Arma
RCTalk Member
- Messages
- 28
- Reaction score
- 43
- Points
- 73
- RC Driving Style
- Bashing
- Crawling
- Flying
Hey guys, just dropping this here in case it saves someone else from what happened to me — a full-on, bash/blast throttle runaway with my SCX6 powered by a RadioMaster MT12 and ELRS.
It's always better to learn from someone else's mistakes.
I haven't found any information regarding the runaways until I got motivated (after my SCX6 hit my shin) to dig deeper.
MT12 v2.10.6 (latest as of now 2.11.1)
ER5C v2 3.3.1 ((latest as of now 3.5.5)
Model: SCX6
While running my SCX6, I suddenly experienced a full throttle runaway while standing 2m (7ft) from the model. The rig went completely out of control and didn’t stop until the RX rebooted and connected to the TX after 3 about seconds.
Other people are reporting either full throttle runaways mid-drive or signal loss / RX reboots when stationary with no throttle input.
After some digging, I realized the RX ignores the correctly configured failsafe and sends unsafe signal to the ESC.
Turns out, when Radiomaster ELRS RX loses signal or reboots (mid-drive) by itself for at the moment unknown reasons, the default PWM output spikes to 2000 µs, which ESCs interpret as full throttle.
The issue is especially common with PWM receivers like the ER3C(i)/ER5C(i)/ER5C-V2 (3.3.0+).
After further testing and research (and some excellent community feedback - thx u/sonic192), it looks like that the single most reliable way to prevent full-throttle runaways or glitches with ELRS and the MT-12 is to set up a dedicated ARM switch on Channel 5 (AUX1) - https://www.expresslrs.org/software/switch-config/
What this means is: you assign a physical switch on your radio (I used SD with logical toggle - use Stky, but any switch works) to Channel 5, and configure your transmitter so the car is only “armed” (and able to move) when you explicitly flip that switch. When disarmed, the receiver does not send throttle commands to the ESC—no matter what else happens (including brownouts, glitches, or reboot events). If you lose signal or the receiver reboots, it defaults to “disarmed,” which means the car stays safe and immobile. It even cuts off power mid-drive if you flip it. Of course TX start up is default disarmed.
I’ve now implemented this setup and confirmed that the throttle is 100% locked out when disarmed, but instantly responsive when armed. No more runaways, ever—even if something goes wrong with the radio link or power. For anyone using MT12 and ELRS and a surface vehicle, I highly recommend making the ARM switch on Channel 5 your very first safety step. It’s easy to set up and makes your rig much safer for you and everyone around you. I suggest adding Special Functions - LED and Tracks to the ARM switch.
And of course, always update:
It's always better to learn from someone else's mistakes.
I haven't found any information regarding the runaways until I got motivated (after my SCX6 hit my shin) to dig deeper.
The Incident:
MT12 v2.10.6 (latest as of now 2.11.1)ER5C v2 3.3.1 ((latest as of now 3.5.5)
Model: SCX6
While running my SCX6, I suddenly experienced a full throttle runaway while standing 2m (7ft) from the model. The rig went completely out of control and didn’t stop until the RX rebooted and connected to the TX after 3 about seconds.
Other people are reporting either full throttle runaways mid-drive or signal loss / RX reboots when stationary with no throttle input.
After some digging, I realized the RX ignores the correctly configured failsafe and sends unsafe signal to the ESC.
The Root Cause:
Turns out, when Radiomaster ELRS RX loses signal or reboots (mid-drive) by itself for at the moment unknown reasons, the default PWM output spikes to 2000 µs, which ESCs interpret as full throttle.The issue is especially common with PWM receivers like the ER3C(i)/ER5C(i)/ER5C-V2 (3.3.0+).
The REAL Fix:
After further testing and research (and some excellent community feedback - thx u/sonic192), it looks like that the single most reliable way to prevent full-throttle runaways or glitches with ELRS and the MT-12 is to set up a dedicated ARM switch on Channel 5 (AUX1) - https://www.expresslrs.org/software/switch-config/What this means is: you assign a physical switch on your radio (I used SD with logical toggle - use Stky, but any switch works) to Channel 5, and configure your transmitter so the car is only “armed” (and able to move) when you explicitly flip that switch. When disarmed, the receiver does not send throttle commands to the ESC—no matter what else happens (including brownouts, glitches, or reboot events). If you lose signal or the receiver reboots, it defaults to “disarmed,” which means the car stays safe and immobile. It even cuts off power mid-drive if you flip it. Of course TX start up is default disarmed.
I’ve now implemented this setup and confirmed that the throttle is 100% locked out when disarmed, but instantly responsive when armed. No more runaways, ever—even if something goes wrong with the radio link or power. For anyone using MT12 and ELRS and a surface vehicle, I highly recommend making the ARM switch on Channel 5 your very first safety step. It’s easy to set up and makes your rig much safer for you and everyone around you. I suggest adding Special Functions - LED and Tracks to the ARM switch.
And of course, always update:
- RX firmware
- Internal MT12 ELRS module firmware
- MT12 firmware
Last edited:
