Happymodel (Quzhou Yunduan Intelligent Technology Co., Ltd.) EP1 ELRS 2.4G Receiver

The Happymodel EP1 ELRS 2.4G Receiver is a tiny ExpressLRS receiver for 2.4 GHz with an external antenna, made by Happymodel (Quzhou Yunduan Intelligent Technology, China). It works with an ESP8285 and an SX1280 and is meant for micro drones where every tenth of a gram matters. Antennas of 40 and 90 mm length come with it.

The receiver weighs 0.42 g without antenna and measures 10 x 10 x 3 mm. The packet rate is 500 Hz at most, which gives 2 ms between two packets by calculation. This packet interval is not end-to-end latency, but it shows the margin for fast response. Telemetry is carried on the return channel and reports signal strength and battery voltage to the radio. There is no second antenna and therefore no diversity; the receiver depends on a single antenna.

In the EU the limit in the 2.4 GHz band without a licence is 100 mW EIRP; the transmitter module in the radio has to be set so that it respects this limit, and antenna gain counts too. Equipment may be operated in the EU only in the approved frequency ranges and power levels. In the open category visual line of sight applies, and long ranges are no selection criterion there.

When choosing, the antenna choice counts: the 40 mm antenna saves weight and space, the 90 mm antenna gives more range, and both should be routed in the right orientation and secured against pull. The ExpressLRS version of receiver and transmitter module has to match. At 0.42 g the solder pads and antenna connection are the places crashes damage first.