Here 2 UAV CAN Safety Switch

Hi Philip, as Plane 4.0 is out and ads support for UAV CAN safety switch will this work with the here 2 built in one ? Not sure if it’s connected that way internally.

To start with… let’s unpack my absolute hate of that switch.

First… calling it a safety switch… it’s not… is would be better to call it a finger removal tool!

Second… For it to be a safety button it would need to be monitored, checked and verifiable in functionality, it’s not, the design is a flawed concept.

Third… consider the use case… on a multicopter, props are stopped, arming is prevented by the “safety” switch, so to make it arm-able… you put your hand between the potentially spinning disks… and make it “unsafe”.

Forth… for some strange reason the button or wire gets damaged in flight… triggering the button… disabling the vehicle? In flight? Nuts!
I hate this button…

My advice to all is to set ardupilot to prevent this button from being able to be used while the aircraft is armed, and don’t use it at all.


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Not 100% sure but your giving me the impression you’re not a fan of this button :joy:.

I was only asking from a technical standpoint lol.

No worries and PS, I don’t like it either :wink:


I’ve now decided NOT to use it :joy::joy:
Steve :slightly_smiling_face:

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…so… are you of the opinion that there is no place for some sort of device that forces the vehicle into a ‘safe’ state (…or forces an ‘unsafe’ state) to enable the operator to have the vehicle powered on, but still in a ‘safe’ state?

If not and you DO think a safe/unsafe device has merit; what, in your opinion, should the device look like in terms of function and form?

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In case someone else stumbles across this in the future. See this thread. The safety switch on the Here2 is not set up to be used as a UAVCAN safety switch. It’s the closest thing we have to a physical on off switch.

Now to respond to @philip above me.
First…So long as arming procedures are properly followed (prearm checks and rudder/GCS arm) the vehicle will not turn on any moving parts when the safety switch is pressed.

Second…If the safety switch fails in an open state, the vehicle remains in a state of no output. If the switch fails in a closed state, the vehicle is still not armed (assuming proper arming procedures are followed).

Third…Yeah that one is still not a great way of dealing with the issue. Not really a great place to put a switch, but it at least is easier to jump away from pressing a button than it is from plugging in a battery.

Forth… The bitmask parameter BRD_SAFETYOPTION allows for the safety switch to only be used while the vehicle is disarmed. Your following sentence after this point states this as well.

A simple yes or no at the top would have worked too.

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The safety button is still on the device, and still physically connected to the connector.

Feel free to use it if you insist.

We also supply a free safety button with every Standard carrier board.

Either can be used while the GPS is in CAN mode.

No a simple yes/no would not suffice, as the word “safety” and that button do not belong together

I will be using the terminology of that piece of hardware being a called safety switch due to the usage of the term in the firmware documentation.

The free external safety button provided with every standard carrier board is far from the same quality as the one on the GPS puck. Many of those external buttons have failed when the PCB mounted switches have continued working. The external safety switch is a safety and operations liability. I would not consider using that particular button if the GPS and safety switch had to be in different places or CAN bus had to be used. I honestly would not mind paying for a nicely packaged, robust, and reliable PCB mounted safety switch that could be surface mounted to the skin of a vehicle. That would be one way to push me to use CAN bus over I2C.

The OP asked if the switch on the Here2 could be used as a UAVCAN safety switch. Your response did not answer the yes/no question. The other pieces of information that you did respond with are good to know when using the safety switch, but no clear answer was given. Stating that the most reliable safety switch provided with the hardware only works on I2C would have good information to include as well.

Future hardware feature request (Here2.1?): Add in a relay (or make the I2C/CAN slide switch change the circuit?) such that the safety switch could be used on UAVCAN as well as I2C. This would also make switching the CAN bus trivial. As it stands right now though, switching to UAVCAN has a major drawback of loosing a safety feature.

How many times do I need to explain to you that it’s NOT a safety feature!

Do I need to issue a new safety Bulletin?

The way it works is not safe, and we have every intention of removing it completely.


People have been injured!

The button is not locked to can or I2C.

If you insist on having that button function while using CAN, then connect it!

The two I2C wires, ground and power should go to the CAN plug, then run the safety button and LED to the old GPS1 connector. Don’t connect the serial wires.

It’s 100% up to you how you choose to wire your gps.

So there is no Yes/No answer.

You can feel free to continue arguing with me… or, you can sit back and think…

Why would someone make a stand on this issue, and risk loosing customers, if there was not a very serious reason why?

Hi there, got a question.

I’m use Here2.

When setting up in MP I want to calibrate the ESC’s automatically with MP. That requires to hold the Safety Switch for Three seconds

Unfortunately I can’t split the GPS connector to GPS1, because that socket had come off the circuit board.

Is there another way around this?


Just disable HW Safety switch in the prams up pre arm check.