As an attempt to eventually build a tandem, I have 2 JR Propo Nex E6 550 heli’s I’m wiring up with a spare Pixhawk 2/ Cube. The first goal is to simply get one of the heli’s up in the air with the pixhawk, and then machine a custom frame for the tandem later. I spent a while setting up a decent vibration dampening system, and also watched as many videos as I could to setup the swash servos. However, it just crossed my mind that the swash plate isn’t the usual 120 degree CCPM type, but instead the 140 degree style by JR Propo. I configured the servo positions to 40, -40, and 180 degrees, but the distance from the ball joints to the shaft varies. The forward 2 arms use standoffs and are about an inch in length each. The rear servo is only about 0.5" from the shaft. The problem is if I roll the heli, the swash moves up and down which causes some funky flight behavior. Pitching the heli keeps the swash from sliding vertically. Is there a way to compensate for uneven swash arms in the software before redesigning the swash plate? You can see the swash on JR’s website here:
http://www.jrpropo.co.jp/english/heli/nex-e6/image/gallery/550/img04.jpg [JR Nex E6 Swash]
Kris,
As far as I know, the software currently doesn’t support that kind of swashplate. All of the arms are assumed to be of the same distance from the shaft.
Bill
Bill,
Thanks for the quick reply. Yeah, I had a feeling this might not be possible through software. I suppose I’ll permanently alter the swash plate to make all arms equal or just replace the rotor head with something better.
Kris
It won’t make any difference on collective. But don’t you think, Bill, that the attitude controller would just sort of compensate? There will be slower response on roll, and quicker response on pitch for the same respective servo travel. I think. But I can’t think of a logical reason why the system wouldn’t handle that with some tweaked tuning.
Edit:
Actually, I wonder if the mechanical part of the elevator servo isn’t made with a different ratio so it’s not all that much difference between the swash links for the same servo travel?
Chris,
So I haven’t modified the swash plate yet, but instead decided to finally look into the PX4 Toolchain to see if I can make a tweak in the motor mixing on motor 3. As for the cyclic servos, all three are identical; that also includes the distance the servo horns are from servo to linkage arm. I might be able to post a video tomorrow showing the weird behavior when rolling the plate.
It might, but it would be a little bit of a handful in a mode where the vertical axis was controlled manually. Althold and loiter might work. I think it would be better to either make a swash type that can handle this or go to a swashplate that has equal arm lengths.
If you have the coding skills then this is a low cost, fairly easy change. You would be running custom code at that point but probably not that hard to port it to newer releases as they come out. Ultimately, if done right, this could make it into master but I don’t have any idea of the number of users that have this type of swashplate.
Hi
Support for 140 degree style on the swashplate has been added on the recent 3.6RC1