Servers by jDrones

Emergency Stop Button for Large Rover

pixhawk

(Drew Sandlin) #1

I have a rover built on an electric wheel chair platform and I’m looking for a bigger emergency stop switch to replace the small illuminated switch that comes standard with the Pixhawk. Is there an off the shelf option for this? I haven’t been able to find one.

I’ve been thinking about using a larger switch and then having an LED light beside it. This way I can still wire it into the Pixhawk and get the information conveyed by the LED. Something like this:

Is the standard Pixhawk switch normally open or normally closed? I should probably dig into the Ardupilot code to figure out how the logic works…

If someone were to make a larger mushroom emergency stop switch that has a DF13 connector identical to the standard Pixhawk switch I would pay $25 for it, if any entrepreneur out there is looking for ideas.


(Hunt0r) #2

I recommend that your “safey switch” disconnect all motor power, rather than the safety-switch behavior which is implemented via ardupilot.


(hans bert) #3

you need relais that cut the power from the motors.
the pixhawk switch is not the way to go.


(rmackay9) #4

I think this emergency stop is a really important feature and I’m happy to help implement support for this button in AP but as the others have suggested, the safest method is to make the switch directly cut the connecting to the ESCs or the battery (or something similar)… a method that doesn’t rely on the flight controller at all is best.

If we do figure out a way to implement this I’d be very happy to add it to the wiki even though it’s not directly related to AP, it’s an important safety feature. Certainly if a person is going to get on the vehicle this is critical. ArduPilot is really not designed for manned vehicles and it is in our developer code-of-conduct that core developers should not assist in applications where ArduPilot is effectively in control of human life. Rovers with a big stop button that’s implemented separately from the flight controller are a grey zone and might be OK especially if the vehicle is not travelling too quickly.

… in any case, I’m happy to help with implementing support for a big red stop button… and I suspect in this case, it’s not meant for a person to get on it anyway so that whole part of the discussion is just as a reference.


(Drew Sandlin) #5

So I think maybe a little more detail about my situation would help clarify my question. This is what my rover looks like.

Right or wrong, the way I designed it was to have all of my “power” electronics separated from the Pixhawk, GPS receivers, compass, etc. to prevent any magnetic interference. In that picture you can see the top box has the Pixhawk and GPS receivers, and the box on the back has the BEC and Sabertooth motor controller.

The idea was to segregate all of my wires carrying large amounts of current away from my compass.

The problem is that the ideal place for the emergency stop button is right on top of the box with the Pixhawk, GPS receivers, compass, etc. And what you guys are saying (correctly in my opinion) is that the emergency stop should cut off all power to the rover, or at least power to the motors.

This means I will need to run one of my large current carrying wires through the enclosure with the compass on it. Maybe that isn’t as big of an issue as I think it is. But that’s my concern, anyway.

So as a work around, I was going to see if there was a way to simply replace the standard Pixhawk arming switch with a larger one.

Alternatively, I could have the emergency stop switch run a relay as @aamadeuss suggested. I’m not opposed to this method either, but it is a little more complex. It does solve both issues though.

Another option would be to put the emergency stop switch on the “power” box on the back of the rover, but it is less accessible there. It would be very close to the on off toggle switch on the rover at that point, kind of defeating the purpose of using an emergency stop switch in the first place.

Thanks for all of the feedback, I do appreciate it. It’s very helpful, as I’ve been stuck pondering this for a few days now and haven’t found a good answer.


(rmackay9) #6

thanks for sharing the pic, a fine looking rover!


(Drew Sandlin) #7

Having had some time to think about this, I think I am going to do what @aamadeuss and @hunt0r suggested and use two relays to switch on the motors. I am wondering if something like these relays would do the trick. I have no clue how much current the motors pull during normal operation, I imagine 10A relays are sufficient.

I received the switch I linked to above in the mail today and it has two switches operated by the push button, one NO and one NC.

What I’m thinking I’ll do is route 5VDC through the NC switch to power the two relays. When you hit the button, the switch will open, de-energizing the relays, shutting off power to the motors. The motors are the only thing affected, the Pixhawk will still remain on. I am operating under the assumption these relays can be turned on by simply applying 5V to the appropriate pin.

Here’s the part I’m not sure how to handle: I’d like to have the NO switch on the emergency stop button connected to the Pixhawk somehow so that it can read the status of the emergency stop button. It’s really just reading an on or off state on the emergency switch.

The Pixhawk Overview page of the documentation mentions the auxiliary servo connectors can be used as inputs. Not sure how the nuts and bolts of such an implementation would work though.