiring in Position mode

AX2500 Internal Resistors and Converter

47kOhm

A/D 10kOhm

47kOhm

The potentiometer must be attached to the motor frame so that its body does not move in relationship with the motor. The potentiometer axle must be firmly connected to the gear box output shaft. The gearbox must be as tight as possible so that rotation of the motor translates into direct changes to the potentiometers, without slack, at the gearbox’s out- put.

See “Closed Loop Position Mode” on page 115 for complete details on Position Mode wir- ing and operation.

Important Warning

Beware that the wrong + and - polarity on the potentiometer will cause the motor to turn in the wrong direction and not stop. The best method to figure out the right potentiometer is try one way and change the polarity if incorrect. Note that while you are doing these tests, the potentiometer must be loosely attached to the motor’s axle so that it will not be forced and broken by the motor’s uncontrolled rotation in case it was wired wrong.

Connecting Tachometer to Analog Inputs

When operating in closed loop speed mode, tachometers must be connected to the con- troller to report the measured motor speed. The tachometer can be a good quality brushed DC motor used as a generator. The tachometer shaft must be directly tied to that of the motor with the least possible slack.

Since the controller only accepts a 0 to 5V positive voltage as its input, the circuit shown in Figure 30 must be used between the controller and the tachometer: a 10kOhm potentiom- eter is used to scale the tachometer output voltage to -2.5V (max reverse speed) and +2.5V (max forward speed). The two 1kOhm resistors form a voltage divider that sets the idle voltage at mid-point (2.5V), which is interpreted as the zero position by the controller. The voltage divider resistors should be of 1% tolerance or better. To precisely adjust the 2.5V midpoint value it is recommended to add a 100 ohm trimmer on the voltage divider.

With this circuitry, the controller will see 2.5V at its input when the tachometer is stopped, 0V when running in full reverse, and +5V in full forward.

58 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005