View Full Version : Kill switch?

08-05-2010, 10:24 AM
Hi All, The following YouTube video shows a bit of evolution in getting a hexapod to walk. The narration notes that a kill switch was installed, and I was wondering how this is done? If this is a pretty simple question that requires a pretty involved answer I'd be more than happy with simply being pointed in the right direction to track down possible implementations. TIA!

[Trials] of Walking
Edit: corrected spelling to "Trials"

08-05-2010, 10:40 AM
Switch off the power to the servos.. voila...

I have 4 switches on Bheka

Logic power
Servo power
Camera power
Gun power


08-05-2010, 12:22 PM
I didn't see him reaching for a manual kill switch on the bot in the video though.

08-05-2010, 12:35 PM
I know Jon created a kill switch for his rover using a pair of XBEEs and a micro on each end. The transmitting handheld kill switch repeatedly broadcasts a message over XBEEs until it's pressed, the receiving end shuts down the bot any time it doesn't get the message within a certain amount of time (for instance, if broadcasting at 30hz, you might stop if you don't get any messages for 1/10 of a second). This has the added advantage that it will kill the bot if you go out of range of the transmitter.

PR2 also has such a design (although it's actual industrial control runstop, probably several hundred dollars) -- which was amusing at Robogames, because the person with the runstop kept walking away and getting out of range, at which point PR2 went limp and stopped working....


08-05-2010, 12:53 PM
Thanks gdubb2 & lnxfergy for your replies, very much appreciated. :)


08-05-2010, 01:43 PM
We had to have failsafes on the battlebots too. If you lost communication for any reason, the thing shut down. I had to have mine set so the drive power and pneumatics were cut off.

08-05-2010, 10:08 PM
I'm the one responsible for that video... Let me clarify what I meant.

That version of Ally was controlled entirely via bluetooth link to my laptop. Onboard, she had a SSC-32 paired with a BlueSmirf module to deal with movement. In my main control loop of the program the "escape" key would immediately cut power to all of the servos connected to the SSC-32 (by sending the position command "0") and exit the program. That's what I meant by "killswitch" in the video- it wasn't a physical switch on the robot (although I suppose hitting the power would do the same thing) but it would stop the robot from doing any harm to itself or to others. I apologize if using the term "killswitch" was ambiguous... perhaps I should have coined the phrase "failsafe" instead.

Whatever you call it, the proverbial "killswitch" is a great feature to have. ;)

I would also like to point out to anyone reading this thread and watching that movie that what you are seeing are not "best practices" when trying to teach your robot to walk. At the time that footage was shot I was working through trying to figure out the IK and would literally make changes on the fly by running a debug version of the control program in VS 2008 and recompiling the program for each attempt. I'm *really* lucky I didn't damage anything too badly. I was being impatient and wanting to see results right then and not working through the equations to see where the errors were. The video was meant to be humorous and inspirational, and is by no means meant to be educational.

One final note just as an aside: The end result in the video isn't IK at all, in fact. What you are seeing there is a series of poses. I am embarrassed to admit that it wasn't until months later that I realized the "errors" I had been trying to iron out in the final IK engine weren't errors at all (I had it right), and that I had done something so incredibly stupid in my haste to make it work... I was measuring the base coordinates for each leg assembly the wrong way, so my results for leg angles were all off kilter.

Realizing this has caused me to re-evaluate the bot entirely and I'm now working on a new incarnation...the right way this time: using patience, good planning, and correct/safe troubleshooting ;)

08-05-2010, 11:02 PM
Thanks for posting the video to begin with parallax, as without it I may not have been inspired to integrate a killswitch for my upcoming bot! ;) BTW it's not an issue, for me anyway, about using the term "killswitch" in generically referencing the act of shutting down the bot, whatever the actual mechanisms and/or processes. Nice work on Ally and the video - I certainly had the impression that it wasn't so much a tutorial, as a tongue-in-cheek expose on your experiences. When I get to the point of documenting my builds I'm sure I'll have similar such videoS to post! :D