Re: [Paparazzi-devel] Lisa/L Servos

[Andreas Gaeb]

Hi Poine,

Am 19.11.2010 14:48, schrieb 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. 
so the PPM input is not on the CON_SERVOS_2 connector, though it is
named RC_PPM on the schematic? What pin do you connect the receiver to?

> 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 ).
I'll probably need one I2C for sensors. Is I2C2 used by default?

> [...] 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 servos will definitely need their own power, as even the motor BECs
cannot provide enough current for eight metal gear servos.

> 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.
I had already thought about using an Atmega or PIC based I2C to PWM
converter, there are some on the internet.

> 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.
Do you know if CAN is better in this case than I2C?

> The CSC board (Can Servo Controller) could be used for that (
> http://www.poinix.org/images/csc_1_0.jpg )
is this what the sw/airborne/csc software and misc/csc hardware is
about? Is there any documentation on this?

> An even better solution would be to use a lisa/M (
> http://paparazzi.enac.fr/wiki_images/Lisa_m_top_small.png )
Is there already more information about this than on the Lisa wiki page?

> 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.
Ailerons, flaps and motor controllers are no more than 60 cm away. I
think I'll to drive these directly from Lisa and see about the jitter.
The tail is farther, so I'd rather put an extra controller there.

> 
> HTH
It does.

Thank you very much,
        Andreas