[Robotgroup] Safety Circuit Design Question

[Michael Boswell]

Awhile back there was a discussion about the importance of a safety cut-off
circuit in robot designs.  The video of the 300# robot going straight at
people was very sobering. While I am not contemplating working on anything
that big and deadly, it still seems like a good idea to have some sort of
safety circuit. 

 

I have a dual coil latching relay that I am planning to put into the main
motor power buss. This will be after the feed for the low voltage regulators
so the processor and any sensors will not be effected by the state of the
power relay but the Motor of course will only get 12vdc or 24 vdc when the
relay is latched.  My question is around the trigger circuit for the relay.
I would expect to put some sort of N.O. switch(s) like Bump Switches on the
chassis that will close on contact and energize the RESET coil to open the
relay.  The coils in the relay I found are 4.5v nominal. Now for my
philosophical question. Should I put the switch part of the circuit on the
supply side or ground side of the relay coil?  Is there any standard for
this or reason to go one way or the other ?

 

Thanks for any thoughts you all have on the subject.

 

Michael Boswell

Austin End Of the Line Kite Team - Kite #4

http://Austineol.com

Picture Gallery at http://www.pbase.com/mboswell