Hello Bill,
What are the feet forward gains (param name)?
So in total four flight, two at the current setup and two after changing the feet forward gains, yas?
Thank you
Rotem
Thank you Fred,
I will try to export it.
Rotem
Two flights. One with your current setup with the log_bitmask changed and the second with the feedforward gains increased.
ATC_RAT_RLL_VFF set to 0.18
ATC_RAT_PIT_VFF set to 0.18
Keep the log_bitmask at 131071
Hello Bill,
I’ve performed the two flights today (very short flights).
Please see the log files in the attached link.
Thank you
Rotem
Rotem,
It’s going to take longer than I expected to look over your data. I took a quick look last night and noticed that you have a lot of noise in your roll axis. If you have balanced and tracked your blades and you think you did a good job on the mounting and placement of the flight controller, then you can use the notch filter, INS_NOTCH_ENABLE, to attenuate the noise from your rotorhead. I think the first step would be to notch the rotor speed frequency. Once you enable the notch filter then you can set the notch width and depth and center frequency. The center frequency will be your rotor speed in Hz. Set your width to 5 and your depth to 30. If you are using a governor then a width of 5 is good but if your are using a throttle curve and think the rotor speed will vary more then set the width to 10.
Conduct a flight with the notch and post it. Hopefully that will clean things up a lot.
Hello Bill,
I’m having problem with this clone Trex 700 frame from day one, I’ve already replaced the main shaft, feathering shaft, all plastic gears to original Align parts, blades (all balanced) and still having vibration problems.
I will try to set everything again and try to fly and see if something changed, if not I will start from the beginning with a different frame.
Thank you
Rotem
Hello Bill,
I’ve disassemble the heli head and set everything again.
I hope it’s helped to reduced the vibrations.
Thank you
Rotem
Rotem,
Unfortunately I am seeing the same amount of noise in your data. Please use the notch filter as I instructed here
Also please enable batch logging. I want to see what frequency is causing this much noise. so please set INS_LOG_BAT_MASK = 1. Go fly you heli and provide me the log.
Do you tighten down your blades really tight, loose or just tight enough so they won’t fall down if you turn your heli on its side. I’m just trying to figure out if that has something to do with this.
Thanks,
Bill
Hello Bill,
I’ve changed NS_LOG_BAT_MASK to 1 and fly.
Regarding changing INS_NOTCH_ENABLE, I can change it to 1 but I could’t find how to change the depth & width, Please advise.
Thank you very much for your help.
Rotem
Rotems,
after enable the NOTCH filter with -1- you write it to the FC. After that you must REFRESH the Parameter List and you will see the additional options.
Or now after the restart of the FC you will see everything you need.
Rotem,
It looks like you need to balance your blades better and there could also be an issue of blade track. here is a snapshot of your vibrations in flight
So the frequency is on the bottom and the first peak in both plots corresponds to your rotor speed or rotor imbalance. To give you an idea of a well balance rotor system will be for this first peak. Mine was around 0.5 to 0.7 for the Y acceleration plot and around 0.3 for the X gyro plot. So your vibrations are about 10 times more than mine. You can use this batch logging feature to dynamically balance your rotor system. you can find how to use Mission planner to do this analysis here. http://ardupilot.org/copter/docs/common-imu-batchsampling.html Be aware that I manually pulled out the section of data from your log to look at just the flight. This feature basically uses all of the samples in the log and averages them. So if you use the whole log then you will see much higher values because it includes the data on the ground too and this is where we see a lot higher vibration. So you can still do the blade balancing using the whole log but you will have to look at what it is initially and then see how low you can get it. Then you can pass me a log and I can pull out just the hover and see how it compares to mine. The way I tackled doing the balancing was to use a small piece of tape 4 cm by 0.5 cm and put it at different points along one blade. You will have to restart the controller each time so you get a separate log in order to conduct individual analyses using this tool. look at the first peak and see if there is any improvement. keep on adding weight or move to the other blade if the vibrations just keep getting worse as the tape is moved further out on the one blade. I hope this makes sense.
The peak at twice the first peak is the 2/rev which I believe is due to lead-lag of the rotor blade and tracking but I’m not positive. Look at your blade tracking as the heli is in flight. If the blades don’t look like a knife edge (meaning each blade is passing right in the same location that the previous one did) then you may have to adjust your blade track.
The only other thing that might affect the magnitude of your vibrations is the tightness of the blade bolt which if you made it really tight would put more vibrations in the heli. However, I have not played with this to see if that has any affect.
The last thing I will point out is these vibrations are also dependent on the flight controller location and mounting which could have a big effect. So try the dynamic balancing of the blades to see if you can significantly lower that first peak. If you can get it down into the range of my readings then your flight controller mounting may be fine and it was just the rotor blade balancing.
@rotems. Disregard the method I discussed above to determine if your rotor blades are dynamically balanced. I’ve learned a little bit more about the FFT tool in mission planner. It will not be able to predict this. Sorry about the misinformation.
Hello Bill,
I appreciate your help in this issue.
I think the blades are dynamically balanced, my balancing method is to lay the blade on an knife edge and mark the balance point and add tape as needed until both blades balancing point is match.
I will try to work it out, maybe replace the heli head (as I mention before, it’s clone trex 700) or in the worse case I will buy a new frame and start all over (considering Protos700X).
Thank you
Rotem
Rotem,
This is not the best way to statically balance and rotor blades. This just ensures the CG of each blade is the same. you would also have to ensure that the blades weigh the same for this to work. The best way I found two statically balance rotor blades is to remove the shaft and hub from the helicopter and attach the blades to the hub so that they are straight out from the blade grips and tight. Then I use a prop balancer that I mount to my bench so as to not fall over due to the weight of the rotor. I start with the blades parallel to the ground and see which blade falls. I put tape on the blade that doesn’t fall. And then check to see that the rotor blades stay parallel to the ground when I let go of them.
Hello Bill,
I will try this balancing method and will try to fly again.
Regarding the tape that you are adding, it will change the CG of the blade, no?
So you can balance the blades using your method to get the CG the same. Then mount them on the rotor hub and see if they balance on the hub. If they don’t then add the tape to the CG of the blade. That way it will change the weight of the blade but won’t change the CG of the blade.
Hello Bill,
I replaced the Heli head and during disassemble the original head I’ve found that one half of thrust bearing in one of the blade holder is missing!
I performed a flight with the new head hoping that the vibration will disappear but I think it’s almost the same (I’ve attached the flight log file).
Please advise what do you think and how to proceed from here.
Thank you very much
Rotem
Hi Rotem,
Yeah it doesn’t look much better. Please do the following
set INS_NOTCH_ENABLE to 1. Then restart the flight controller and make the following settings
INS_NOTCH_FREQ 24
INS_NOTCH_BW 10
INS_NOTCH_ATT 30
Also
INS_GYRO_FILTER 10
INS_ACCEL_FILTER 10
ATC_RAT_PIT_FILT 10
ATC_RAT_RLL_FILT 10
PSC_ACCZ_FILT 10
After making all of these changes, be sure to restart your flight controller. do a short flight in stabilize and we can look at how the filters did. We’ll see if we can get the vibrations knocked down some. then we can look at how well your heli is tuned.
Hello Bill,
I’ve change the parameters and performed a short flight.
I can see any differences in vibration from the last flight.
Please see attachedParam 290919.param (14.6 KB)
the flight log and param file.
Thank you very much
Rotem
@rotems have you tried increasing your headspeed? I think I read earlier that you are running ~1,300 rpm? That is only ~350 fps blade tip speed, which is very, very low for a 700-class machine.
I have never had good results from running low headspeed. Your helicopter will likely run smoother at higher headspeed, it will produce more lift and provide better control response. You don’t have to run 3D speed. But for the various sizes of heli for UAV I like to see:
- 600-class, 350-400 fps
- 700-class, 425-450 fps
- 800-class, 450-500 fps
This equates to approx rotor speed in the various sizes:
- 600-class, 1600-1650 rpm
- 700-class, 1550-1600 rpm
- 800-class, 1500-1600 rpm (higher rpm for heavy-lift 800’s over 1lb/ft^2 disc loading)
Helicopters will exhibit dynamic imbalance at various speeds. It’s like balancing a tire for your car. You can static balance the tire with a bubble balancer. But put that statically balanced tire on a dynamic balancer and the tire might wobble at say 38 mph, but it runs smooth at 55 mph. That wobble at 38 mph is due to a dynamic imbalance at that speed.
It is very difficult to dynamically balance helicopter rotors without the aid of an electronic balancer like a RPX DynaVibe. But it is easy to identify the dynamic imbalance speeds by looking at vibration. So if you find a speed that exhibits high vibration, run it either faster or slower than that speed to see if it clears up. You should be able to find a “sweet spot” within the acceptable rpm performance range where it runs smoothest. And that is the speed to run it at.
This is how I have determined what to set the governor at in all my heli’s. I run it at the highest possible speed within the acceptable tip speed range, at which it runs smooth. And then track it with the RPX DynaVibe to get rid of the 2/rev “beat” of a two-blade rotor in static hover. You’re still going to get the 2/rev “beat” with a two-blade in forward flight. But it can be tuned out in forward flight too, in full-size, in trade for having a little higher vibration in static hover.
At any rate, I would suggest trying a higher headspeed. It won’t make much difference to your flight time with your electric heli. And I’m afraid you might be beating your head against the wall running it at 1,300 rpm and trying to solve vibration problems.