[ros-users] About ROS NXT

[Tully Foote]

On Sat, Dec 18, 2010 at 1:41 PM, Max B <skinkworks42 at gmail.com> wrote:

> NXT bluetooth has extremely high latency specific to the NXT communications
>> protocol.
>
>
> Would it be possible to work around this by writing an NXT program (or
> firmware) that checks the bluetooth every so often for commands, acts on
> those commands, and feeds back sensor data to the computer? MSRS uses this
> approach to NXT development.
> I am on an FTC team, and our robot can get joystick messages at 10Hz over
> bluetooth, which is much faster than ROS can send the motor commands to the
> NXT.
>
> It is my impression that it is a hardware issue for the NXT radio switching
between send and receive mode.  I've attached some references below, though
I can't find the best writeup I remember reading.

We determined that the performance of the bluetooth was inadequate for
closing the loop for over bluetooth and decided not to optimize the ROS
interface.  You'll find that much of the current bandwidth is used for
reading from the sensors at high rates.  Optimizations could be made so as
to batch up messages and send them together so as to not require the
bluetooth radio to switch directions as often.

Tully

http://www.tau.ac.il/~stoledo/lego/btperformance.html
http://lejos.sourceforge.net/forum/viewtopic.php?p=8972&sid=47e39507ce3c3944b196466737a6794b
http://forums.nxtasy.org/index.php?showtopic=4320 Link broken, it might come
back but I think not. I haven't been able to find a copy anywhere.

-- 
Tully Foote
Systems Engineer
Willow Garage, Inc.
tfoote at willowgarage.com
(650) 475-2827
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