April 2, 2010 12:47
I did make the waypoint arrival circles smaller. This problem is happening when I'm using nav, so there isn't any XTE built up, beyond the ordinary minor course variation. This is only happening when I reach a waypoint on nav and MacENC switches to the next waypoint, so it is hard to imagine that the fluxgate is intermittently going bad at exactly that moment. Further, the magnetic heading data from the autopilot and MacENC are in agreement while this happens.
Though I see this problem when switching from one waypoint to the next, it is not strictly true that the problem is isolated to that precise situation. Some times I see it happen when I first switch to nav, immediately after hitting goto (no XTE yet). When it happened a few days back, I had been on nav only 7-8 minutes before the waypoint advanced on my route. I could see that MacENC was sending new headings in a smooth steady fashion with XTE increasing sharply from zero. It even stopped momentarily, for example going to 70° when it should be 90°, and after some XTE was generated, it decided to change the heading to 30°. I steered the boat back to the proper course with XTE at zero again and switched to nav, and it immediately veered back toward 30°. After steering the boat along the route line for another 10-15 minutes, I switched to nav again and the problem was gone. The boat then steered on nav literally almost into its harbor stall.
The one thing I see in all of this is a time component. It seems that the problem only exists during the first 20 minutes or so of following a route. The autopilot doesn't do anything unexpected at any other time (i.e. not on nav). MacENC will eventually correct itself and come back to the original course line if I have enough room to let it do so. While this strongly resembles the action I saw with the NMEA feedback loop, it happens at a different (nonrandom) time.
I've seen this happen dozens of times. The impression that I get is that there is a data table somewhere and it takes a certain amount of time to overwrite the old data. It is like MacENC needs to calculate some compensation to account for XTE before it can follow the route accurately. One thing I haven't tried is testing nav to a single waypoint vs a route. Every time that stands out in my mind I was following a route.
Though I see this problem when switching from one waypoint to the next, it is not strictly true that the problem is isolated to that precise situation. Some times I see it happen when I first switch to nav, immediately after hitting goto (no XTE yet). When it happened a few days back, I had been on nav only 7-8 minutes before the waypoint advanced on my route. I could see that MacENC was sending new headings in a smooth steady fashion with XTE increasing sharply from zero. It even stopped momentarily, for example going to 70° when it should be 90°, and after some XTE was generated, it decided to change the heading to 30°. I steered the boat back to the proper course with XTE at zero again and switched to nav, and it immediately veered back toward 30°. After steering the boat along the route line for another 10-15 minutes, I switched to nav again and the problem was gone. The boat then steered on nav literally almost into its harbor stall.
The one thing I see in all of this is a time component. It seems that the problem only exists during the first 20 minutes or so of following a route. The autopilot doesn't do anything unexpected at any other time (i.e. not on nav). MacENC will eventually correct itself and come back to the original course line if I have enough room to let it do so. While this strongly resembles the action I saw with the NMEA feedback loop, it happens at a different (nonrandom) time.
I've seen this happen dozens of times. The impression that I get is that there is a data table somewhere and it takes a certain amount of time to overwrite the old data. It is like MacENC needs to calculate some compensation to account for XTE before it can follow the route accurately. One thing I haven't tried is testing nav to a single waypoint vs a route. Every time that stands out in my mind I was following a route.
Edmund