Review of RadioMaster ER6G, ER6GV, ER8G and ER8GV receivers for ELRS

Good news: RadioMaster have released a bunch of ELRS receivers specially for gliders and electric models! These  are notable for being some of the first ELRS receivers to have servo connectors integrated on the main board. 

I've had a lot of fun evaluating these receivers, including flight testing them in DLG and F3F models. In this review, you'll find detailed descriptions, with example configurations, best practice, and tips for ALT telemetry. 

Let's take a closer look! 

Protection

The receiver is wrapped in layer of thick heatshrink tube. Two spare lengths of heatshrink are provided in case you make the channel 6 mod (see below). 

The antenna connectors lack the usual yellow glue, instead they rely on the heatshrink to keep them in place. 

Adding the channel 6 connector

If you want the sixth PWM port, then you'll need to get soldering! 

One option is to solder in the supplied PWM connector. Personally I don't like this method because (a) it means re-routing one of the antennae, and (b) I'm pretty sure the connector will have to be outward-facing, which will increase the effective length of the unit.

Instead, I've soldered a flying lead directly to the pads, using the spare heatshrink to cover the work. To relieve pressure on the boot button, I bored a hole through the heatshrink using the sharpened end of a brass tube. 

Channel 6 flying lead mod (heatshrink covering not yet applied)

Completed CH6 mod. Note hole to relieve pressure on boot button.

Battery connection (don't use the CH6 port!)

According to the instructions, power must be supplied through one of CH 1-5, not CH6.  This is because CH 1-5 share a robust power bus, whereas the CH6 power lines are tapped via tracks on the PCB.

If using six servos, or five servos and no CH6 connector, then a Y-lead will be needed to share a port between a servo and the battery.

Voltage telemetry

It's always a good idea to calibrate the RxBt telemetry (On my ER6G it was under reading by 0.2 V). Use a meter to measure the voltage and adjust the sensor offset in the Telemetry menu. 

The voltage range for external telemetry is 3.0 - 26 V. 

S.Bus support

The forthcoming ELRS V3.3 will enable one of the PWM ports to be repurposed for S.Bus. A typical setup would be PWM for the fuselage servos, and  S.Bus for the wing servos (an S.Bus to PWM converter will of course be needed if the servos don't support S.Bus).

Compared with the FrSky RX6R

The ER6G is an obvious candidate to replace the popular FrSky RX6R. However, while the ER6G is slimmer, it is also longer by ~12 mm. Worth bearing in mind for tighter installations.

FrSky RX6R and RM ER6G compared

Flight testing the ER6GV in a DLG

For flight testing the ER6GV I used my TopSky 1.5 m DLG. This is equipped with four servos and 4 x 300 mAh NiMH cells.

For my flight tests, I used the Wide Switch Mode - this provides four full-res (10-bit) channels. Max Power was set to 50mW, with Dynamic enabled. However please note: I have since learned that the ELRS devs recommend using Full Res 8Ch switch mode, with a 100Hz packet rate. I have therefore removed the original screenshots.

CH5 is set high ('armed') on startup. Pressing a button for 1 second flips to 'disarmed'. There are voice callouts for each state.

I've had several sessions and there have been no problems at all. See below, though, for TLM tweaks.

Capturing DLG launch heights.

My DLG templates (4-servo, and 6-servo) offer a launch height callout, when used with a receiver with altitude (ALT) telemetry. In order to capture launch height with sufficient accuracy, the ALT data must be sent at a high rate. 

On ELRS setups, the data rate depends on the telemetry ratio (TLM). This is the proportion of telemetry frames (downlink) to all frames (uplink an downlink) in a given time interval. The smaller the ratio, the higher the telemetry rate. TLM is configured in the transmitter, via the ELRS Lua script. 

During flight tests using a packet rate of 250 Hz, I found that the default TLM (1:64) did not provide sufficient resolution to capture my launch heights accurately. Decreasing TLM to 1:8 made a significant improvement.

Below are extracts from the SD card logs which demonstrate the issue. The log recording interval was 0.4 seconds.

• The left hand plot is with TLM = 1:64 (the default). Note the blocky appearance. From the log, it appears that the ALT telemetry data was refreshed every ~2.8 secs. This is insufficient to capture the launch peaks.
• In the right hand plot, TLM = 1:8.  From the plot it can be deduced that the ALT telemetry is being sent every 0.4 seconds or less. I think this is just about sufficient.

ALT log resolution with TLM = 1:64 (left) and 1:8 (right)

ER8G receiver

The second receiver provided was the ER8G. This unit has 8 channels. It uses two boards, with connectors at both ends. Length is 60 mm and weight is 12 grams. 

The unit is supplied with a UART cable, a length of wire for connecting to the external voltage pad, and two lengths of extra heatshrink tube.

ER8GV receiver. There are PWM outputs at both ends.

Battery connection

Unlike its junior sibling, the ER8G has a dedicated port for the battery. The unit also supports external voltage telemetry in the range 4.0 - 35 V. 

UART

External sensors can be connected via a UART port on the side of the unit. Voltage, current and GPS sensors are planned. 

Form factor issues

My only gripe with the ER8G/V is the form factor. At 60mm it's too long for a modern F3F ship. Having servo connectors at both ends further complicates installation. (Yes, the ER8G fits in my Sting, however this is an old model with lots of room.)

ER8GV in my Sting F3F model. The length is not ideal!

Flight testing the ER8G

For flight testing the ER8G I used my Sting F3F moulded glider, with six servos and 4 x 2100 mAh Eneloops.

I set the Switch Mode to '8-channel'. This provides eight 10-bit channels in addition to the (reserved) CH5. Max Power is 100 mW with Dynamic Power enabled.

On the transmitter, I swapped CH5 with the (unused) CH7. I then set the CH5 source to 'MAX' to represent the 'armed' condition. For more info on the CH5 requirements, see my Introduction to ELRS (link at end).

The ER8G performed well in spite of using just a single antenna - it turned out that antenna diversity was not enabled! Antenna diversity is configured via the ELRSv3 Lua script.

Maximum distance reached during the flight was approximately 150 meters. The maximum recorded RF output was 25mW, and RQly remained at 100% for almost all the flight, only momentarily dropping to 95%.  On would expect improved figures when using both antennas.

Telemetry logs showing link quality (RQly) and transmission power (TPW2). Three flights.shown.

Incidentally, the little Zorro was fully loaded with F3F template, plus Lua scripts for adaptive trim and adjustable snapflap.

Ranger Nano tx module

RadioMaster also sent me a Ranger ELRS module to use in my Zorro. It fits nicely in the nano bay, although it does increase the overall depth significantly.

A T-shaped antenna is provided, this screws into the top of the unit. 

At the back is a USB data port. Adjacent is an XT30 socket for an external battery, though this will not be needed for LoS use. 

An internal fan is triggered when RF power exceeds a configurable threshold. The default threshold is 250mW and, given that 50 or 100mW is sufficient for LoS, the fan should never be needed. 

As with the receivers, the Ranger can be configured over WiFi. 

Zorro with Ranger module

Benefits