[ros-users] Navigation Stack on tight places

Steven Martin s34.martin at connect.qut.edu.au
Thu Nov 18 15:45:17 UTC 2010

Yeh I think my problem is related to odometry, the iCreates don't have any encoders. I thought they did but after looking closer at the driver I am pretty sure its just openloop. Do you have the parameters for amcl in your repository? I had a look but couldn't see them anywhere.

I have the code for the pursuit path follower checked in @ launchpad.net/cmr but its very incomplete. It will compile, you can launch it and it will try and follow a path but it doesn't have any obstacle avoidance and I think I have one of my signs wrong in the code as it  didn't appear to do much following  from the very limited testing I have done.

Have a look, its basically as stripped down as I could make a local path planner while still fitting in the ROS framework. Also due to the pretty well useless iCreate odometry I chose to implement this in the global frame and this may have some adverse affects if you are only running localiser @ 3Hz.

I will probably have time to look at this next week but I think this is a problem for anybody using nonholonomic robots with the Nav Stack so I would be surprised if someone else hasn't already got a better solution.


From: ros-users-bounces at code.ros.org [ros-users-bounces at code.ros.org] on behalf of Gonçalo Cabrita [goncabrita at gmail.com]
Sent: Friday, 19 November 2010 12:52 AM
To: User discussions
Subject: Re: [ros-users] Navigation Stack on tight places

Hi Steven!

"ts not a failure case but do you also see the one where it turns a little bit away from the path then does loop around to rejoin it.?"

You we also get that a lot! The robot never sticks to the path the planner outputs, it wonders around a lot.

We are using Roombas 560 with Eee PCs and Hokuyo lasers. We launch the Roomba the laser and the tf broadcaster on one file and map server, amcl and move base on another one. We have the map updaters running at 3Hz and the path planner at 5Hz. Still sometimes the EeePC skips a loop! Furthermore, I dunno how the Create is but our Roombas have nasty odometry! The encoders have only 1 channel with 4 pulses per motor turn!

Anyways, I'm not familiar with the nav stack code, but I would like to help if possible!

Gonçalo Cabrita
ISR - University of Coimbra

On Thu, Nov 18, 2010 at 2:35 PM, Steven Martin <s34.martin at connect.qut.edu.au<mailto:s34.martin at connect.qut.edu.au>> wrote:
Yep see that one all the time. I think the implementation of DWA is flawed for tank steer robots.

Its not a failure case but do you also see the one where it turns a little bit away from the path then does loop around to rejoin it.?

I started implementing just pure pursuit path follower to replace DWA but haven't quite got it working and been too busy with other stuff. I think we need to implement some other local planners or just path followers.

Also what are you using for the localization? I haven't been able to get AMCL to work reliably on the iCreates.
From: ros-users-bounces at code.ros.org<mailto:ros-users-bounces at code.ros.org> [ros-users-bounces at code.ros.org<mailto:ros-users-bounces at code.ros.org>] on behalf of Gonçalo Cabrita [goncabrita at gmail.com<mailto:goncabrita at gmail.com>]
Sent: Thursday, 18 November 2010 11:51 PM
To: ros-users at code.ros.org<mailto:ros-users at code.ros.org>
Subject: [ros-users] Navigation Stack on tight places

Hi everyone!

We've been using the nav stack on our Roombas for quite a while now, mostly on the corridors of ISR without any problems.

However we have a small 4mx3m arena we built specifically for testing odor search algorithms in which we recently started to run some experiments. We quickly found out that the nav stack has some problems moving the robot around in tight places. Quite often we get the behavior that can be seen in the following video...


In the video we are running a Roomba inside our arena in Stage with perfect odometry. The robot stalls against a wall and stays there for 30mins until we stop it. On occasion the robot eventually gets out after a while.

At first I thought this could be happening because of the poor performance of the EeePCs the Roombas carry around or because of the Roomba's crappy odometry, but in Stage on a Core2Duo laptop we were able to see the same behavior.

Has anyone experienced this behavior before?

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