What FC

[Pumpkinguy]

In that other thread there was a lot of talk about reducing vibrations. Balancing props and levelling motors. I have seen the kloner vids on levelling. Has anyone tries something like this between the motors and motor mounts to reduce the resonance from traveling down the arms?

 

[Bartman]

not sure how you'd work those into your motor mounts

balancing the props (really balancing them!) and using good quality motors goes a long way towards keeping vibrations down.

 

[Pumpkinguy]

The logistics would be easy. Cut 4mm stud to lenght and loctite into motor. Feed other stud thru motor mount slots and put a nut on back side. Just thinking out loud here.
If I get superx I can do a vibration analysis with and without.

 

[kloner]

i use something similar, neopreme anti vibe stuff from mc master carr

prop balance is important too.... for that i use top-flite mag balancer

 

[Pumpkinguy]

I have a dubro but it doesn't look as cool as the mag balancer.

 

[kloner]

it's just less accurate... to me in my experience is the most important part,,, nothing worse than an almost balanced prop... i'd rather have em way off, less vibes. I've spent no less than an hour to hour and half on every prop i've ever flown starting with something called pre balanced like tiger cf

 

[Bartman]

The magnetic balancer, a can of spray paint, a roll of lead tape, a micro-brew six pack and a few hours or so later you've got balanced props.

@Pumpkinguy; vibration dampening isn't an exact science so there can be a lot of trial and error to find worthwhile improvements. keep in mind, lots of GoPro videos looked great with nothing but a GoPro taped directly to the frame. Get the most simple parts of the build as perfect as possible and chances are you'll be happy with the results.

 

[Pumpkinguy]

I've gotta ask. Spray paint?

 

[kloner]

i use sand paper to remove surface, he is adding to them. both work, it just has to not move in any position on the balancer.

 

[Bartman]

yup, i use wood props so you can't sand off the finish and with carbon fiber i wouldn't want the dust so I use a blast of spray paint on the tips to balance them laterally and then a small piece of lead tape to balance the hubs. it all depends on the material of the props and what you're comfortable with. i'll hold the prop down in a garbage can next to where i'm sitting and just hit the tip with paint and then set it aside to dry.

 

[Old Man]

Kloner,

Something that has been seen with really large X-8's is some dynamic instability that occurs due to propeller "coning" effects. Some will scoff and say there's no proof but graphing out the wattage between motor/propeller pairs that are horizontally "level" with each other and those that are both canted about 1-1/2 degrees clockwise clearly demonstrates a balancing of output between the motor pairs. An issue with canting the props away from horizontal is the controller type. With DJI there is a propensity to spin all the upper props in one direction and all the lowers in the opposite. This does not work out when canting props, they have to be set up in the classic quad configuration where each pair of motors spin as opposites.

Stability increases when x-8 propeller pairs are canted, as does the thrust by about 5%. Again, there are those that will argue a lack of proof but it has been well established to be extremely effective with ultra heavy lifters. By "ultra" I'm talking well in excess of 120lbs of lift capacity.

 

[Bartman]

@Old Man; another prop rotation scheme I've tried is to have all of the tops rotating so the inboard blade is advancing (both props on one side turn the same direction) with the bottoms all turning to have the outboard blades advancing. the benefit is to have laterally balanced centers of lift as the helicopter transitions from a hover to a fast forward flight. I've seen in older heli's where I had them all CW on top and CCW on the bottom I'd see some slight wobbling while transitioning. not so much with the newer scheme I've been using.

but what about canted props? can you explain what "1 1/2 degrees clockwise" means?

 

[Old Man]

Everyone "levels" their motors to match a horizontal plane. In a standard quad, hex, or octo config with all the motors on the same level that's the way things should be. OTH, in a coaxial config having all the motors on a horizontal plane is counter productive because the upper prop blows a cone of seriously disturbed air through the bottom prop. That allows the lower props to turn a lot faster than the tops since they are not loaded as much. So instead of breaking out the level to have all the motors on a split bubble, lean the top and bottom motors to be on an angle. The propeller tips will be higher than center boom on one side of each motor pair.

 

[R_Lefebvre]

Wouldn't 6S be a problem with Pixhawk?

No. Please stop this rumor people. This is trivial. I have use it with 12S. It is a non-issue.

i need "stupid simple" lol

Pssst. You live like 1 hour away from a guy who helped write the program.

I'm going to be quitting my day job next week, and will have plenty of time to show you how it works if you want the best system available for the lowest price.

 

[R_Lefebvre]

In that other thread there was a lot of talk about reducing vibrations. Balancing props and levelling motors. I have seen the kloner vids on levelling. Has anyone tries something like this between the motors and motor mounts to reduce the resonance from traveling down the arms?

Why the big discussion? Is the Xaircraft having a problem? Or this is just a general discussion about reducing vibes for video?

I don't put a lot of effort into balancing propellers. Soon as the air starts moving (which is always) they start vibrating anyway. As long balance is close enough, you have bigger things to worry about.

 

[Pumpkinguy]

No. Please stop this rumor people. This is trivial. I have use it with 12S. It is a non-issue.



Pssst. You live like 1 hour away from a guy who helped write the program.

I'm going to be quitting my day job next week, and will have plenty of time to show you how it works if you want the best system available for the lowest price.

Rob. You need to get to know me. Other than online advise I don't ask people for help. Not unless I've helped you first and then I don't mind asking. . Plus I am like a sponge. Love learning, love doing things myself.

 

[Bartman]

Rob, I know you know the software but I don't know to what degree you've tried to capture pro-level images. balancing props is probably the most important thing you can do to quiet the airframe vibrations that can make their way to the camera lens/sensor. your comment is the fist I've ever heard anyone say not to worry about prop balancing, ever.

and if you run the helicopter on larger packs using regulators to power the Pixhawk, what happens to the power monitoring and telemetry that is native to the flight controller?

 

[R_Lefebvre]

If you use an HV BEC to power the Pixhawk, then you will lose the battery voltage and current draw data. Unless, you set up a voltage divider, which is very easy to do, and is what I do on most of my aircraft. That gets you voltage. I just don't worry about current normally. It really doesn't concern me much. But, even that can be done if you really want. I can build a current sensor that will be good for unlimited voltage, and 100A current, with exactly ZERO resistance, and ZERO chance of failure, if somebody wants.

I'm not saying to not balance the props. What I'm saying is that there's a point of diminishing returns. And also too much focus on prop balance while ignoring other issues that affect the image is problematic. I've seen many cases where people spend lots of time balancing props, but still get vibration soon as they are actually flying. They probably think they need to spend even more time balancing, but that's not the problem. The problem is, as I've said many times, that aerodynamic forces, namely disymmetry of lift, will cause even the best balanced prop to vibrate anyway. You can't stop it, unless you went to a complicated articulated rotor, which nobody is doing. Therefore, you must have an effective vibration damping system for the camera. If this system is effective for the aerodynamic vibrations, then it will also be effective at eliminating the remaining minor vibes coming from a prop that hasn't had hours spent balancing.

Yes, I know many of the concepts I present are revolutionary, but it's because I come at this from a firm grasp of science and engineering, and usually backed by data. Too much of this industry relies on a black-magic mindset.

I've seen several situations where people have crashed, because they spent so much time balancing props and motors, got everything perfect, no vibes. So they hard mount the Pixhawk. And then they actually go outside, and fly at 10m/s, and the thing starts shaking like hell, and crashes, and they can't understand why.

 

[Old Man]

Have to agree with Bart here about prop balancing. Using a 3DR quad run with APM and a hard mounted Go Pro I experienced some jello in the video at all times. Balanced the props and the jello went away. Had the same occur with a custom built 650 using Pixhawk. No jello after prop balancing. Moving to "real" UAV's, prop balancing is a step that removes one of the forms of vibration from a carbon airframe, minimizing the telegraphing of vibration pulses from aft forward to the payload, in turn increasing the performance of the optical smoothing software. Anything that removes a vibration source is a good thing, and props are a big one. With enough of an imbalance a propeller can tear an engine from it's mount, so the amount of imbalance is something of some significance.

I will agree there is more to vibration that just the propellers. You certainly have me interested in your power divider concept.

 

[R_Lefebvre]

I'm not saying not to balance props. I just don't put that much effort in. However, this video was shot with with props right out of the box, not balanced at all:

The situation you present though, is exactly what I say is not a good idea. Balanced props, and a hard mounted camera. That will start vibrating soon as the air starts moving past the copter. So moving, or flying in wind. In my video, I hit 60 km/h.

This is from a 3DR Quad with nicked props. Fixed mounted camera obviously. But vibration damped. Proper damping is critical.