Re: [Paparazzi-devel] Lisa/L Servos

[antoine drouin]

Hi Andreas

You're correct, lisa/L is designed to drive 6 servos directly. All
pins of the 64 pins STM32 are used. If you're not using some
peripherals ( like I2C1, which is commonly used to talk to the I2C
motor controllers on quadrotors) I could write code to use those pins
to drive two more servos ( this is how I designed lisa/M, 6 servos and
I2C1 or 8 servos ).
Now what worries me with driving many servos from the autopilot is
that your many servos are probably located far from the autopilot. The
PPM signal is not meant to travel long distances and you might end up
with jitter. Also you may not be able to supply them from the internal
power supply of lisa/L ( there's one dedicated power supply for servos
and USB but it's only good for 2 amps).
The solution that I would advise in a big vehicle is to use a servo
driver and a dedicated power supply ( BEC) located close to groups of
servos. The connection between the autopilot ( lisa/L) and the servo
driver would be CAN which is a differential signal designed to travel
long distances and be immune to electrical perturbations.
The CSC board (Can Servo Controller) could be used for that (
http://www.poinix.org/images/csc_1_0.jpg )
An even better solution would be to use a lisa/M (
http://paparazzi.enac.fr/wiki_images/Lisa_m_top_small.png )

You could have for example one servo driver in each wing of your
vehicle ( and maybe another one in the tail ). The electrical
connection would be only two wires for CAN and two wires for power.

HTH

Poine


On Fri, Nov 19, 2010 at 9:20 AM, Andreas Gaeb <address@hidden> wrote:
> Hello everybody,
>
> I'm thinking about using the Lisa board in an airframe (fixed-wing twin
> engine) with rather a lot of control elements. Studying the schematics,
> I'm not quite sure how many servos can be connected as a maximum. Am I
> right to assume that there are 6 PWM pins available in the connectors,
> of which one has to be used as input for the PPM signal?
> Are the motor controller connectors designed to run the MicroKopter
> motor controllers?
> If so, does anybody know of any other converters to transform the motor
> controller signal to PWM?
>
> Thanks in advance for any help,
>        Andreas
>
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