We have a 8 motors mounted coaxially on 4 spars in an X configuration. We originally used the Hoverfly Pro board but switched to the APM1 hoping it would give us more flexibility. I was hoping we could use the APM Planner (ver 1.1.45) to upload a firmware version that supports our motor configuration but didn't see it in there. It seems you have a setup similar to ours controlled by an APM1? I was curious how you got it running if you did.
Here is a video of our copter controlled by the Hoverfly Pro board.
You have two options to set up the X8 coaxial quad with. One option, which is what I'm currently using is that the two motor on one arm take the APM output signal from just one output channel so only 4 output channels are used. The top and bottom motor counter rotate because one is upside down. (in other words they are actually turning in the same direction) So the setup on the APM for this is the same as if its a quad with only 4 motors.Mine is setup as X configuration but + can also be done.
The other option is you can have it set up that all 8 motors are controlled independently by the APM and this is just a new feature added last month on APM. Ive not tried this yet, but will do in a few weeks time.
The advantage of having the eight motors independently controlled is you can have the top and bottom group set at different speeds. Some research shows that its much more efficient for coaxial props if the bottom motors are slightly faster then the top motors. From memory I think its a ratio that the top props turn at between 93% to 95% of the speed of the bottom motors to get the best efficiency. There is quite a lot of discussion on this on the www.openpilot.com web site forum.
The other advantage is if you loose one channel then you only loose one motor and it will still fly where as if its as I have it setup now and I loose one channel then it will drop out of the sky because both motors will stop. Although the likely hood of loosing a channel signal is quite rare and failures are usually hardware related. A few weeks ago I had one motor burn out while in flight and the copter APM full compensated and it kept flying with hardly a noticeable difference.
This is very helpful. We are forced to go with 8 motors because. It seems that the counter-rotating X8 setup has just been or will very soon be supported on the APM1. That's great news. Do you have any idea where we would find the X8 firmware might be found?
In the meantime we'll definitely try your brilliant technique of fooling the APM1 into thinking its flying with 4 motors. Fingers crossed!
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