hi Brice,

The teleop requirements for different robots tend to be a little
different, so there isn't a unified teleop node (either joystick or
keyboard) for all robots.  Usually what happens is what you're doing:
take the most similar teleop node you can find and adapt it to your
circumstances.  If someone were to take the time to develop
sufficiently parameterizable teleop nodes (probably one for joystick
and one for keyboard), it would be a great service to the community.

As to sending zero velocity, you want to do this in two places:

(1) In the driver (the node that's talking to the motors), there
should be a watchdog that will halt (or limp, as appropriate) the
motors if a fresh command hasn't been received within a certain period
of time (depends on the robot, but often a couple 100s of ms).
(2) In the teleop node, there should be a watchdog that sends zero
velocities if there hasn't been fresh input from the user within a
certain period of time.

The watchdog in (1) is essential, regardless of whether you want to
teleop the robot.  You need to know that the robot will stop if nobody
has very recently told it to go.

The watchdog in (2) is also important, but less so than (1).  Btw, you
can figure out when to send zero velocities from a console-based
program without Xlib by noticing that it's been a while since you
received a new character.  The downside of this approach is an initial
stutter when holding down a key: the first keypress generates one
character, which gets the robot moving; then there's a delay, during
which the robot stops; then the keyboard's repeat mode engages and you
get a stream of characters, which gets the robot moving continuously.
This behavior is not ideal, but then, keyboard teleop isn't ideal.

	brian.


On Tue, May 24, 2011 at 9:44 PM, brice rebsamen
<brice.rebsamen@gmail.com> wrote:
> I am looking for a way to remote control my robot
> - for quick testing of the base control drivers
> - for data collection
> - to return the robot to the storage area without having to carry it
> - etc.
>
> The only code I could find was the teleop_turtle_key.cpp. I adapted it
> to my robot (i.e. changed a few names, and converted from
> turtle::Velocity msg to geometry_msgs::Twist) and it works. However,
> it has a problem: there is no way to set the velocity to 0 (I could
> introduce an extra key to stop though). This is due to the nature of
> the code: it does not handle key press and key release events. This
> also means that it cannot move and turn at the same time.
>
> I have written a code to do that. It relies on Xlib. It opens a small
> X window and get the key events from there. It works fine. I could
> port it to ROS and make it available.
>
> But I wanted to know what was already there. I cannot believe nobody
> has done this before.
>
> Regards
> Brice
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