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AX2550 Motor Controller User’s Manual 115
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 AX2550 defaults to the timing val-
ues shown in Figure 77. These vales can be changed and stored as new defaults.
For best control accuracy, the AX2550 can be calibrated to capture and use your radio’s
specific timing characteristics and store them into its internal Flash memory. This is done
using a simple calibration procedure described on page 119.
The AX2550 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 AX2550 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.
1.05ms
min center max joystick position:
R/C pulse timing:
0.45ms
0.9ms
FIGURE 77. Joystick position vs. pulse duration default values