Hi, Guys, I am new here so be gentle lol
Here we go, I just finished building a 700e low head speed 6s helli, very low budget and so far she flys great! but I would like to install a flight controller, I have been looking at a few FCs, the ones that interest me are the Ardupilot APM 2.8 the MINI APM PRO and the Pixhawk PX4 2.4.8, which one would you guys go for? I would like all so to use the GPS for more flite option, do these FCs replace the FBL unit I already installed on my helli? and because I run a 6s setup the thr curve is all-wise that 100% when flying would this cause any problems in certain flite modes?
Thanks Guys for any help
P.S. sorry for the spelling or the grammar I am dyslexic!
Hi John,
The software for the APM-series is no longer supported. So I would recommend the Pixhawk controller. It will replace your FBL unit. You can use your FBL unit downstream of it as well and use the Pixhawk only for an autopilot if you wish.
The throttle being at 100% on 6S power will not be a problem as far as the ArduPilot system.
Do you know if there is a video somewhere that shows a set-up of the Pixhawk on a helli? and, I think the GPS is only used for only a couple of flite modes like alt hold and RTL? and would you go with the mini Pixhaw or the full size?
The PH2.1 is better than the first gen Pixhawk. I have my PH2.1’s screwed to an aluminum plate and the plate mounted on the FBL tray with double sided tape. The aluminum plate adds some mass to the base of the carrier board. It’s IMU’s are internally damped and that’s all it takes to get suitable results.
You will need to engineer a good mount for the first gen Pixhawk.
Another “trick” is to run the engine at the rpm it is balanced for. And change the gearing to run the head at the desired speed. There is not a big penalty in running higher headspeed with a gasser like there is with electric in power consumption. If you know the “sweet spot” for your engine and drivetrain, run it there and they’re just as smooth as any electric.
I would tend to go with the full-size one. The non-integrated servo rail on the mini is necessary to find the room someplace to put it. And it only has 8 servo outputs which can be a problem if you need channels 9+ to run a payload or engine governor. With a heli, channels 1-4 will be used up for normal fight controls, 6 or 7 for power to the servo rail, 8 for throttle, so 8 servo outputs leave you with only one channel that can be mapped for an extra servo output. If you use that remaining output to run the governor for a gasser, that leaves you nothing to control the payload.
The mini’s small size makes it suitable for mounting on the FBL tray because it’s about the same size as a FBL unit. But all the extra wiring associated with it on the output is a pain. And it doesn’t come with a decent power module for a helicopter. IMO the mini was designed for small quads.
You will get the best results in a heli with a Pixhawk 2.1. Mount it flat on an aluminum plate and it is virtually impervious to vibration at heli vibration frequencies. I get vibes less than 8 on all three axes in my big gasser, mounted with nothing more than the foam mounting tape that comes with it.
With a first gen Pixhawk it will be more of a challenge designing a mount to damp vibes.
I hope I am not bothering you too much with my question, I do have one more?
because I am running 100% throttle curve and not using a governor, will the Pixhawk control the pitch of the main blades to hold the altitude in Atl Hold?
Yes, it will. But it will not hold headspeed constant as you have no overhead for power. So on heavy collective loading it will likely lug it and lose headspeed. This probably won’t be a problem, as a 700-class machine flying on 6S at 100% throttle is not expected to be a high-performance heli anyway, and more designed for scale-type flight at reasonable speeds and payload.
It will not fly any different than it does with your FBL unit. However, I would recommend limiting the maximum amount of collective pitch available so it doesn’t overload the power unit by pulling more pitch than it can handle on 6S power. A 700-class heli can easily pull 150 amps on 12S - that’s 300+ amps on 6S for the same power.
So where you may be able to run 11-12 degrees of pitch on 12S, on 6S you may have to limit to 8 degrees or so to prevent lugging it. The amount of lift from your rotor increases with the square of the speed. So there is a point of no return where if you pull pitch, lose headspeed, increasing pitch further will not create more lift and simply stall the blades. And the losses in the drive go exponential due to the amps and ohm’s law.
If it runs into a situation where the autopilot calls for maximum pitch (like in a high speed turn or sudden wind shear) the autopilot is kind of “dumb” in any altitude controlled flight mode. Unlike a human pilot who realizes he/she has hit the max power and backs off the collective - the autopilot will not do that. It will simply pull more pitch and try to maintain altitude. So the setup in limiting the heli’s performance to fit the power becomes quite important for a configuration like you are running.
No. You can set it up with the FBL unit downstream from the Pixhawk, with Pixhawk handling attitude and the FBL unit handling rate control. And have the Pixhawk set up to use flybar mode so in Acro it passes control direct-thru to the FBL unit for rate-only manual control.
But, unfortunately, that is not a supported setup as there is too many differences in FBL units to provide support for such a thing. You can find reference in the forum to where people have done it. But the setup of it you will have to figure out mostly on your own. I can only provide you with the settings you need to make in the Pixhawk to do it.
OK, thanks again, I just order a Pixhaxk and I will keep you updated on the progress, with all the info, everything should fine! I was thinking of removing the FBL unit and just go with the Pixhawk, if I install it on the 700e, with all the different software out there with one is the best for hellis?
You know my 700e helli with the FBL unit flys great! I was thinking I might install the Pixhaxk on my flybar gasser, but I would need a governor what governor are you using on your gasser?
And by the way that is a super nice gasser you have in your videos.