RoboteQ AX1500, AX2550 user manual Reception Watchdog

Reception Watchdog

ond indicates the minimum joystick position and 2.0 milliseconds indicates the maximum joystick position. When the joystick is in the center position, the pulse should be 1.5ms.

Note that the real pulse-length to joystick-position numbers that are generated by your R/C radio may be different than the ideal 1.0ms to 2.0ms discussed above. To make sure that the controller captures the full joystick movement, the AX1500 defaults to the timing val- ues shown in Figure 70. These vales can be changed and stored as new defaults.

joystick position: min center max

	1.05ms
		0.45ms
R/C pulse timing:
			0.9ms

FIGURE 70. Joystick position vs. pulse duration default values

The AX1500 has a very accurate pulse capture input and is capable of detecting changes in joystick position (and therefore pulse width) as small as 0.4%. This resolution is superior to the one usually found in most low cost R/C transmitters. The AX1500 will therefore be able to take advantage of the better precision and better control available from a higher quality R/C radio, although it will work fine with lesser expensive radios as well.

Internally, the measured pulse width is compared to the reference minimum, center and maximum pulse width values. From this is generated a number ranging from -127 (when the joystick is in the min. position), to 0 (when the joystick is in the center position) to +127 (when the joystick is in the max position). This number is then used to set the motors’ desired speed or position that the controller will then attempt to reach.

For best results, reliability and safety, the controller will also perform a series of correc- tions, adjustments and checks to the R/C commands, as described in the following sec- tions.

Reception Watchdog

Immediately after it is powered on, if in the R/C mode, the controller is ready to receive pulses from the R/C radio and move the motors accordingly.

If no pulses are present, the motors are disabled.After powering on the R/C radio receiver and transmitter, and if the wiring is correct, the controller will start receiving pulses. For a preset amount of time, the controller will monitor the pulse train to make sure that they are regular and therefore genuine R/C radio command pulses. After that, the motors are enabled.

This power-on Watchdog feature prevents the controller from becoming active from para- site pulses and from moving the motors erratically as a result.

AX1500 Motor Controller User’s Manual 107