Emlid Reach RS+ Tutorial

 Emlid Reach RS+ Tutorial

Introduction

Two Emlid Reach RS+ receivers were obtained for use on the Mongolian bi-lateral projects (SESMIM and MERIT) to establish ground control points (GCP) for drone aerial mapping. In 2016 the Reach RS+ receivers were the most cost effective GPS/GNSS RTK units for ground control and engineering surveys. One notable limitation is the receivers are single L1 band only so they were not accurate enough for legal surveys.

In addition these units were powered by LiFePO4 batteries which uses a BMS that puts the battery into a dormant state below a minimum voltage. In that state it cannot be charged with a standard 5V 1A USB charger that is provided for the unit by Emlid. The version we had did not shut off the battery before the minimum limit is reached if the receiver is not used or charged frequently.

Emlid support was available but not helpful to resolve the situation. After a lot of emails our option was to replace the batteries or figure a way to get the BMS to accept a charge. Replacing the batteries was expensive. The battery connector to the board was non-standard so we had to splice the wires in order to connect to a bench DC power supply to apply 3.65 Volts at 1.92 A (0.2 C). This worked and the batteries were chargeable by the USB connector again.



The use of LiFePO4 batteries by Emlid meant they should have provided a simple mechanism for the users to reactivate the USB charging due to BMS-induced shutdowns from voltage drops when the units are not used over a long time or over-discharge. 

Firmware Updates

Emlid updated their mobile app which required a firmware update to connect to the RS+ receivers. It took several attempts to succeed. Emlid support did provide feedback on the problem. They identified the problem being the USB cable. We were able to flash the firmware using a DJI drone cable.

The Emlid Reach RS+ primarily communicates through a built-in LoRa radio for base-to-rover setups, or via internet-based protocols (NTRIP) for network RTK. It is managed primarily through the Emlid Flow app (formerly ReachView) on iOS or Android via Bluetooth or Wi-Fi.

Power and Charging

The Reach RS+ has a built-in LiFePO4 battery providing 30 hours of operating time. You can power and charge the Reach RS/RS+ over the micro-USB cable using a power bank or USB wall adapter. 

To charge the receiver  5 W is required. For operating 7.5 W on average is required (10 W maximum). For the 3.65 V battery, standard recommended charging of a 9600 mAH battery the max is 1.92 A (0.2C). For discharge maximum recommended is 5 A.

Note: The voltage 3.65V is usually the maximum charging voltage for LiFePO4 cells, not the nominal voltage (which is 3.2V or 3.3V). The device or charger should be set to a "constant current/constant voltage" (CC/CV) mode. However Emlid has provided a USB port and circuit to use standard 5 V (2A) power to charge the receiver.

Key Communication Methods

  • LoRa Radio (Base-Rover setup): The RS+ includes a built-in LoRa radio, allowing it to communicate with another RS+ (or RS2/RS2+/RS3) unit for RTK corrections. This is suitable for distances up to 8 km, depending on terrain.
  • NTRIP (Network RTK): The rover can receive corrections from a virtual reference station (VRS) or local NTRIP caster over the internet. The receiver connects to the internet via the smartphone's connection (through the Emlid Flow app) or via a Wi-Fi hotspot.
  • Bluetooth/Wi-Fi: These are use to connect the receiver to the Emlid Flow app on a mobile device for configuration.
  • External Radio (RS-232/USB): The RS+ can communicate with external radio modems via its bottom connector.

Configuring Communication

  1. Connecting to App: Connect the smartphone/tablet to the Reach RS+ Wi-Fi network (default: reach-XX:XX) or via Bluetooth in the Emlid Flow app. Note if a pairing code passkey is requested use: 123456.
  2. Base Setup: Set the base to output RTCM3 messages over LoRa or a local NTRIP caster.
  3. Rover Setup: Set the rover's "Correction Input" to "LoRa" to match the base, or "NTRIP" to connect to a network.
  4. Pairing: Ensure that both units are named differently (e.g. "reach-base" and "reach-rover") to avoid conflicts.

SW Maps

The Reach RS+ can also be configured to work with SW Maps. The following are steps to connect the RS+ receiver to SW Maps. To integrate these two, you must configure the RS+ to stream its position data via Bluetooth in a format SW Maps can read.
  1. Configure Reach RS+ (via Emlid Flow app):
    1. Enable Bluetooth: in the Emlid Flow app go to Settings > Bluetooth and turn it on. Ensure it is Discoverable.
    2. Postion Streaming: Navigate to Position Streaming 1. Select Bluetooth as the output and set the format to NMEA.
    3. Correction Input: If you are using an NTRIP service for RTK corrections, configure it under Correction Input in the Emlid Flow app.
  2. Pair with Android Tablet/Phone:
    1. Open your Android's device's Bluetooth settings and pair with the "Reach" device. The default pairing code is typically 123456.
  3. Configure SW Maps:
    1. Open SW Maps and tap the Bluetooth icon or go to the Communication menu.
    2. Select Bluetooth GNSS as the instrument type.
    3. Select your paired Reach RS+ from the device list and tap Connect.
    4. Once connected, SW Maps will display your high-precision coordinates, altitude, and accuracy status (e.g., "Fix" or "Float").
SW Maps provide GIS Versatility and is great for simple point collection and offers advanced GIS features like custom feature layers, attribute forms and professional data export formats. It also has built-in NTRIP client allowing direct corrections to the receiver through the app if needed. SW Maps primarily records data is the WGS84 coordinate system (EPSG:4326).

References

1. GNSS survey with EMLID Reach app and EMLID RS+ (or RS2). Link: Emlid Reach RS+

2. PPK Post-Processing Kinematic - Emlid Studio Tutorial. Link: https://youtu.be/MLRFHn9tQZM?si=71Rwu2Jd5hre6MS2

3. RTK GPS/GNSS with Base and Rover. Link: https://youtu.be/Rk09oMD_I24?si=nEoKPbjhJx_o9Rqy




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