Intermittent RX Reboot sending junk signal to ESC #3248
Description
Current Behavior
When using Radiomaster ER3C(i), ER5C(i), and ER5C V2 ELRS receivers, there is a serious issue where the receiver intermittently reboots (we can rule out brownout and power loss, or dynamic power/signal event - it's caused by something else) and, during the reboot outputs a junk or out-of-range PWM signal to the ESC.
If this happens while the vehicle is at rest or bench testing, the receiver sends no throttle output.
However, if the reboot/signal loss occurs while throttle is applied (mid-drive), the receiver momentarily sends a full throttle PWM signal to the ESC, causing the vehicle to accelerate uncontrollably resulting in a full-throttle runaway.
The failsafe configuration is ignored during this event.
This leads to runaways and serious, dangerous behavior with large surface vehicles.
Steps to Reproduce
Some people have been able to simulate the reboot by shorting RX pins. Real-life reproduction is almost impossible due to its unpredictability.
Possible Solution (Not obligatory)
• Investigate whether the receiver’s bootloader or recovery sequence defaults to outputting the last valid PWM value or outputs random/junk PWM during reboot.
• Ensure that during any reboot or signal loss, the receiver immediately outputs a neutral or user-configured failsafe PWM value, regardless of previous stick position.
• Optionally, suppress all PWM outputs during reboot or link reacquisition, and only resume after a valid TX link and ARM channel state are confirmed.
Details
Critically, this is most dangerous in surface RC use: a full-throttle runaway is a safety hazard with 10+ kg vehicles like the Axial SCX6.
• Setting up an ARM switch on channel 5 in the transmitter prevents this problem (the receiver stays disarmed after reboot and does not output throttle), but many users will not have this configured by default.
• Affected ExpressLRS versions: 3.1.x, 3.3.x confirmed.
• The issue is seen on both original and V2 receivers.
Your Environment
• TX hardware: RadioMaster MT-12
• RX hardware: ER3C(i), ER5C(i), ER5C V2
• Handset model: RadioMaster MT-12
• OpenTX/EdgeTX version: EdgeTX 2.10.6
• ExpressLRS version (TX & RX): 3.3.1 (matched)
• Dynamic Power: Off
• Packet Rate: 250Hz, also 50Hz and 100Hz tested
• Telemetry Ratio: 1:16
• user_defines: Standard (no unusual config)
• Vehicle: Axial SCX6, Spektrum stock ESC; Arrma Gorgon, Hobbywing ESC (the bug is unrelated to the setup)