[ros-users] controllers for car-like robots

[Jack O'Quin]

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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