Transmitter failure, but APM saves the day
I finished my SkyWalker build last night, and went out to CMAC to take it for its first flight. All the ground tests looked good (including the new 'system check' in mavproxy) so we took it for the first flight. About 60 meters into the flight I heard "MODE STABILIZE" from mavproxy, and I lost control. Jack and I watched as the SkyWalker glided gracefully to a perfect landing in the grass while we wondered what had happened.
After looking at the mavlink logs, we saw that the APM had started to receive failsafe values from the receiver soon after takeoff. Jack thought the antenna on the receiver might be a bit dodgy, so we replaced it with a 2nd receiver I happened to have in my box of spares, and we tried again. It was almost an exact repeat of the first flight, losing transmitter control soon after takeoff, APM going to STABILIZE mode, and the SkyWalker landing perfectly in the grass.
We then started to do more extensive ground tests and found that the Turnigy TGY 9X transmitter had failed. It has previously had good range, but for some as yet unexplained reason it now doesn't do more than 60 meters or so.
We had a good look inside the transmitter module, and we can't see anything wrong. The antenna cable is a little bit abraded on the transmitter, although it isn't clear if that is the cause of the issue. Strangely, the range test button doesn't find the problem. I get the same range with the range test button pressed as when its off. When I got home I checked the range test switch in case it was faulty and it seemed to be working fine (at least as far as my multimeter can tell). It looks like I might need to buy a more expensive transmitter. Pity, as otherwise the TGY 9X has performed well!
The real hero of the flight was the APM. The failsafe values in my receiver had the mode switch set to STABILIZE, and it glided the plane down to a perfect landing both times. I don't have it set to RTL for failsafe as it would be a breach of the club rules to circle above the takeoff point (you'd be going over the clubhouse).
Tomorrow we're going to try a different transmitter and see if the SkyWalker can live up to its reputation as a great UAV. We've got a "mow the lawn" search pattern setup to simulate the type of search we will be doing for the outback challenge. If that goes well we will put the pandaboard and ptgrey camera in the plane and get back to testing our algorithms for finding Joe.
Once things look OK with the SkyWalker we'll see about putting all the equipment in our CyberHawk UAV, which is what we plan to use for the OBC next year.
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Comment by Chris Gough on April 25, 2011 at 6:07am -
You learned this lesson cheaper than most :)
+1 for multiplex RC gear.
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Comment by simonl on April 25, 2011 at 7:57am -
+1 for UAV gear making r/c SAFER ;-)
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Moderator Comment by Darren on April 25, 2011 at 8:57am -
I would suggest a new module and receiver pair. Proably not the radio itself.
I am real happy with the FrSky combo I bought last year for it...
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Comment by Teejay on April 25, 2011 at 9:59am -
Well, you could also try using a separate power system? Maybe with a BEC for the RX and APM?
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Moderator Comment by Gary Mortimer on April 25, 2011 at 10:09am -
Is that a CASA reg in the side of the machine?? 08 Western Australia??
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Moderator Comment by Hooks on April 25, 2011 at 11:44am -
08WA looks like a bird I know :-) 3m platform (I call it Mugin)
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Comment by Nathaniel Caner on April 25, 2011 at 2:21pm -
With regard to the use of RTL at club fields that do not permit flight behind the flight line (which would be any AMA club field). I had suggested a while back that an option to offset the home position based on it's relative position perpendicular to the runway. In other words it would allow you to offset the home position say 50 meters to the East when you are located on the West side of a North South oriented runway. This would place the RTL location in the "legal" zone. The suggestion was accepted as an Enhancement for a later release (this was before 2.7 Ardupilot), as of yet it hasn't been implemented yet.
Regards,
Nathaniel
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Developer Comment by Andrew Tridgell on April 25, 2011 at 2:55pm -
yep, its from Perth in Western Australia, and yes, it looks just like a Mugin :-)
btw, does anyone know what transmitter modules you can use to replace the one in the Turnigy TGY 9X transmitter? Can I just put in any of the Spektrum ones?
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Comment by I.S. on April 25, 2011 at 4:51pm -
I am very curious about the 9X problem since I have the same transmitter.
Did you try the range function but a few meter away (say 5-10m) and with your body between the Tx and Rx path?
This should perform a real range test.
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Moderator Comment by Brian on April 25, 2011 at 6:49pm -
The STABILIZE mode is the better option for failsafe. RTL would put you circling around with no transmitter to land with... FBW keeps you flying to where you have pointed it to go, again without a transmitter. As explained it safely glided is way down to a safe landing.
Good job.
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