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Altitude limiter (like a CAM) Version:1
(1 vote)

This is a working example implementing an alititude limiter (like a CAM) with a vario and the Taranis.

Features a programmable altitude and an ON/OFF switch.


Whats new
v1 Original version, for opentx r2940 and up

This is a working example of implementing an alititude limiter (like a CAM) with a vario and the Taranis.

The example is for a 3-ch Parkzone Radian but can be ported to any other system that has a vario.

The features are as follows :
- Shuts motor down at the programmed altitude or after 30 seconds.
- Programmable altitude in 8 meter increment (172, 180, 188, 196, etc)
- SA-down also implements a sticky motor cutout protection (SA-down enables THR)
- SG-mid enables the altitude limiter. Will cutout CH1 (throttle) at the programmed altitude or after 30 seconds. Needs THR fully down to re-enable another 30-seconds run.
- Plays a sound when altitude limit is reached and a different sound if time limit is reached first.
- SD-mid speaks the altitude every 5 seconds
- SD-low enables vario tones
- Spoken "Altitude limiter" on SG-mid (file provided)
- Spoken "Throttle held", "Throttle released", and "Throttle warning" (file provided)

The archive contains the program, the spoken Flight Mode WAV files to be placed in a subdirectory named "Sound/en/Libelle", and a few other wav files that need to be in the Sound/en directory.

How it works
The sticky motor cutout is pretty much the one that is installed by the "Sticky T-Cut" template. It replaces CH01 with -100 in the CH01 mix (see SAcutout) with the help of CH14, CSB and CSC.

SG- enables the altitude limiter function. Timer2 begins to run when the THR stick (by way of CH1) is first pushed forward. CS5 turns ON when Timer2 reaches 30 seconds. CS6 turns ON when the altitude reaches the programmed limit. There is a programming trick here with CS7 and CS8 to implement a logic flip-flop (latch) by ORing with self. CS7 latches CS5 (time limit) and is reset by CSB (THR stick returned to -100). CS8 latches CS6 (altitude reached) and is reset by CSB as well. CS9 (altitude limiter tripped) is an OR of both latched conditions (timer, altitude). In the mixer, CH1 (throttle output) is replaced by -100 if CS9 (altitude limiter tripped) is ON.

In the custom functions, Timer2 is reset when the THR stick returns to -100, ready for another run; each latch (timer, altitude) plays a distinct sound, and the main altitude limiter switch (SG-) lets know that the limiter is enabled.

The motor is actually permitted to run for 31 seconds (a>30) because of the limited resolution in the Timer custom function of opentx. Workaround: could be set for a 28 second run using value 00:27.
For the same reason, the altitude limit has a resolution of 8 meters.


Size 273.16 KB
Downloads 1492
Created 2014-03-20
Created by FabFlight
Changed at 2014-04-21
Modified by FabFlight

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#1 Fabien Gagne 2014-03-31 01:20
If the model climbs at 10 m/sec (which is typical for an ALES ship) and the telemetry refreshes every 100 msec, the worst this feature would overshoot compared to a CAM would be 1 meter. So setting the altitude limit to 196 meters should not overshoot what an actual CAM would have done.

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