EVK-M8L User Guide
UBX-20028627 - R01
Setting up
Page 15 of 33
C1-Public
4.3
Recommended configuration
Only NMEA messages have been activated by default. During calibration and test drives we
recommend enabling certain UBX messages (see section 4.4 and section 5).
For optimum navigation performance, the recommended navigation rate configuration is as follows:
The default DR/GNSS-fused navigation solution update rate is 1 Hz. You can set the navigation
update rate with the message UBX-CFG-RATE. (In this mode, navigation rates up to 30 Hz are also
available from the UBX-HNR-PVT message.)
Also, you need to configure the installation-specific ADR configuration parameters discussed in
section 4.3.2.
4.3.1
Serial port default configuration
Parameter
Description
Remark
UART port 1, input
UBX and NMEA protocol at 9600 Bd
UART port 1, output
UBX and NMEA protocol at 9600 Bd
Only NMEA messages are activated
USB, input
UBX and NMEA protocol
USB, output
UBX and NMEA protocol
Only NMEA messages are activated
Table 6: Default configuration
4.3.2
ADR configuration
The following sections describe how to configure the parameters specific to the installation.
4.3.2.1
WHEELTICK and FWD configuration
By default, the wheel-tick count is based on the rising edge of the wheel-tick pulse signal. To improve
performance with lower rate, mechanically derived wheel tick signals, the receiver may be configured
to use both the rising and falling edges of the wheel tick signal on the condition that the wheel-tick
pulses have approximately 1:1 mark:space ratio regardless of speed.
The wheel tick direction pin polarity is now automatically initialized. The car needs to drive with a
minimum speed of 30 km/h for proper initialization.
You can also manually establish the polarity of your FWD signal (e.g. with a multimeter when the gear
is set forward). Depending on the setup you may have to drive slowly as well. Set the Direction Pin
Polarity (FWD) correctly using message UBX-CFG-ESFWT or in u-center (see Figure 5 below). Usually
there is no need to change other parameter values. For more information, refer to the u-blox 8 / u-
blox M8 Receiver Description including Protocol Specification [5]. Click the Send button in u-center
if you changed the default values.
WHEELTICK maximum frequency is 20 kHz. Minimum recommended pulse width is 10 us. The wheel
tick pulse must have a clean slope transition, the input is Schmidt-triggered
.
This signal input is
single edge triggered. Pulse interval (WT resolution) must be less than 40 cm per tick over distance
traveled. The wheel tick pulse output shall change linearly with the change in speed (navigation filter
estimates only the linear scale factor).
If the vehicle is standing still, there should be no wheel tick pulses. This is particularly important at
system shut down and power up. If there is a dead-band (wheel tick pulse does not change or is not
output below a certain speed) performance will be affected
.
