Hi everyone
I'm thrilled to say I've just had a set of successful test flights of my X8 platform ballasted up to about 5.6kg. This is the platform:
http://www.horizonimaging.co.uk/blog/20 ... -platform/
It seems to fly very well, however I have a few questions.
This is too much vibration isn't it
I'm really at a loss as to what I can do to reduce the vibrations. I've spun each prop up in turn to around 60% throttle and the chassis has felt very smooth and vibration free. I also spun up each pair of props and it's been similar. Here's a plot of the ACC values when I did these tests:
There are 4 sets of 3 tests: top prop, bottom prop, both together (again, spun up to 60% throttle each time). Since producing this plot I balanced the props still further by adding tape and checking the vibration in the frame so it should be even better now.
I still wonder whether it's the harshness of the motor demands that's causing additional vibration – here are all 8 MOT plots from my flights today:
And here's just a single MOT plot from a single hop so you can see it better:
I've seen other people's MOT plots and they're practically slightly undulating lines – none of this harsh noise nonsense! Is there anything I can do to tame these MOT demands? I very much doubt the motors can respond that quickly anyway, and in the worst case it might even cause the ESCs to lose sync the demands are changing so rapidly ...
The AQ board is mounted on reasonably hard M3 bobbin anti-vibration mounts. Before I added these I had an incurable motor 'ringing' problem, so they do seem to be helping slightly (the vibration was just as bad without them, but they've obviously made a subtle difference to the type of vibration being picked up).
Another slight problem I noticed was that engaging alt/pos hold always made the platform sink very slowly. You can see this in this GPS HEIGHT plot – you can actually see the height decreasing each time I engage the alt/pos hold mode:
I tried increasing the Navigation Altitude Position P and I values but to no real affect. What parameters should I be adjusting to give the altitude hold more authority?
Other than that it seemed to fly very well, quite remarkable considering the heavy vibration present! I wasn't able to induce any oscillations in flight when giving sharp control inputs so that's good. When hovering in ground effect there was a little oscillation though, but maybe that's a good sign – not to see it in flight but to see a little oscillation in turbulent air just above the ground?
By the way, here is my EagleTree plot from the same flight:
Approximately 31A to hover which equates to around 12.5 minutes of flight time if using 80% of the battery's capacity – not too shabby
Many thanks for your help, it's always much appreciated.
David