Chad, yes please do post the log from the Stabilize flight test. That will tell a lot about your setup and how much tuning it needs yet (or not). Stabilize is the best mode to test operation of the attitude controller. The only difference from Acro to Stabilize is that in Stabilize the system self-levels if you let go of the sticks, and the maximum frame angle is limited. So, for instance, it won’t let you pull a loop or something in Stabilize. But the part of the attitude controller that is doing that is important to everything else and gives an indication of what adjustments need to be made before you progress to modes where the autopilot has increasing levels of control.
As you progress to letting the autopilot have more control, the response on the sticks gets increasingly “sloppy” to where in Auto it does not respond to stick input at ALL. So we have:
Acro - best pilot’s mode for real flying
Stabilize - some limitations from Acro, as noted above
Alt Hold - one more limitation in that the autopilot has altitude control and collective is “sloppy”
Loiter - autopilot has control - sticks only make a request to the autopilot to do something
Pos HOld - same as Loiter except when you move the sticks it switches to Alt Hold then back to Loiter when you let go of the sticks
Auto - autopilot has full control - no response from collective or cyclic sticks at all.
No, there is no parameters for that. We just have to look at the log from the first flight and see what it is. If there is too much and it is aliasing the IMU’s, then have to look at better vibration isolation, or damping, for the mount for the Pixhawk.
Which Pixhawk are you using? The Pixhawk regular one, or the new Pixhawk 2.1? In my experience the internal damping of the IMU’s in the Pixhawk 2.1 is quite effective. The older Pixhawks are a bit more of a challenge.
Chad, There are filters in place that are meant to help “tune out” the vibrations. Currently the parameters are INS_GYRO_FILTER and INS_ACCEL_FILTER. I’ve listed them below with the associated description for the parameter.
INS_GYRO_FILTER -Filter cutoff frequency for gyroscopes. This can be set to a lower value to try to cope with very high vibration levels in aircraft. This option takes effect on the next reboot. A value of zero means no filtering (not recommended!)
INS_ACCEL_FILTER -Filter cutoff frequency for accelerometers. This can be set to a lower value to try to cope with very high vibration levels in aircraft. This option takes effect on the next reboot. A value of zero means no filtering (not recommended!)
They are defaulted to 20 hz. In the next major software revision (3.6) which I’m not sure when will be released, there are also notch filters which would allow you to target specific frequencies. There are also filters in each of the PID loops as well. However since you are running an FBL downstream of the pixhawk, you won’t need to worry too much about tuning PID loops and filtering, if required, for that.
As Chris suggests, it is typically better to address any vibration issues as much as you can through physical means (i.e. mounting).
I am using the new 2.1 cube, I specifically got it because I read about the vibration resistance.
I was thinking about this. I have it hard mounted to the side of the frame right now. I ordered some parts to get my 3d printer back up and running and I plan to print a mount for it on top at the rear of the frame as well as a gps boom mount. Should have the parts Monday or Tuesday and I can start designing something.
Great to know if I do have any problems!
@ChrisOlson how is yours mounted on your gasser? Any pictures you could share?
Absolutely. It’s mounted right on the FBL unit tray using four blocks of the tissue tape that comes with it, the Pixhawk is bolted to a .125" aluminum plate with two lead bars screwed to the bottom of the plate to add mass and dampen the vibes. I got vibes less than 8 with this setup.
Generally, if you can get x and y below 30, and z below 50 is considered acceptable. But it depends on the vibration frequency too. The PH2.1 is quite good at damping high-frequency vibrations, lower frequency vibration can also cause issues and must be handled by the mount. With an otherwise well-engineered mount, adding mass to the Pixhawk itself in the form of lead weights or bars significantly damps low frequency vibration.
Well, there’s a lot more wiring than what it appears in that photo because there’s two headspeed sensors, engine temperature sensor, fuel mixture control servo, flight systems power, FPV transmitter, payload and generator wiring as well. The landing gear is designed to accept a 2 liter belly fuel tank and the pickup on that hooks to the vent line on the main tank. There’s a seperate bracket for a servo-controlled belly hook for glider towing and tethered loads. And another bracket that goes on the front under the nose for cameras or LIDAR mapping unit.
But on these heli’s it’s all hidden under the fuselage and bodywork except for the belly loads. I designed the height of the landing gear so it just barely fits under the tonneau cover on a 1/2 ton pickup. Fully loaded running at Idleup 2 (1,550 rpm) it burns 29cc/min. The engine is not stock. It is a VX310SX 2mm stroker from Toxic Al.
Position hold is switching to althold on stick move??
Can anybody confirm this? I thought position hold is moving the position x/y-coordinate and Autopilot follows…
ok @ChrisOlson I have installed the Spartan vortex now so I have gov. Do I need to change anything for the gov to work? I also need to figure out how to control the modes in the Vortex if possible. The modes are controlled by channel 5 in the Vortex. Currently it thinks it is in Hold. I guess If I only need one head speed I could have the gov on in hold mode.
Yeah, it kinda does. The difference between moving the heli around in Loiter vs Pos Hold is that in Pos Hold it acts like Alt Hold as far as handling - it doesn’t actually switch to Alt Hold. Loiter is very sluggish until you turn up some WPNAV_ params for it.
Well, using a MODE 3 throttle I guess I would set the throttle points to what you think they should be based on your experience flying with just a RC radio. I’m not familiar with the Vortex - does it have a governor on/off function using a channel? Does it use a “stick switch”? Or just mode switching?
Edit:
If you need control functions for your governor, that are usually on separate channels, I use channel 9 or above for those things.
In ArduPilot channels 1-4 are normal flight controls.
Channel 5 is flight modes
Channel 6 is used for tuning params and many other tuning functions
Channel 7 is used for functions that do various things
Channel 8 is throttle control
Channels 9-16 can be used for anything, but only 9-12 are enabled by default on the Pixhawk’s aux pins for PWM out. They should all be available on S.Bus out.
The modes are controlled by the gyro channel, which is channel 5, and you would normally just change the rate of each of the switch positions to get it to change flight modes.
That’s what I was afraid of. I know Aris is using idleups with his Vortex, so the S.Bus channels in the Vortex must be able to be mapped?
Edit:
Need to verify if you are using S.Bus input to the Vortex, or using individual channels to it with PWM. It can do either, I’m pretty sure. Aris is using S.Bus on his, that I know.
I am using sbus and I can change which channel the modes are activated by. I tried changing it to 10 and activating channel 10 with a 3 position switch but the modes are not changing.
When you calibrated your RC, did you make sure to calibrate all the channels by throwing switches, etc, to get full range? And have you enabled S.Bus out on the Pixhawk by setting it to a value other than zero? The S.Bus out is disabled by default.
I did redo the calibration after setting that switch. I was previously using sbus so it is all set up. Everything else it set up and ready to except the flight modes.
Aris will be able answer that better than me. He’s quite familiar with that unit.
When you say “flight modes” I assume you mean the traditional Normal and Idleups so you can change your headspeed.
For the Pixhawk setup, zero out the rate PID’s, set VFF to about .35 at least. Some people even use 0.5 for the VFF with a downstream FBL unit. Make sure H_FLYBAR_MODE is set to 1. Then tune the FBL unit as normal and make sure it is using rate control only. The pitch ranges and everything else is set in the Pixhawk as is for any other setup. The only real difference is that the FBL unit handles the rate control and Pixhawk gives you pass-thru direct to the FBL unit in Acro.
The common starting point for VFF when tuning the Pixhawk is 0.15. That is different with downstream FBL unit.
Aris said he just used channel 6 and set 6 to pass through. I did not realize you had to change a setting to get the channels to pass through. I will try that and see what happens.