Regarding the shock absorption of large drones, I hope to add it to the wiki

I have recently been debugging large drones, which have huge props. This means that once there is any imbalance, the vibration intensity will be much greater than that of small drones.

Since large drones may also experience some minor bumps outdoors, their expensive price makes it impossible to replace the propellers when the props are slightly damaged. In other words, the dynamic balance of large drone motors and propellers often has problems and can only rely on the flight control’s shock absorption platform to solve them.

Due to the low vibration frequency and high energy of large drones, many shock absorption platforms that work well or barely on small drones cannot be used on large drones at all. Next, I will talk about some of my own insights.

The most common shock absorption platform we see probably looks like this, and they are designed for lightweight FCs like APM. The latest FCs are mostly metal shells, and the huge weight causes the CG of the upper shock absorption platform to move up.

When horizontal vibrations reach the lower shock absorption platform, the vibrations will pass through the anti-vibration grommets and be applied to the upper shock absorption platform. Since the CG and the impact direction caused by the vibration are not on a straight line ------ just like the thrust line of a fixed wing, this will cause interference to the flight control’s attitude.

In short, for parts above the shock absorption ball, a high center of gravity will cause the flight control to sway.

The ideal shock absorption platform should look like this, by sticking counterweights (usually lead) under the upper shock absorption platform to lower the CG, thereby eliminating the interference of horizontal vibrations on the flight control attitude. The added counterweights can also compress the shock absorption ball, making it better at filtering low-frequency vibrations. The CG position relative to the top of the anti-vibration grommets can only be biased downwards, not upwards.

I think controlling the CG position of the upper shock absorption platform is an important part, because it is almost impossible to use high-damping materials to filter low-frequency vibrations, and soft materials cannot suppress the sway of flight control. I took some detours here and found that these were not mentioned in the wiki. Based on my experience, I believe these things are important.

The cable connecting the flight control should preferably use high flex wire no more than 30awg, the kind with a silicone skin. I used 26awg and it didn’t work very well. If possible, I think using FPC might be better, provided you spend some time making them.

Also, I found that cylindrical anti-vibration grommets may be worse than spherical anti-vibration grommets. Because cylindrical anti-vibration grommets are like straws, when subjected to a certain amount of force, they will collapse. Spherical anti-vibration grommets will not collapse like straws, their response is almost linear. Of course this is just my guess, I just pinched them with my hands and didn’t go through a lot of experiments.

I think the above views may be worth adding to the wiki because shock absorption for large drones has always been troublesome. I think my experience should be able to help some people who are troubled by these problems, at least some of them.

That is a wrong postulate and safety issue …

Same …

You need to understand what are the vibrations caracteristics and how to filter it. You can also cut it off numerically in the FCU . And if the frequency change, in most case your shock absorption platform will not do anything since the caracteristics changes.
Moreover, most high end FCU already have internal IMU dampening that match most common drone vibrations frequencies. So adding random dampening just negate the internal dampening.

Anything with vibration should be carefully reviewed and could not have a simple solution as using a dampner on FCU. Reworking the frame is IMHO a better move as you prevent vibration issue on the whole drone (lose screws, video, etc.) but this need evaluation

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I admit that this is a behavior of shooting first and then drawing the target, but I don’t think it’s a wrong assumption. Many teams around me are like this, they won’t care about the stains and minor damage on the porp, and even try to use porps with broken front ends (just for experimentation). And the tiny stones, leaves, and mosquito corpses blown up by the downwash airflow, of course these may not cause huge dynamic balance problems, but these situations do exist and will happen. You can’t ensure that drones will be treated as carefully as hangar queens, at least to some extent. Internal IMU damping that matches the most common drone vibration frequency does not mean it can adapt to any drone, especially large drones. I think ap shouldn’t only be used on small drones in the lab.

The vibration source of large drones can almost certainly be determined to be brought by porps and motors (at least the several large drones I am currently trying to debug are like this), at least I spent a lot of money testing propellers and motors from three manufacturers, and they are all like this. Large things are always expensive, and they have almost done their best. I have also tried many high-end FCs (not expensive compared to the power system), as well as different frame structures. These FCs are almost unable to operate normally without an external shock absorption system.

The ideas I mentioned are mainly aimed at the problem of CG, because a CG that is too high will definitely cause problems (if they use external damping), and I hope this can remind everyone in the wiki. And the specifications of the cable, the wiki only mentions using high flex wire. I initially thought that 26awg silicone skin cable was thin enough (compared to 14awg starting power cable), but 30awg is indeed more suitable. I think this recommended value should appear in the wiki because vibration problems are always one of the most troublesome problems on drones.

Of course, I have to admit that the large copters (150-200kg-max) I tried are rare in the community because they usually try to use heli. But the center of gravity problem I mentioned should not only apply to large drones like me, because more or less, many people will use external damping. I agree with what you said that anything with vibrations should be carefully checked, and redesigning the frame is a better move, but the world is not perfect.

There is this sort of antivibration 3D printed mount a lot like what you are talking about. This was designed for the Cube with standard carrier, but could be adapted to any other FC.
You could experiment with different grade damper balls.

One thing not mentioned so far, that applies equally to all sizes of copter is the wiring.
Wiring needs to be secured to the frame, not pulling or rubbing against the flight controller, and flexibility where it plugs in to the FC so as not to transfer vibrations - but not so loose and flexible that vibrations are amplified by the wire moving around.

And prop wash, the FC needs protection from prop wash.

Yep, I also saw this and shared it with my friend. In my friend’s test, this kind of shock absorption is very suitable for FCs with structures like V5 and Cube. But he also tested other FCs, and it seems that the effect is not good for FCs with shapes like V3 and QiotekH743. I guess it is because the CG position is too low.

I have seen the discuss of the author of this shock absorption platform. Although his original intention was not to lower the center of gravity, it did achieve the same thing; I think this is good. I never thought that too loose cables would also cause problems, this is a blind spot! Although I tied all the cables together, I did it unconsciously, and I think this is indeed a point worth writing into the wiki.

Regarding prop wash, I don’t think any attempt to expose the FC to the external environment should be encouraged. Of course, very small drones may have to do so, but if possible, I think it would be more appropriate to install them in the fuselage or wear a hat.

I think the vibration-damping page in the wiki is missing a lot of things, but of course I’m also worried that too many elements will make newcomers dizzy.

I totally agree with Ben_billi and his findings. I sorted the same problems with my two big RC Helicopters that way and it worked very good with weight under the Pixhawk and Pixhack .
Because of my age (74) I stopped flying Helicopters.
You also should change your style of response.

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Thank you, sir!
I think they may not have enough energy to pay attention to these things and classified my article in the wrong place after a rough reading. I think Developers are probably very busy and don’t have enough energy to carefully check these things. Flying heli is indeed a dangerous thing because the huge prop can easily hurt oneself.
I hope you are in good health!
I once flew heli with pixhawk in 2017, although it was using 450L, its destructive power still remains fresh in my memory.

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for the CG issue, would spacing the dampeners farther apart be a good solution to mitigate the sway?

I think so, you can think of the sway as the FC using a lever to lift itself up with the CG as the fulcrum.

This analogy is not very appropriate, but further dampeners can theoretically reduce sway, like a laborious lever.

I don’t know how to increase the distance between them specifically, and I think it may cost a lot to achieve the ideal effect. Plus, there isn’t much space in my copter, so I ignored this option. Thank you for reminding me of these things.

I am surprised that pixhawks don’t have a natural rigid mount option, such as by screws. the makers assume usage of 3M adhesive on the back. I dont trust adhesives after exposure to the elements, so i made an aluminum rig to enclose the pixhawk while allowing access to all ports and then use spherical grommet dampeners as the interface to the drone frame.

this way, i think ive (accidentally) addressed the concerns you bring up in this post: weighted FC with relatively far-apart dampener supports. thanks for starting a thread on this.

In my attempts, I found that the gray 3M foam double-sided tape works quite well, at least they have been running well for two or three years. I agree with what you said, the best way to fix it is of course to use bolts, although this is sometimes troublesome.

I haven’t seen the shock absorption platform you made, but I don’t think it necessarily has a high CG position problem. The CG position I pointed out in my article is judged relative to the contact point of the damper in the vertical direction, and I think your shock absorption platform may not have this problem.