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Sat, 07 Oct 2006

more SRV-1 "swarm mode" adventures ...

After starting to consider how to employ IR beacons for localization and navigation in a multiple robot environment, we recognized a benefit to assigning specific ID's instead of random ID's to robots that were acting as beacons, as that would give us control over the positioning of the beacons. Fortunately, there's a convenient mechanism on the SRV-1 controller which enables us to assign fixed addresses using some of the unassigned i/o pins.

As seen in the photos below, we added 2.7k-ohm pull-up resistors to some of the robots to connect any combination of E5 E6 E7 and E8 pads to the +3.3V connection on the right rear edge of the controller. Basically, this gives us 4 bits of addressing (16 combinations), though 0x00 (no connection) is a reserved address. As you can see in the first photo, we've connected E5 to +3.3V through a 2.7k resistor, and when we read the data bits, we find that this robot has been assigned ID = 0x01.

With a second robot, we connected E6 to +3.3V through a 2.7k resistor, which provides this robot with a fixed ID = 0x02.

Robots that don't have fixed ID's are still assigned a random ID, as described earlier. Beyond this, we added commands to enable/disable a beacon transmit (xmit) function and commands to enable/disable a beacon locate function. Putting this all together with the "swarm mode" addressing functions, we have a control mechanism that provides a lot of flexibility without a lot of complexity.

Command	Response	Description

'x'	'#x'	enable "xmit IR beacon" mode -
		robot in this mode will transmit 1's complement of its ID number
		e.g. if ID = 0x01, bit pattern 0xFE will be sent via IR xmit function

'X'	'#X'	disable "xmit IR beacon" mode

'laa'	'##laa'	enable "locate beacon" mode - search for beacon with ID = 'aa'
		only functions in "wander mode" - if beacon is detected, robot will steer toward it
		though "wander mode" function will prevent collisions

'L'	'#L'	disable "locate beacon" mode

Swarm Mode

'r'	'##raa'	read robot ID bits (E8 E7 E6 E5) or pick a random robot ID number for swarm operation
		'aa' is an 8-bit binary value that can't equal 0x00 or 0xFF
		once robot ID is set, robot goes automatically into "swarm mode" and only processes '@' commands

'R'	'##raa'	pick a different robot ID number (used if several robots picked duplicate random ID's)
		'aa' is an 8-bit binary value that can't equal 0x00 or 0xFF

'@abc'	'#c or ##c...'	swarm mode command - only active after robot ID is set ('r' or 'R' commands)
		ab = robot id, a=high digit, b=low digit, c=command
		e.g. '@275' tells robot 27 to stop
		if ab = 'FF', command goes to all robots
		e.g. '@FFw' tells all robots to enter "wander mode"
		response code is identical to non-swarm mode response for command

Here's a 600kb Quicktime clip of 4 SRV-1's operating in close proximity in "wander mode", where the robot (0x01) in the lower right of the video has been designated as the beacon, and the other robots have been instructed to locate the beacon. As before, the robots are controlled by a single base station on a common radio channel using the new "swarm mode" commands. You can click on the screen shot to launch a viewer -

Posted Sat, 07 Oct 2006 22:02 | HTML Link | see additional stories ...