I am going to try and explain the issue of the Jello effect, or Jelly if you live outside of the US, and do so without making the whole discussion too technical. So please excuse me if it is a bit on the light side technically. This is not aimed at the engineers.
Jello does not seem to be well understood and there are some myths being put around that are not helpful in understanding it and what to do about it, so I hope to set some of them to rest. The problem is becoming more common with video being shot from quad copters, whereas the GoPro set have known about it for some time.
There is a single cause of Jello, vibration of the camera. The fantastic gimbals being used on the cameras do a great job of removing the unwanted movement of the aircraft, but they will not deal at all with high frequency vibrations. They try to, that is why you have the 4 silicone rubber suspensions on the corners of the Phantom gimbal unit. But silicone suspensions have a tendency to only deal with vibrations over a narrow range of frequencies, so if the suspension is not ‘tuned out’ to the particular vibration frequency present, then they cannot cope with it, and in some cases, actually make the vibration worse if it resonates with the suspension system.
CAUSES OF VIBRATION
In regard to the DJI Phantom, there are two main causes, the first is improper operation of the gimbal assembly and the second is out of balance propellers.
Dealing with the gimbal first. Sometimes the gimbal control system can be out of adjustment and the 3 gimbal motors may cause the entire camera to vibrate quite severely and rapidly. These get reported as ‘Gimbal Gone Nuts’ or similar, and posters have put up very convincing videos of the madly vibrating camera. You can try doing an automatic gimbal calibration from the DJI Go app, but the truth is you are most likely going to have to return the aircraft to DJI to be adjusted.
You can easily test for this situation by powering on your aircraft, then picking it up by the landing gear. If you can see or feel any vibration, try gently touching the camera to see if it is vibrating. If so, you have a gimbal problem.
The second cause, out of balance propellers, is the most common reason for experiencing Jello. I found that all 8 of the factory supplied propellers were a small amount out of balance. I will go on to explain how to balance them further on.
There are stories doing the rounds that altering the shutter speed or fitting ND filters will cure Jello. The truth is they won’t. Selecting a slower shutter speed will appear to reduce Jello, but it is only adding motion blur to the image, and that will reduce the apparent resolution of the camera. Using a faster shutter speed will make Jello worse. ND filters do nothing.
You can either fix the cause and reduce or eliminate Jello in your video, or deal with it later. The German company ProDad, who supply very useful tools for the post-production industry, have a piece of image stabilising software called Mercalli V4 SAL (for Stand Alone) that can remove the Jello effect if you get caught with it. Mercalli V4 does the job very well, but it is not a free or cheap solution. Earlier versions of Mercalli, particlulary the plug-ins for editing packages, do not have the Jello removal capability, only the version 4 SAL package has it.
HOW JELLO OCCURS
There is nothing new about Jello, it happens on most modern digital cameras, even some of the most expensive ones. . You could put a $10,000 DSLR up there, if the quad copter could carry it, and still get Jello. Digital video cameras employ two main types of sensor, the difference being the type of shutter used on the sensor. The majority of sensors employ a ‘rolling shutter’, so called because it captures the lines of video information in sequence down the sensor from the top to the bottom. In effect, the shutter ‘rolls’ down the screen grabbing each line in turn. This type of shutter is prone to the Jello effect.
The second type of shutter is the ‘global shutter’, so called because it captures the entire frame of lines in one action, and is not prone to Jello effect. Unfortunately, the global shutter is not common at this time, being relatively ‘new’ and is mostly found on quite expensive dedicated cinema cameras.
Drawing 1 demonstrates how Jello occurs in the rolling shutter type sensor employed in the Phantom cameras:
The pale blue lines represent the scan lines of the camera sensor, however only 18 are shown for simplification. The example image is the dark blue circle with a vertical line through it. The rolling shutter captures the lines in order, from Line 1 down to Line 18, in sequence.
If a vibration is introduced to the camera and sensor during this scanning process, Drawing 2 shows the result:
The vibration in this example is shown at A, where it is a back and forth or rapid side to side vibration. Because the camera is moving rapidly side to side, the position of the circle with vertical line is moved very slightly from side to side with the vibration, and the scanning process catches it in the form shown at B. Because it takes a fraction of time to capture each line, the image is in a very slightly different position from one line to the next.
As you can see, it looks very much like a lump of Jello, and because the vibration is not likely to be synchronised with the rolling shutter, it takes on an animated wobbly look. Adding to that, the same thing can occur in the vertical direction as well, making it even more annoying.
PROPELLER IMBALANCE
An out of balance propeller can give the same effect as out of balance tires on a car, most particularly the front tires, and you can feel the vibration in the steering wheel. But unlike a car, where the wheels are (mostly) rotating in synchronism with each other, the propellers on a Phantom are not in sync, so the vibration passed on to the camera, and seen as Jello, can come and go during the flight, or get better for a time then far worse.This is illustrated in Drawing 3:
The blue circle represents the propeller, the hole being the black circle. The green blob on the edge represents an out of balance mass and its position indicates what side of the propeller it is on. Note that each pair of propellers are shown counter-rotating, as the ones on the Phantom are designed to do.
In the top example, the two out of balance masses are on opposite sides, and the equation reveals that they cancel out to give a resultant imbalance of zero.
In the middle example, they are on the same side, so the imbalance is the addition of the two, making a larger imbalance.
The bottom example shows the out of balance masses at 90 degrees to each other, so the resultant imbalance is at 45 degrees between the two and slightly lesser in magnitude.
The four propellers on the Phantom are not rotating always at the same speed, they are sped up or slowed down in order to control the aircraft, so the out of balance masses change position with relation to each other as the aircraft moves along. This is why you may see no Jello effect while the aircraft is stationary, or hovering, then the effect gets worse when it moves off, or winds cause the aircraft to try and hold position.
BALANCING THEPROPELLERS
I trawled the net for some time looking to find which prop balancer was regarded as being the best, and there are quite a range to choose from. But in the end I discovered that the DuBro True-Spin balancer was most often recommended, so that’s what I bought. A little note here, the DuBro comes with a shaft to take a wide range of propellers, but not the ones used on the Phantom. Most props have a hole that goes right through the hub, but the Phantom ones have a blind hole. Therefore you need to order the DuBro #3381 6mm shaft. This shaft has the correct 6mm right hand thread on one end, and the left hand thread on the other end. All up it is not a very expensive tool, but worth the investment.
When I fitted the DJI props to the balancer, I found all the 8 supplied props were slightly out of balance, most of them in the hub area, and always on the same side. After a while I became quite expert in being able to visually identify the side that was heavy.
There are two ways a prop can be out of balance, one is when one blade is heavier than the other and the other when one side of the hub is heavier than the other. I only found one prop that was very slightly out on one blade, but all of them needed to have weight taken off the hub.
This is not to be taken as criticism of the DJI props, as I now know that almost any model aircraft prop will be bought with an out of balance condition.
This video is a good one on how to use the DuBro balancer:
GEEBAX great article learnt something else to store in my arsenal of information.But must slightly disagree nd fiters do work in a mild jello situation as you stated the faster the shutter speed the more the jello affect is increased the nd filter allows one to reduce shutter speed.This i have experianced myself by balancing the props i still had occasional jello with the addition of nd filters problem gone.OHH by the way you didnt waste your time
Thanks, good to know you appreciated it. Perhaps I should clarify the ND bit. The filters allow you to slow down the shutter speed, and a slower shutter speed introduces some motion blur and the motion blur is what masks the jello to some extent. What I was trying to say is the ND filters are not a cure for jello, the only cure is to remove the vibration that is causing it.
Excellent article Geebax. To be honest, it's the first time anyone has explained jello in a way that I can truly understand both its cause and effect. I found myself thinking a few times, "Oh, so that's what they've all been talking about."
So, yes, based on what you wrote, ND filters do work to "hide" jello to some extent, but do nothing to fix the actual root cause of jello.
So now I'm wondering is there a better alternative to the gimbal bulb dampers. A quick search found an article that compared several alternatives (gel pads, O-ring suspension mount, ear plug mount, and the bulb dampers). According to that article, the bulb dampers do appear to be the best design for reducing vibration.
Interestingly, there appears to be a point of diminishing returns; the closer you get to reducing gimbal vibration to zero, the less responsive the camera gets to subtle movements of the quad because the gimbal has become too isolated from the quad.
Anyway, great article. Please share more topics of clarity, especially around areas of consistent frustration and debate from within the community.
Thanks Geebax,
Great piece of original work, the rolling shutter explanation is the best I have seen.
Will definitely get a prop balancer, and smooth out my P3.
I take mostly stills so not experienced jello to any extent, but the jerking of the video when panning is always present. Do you have an explanation for that?
Thanks for taking the time.
liningiv Posted at 2015-10-31 20:09
Thanks Geebax,
Great piece of original work, the rolling shutter explanation is the best I have seen ...
The jerking on pans is largely caused by the relatively slow frame rate. In the UK you are probably using 25 fps. It is made worse by a fast shutter, so the best way to mitigate it is to slow down the shutter by fitting ND filters to the front of the lens. Try to fit an ND strong enough that you can gert the shutter speed down to 1/50 th.
Getting rid of vibration is a lesson in frustration. I frequently mount GoPros to moving vehicles and have experimented with various gel suspensions and shock absorbers over a long period, but without a great deal of success. The hollow bulbs as used on the Phantom gimbal seem to work best of all but I found that I often needed Mercalli to sort out vibrations I could not isolate. The Phantom suspension is actually very good.
Great way to explain the problem. Here is a good video that explains the rolling shutter, using slow motion, and its function as you described attaining jello.
Dronebow Posted at 2016-12-28 12:07
Does temperature affect the rubber suspension system and introduce the jello effect as well? And if so, is there a way to compensate for this?
I don't believe temperature has a great effect, although it is perfectly possible that extremely low temperatures may make the suspension stiffer and less able to isolate the camera from vibration. However this still presumes that the aircraft is vibrating excessively, so if you take steps to eliminate that vibration it should not be an issue.
Geebax Posted at 2016-12-27 21:00
I don't believe temperature has a great effect, although it is perfectly possible that extremely low temperatures may make the suspension stiffer and less able to isolate the camera from vibration. However this still presumes that the aircraft is vibrating excessively, so if you take steps to eliminate that vibration it should not be an issue.
Geebax:
Information isn't possessed with a use-by date. Great article. Thanks for writing it.
Do you think the quality control of balance is better now, with the Phantoms 4 and 4 Pro and Mavic, etc., than it was in prior models (or do the more expensive models address it?)? Or is this an inherent issue possible with the propellers of all drone models and makes?
Information isn't possessed with a use-by date. Great article. Thanks for writing it.
The propellers are a simple injection moulded product. The inherent balance will be a product of the die used to mould the props, as I doubt that DJI would undertake any additional balancing. So the question then becomes, are the dies better cut now? Can't say, but I don't imagine there would be any change in the procedure.
one thing i noticed cause some "jello" with my p4 i was using sone nd lenses ( Digital Concepts ND16 )never seen any while using the stock lens cover ..... thinking of ordering the dji one too see if those work w/o the jello
The Vaping wolf Posted at 2016-12-29 10:07
one thing i noticed cause some "jello" with my p4 i was using sone nd lenses ( Digital Concepts ND16 )never seen any while using the stock lens cover ..... thinking of ordering the dji one too see if those work w/o the jello
ND filters do not cause jello, if anything they help hide it to a small degree. Jello only has one cause, camera vibration.
Geebax Posted at 2016-12-28 15:34
ND filters do not cause jello, if anything they help hide it to a small degree. Jello only has one cause, camera vibration.
just stating my experiences so far with these " cheap" nd lenses i have had. maybe a gimbal calibration with them installed would alleviate the issue ( definantly heavier than the stock uv lens cover ) ... but why add another step in the setup process before i get to enjoy my flying time. anyhow, moot point cause ill be getting the dji made nd16 lenes cover when i buy an extra battery later today
Geebax Posted at 2016-12-28 15:34
ND filters do not cause jello, if anything they help hide it to a small degree. Jello only has one cause, camera vibration.
Excellent article for Jello, Geebax. Could you clarify something please?
Can you explain little more how exactly you check if the gimbal is vibrating? You said to start the aircraft and pick it up, however, do you start the motors or not? Do you turn the battery on and just touch the camera to feel any vibration? Please elaborate a bit, because I would like to be sure, before I send my Phantom 4 Pro to DJI, where the cause of vibration is, on propeller or on camera or on both?
kykphantom Posted at 2017-1-4 10:53
Excellent article for Jello, Geebax. Could you clarify something please?
Can you explain little more how exactly you check if the gimbal is vibrating? You said to start the aircraft and pick it up, however, do you start the motors or not? Do you turn the battery on and just touch the camera to feel any vibration? Please elaborate a bit, because I would like to be sure, before I send my Phantom 4 Pro to DJI, where the cause of vibration is, on propeller or on camera or on both?
Sure, there is no need to start the motors to check for vibration of the gimbal. Just press the button on the battery to fire it up, let the gimbal do its dance then see if it is vibrating.
Geebax Posted at 2017-1-4 13:23
Sure, there is no need to start the motors to check for vibration of the gimbal. Just press the button on the battery to fire it up, let the gimbal do its dance then see if it is vibrating.
Thank you for your quick reply. If I do that I do not see any gimbal vibrations. If I touch the camera, you can feel some sort of movement but I think it is normal, as the drone is moving a bit in my hands.
I will try to check the propellers balance before I send it to DJI for gimbal adjustment. If there is anything else, we would be very grateful te hear it from you.
kykphantom Posted at 2017-1-5 01:21
Thank you for your quick reply. If I do that I do not see any gimbal vibrations. If I touch the camera, you can feel some sort of movement but I think it is normal, as the drone is moving a bit in my hands.
I will try to check the propellers balance before I send it to DJI for gimbal adjustment. If there is anything else, we would be very grateful te hear it from you.
If you can feel any movement, then that is most likely what is causing the jello. It should be quite still when the motors are stopped.
Geebax Posted at 2017-1-5 14:08
If you can feel any movement, then that is most likely what is causing the jello. It should be quite still when the motors are stopped.
It is not actually a movement but the feel of the gimbal motors trying to resist the force of touch.
Many Thanks for the excellent write up, really helped it to sink in
When I power up my p3a I get no gimbal vibration but when I fly get major jello especially when I get crosswind and it seems only when it hits the one side....
I have a bunch of issues with Jello on my A6500 and other CMOS non flying cameras when filming, especially at super high zoom for wildlife. That said, I'm pleased to say since the P2V+ in 2014, and particularly P3 series (early 2015), I've *never* had a jello problem with any subsequent DJI copter (P3A, P4, P4P, MP, MA). This is with over 1200km of flight in a very wide variety of scenarios. The gimbals and mini dampening system they now build in, I think, make this a non issue. No?
parallax. Posted at 2018-8-5 10:12
I have a bunch of issues with Jello on my A6500 and other CMOS non flying cameras when filming, especially at super high zoom for wildlife. That said, I'm pleased to say since the P2V+ in 2014, and particularly P3 series (early 2015), I've *never* had a jello problem with any subsequent DJI copter (P3A, P4, P4P, MP, MA). This is with over 1200km of flight in a very wide variety of scenarios. The gimbals and mini dampening system they now build in, I think, make this a non issue. No?
'The gimbals and mini dampening system they now build in, I think, make this a non issue. No?'
As long as all those things are working as intended, and the propellers are balanced, then no, it should not be an issue. But there have been many times that someone had a gimbal system that was not correctly adjusted and would introduce vibration and therefore jello.
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