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Re: [Paparazzi-devel] simultaneously using two autopilot systems for rel

From: Chris Gough
Subject: Re: [Paparazzi-devel] simultaneously using two autopilot systems for reliability
Date: Mon, 25 Nov 2013 19:54:14 +1100

How will you (the FPGA or the second autopilot) know if the primary autopilot freezes?

We did this with 74LS157 multiplexer chip & AVR for the Outback Challenge 2013 competition. It was a proto-board/wire-wrap implementation (no PCB to share sorry) but another team has made a cleaner version here:

That device is for complying with competition rules, not solving a reliability problem. The extra complexity is dubious safety in my opinion.

Why is your autopilot freezing? Have you ruled out brownout? Can you reproduce it on the bench?

Chris Gough

On 25/11/2013, at 6:57 PM, Refik Sever <address@hidden> wrote:



Our autopilot (Lisa_M) freezes sometimes. We want to implement a reset procedure using watchdog. Did somebody use watchdog timer of stm32 and implement a reset procedure?


When the autopilot freezes, we can not use manuel mode and the airplane becomes out of control. Last week, the modem power was 25mW (Digi 868Mhz) and the autopilot was gone.


We are planning to use an FPGA board and take the RC receiver signals to the FPGA. If the autopilot freezes, then the FPGA will continue to drive the servos using manuel mode. We added 2 ppm inputs to the FPGA, and if one of the receivers fails, FPGA switches to the other receiver. We can add more receivers. Currently we are taking ppm inputs, but we can also take RC signals directly to FPGA and then there will be no need for 8 ch ppm encoders. The FPGA board must be very reliable.


We are also planning to add a second autopilot (maybe umarim) to the system. The servo outputs of the autopilots will be connected to FPGA, and if one of the autopilots freezes, then the FPGA will switch to the other autopilot.


We haven't yet decided how to connect the autopilots. There are some options:

1. We can add the second autopilot with a second modem using API mode and the GCS will see the two autopilots as 2 different airplanes.


2. We can add only one modem and both of the autopilots will receive same commands from GCS, but only one of them transmits data to GCS. 


3. The second autopilot will not have a modem. It will always be on standby mode. If the primary autopilot will freeze, the second autopilot will bring the plane to the standby.



We haven't started working on 2 autopilot system and I don't know if the second option will work or not.


I am waiting for your comments and help about watchdog timer.









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