[ros-users] Inconsistant timing issues with powerbot-sh running P2OS

[Matt B]

Both the robot, and my laptop are running the latest version of Cturtle,
along with the latest version of the p2os node, and have run a few more
tests, while watching the output (the failsafe node, reports to ros_out when
either mode is activated or configuration changes are made)

And what I’m seeing is my code sending the commands as expected, when
expected based on the sonar data itself (both sonar data and the times of
activation, agree with the previous performance under ARIA libraries) but
especially in the case of the disable command being sent since an audible
response from the brakes on the powerbot engaging can be heard, a lag of up
to ½ a second or so can be heard, between when the failsafe algorithm sends
the disable command to /cmd_motor_state and when the motor brakes engage.  I
do expect a less noticeable lag on occasion of up to 100mS due to the way
the ARCOS controller itself works, but this is well beyond that. 

 

As for more specific information on each computer, the powerbot is currently
running ubuntu 9.10 and my laptop is running ubuntu 10.04x64. Without
modifying the p2os node itself, theres no way I can think of to be able to
tell whether the lag is coming from our network, the p2os node, or the ARCOS
controller communication itself. 

 

Matt

From: Tully Foote [mailto:tfoote at willowgarage.com] 
Sent: Tuesday, December 07, 2010 9:53 PM
To: User discussions
Subject: Re: [ros-users] Inconsistant timing issues with powerbot-sh running
P2OS

 

Hi Matt, 

Without a lot more information we can't help you much.  Please see
http://www.ros.org/wiki/Support#Guidelines_for_mailing_list_messages

I would suggest that you put in some debugging statements to make sure that
the obstacles is being detected.  If you can track down more specifically
where you think there is a problem and provide a way for us to reproduce the
problem that would allow us to help you.  

Tully

On 12/07/2010 09:20 PM, Matt Bergsma wrote: 

Hello;

 

Currently working on a Sonar Based ‘failsafe’ object avoidance code, which
was originally developed and tested in Aria, and since porting it from Aria
to ros – p2os I have found its gone from behaving as expected to being very
inconsistent at best, even after increasing its internal parameters so both
stop and stop/disable zones are significantly larger. I would expect part of
this would be lag in the subnet the robot and my laptop are connected into,
but even moving the code onto the powerbot these same issues are occurring.
Eg. The robot is hitting our test object.  

Note – The first set of tests had only the p2os node on the powerbot, and
roscore, my failsafe code, and a modified version of the teleop_keyboard
base code from the p2os package running on an hp tm2-2050 laptop, and when
the code was moved to the powerbot everything except for the teleop code was
moved to run on the powerbot but not utilizing the local loopback.

 

When this code was developed and tested in aria, it behaved as expected, and
its very light weight (running a simple profile in aria was giving run times
of around 28s for 1,000,000 sets of readings and decision on all the sonar
sensors) which ran on the powerbot itself, and the code hasn’t been
significantly modified, except to talk using the ROS framework to the
applicable channels. So I would expect it isn’t the issue. 

 

Hopefully someone can shed some light on the issues encountered.

 

Thanks, Matt Bergsma

 
 
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