SimuRC-Pro: Direct USB for ELRS TX Modules (No Bridge)

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This page is for SimuRC-PRO users who want to plug their ELRS TX module straight into the PC by USB, with no Pico Zero adapter in between. Read this first, even if you are in a hurry. The wrong module setup can leave you unable to use the module on your radio afterwards until you revert it.

What is “Direct USB” mode?

SimuRC-PRO normally talks to your buggy through a small USB-to-serial board called the Pico Zero. The Pico Zero relays the RC channels to a tiny ELRS receiver wired to it, which then transmits over the air. That is the recommended setup.

Some users prefer to skip the Pico Zero and plug a full ELRS TX module (Radiomaster Ranger Micro, BetaFPV 1W Micro, etc.) directly into the PC by USB. SimuRC-PRO 20260602 and later has a Direct USB checkbox right next to the COM port selector that enables this path.

The two paths solve different problems:

Pico Zero (default, Direct USB unchecked): works out of the box, no module reconfiguration, the module stays usable on your radio. Recommended for most users.
Direct USB (checkbox ticked): one less cable and one less component, full transmit power from the module’s antenna, but requires reconfiguring the module’s hardware pins, and the module cannot be used on your radio while in this mode (until you revert).

Module compatibility

Module	Direct USB	CRSF RX / TX pins	DIP switch
Radiomaster Ranger Micro	Yes	3 / 1 (NOT the Backpack values 16 / 17, which do not work on this module)	No
Radiomaster Ranger Nano	Yes	3 / 1	No
Radiomaster Ranger (standard)	Yes	3 / 1 or 16 / 17 (depends on revision)	On some revisions
BetaFPV 1W Micro	Yes	3 / 1	Yes, set to “Firmware Upgrade” position
HappyModel ES24 / ES900	Partial (ES24 works, ES900 reportedly does not)	Check the official ELRS target JSON for your model	Varies
Internal modules (TX12, Boxer, MT12, etc.)	No	Not applicable	Not applicable
Radiolink ATA Nano 1W and other Radiolink proprietary modules	No (not ELRS)	Not applicable	Not applicable

If your module is not in the table, two cases. STM32-based modules (most BetaFPV, older HappyModel): try the Backpack values from the official ELRS hardware repository at github.com/ExpressLRS/targets/tree/master/TX, fields debug_backpack_rx and debug_backpack_tx. ESP32-based modules (most recent Radiomaster including Ranger Micro and Ranger Nano): the Backpack values are misleading. The USB port is wired to the ESP32’s native UART0, which is GPIO 3 (RX) and 1 (TX) by convention. If a JSON file does not exist for your module at all, it is not officially supported by ELRS and Direct USB will not work.

Important note: Backpack values are misleading on the Ranger Micro

For the Radiomaster Ranger Micro specifically, the common kaack recommendation “copy the Backpack RX/TX values into CRSF Serial RX/TX” gives 16 / 17, which does not work. The Backpack chip on this module does not pass the CRSF stream from USB to the main MCU. The correct values to use are RX = 3, TX = 1, which point at the main MCU’s USB UART directly. This is confirmed by field testing. The same caution applies to other ESP32-based modules with a Backpack chip: prefer the main UART pins (typically 3 / 1) over the Backpack pins.

Step-by-step (example: Radiomaster Ranger Micro)

Plug the module into your PC by USB. Wait for Windows to recognize it. A new COM port should appear in Device Manager under Ports (COM and LPT), most commonly as Silicon Labs CP210x USB to UART Bridge. If no COM port appears, install the CP210x driver from the Silicon Labs website.
Connect to the module’s WiFi access point (the SSID starts with ExpressLRS_TX_, default password is expresslrs).
Open a browser at http://10.0.0.1 and go to the Hardware tab.
Write down the current CRSF Serial RX and TX values before you change anything. For the Ranger Micro the defaults are 13 and 13.
Set CRSF Serial RX = 3 and CRSF Serial TX = 1. Do not use the Backpack values (16 / 17) on this module, they do not work even though the kaack tutorial suggests them as a generic method.
Uncheck “Use Backpack”.
Click Save. The module will reboot.
Disconnect from the WiFi access point, unplug and replug the USB cable.
Launch SimuRC-PRO. In the ELRS section, tick the “Direct USB” checkbox next to the COM port selector.
Set the baud rate dropdown to 115200. The Ranger Micro does not accept 400000 over USB. If for any reason 115200 does not work, try 921600 next.
Select the COM port the Ranger Micro shows up as.
Click Connect. The module’s LED should switch from orange-blinking to green-heartbeat. You can now drive the buggy.

How to revert the module to use it on your radio again

While the module is in Direct USB mode, your radio cannot use it. The CRSF pins are pointing at the USB bridge instead of the JR-bay pin. To put it back into radio mode:

Plug the module into the PC by USB.
Connect to the ExpressLRS_TX_ WiFi network and open http://10.0.0.1.
Go to the Hardware tab.
Restore the original CRSF Serial RX and TX values you wrote down earlier. For other modules, check the official ELRS target JSON.
Re-check “Use Backpack”.
Click Save. The module reboots.
Unplug it from the PC. Slide it back into the radio’s JR-bay.
The radio detects the module normally again.

Tip: if you switch between Direct USB and radio use often, save the two sets of values in a text file on your PC so you do not have to look them up every time.

Original factory values per module

Use these values to restore your module to its original radio-mode configuration. They come from the official ELRS hardware target files but are presented here in a readable form.

Module	CRSF Serial RX	CRSF Serial TX	Backpack RX	Backpack TX	Backpack baud	Use Backpack
Radiomaster Ranger Micro	13	13	16	17	460800	Yes
Radiomaster Ranger	13	13	16	17	460800	Yes
BetaFPV 2400 1W Micro	13	13	3	1	460800	Yes
BetaFPV 2400 Micro	13	13	3	1	460800	Yes
BetaFPV 2400 Nano	13	13	3	1	460800	No
BetaFPV 2400 Nano V2	21	21	18	5	460800	Yes

Source: ELRS hardware target JSON files in github.com/ExpressLRS/targets/tree/master/TX. If your module is not in this table, look it up there. Open the JSON file for your model, and copy the values of serial_rx, serial_tx, debug_backpack_rx, debug_backpack_tx, debug_backpack_baud, and use_backpack back into hardware.html.

Troubleshooting

SimuRC-PRO connects but the buggy does not move (module LED stays orange-blinking)

Most likely cause: the baud rate is wrong for your module. CRSF standard is 400000, but several ELRS TX modules do not accept that rate on their USB bridge. Use the baud dropdown next to the Direct USB checkbox and try the values in this order:

115200 (confirmed on Radiomaster Ranger Micro)
921600 (confirmed on BetaFPV 1W Micro)
400000 (CRSF standard, works on some)
The higher rates (1.87M / 3.75M / 5.25M) as a last resort

You need to disconnect before changing the baud, then click Connect again. As soon as the module switches from orange-blinking to green-heartbeat, you have the correct baud for your module. Persist it and you will not need to change it again.

Second possible cause: the Direct USB checkbox is unticked. With it unticked, SimuRC-PRO talks to the COM port using the legacy path which works for the Pico Zero but not for direct TX modules. Tick the box, click Connect again.

The module reboots every time I click Connect or Disconnect

Same cause as above. The legacy serial path pulses the DTR/RTS lines, which the ELRS module’s USB bridge interprets as a reset signal. Tick Direct USB.

The COM port does not appear in Windows

The USB-to-serial driver is missing or the cable is power-only. Check Device Manager for an unknown device with a yellow exclamation mark. Install the appropriate driver:

Silicon Labs CP210x for most Ranger Micro / Ranger Nano modules.
STMicroelectronics Virtual COM Port (STSW-STM32102) for BetaFPV 1W Micro and similar STM32-based modules.

If still nothing, try a different USB cable. Many phone charging cables only carry power, not data.

The module’s LED stays orange and blinks

This means the module sees no valid handset signal coming through its CRSF input. Two possible causes:

The pins in hardware.html are wrong. Double-check the values from the table above or from the official ELRS target JSON for your exact model.
For some modules with external receivers paired to a different radio, the receiver refuses to bind after the CRSF input is remapped to the USB. There is no clean workaround in this case. Revert the module to its original configuration and use it on your radio instead.

The module disconnects randomly during use

Power is the usual culprit. A 1W ELRS module pulls around 700 mA at 5V in full transmit, which is fine on a USB3 port (900 mA available) but marginal on USB2 (500 mA) or on a passive USB hub.

Plug the module into a USB3 port directly on the motherboard.
Use a quality USB cable, not a thin or long phone cable.
Lower the transmit power in hardware.html (250 mW is plenty for indoor or RC track range).

I get an “Access denied” or “Port busy” error when clicking Connect

Another program is holding the COM port open. Common culprits are the ExpressLRS Configurator, Betaflight Configurator, or a leftover instance of SimuRC-PRO. Close them all and try again.

Should I use Direct USB or stick with the Pico Zero?

Honest answer: the Pico Zero is the simpler, safer recommendation for most users. It just works, no module reconfiguration, no rollback to remember. The Direct USB path exists because some users explicitly asked for it (one less cable, full module antenna instead of the small Pico Zero antenna), but it requires more care.

If you only own one ELRS TX module and you also use it on your radio for FPV, do not switch it to Direct USB. Get a Pico Zero. If you have a dedicated module you do not mind reconfiguring, Direct USB is fine.

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