Re: [Paparazzi-devel] Joystick question

[Martin Mueller]

Hi Chris,

the original idea for joystick was to have a very short transmission 
time. It turned out that the first implemented RC_3CH message takes 1ms 
to transmit as XBee broadcast message (measured with a HF meter). Most 
of that time is guard time, addressing and checksums. An additional byte 
only takes some tens of microseconds to transmit.

The mode information is vital to the message. If mode change information 
is lost and the aircraft interprets auto1 controls as manual controls 
you could have an issue.

For RC_3CH the mode was encoded into the throttle byte. As long as you 
do not want to do 3D hovering UAVs should be fine with a 6-bit only 
throttle resolution.

Martin

On 08.05.2011 07:44, Chris wrote:
> Hi.
> I finally made everything work well with my Saitek Aviator and i also
> made some changes
> that aim in reducing modem bandwidth so i need to ask for your opinion
> on those.
>
> 1) added a variable to the rc_datalink.h and .c files
> ("datalink_pprz_mode") that controls the autopilot's mode:
>
> extern volatile int8_t datalink_pprz_mode;
>
> #define NormalizeRcDl(_in, _out) { \
> _out[RADIO_ROLL] = (MAX_PPRZ/128) * _in[RADIO_ROLL]; \
> Bound(_out[RADIO_ROLL], MIN_PPRZ, MAX_PPRZ); \
> _out[RADIO_PITCH] = (MAX_PPRZ/128) * _in[RADIO_PITCH]; \
> Bound(_out[RADIO_PITCH], MIN_PPRZ, MAX_PPRZ); \
> _out[RADIO_YAW] = (MAX_PPRZ/128) * _in[RADIO_YAW]; \
> Bound(_out[RADIO_YAW], MIN_PPRZ, MAX_PPRZ); \
> _out[RADIO_THROTTLE] = ((MAX_PPRZ/255)*(127+ _in[RADIO_THROTTLE])); \
> Bound(_out[RADIO_THROTTLE], 0, MAX_PPRZ); \
> _out[RADIO_MODE] = MAX_PPRZ * (datalink_pprz_mode - 1); \
> Bound(_out[RADIO_MODE], MIN_PPRZ, MAX_PPRZ); \
> }
>
> 2) The variable was added to the settings.xml file and the joystick .xml
> file was configured to change the variable like this:
>
> <message class="ground" name="DL_SETTING" on_event="stick_right_button">
> <field name="index" value="IndexOfSetting(datalink_pprz_mode)"/>
> <field name="value" value="2"/>
> </message>
>
> <message class="ground" name="DL_SETTING" on_event="stick_center_button">
> <field name="index" value="IndexOfSetting(datalink_pprz_mode)"/>
> <field name="value" value="1"/>
> </message>
>
> <message class="ground" name="DL_SETTING" on_event="stick_left_button">
> <field name="index" value="IndexOfSetting(datalink_pprz_mode)"/>
> <field name="value" value="0"/>
> </message>
>
> That way i don't need the "MODE" portion of the RC_4CH message so the
> message length is now reduced by one byte and since that particular
> message is repeated at a high rate this should reduce bandwidth usage,
> am i correct or i dont gain anything by doing that?
>
> Chris
>
>
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