RoboteQ AX500 manual Selecting the Potentiometer Value, = U/R = 5V / 1000 Ohms = 0.005A = 5mA

Analog Control and Operation

	+5V	14
			Internal Resistors
	Analog		and Converter
		10	47kOhm
	Input 1
	2	11		A/D
	3	12
			10kOhm
10kOhm	or 4	8
			47kOhm
		13
	Ground

FIGURE 63. Potentiometer connection wiring diagram

The controller includes two 47K ohm resistors pulling the input to a mid-voltage point of 2.5V. When configured in the Analog Input mode, this will cause the motors to be at the Off state if the controller is powered with nothing connected to its analog inputs.

Important Notice

The controller will not activate after power up or reset until the analog inputs are at 2.5V

Selecting the Potentiometer Value

The potentiometer can be of almost any value. Undesirable effects occur, however, if the value is too low or too high.

If the value is low, an unnecessarily high and potentially damaging current will flow through the potentiometer. The amount of current is computed as the voltage divided by the poten- tiometer’s resistance at its two extremes. For a 1K potentiometer, the current is:

I = U/R = 5V / 1000 Ohms = 0.005A = 5mA

For all practical purposes, a 1K potentiometer is a good minimal value.

If the value of the potentiometer is high, then the two 47K resistors built into the controller will distort the reading. The effect is minimal on a 10K potentiometer but is significant on a 100K or higher potentiometer. Figure 64 shows how the output voltage varies at the vari- ous potentiometer positions for three typical potentiometer values. Note that the effect is an exponentiation that will cause the motors to start moving slowly and accelerate faster as the potentiometer reaches either end.

This curve is actually preferable for most applications. It can be corrected or amplified by changing the controller’s exponentiation parameters (see “Command Control Curves” on page 42.

96 AX500 Motor Controller User’s Manual Version 1.9b. June 1, 2007