Hey all you Pixhawk experts! I have acquired my first Pixhawk system and intend to implement in into a gas powered Vario helicopter. I may have simply missed this while searching through the forums and wiki, but here is my initial question.
I plan on powering the system off of a 2s Li-Po run through a PowerBox Digi switch which regulates the output power to 5.7v. I have no need to use the 3DR Power module. After messing with this for only a day I am very confused on how to power the system. If I run 5v power to the servo rail from the battery/switch, the Pixhawk does not power up nor do I get power to the servos, only to the RX. If I use the power module the Pixhawk obviously powers up fine, although still no power to the servos. In either configuration, I am not getting power to my servos, why is this? I am not using any ECS or BEC units. My RC link is using a DX8 and satellite RX plugged into the SPKT/DSM port on the Pixhawk. When powered through the power module or usb from my computer, Mission Planner shows that the transmitter is working and all but I still have no power to the servos.
Forgive me for the dumb questions but how do I get power to my servos? Do I need to use the power module? If bypassing the power module, how do I provide power to the servo rail and Pixhawk?
Another note, does anyone have a base parameter file or a traditional helicopter that I can use for reference is setting mine up?
Thanks,
Chris
Replies
I tried running a compassmot test setting the compass_motCT to throttle. If I have the engine running my throttle is slightly above zero and the compassmot calibration menu says "throttle not zero" and it wont run the test. If I leave the engine off (throttle zero) I can run the test but it locks out control over the entire heli, so I cant start the engine...
Any thoughts?
So I guess a compassmot is not possible.
I think I may have solved my compasses inconsistent issue. Apparently the internal compass is subject to interference while being mounted directly over the engine as shown in a previous post. This was causing the two compasses to be inconsistent even though my external compass is mounted on the tail boom and getting good offset and mag field numbers. I have since moved the pixhawk to a tail boom mount. This seems to have solved my compasses inconsistent issue.
Now I have to work out some new tail boom vibration issues before continuing loiter testing...
Hi all, I have made some progress on the Vario. AltHold is good now, vibration has been reduced and I have moved to Loiter testing. I got my Rate PIDs dialed in a little better and initial Loiter results were pretty good. Had some toilet bowl once in a while, seems to fight me a little when pushing the stick to move the heli to a new location but not terrible. One issue I am having now is the compass. I have tried many different locations, copper shielding, long & short cables, different orientations etc... and I will calibrate it, it shows good numbers and the heading is right but then after only a minute or two the heading starts drifting. If I try to fly in Loiter like this it just goes into severe toilet bowl as it doesnt know where it is. Thinking my compass was going bad, I tried a another one (3DR UBLOX). No noticeable change was made.
After this I decided to try setting the GPS_GAIN to 0. I re-calibrated and got some really good offset numbers. The flight following this was very good, nice solid loiter and the heading was solid. Going into a second flight, first thing upon powerup I get a PreArm compasses inconsistent warning... I did another powercycle to try and clear this then waited a few minutes and it went away but my heading was 30-40 degrees off and drifting... no chance for a successful loiter flight like this. My mag field is as low as I can get it... around 400. My X,Y& Z offsets have been between 10-700, typically getting in the 100 range or so. My last calibration gave me these numbers: -32 -49 78.
Is the compassmot calibration possible with a gas heli? The wiki describes it to be used with a battery current monitor to measure current related issues, but it also says that you can do it with throttle. I am not using the battery current monitor module nor am I concerned about current. Can I do this at all?
So basically at this point, my compasses are consistently inconsistent! I get a good calibration and then it starts drifting, sometimes it doesnt drift until after the flight. One power up its good, another its not. I have probably done 20+ compass calibrations at this time... I'm getting tired, this 20lb heli is not easy to move around its axis!
Any recommendations would be much appreciated!
Chris, Post a Data Flash log of your flight and I'm sure some people will have some ideas about what is wrong. Is your Heli really 20 Lbs ?
Regards,
David R. Boulanger
David,
Yes it is 20lbs, without fuel or payload...
Here is a dataflash log of a good flight and a bad flight.
Thanks
GOOD LOITER_GPS_GAIN_0.bin
2015-06-12 15-58-31 83.bin
I have made some progress.
I'm working on ATL Hold now and am having some problems. With stock PIDs and anything higher than stock I got this rapid oscillation up and down (collective pitch). I notice that MP gives you a warning (out of range) when trying to reduce the Throttle acceleration P setting to lower than .5? This wiki says to keep a 1:2 ratio between P & I, is this true? Ignoring this warning I reduced the PID to P=.3 I=.6 D=0. This got rid of the rapid oscillations but now it either climbs rapidly or descends rapidly. I have set my Throttle MID position but it doesnt seem to help. My datalog for baro and altitude seem strange. Any ideas?
To follow up on this... after further testing I am even more confused. After taking off and doing a stable hover in stabilize mode, I am noticing that the reported altitude is changing dramatically. I would be hovering fine and the reported altitude was accurate at first and then would steadily climb off the charts... Using the 3DR radios I can see this happen in real time and then the reported datalog shows it in detail. Maybe someone can help me understand the difference between BarAlt, and Alt. My understanding is, BarAlt is barometric altitude and Alt is what the pixhawk thinks its at? Would lowering my INAV_TC_Z value help this difference between Alt and BarAlt? I am afraid to even try AltHold again with this data in mind.
I may have answered my own question. I lowered the INAV_TC_Z value from the stock "5" value to 1 and this is what I get....
The last picture was showing the INAV Z value at 2 actually... this picture is with it at 1.
I have done a couple test hovers now in ACRO mode. I noticed during setup that my servos are all very jumpy when reacting to TX inputs. I figured this might just be how it is... however, during flight it became notable that these jumpy movements make it hard to control. Is this a PID tuning issue or something else?
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