Maxwell Gets an Emergency Stop

22 Mar 2011 maxwell  robots  I had ordered the emergency stop when I bought the first round of parts for Maxwell, but I hadn't actually designed a location to attach it to on the robot. This weekend I rebuild a number of components on Maxwell, installing a new base, upgrading the torso wiring harnesses, and installing the E-stop (seen behind the arm, protected by the torso column):


The E-stop is from Digikey and is the type it latches when pressed, such that you need to twist it to release and restart the current flowing.

Maxwell's ArbotiX is powered off the USB connection, allowing all 12V power to run through the E-Stop. Pressing the E-Stop then stops all the motors and servos, while the ArbotiX continues to run and interact with the PC. On releasing the E-stop, everything comes back to life nicely.

Sensors Hate Dark Surfaces

20 Mar 2011 maxwell  robots  ros  Previously I've mentioned my issues with the low cost Hokuyo URG-04LX-UG01, even going so far as to say that the laser in the Neato XV-11 robot was better. One of the major differences between Maxwell and his little Armadillo cousin is that on Maxwell I have mounted the laser about 6" off the ground, versus the 2" of the Armadillo. Interestingly, this has had a huge impact on performance -- our walls here in the lab are mostly white, and the laser works much better on the walls than the black base trim:

I've also found that the same black paint is on our doors, and wreaks havoc on the Kinect. The image below shows the RGB point cloud -- this is a Sunday, both doors are shut, yet invisible:

Luckily, it looks like the laser picks up the doors when close, so I won't have to worry about Maxwell driving through an invisible doorway.

Mapping with Maxwell

20 Mar 2011 maxwell  arbotix  robots  ros  slam  I've spent a bit of time tuning the PID and cleaning up the control and feedback from the motion system on Maxwell lately. This afternoon I collected a very nice dataset and map of our lab at ILS:


As has been seen before, gmapping "shortened" the hallways (that door at the end of the hallway on the left should be about 2 meters farther down the hallway).