Let me start off by saying I have been searching the discussion boards for some time now and have now found many if any that are building large Quads using the Pixhawk and the U8 Tiger motors. I am a bit of an overachiever and and wanted build and efficient UAV with long endurance. I have put together one using the following equipment.
1200 mm motor to motor frame.
Pixhawk Flight controller.
Castle Creations 50A ESC's
6s 15C Lipo Battery
U8 Tiger Motors
28" Tiger Props
Taranis 9XD Radio
Here is my problem. I have gone through all of the calibrations from the flight controler, motors, ESC's and the radio. When I calibrated the ESC's by using the flight controller bypass the motors spin up in reasonable increments as i increase the throttle. When I arm the system the motors begin to spin at an idle speed. When I try to increase the throttle there is no change in response from 0% to about 60%. At that point the motors spin at 100% RPM from 60% to 100% throttle. I have contacted 3D Robotics and the technician told me that he would speak to their engineers and contact me back. I know I am impatient but a week later I still have not answer. I am hoping that someone here can lead me to a solution. I am thinking that there may be some problem with the flight controller.
Thanks in advance
Will
Replies
Fran,
I feel your pain. Loiter seems to be the trouble when trying to find PID's that will work. Someone has figured it out but they are not sharing. SteadiDrone has it figured out so I'm told. I wonder if the Loiter settings were set similar to the stabilize PID's if that would work. I don't know why Loiter is creating such a problem. The only thing I can come u with is the mass of the motors and props may have a problem slowing down fast enough after making corrections to maintain stability. This may cause the APM or Pixhawk to chase these corrections to the point that it over-corrects itself into these violent oscillations. But I really don't know. I have seen MikroKopter has an ESC that evokes Regenerative braking in the motors slowing them down quickly and as a byproduct allowing a back charging to the batteries. I sure wish someone could help solve this for us. I apparently not smart enough to .do it myself.
Thanks Fran,
Scott has been busy tuning. he listed his params in this discussion, http://diydrones.com/forum/topics/my-heavy-lift-u8-pixhawk-sweep-he... I am trying to rebuild after a battery malfunction and collission. I hope to be up and running in the days to come.
I sent you an add request. I am at the point of troubleshooting the PID's. I too have had the oscillation issues but only in loiter, in windy situations. I am looking for solutions. I am running this at 6S on the 170KV motors. I don't know if it is the PID's or an problem with the ESC timing or what. I have read that in some setups people are using dynamic motor breaking. Their reasoning is that the motors due to the mass are not able to slow fast enough and this can cause the flight computer to create these oscillations. Truly i don't know. Whatever it is in my case it starts when there are (sometime small) gusts of wind. I have been able to switch into ALT Hold or Stabilize modes and a little increase of the throttle and it will settle down.
William,
what flight mode and which firmware version are you using?
When arming in AltHold, Loiter, or PosHold (Hybrid) there was no throttle response up to 50%. If you are using 3.2rc4 there is Pre-takeoff throttle feedback. However I strongly suggest to use stabilize mode for take off.
Kind regards,
Thorsten
I plan to confirm today. I will update when I've done so.
A couple of things....First, are you sure you are in Stabilize mode when arming? The way you describe the motors coming up only after the throttle is raised past half sounds like it's in AltHold or Loiter modes.
Second, Castle ESCs can be a bit....different. If you haven't already you would be wise to invest in a USB Castlelink programmer, about $20. You can change all sorts of settings in the ESCs by way of a pretty good GUI interface. Be aware that if you are running the Castle ESCs in their multirotor mode, they have fixed endpoints and won't respond to calibration. You have to adjust your RC Tx endpoints to fit the ESCs.
A way to have a close look at what's going on is to have your copter hooked up to MP while you are powering it up. Specifically look at the Failsafe setting page which shows you the RC in and RC out values in real time. Your RC out should be matching your RC in. If not, then the issue is with the APM. If they do, then it's an issue with the Castle calibration.
Tom,
Thanks for the reply. i need to check again. My intention was o set the primary flight mode to stabilize. i will check on mission planner when i return home. I have seen that there is some talk of heptic feedback in alt hold and loiter from launch. I am not seeing that in my case, if I made that error. I also have read there are some negative results from some of aircraft flying away.
I have the programmer link for the ESC's. I have not messed around with it much other than to update the firmware. They are set to Airplane mode for now. Is setting the ESC's to multirotor much of a benefit? I am looking for efficiency from my UAV not wild performance.
Yeah, there is a distinct advantage to using the Multirotor setting on the Castles, but as I mentioned, also some quirks. The biggest deal would be the ability to do a 490 Hz motor update rate. That's the case in the Multirotor setting, but I'm not sure what you get when you use the Airplane mode (50 Hz??). The 50 Amp Castles default to the Airplane setting, I believe. I'm surprised you need that high an amperage rating at 6S. I would have thought Castle's 35 Amp Multirotor Quadpack would have been plenty. It would have saved you a bit of weight.
That said, I wouldn't encourage you to mess around much with the ESC settings until you resolve what your present problem is. It sure sounds like it was in Loiter to AltHold.
Tom,
Well you saved the day. You know you an look at something a hundred times and miss every time. The default flight mode was set to Alt Hold. I changed it to Sab and it worked like a champ. I took a few short hops today and other than my having huge adrenaline dumps it flew great. i will upload a vid where I i was trying to get the feel of it. I almost had to buy another set of props. Ouch. I saved it at the last minute. I have many loose ends i need to resolve before I consider it solid. I would like to pick you brain more.
Thanks
Will
Good to hear it worked out OK. For me, that's a rarity.....
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