Specifications
  • Ublox ZED-F9P GPS Receiver
    • Ultracap backup power for fast (hot-start) restarts
    • EMI shield over receiver for improved EMI immunity
  • IST8310 Magnetometer
  • Safety-switch and safety LED
  • RGB LEDs for status indication
    • NCP5623CMUTBG I2C Driver
  • BMP388 Baro on I2C bus
  • External, active antenna (Maxtena M7HCT)
    • SMA connector
  • STM32 MCU for future CAN-based communication
    • FW updates through USB connector
  • Connectivity:
    • USB-C
      • 2-way USB Switch to MCU and F9P
    • SMA for active antenna (20mA max)
    • 4-pin CAN Bus (dronecode compliant)
    • 8-pin UART/I2C
  • Power:
    • Input from either (diode OR'd):
      • USB (5V)
      • CAN (4.7 to 25.2V)
      • UART (4.7 to 25.2V)
    • Power Consumption <1W

RTK Performance over range

The performance of RTK over long distances is typically limited by:
  • Telemetry link: You must have a telemetry link between the aircraft and ground station,
  • RTK degradation over distance: As the aircraft moves away from the base station, the RTK accuracy will degrade. The F9P RTK GPS receiver spec is 0.01m CEP (Circular Error Probability) + 1ppm for both vertical and horizontal.
    • For example, at 10km distance from base station, the typical accuracy would be 0.01m + (1km * 1/1,000,000) = 0.02m CEP

Mechanical Dimensions

Prerequisites

For use on Alta, the following is necessary:
  • Alta X
  • Two RTK Modules (Rover and Base Station)
  • Alta SW 1.3 or above
  • Datalink (FRX Pro recommended)
  • Computer (Mac or Windows) running Alta QGC 1.3 or above
  • Sturdy mount for base stations GPS. Tripod with 1/4-20 mount is recommended
  • USB C cable

I2C Address Table

Description
PN
I2C Address (7-bit)
RGB LED Driver
NCP5623C
011 1001 ($39)
Barometer
BMP388
111 0111 ($77)
Magnetometer
IST8310
000 1110 ($0E)

Connector Pinout

CAN Ports - GH-4 Pin

Peripheral CANbus for future expansion.
Pin
Signal
Voltage (V)
1
VCC
+5V to 25.2V
2
CAN_H
+5V
3
CAN_L
+5V
4
GND
GND

UART/I2C Ports - GH-8 Pin

Peripheral CANbus for future expansion.
Pin
Signal
Signal Notes
1
VCC
+5V to 25.2V
2
SERIAL: FC to GPS
3.3V TTL
3
SERIAL: GPS to FC
3.3V TTL
4
I2C-SCL
5
I2C-SDA
6
SAFETY SWITCH
3.3V = PRESSED
0V = NOT PRESSED
4.7k pull-down
7
SAFETY LED
3.3V, pull low to turn on LED. 20mA sink
8
GND
GND

GPS Antenna Compatibility

The following antennas have been tested with the Freefly RTK GPS module:
  • Maxtena M7HCT
  • UBlox ANN-MB multi-band antenna
The Freefly RTK modules are shipped with Maxtena M7HCT multiband antennas. However, the GPS is compatible with other SMA, L1/L2 multiband antennas.

Sensor Rotation

The IST8310 defines its coordinate system using left-hand rule, which is corrected in PX4 to be right-hand. Orientation is shown below in both native and PX4-corrected coordinates.

Alta X Orientation

When installed on Alta X, the PX4 orientation is with respect to the front-left vertical mounting surface. In other words, when installed on the front-left (where the standard GPS is installed), the "external mag" orientation should be set to Yaw 0° (ie, No rotation). When installed on the diagonal side (rear-right), the orientation should be set to Yaw 180°.