[ros-users] controllers for car-like robots

[DRamachandran at hra.com]

Thanks...I might be able to use the stuff in art_pilot. I'll let you know. 


~Deepak




"Jack O'Quin" <jack.oquin at gmail.com> 
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12/09/2010 02:20 PM
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Re: [ros-users] controllers for car-like robots







On Thu, Dec 9, 2010 at 2:08 PM, <DRamachandran at hra.com> wrote:

Eitan, Tully, Jack, 

    Thanks for your help.  I looked through the  ART code, and it seems to 
me they have divided up the code into task specific controllers for e.g. 
following lane, u-turn etc.  rather 
than using a single control algorithm like DWA. It seems that most of the 
Urban Challenge teams did this... is there a reason why? Is it that 
generic controllers aren't good enough for Ackerman drives? 

I don't know about other teams, but one of the DARPA Urban Challenge 
requirements  was to obey the California Drivers' Handbook when 
interacting with other traffic [1]. For that, we found an hierarchical 
state machine very helpful. None of it was motivated by Ackermann steering 
constraints.

As we re-implement our navigation using ROS, we will probably retain the 
state machine, but migrate it to smach.

Our navigation package was written in a hurry for the competition. It is 
mainly reactive control for following lanes and obeying the rules of the 
road. The main "planning" is  a simple A* to discover a route through the 
road network (in the commander node). The ROS version is not a complete 
port of our 2007 code. It still lacks obstacle avoidance (we are 
reimplementing that using ROS messages), but it does work well on our 
car. 

As mentioned before, art_nav is probably not what you want, but you're 
welcome to any parts that seem useful. The Ackermann steering and servo 
controls are mostly implemented in the art_pilot and art_servo classes. 
Maybe some of those interfaces are worth looking at.

Our "zone" controller, written by Patrick Beeson, deals with navigating in 
unstructured parking lots. It does some planning using Voronoi graphs and 
other techniques. It is not yet ported to ROS, but the code is there if 
you want to look at it. That may be more relevant, depending on your needs 
and goals.

[1]  http://www.jopha.net/index.php/jopha/article/view/14
-- 
 joq
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