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

[Refik Sever]

Hi Chris,

 

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

 

We are planning to take a signal from the autopilot which regularly kicks the FPGA (like regular watchdog timer of microprocessor).  Sometimes, the system timer led of autopilot works (blinks at a different rate then 1Hz), but the imu does not work. Therefore, we may also get the AHRS align led.

Another option is, the FPGA can listen the Modem RX link. And from GCS, we can send a command to the FPGA showing the autopilot that we want to switch.  When the FPGA detects this command, it switches the autopilot.

 

 

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

 

When the modem TX power is 25mw or higher, then the IMU does not work properly and also does the autopilot. It still sends messages, but the behaviour is not normal. The PFD screen does not work properly etc. We can see it on the bench. When the TX power is 1mW, then it works properly.

 

Sometimes, it completely freezes and the leds do not blink. I think that we have also problems in upload.  We haven't yet tried the verification procedure of uploaded stream.  The autopilot starts working, but when it jumps to a problematic part of the code, then it stops.

 

Refik

 

 

 

From: address@hidden [mailto:address@hidden On Behalf Of Chris Gough
Sent: Monday, November 25, 2013 10:54 AM
To: Paparazzi UAV devel list
Subject: Re: [Paparazzi-devel] simultaneously using two autopilot systems for reliability

 

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:

 

http://h2joe.wordpress.com/2013/09/12/team-builds-custom-failsafe-device/

 

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:

Hello,

 

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.

 

Regards,

Refik

 

 

 

 

 

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