Default servo position facility

[Jeremy Morse]

Hi,

One of the things occasionally discussed as an enhancement to the kit,
is allowing people to set the default location of the servos, when the
kit starts up. Right now (AFAIK), they reset to position zero, then can
be modified by the team when the robot code is launched by the button.

I believe it's still a problem as Headington were disqualified from some
matches for not staying in the 50x50x50cm^3 space at the start of the
match. Their workaround was to begin the robot in custom-firmware-setup
mode, set the servo positions, then call robot.wait_start(), leading to
their servos being in the right position at the start of the match.

That's not a general purpose workaround, as there are cases where
position zero on a servo might put a mechanism into an invalid position.
There should be a facility for configuring these positions before the
servo board has it's 5v rail turned on (presumably as part of the
custom-firmware scenario). Are there any plans afoot for this; is there
something I can contribute to here?

--
Thanks,
Jeremy

[Peter Law]

Hi,

Jeremy wrote:
> .. allowing people to set the default location of the servos, when the

> kit starts up. Right now (AFAIK), they reset to position zero, then can
> be modified by the team when the robot code is launched by the button.
>

> ... workaround was to begin the robot in custom-firmware-setup
> mode, set the servo positions, ...

>
> That's not a general purpose workaround, as there are cases where
> position zero on a servo might put a mechanism into an invalid position.

This has just come up again in the forums [1], with the same
workaround being offered.

I think that it's actually perfectly fine to say that people should
use the custom-init flavour of the API for this sort of thing, the
issue is that we could damage things by forcing the servos to position
0.

If we accept that premise, then the problem scope becomes somewhat
smaller and a fairly obvious solution presents itself: don't make the
servo outputs live until they're explicitly set to a value.

While this still (presumably) requires a firmware update, it should be
easier to achieve.

Thoughts?

Thanks,
Peter

[1] http://srobo.org/forum/394