Jack,

I say degrees here because the hardware command to the robot works this way.
You must specify to the robot it's maximum tilt angle, in degrees, with a
hardware configuration command (which will be available as a param or
service call, soon).

The -1 to 1 value of the linear.x or linear.y then acts as a scaling factor,
that is, it specifies the percent of the maximum tilt that should be applied
to the hardware, thus affecting the speed.

I thought it was important to make known what the commands were actually
telling the hardware to do, since this will vary on a per-configuration
basis. Maybe a better way to say it is *percentage of maximum tilt angle*,
which could then be interpreted in radians or degrees, knowing the
configuration of the robot (which is set and reported in degrees at the
hardware level).

Data published by the driver (when it gets there) will conform to all
standards and be specified in radians.

Thanks for the insight,
Nate Roney

On Sat, Oct 16, 2010 at 09:30, Jack O'Quin <jack.oquin@gmail.com> wrote:

> Nate,
>
> This looks like a cool device, definitely interesting for robotics
> work. Thanks for making a ROS package.
>
> On Sat, Oct 16, 2010 at 9:02 AM, Nate Roney <nateroney@gmail.com> wrote:
> >
> > The units are degrees for the forward/backward and left/right tilt. These
> > control the percentage of the maximum tilt (which is currently 30
> degrees).
> > Obviously, the more tilt, the faster it goes. I've found that anything
> more
> > than 25 degrees actually drives the drone to the ground, so I'm thinking
> of
> > adding a limit, and/or adding a rosparam allowing the change of the max
> > angle.
>
> Note that REP 103 also specifies angles in radians:
>
>  http://www.ros.org/reps/rep-0103.html#units
>
> As noted, there can be exceptions, domains where the default
> conventions are not appropriate. We should not be pedantic about it. A
> recent example came up with the GPS message discussion. Latitude and
> longitude should be expressed in degrees, not in radians.
>
> I made some similar mistakes in a couple of our autonomous vehicle
> messages [[http://www.ros.org/wiki/art_msgs]]. I now wish I'd gotten
> them right to begin with. The standards were not so clearly spelled
> out back then. In my experience, it is a lot of extra work to change
> messages later (more due to bag migration than to fixing all the
> references).
>
> Regards,
> --
>  joq
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