I am happy to report that I have achieved a major victory in the battle against the loathed Jello Effect - the asymmetric video motion caused by the high-frequency mechanical vibration. I run a hex setup with a 2-axis gimbal and the GoPro HD Hero 3 Camera. 

Step 1: Replacing stock plastic props with carbon fiber was the first and most significant factor reducing vibration from 1.8 to 0.3 even without balancing, but it did not solve the problem completely.

Step 2: Placing silicone rubber between the camera and the frame and ensuring there is no contact anywhere has done the did. Before, I have tried pretty much everything including foam, rubber, various mechanical setups but nothing worked as well as silicone.

See the video for more details:

https://www.youtube.com/watch?v=rrQhfiRmMGQ

 

Views: 15693

Reply to This

Replies to This Discussion

What's interesting in your videos is the sound of your Hex. I also fly a hex  (DJI Flamewheel w. T-motors & balanced Graupner carbon-filled props). In your vids I'm repeatedly hearing low harmonic beating/pulsing, which may indicate that something is well out of balance. My hex doesn't generate any such sounds, and if it did I would be looking for the source. I get zero jello with either my GoPro 3 (Black) or the 2. Isolation is pretty ordinary rubber grommets between airframe and landing gear frame and then four little rubber-bumper lord-like mounts between the landing gear frame and the gimbal system. I do run my GoPros in their full housings, so the extra mass may help. My gimbal system is also heavy, but I had no jello without it.

Your log readings are for the APM, not for some other place on the hex. Harmonic resonances can have strong local effects in a structure, depending on all sorts of things. For example I have a small trad heli (Blade 130X) that at a certain rotor speed sets the tail to vibrating so violently that it becomes a blur and components can break, while the front shows no vibration at all.

The point is, balance, balance, balance. The good news is that multicopters don't have all the odd rotating bits that trad helis have and that make perfect balance at all speeds impossible. The bad news is that while balancing props is not difficult, balancing motors isn't quite so easy. Some motors are advertised as factory-balanced and in my experience higher quality motors seem to run smoother than cheap ones. I haven't needed to balance the T-motors on my hex. 

Here's a YouTube vid showing how to balance a motor dynamically: http://www.youtube.com/watch?v=_yLRGF5_4XU . You don't really need the app or even to unmount the motors from the aircraft, just use sound and feel and you should be able to get real close to perfect. It's probably impractical to try to use the aircraft's receiver/controller to spin up each motor, rather mash up a cheap ESC, receiver and battery to power up the motors individually. Don't run the motors for long periods or wide open. Before unpluging the three motor leads from the aircraft's ESC make a note of which goes to which so you don't end up with wrong way rotation (and double-check rotation direction before the next flight). Finally, with apologies: DO NOT ATTEMPT THIS WITH PROPS MOUNTED!

 

Oliver, it is an interesting observation about the sound. 

I have not balanced my CFs on principle. That could be a reason for the different pitch. Also, CF props, are much more "vibrant" and unyielding and can produce different sound than plastic.

It could also be that my fully aluminum frame creates a resonance. 

I would really want to know more about any resonance work you have done.  It seems to be a very interesting and often ignored subject but frame geometry has a lot to do with how it responds to vibration. Cheers!

My knowledge of harmonic resonances is mostly subjective mainly from dealing with bagpipes, my profession (all sorts of desirable and some undesirable things happen when multiple reeds are running in proximity to one another). But again, I think the value of fully balancing the motors and props on a multicopter is  not appreciated as much as it should be. 

The simplest way is to reduce jello in your footage is to reduce your gopro shutter speed, now you can't do this from the camera settings but you can trick it into doing it. Read on>>>>> 

You may have noticed that you only usualy get this jello effect on bright (sunny or cloudy) days. When your gopro is recording in these conditions it uses a very (very!) fast shutter speed which picks up all the tiny high-frequency vibrations from your props etc. and causes this wobbly video footage. That's why if you've ever done a recording around sunset you won't get this effect. 

Now as I said, the simplest way to completely get rid of this (trust me I've been doing it for many years now) is to reduce the shutter speed by creating a darker environment for the gopro. All this involves is buying a gopro ND filter lens (basically sunglasses for your camera). This drastically reduces the shutter speed but still lets through enough light for a clear picture. These lenses are available in many places now, even from the Team Blacksheep website under accessories I think. 

Hope this helps!

Reply to Discussion

RSS

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service