Thanks to everyone for your awesome input on our first post! Several of the tips we received have had a strong influence on our development path. We are already working on a radical redesign for our Mark III prototype that will incorporate some of your suggestions.


Where we left off:


Our last prototype had some semi-successful results. Mark I, which we now refer to as the “Tank” was much too heavy. After stripping it down we were able to get it into the air and shoot some decent footage. However, flight control was sluggish and somewhat unpredictable.


So we designed Mark II “Skeleton”



Pictured above you can see Mark I “Tank” and Mark II “Skeleton” side by side


For this version we made several major changes to the design:

  • Used a skeletal approach to the frame design

    • Removed as much metal as possible

    • Shortened the entire frame by 3 inches

    • Used 1/16” metal instead of ⅛”

  • Added multiple weight compartments

  • Simplified gimbal mounting

    • Spread out the placement of vibration mounts

    • Reduced number of plates

  • Moved battery onto the gimbal


Before we designed our new “skeleton” frame, we performed some rigidity testing on 1/16” aluminum. We found that as long as we kept support spacers within 3.5 inches of each other, 1/16” aluminum would be rigid enough to support the gimbal.


We also did some testing to determine optimum GoPro placement. We found that in order to maintain a clear field of view with the widest angle video setting, the GoPro could safely be placed nine inches from the center of the copter. This allowed us to shorten the entire frame by three inches.




We also refined our gimbal balancing approach.  In Mark I “Tank” we tried to selectively cut out metal to balance the gimbal.  Ultimately we had to add a stack of washers onto the back in order to balance everything out. We felt that this was not an elegant approach and the washer stack was rather ugly. So we removed the extra metal, and then designed several compartments for washers. This gave us more flexibility in balancing the gimbal while maintaining our design aesthetic.



On Mark I “Tank” we placed our vibration mounts close together. This created an unintentional joint and the gimbal had a fair amount of play which caused a swaying motion in flight. In response to this problem, we decided to spread out the vibration mounts. This greatly simplified the way our gimbal attached to the Hexa frame by allowing us to remove several heavy aluminum plates.




As many of you pointed out, moving the battery onto the gimbal is a much more efficient use of weight for balance. Coincidentally our 7 ounce battery approaches the weight needed to balance the GoPro carriage on the opposite end of the gimbal. This also allows us to keep more weight below the vibration mounts while lightening the overall payload of the Hexa.



With all of these changes designed into Mark II “Skeleton”, we sent it off to be cut out of 1/16” aluminum!


Our machinist was gracious enough to send us some pictures of the CNC Router used to cut our gimbal parts.  In the image below you can see the cut marks from our plates in the backboard. There are some more pictures and info about CNC Routers on our blog here.


The Results:


Mark II “Skeleton” is 40% lighter than Mark I “Tank”!  Including the battery, our new payload weight is 36.25 ounces (2.66 lbs.) down from the previous payload weight of 56.75 ounces (3.55 lbs.)


When we took to the air it was immediately apparent that the Hexa could easily handle the new payload weight and maneuver smoothly.


How was the flight and footage? Check out this video and see for yourself. Please Note: This video showcases clips from the GoPro that are unprocessed, as well as clips that have been processed. The processed and unprocessed clips are indicated by text in the upper right corner.



As you can see, we were able to fly for a reasonable amount of time with this payload weight. We were airborne for around 6 minutes and still had some charge left on the battery.


The level of vibration in the footage was encouraging. We put 2 clips through the Adobe After Effects Warp Stabilizer filter in an effort to easily identify the “jello” distortion in our footage.  We were pleased to see that there was little to no distortion present. We appear to be isolating the GoPro from the high speed micro-vibrations generated from the spinning motors.


Our footage is still suffering from some macro-vibrations. We believe there are two main  issues. First we need to balance the props and design some new mounts that will dampen the motors vibrations directly. We have noticed some warbles in flight even when the gimbal is not attached.


Second, we need to look into fine tuning the servo response time. We’ve noticed a rocking action in the video when the Hexa quickly accelerates from side to side. It appears to be a result of servo latency.


What we’ve learned from this prototype:

  • It flies!

  • Acceptable level of controllability

  • Reasonable amount of flight time, 6+ minutes

  • Decent raw footage

  • Little to no “jello” from micro-vibrations

  • Issues with macro-vibrations

  • Roll servo response time issues

  • Could be even lighter


Where are we now?


True to form we are ready to confront our next challenges.  We are already designing our Mark III prototype. For this next iteration we are considering a radical redesign:


  • Moving the pitch axis to the center of the gimbal

  • Dropping the “H” frame for more of a single “I” beam approach

  • Getting rid of all the ServoCity parts

  • Isolating the motor mounts

  • Researching composite materials other than aluminum

  • Building a neutral density filter mount for the GoPro




On our first post, several commenters suggested moving the pitch rotational axis from the GoPro Carriage to the center of the gimbal. We have been looking into this option and believe that it may help us in several ways.


Firstly we can get rid of a lot of the hardware needed to rotate the GoPro carriage. Secondly it will allow us to drop the “H” frame and go for a much simpler “I” beam shape. Thirdly, as several commenters pointed out, this puts our axis on the balance point, which means gravity will contribute towards keeping the gimbal level.


Further Weight Reduction:


While we’ve been very happy with the ServoCity parts, they do add a significant amount of weight. Our new goal is to design a direct drive system that is strong enough to support the chassis so we can disregard the heavy aluminum servo blocks.




We’ve also learned that isolating the gimbal alone will not solve all of our problems.  This is why we’ve decided to design some anti vibration motor mounts in an effort to attack the problem at its root. Hopefully our mounts will provide the solid, rigid mounting needed for the motors while providing some vibration isolation for the Hexa frame.




We are in the process of investigating some of the materials that were suggested to us by the commentators of our first post. We are very interested in Garolite G10 as it looks to have the strength-to-weight characteristics we are looking for without the high price of carbon fiber.  However, it’s more practical for us to continue building our prototypes with Aluminum for now.  Once we are satisfied with the functionality of our design we may experiment with Garolite.


Reduce Video Distortion and Improve Picture Quality:


We are also considering the addition of a neutral density filter for our GoPro. As we have been researching the reduction of video distortion in GoPro footage, we have come across several references to that fact that the “jello” effect is less severe on cloudy or darker days. This is something we have seen in our own footage as well.


If you are interested, have a look at our blog post: Neutral Density For The GoPro in which we go into more detail about our hypothesis and how ambient light levels augment rolling shutter distortion.  We’ve summed up our theory below. Unfortunately we’ve been unable to find any concrete information on the subject.  If anyone can provide some additional input we will be greatfull!


Our Theory:


The GoPro uses a CMOS sensor which scans through the entire frame at a fixed rate. This means there is a fixed amount of time required to read the entire sensor. On a very bright day this could lead to a significant time gap between pixel sampling as the exposure time in that situation is very short. This would also lead to a very sharp exposure for each pixel. However, on a darker day the exposure is longer and each pixel is sampled for a longer period of time. This would increase the motion blur of the pixels and a reduction of time difference between pixel sampling. Both of those factors could cause the captured image to be more blended between pixels thus reducing the amount of “jello” distortion visible...

... One way to force the GoPro to use a longer exposure time on a bright day is to basically put sunglasses on it. A neutral density filter is a material that will reduce the amount of light that enters the lens without distorting the color of the image.


In an effort to test our theory, our next prototype will include the ability to insert neutral density filters of different F-stop levels onto the GoPro carriage.


Here is the part where we need your help!


We would very much appreciate any input and or experiences you can share with us regarding the following items:


  • Motor isolation/dampening, what has worked for you? Problems?  Limitations?

  • The use of neutral density filters with a GoPro, has anyone tried it? How did it work for you?

  • Do you know of any supply sources for composite material, especially Garolite G10? Where have you ordered from and what was the experience like?


Though we are very encouraged by the latest results of our test flight, our work on Mark II “Skeleton” has taught us a lot and we still need to refine and improve our design. We are now turning our efforts onto Mark III and look forward to sharing our progress with you soon.


We will continue to post our major milestones here on DIY Drones.  If you are so inclined, you can also keep up-to-date on our incremental progress via our blog: http://www.skyrisfx.com/mission-updates/



-Jeff and David


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  • @SkyrisFX

    Awesome! In regards to my quad, I hope to do a write-up soon, when my schedule calms down a bit.


  • That's great Jordi!  Can't wait to see the pics.  By the way, after you mentioned that you were using a local fablab, we did some investigating and found out that there is one under construction in our neck of the woods!  Should be a great resource.

  • @SkyrisFX

    Thursday evening I decided to lasercut my quad parts out of acrylic at the local fablab. I assembled everything Friday, and flew for the first time that evening. Amazingly, it flew great the first time, and there were no crashes! I am currently using a very underpowered battery, however, so the quad barely wanted to move. I have more on the way, tho, and I hope to do a write-up here soon!

    Thanks for the encouragement,


  • Jordi,

    No worries about response time!  CNC can get expensive.  Luckily we have a friend who has been cutting our pieces off the clock.  In regard to laser cutting, when we started thinking about this project we gathered as many quotes as we could and found that there was huge variance in pricing between shops.  These guys were the cheapest.  If you're looking for a cheap, light, and temporary solution, someone suggested cutting the shape in balsa wood and then coating it with fiber glass or another composite epoxy (though we haven't tried that approach and don't know how well it works).

    Looking forward to seeing your build when you get around to it!

  • @SkyrisFX

    Sorry it took me so long to reply, I've been busy with the end of school. I do plan on cutting the G10 with a CNC, but I don't have one available to me. I've gotten quotes from several local machine shops and they are more than I am willing to pay, so that idea is on hold for a bit. I'm actually travelling to Spain in a couple weeks and would love to be able to take my quad and get some great aerial video. Tomorrow I'll go out and laser cut the parts out of acrylic so that I can at least get flying. I realize acrylic is quite brittle, but it should work temporarily. I'm also interested in using Delrin/Acetal, so I ordered two sheets of 1/16" plastic. When it got here it turned out to be much floppier than expected, so I was forced to return it. We'll see how this goes!


  • We have done some calculations. Garolite G10 has a density of 0.069 pounds per cubic inch, whereas 6061 aluminum, which we are using, has a density of 0.0975 pounds per cubic inch. Switching to 1/16" Garolite G10 in place of 1/16" 6061 aluminum would be about 29% reduction in weight.  

    In regard to your question about brushless motors, for this project we've decided to stay away from brushless (for now) since APM doesn't support and we don't want to spend $ on an IMU board and motors until we have our form factor down.  Our challenge is to get reasonably good footage from a cheap gimbal that uses cheap servos.  In the end we might have to go brushless but we're not at that point yet.

    @Jared S
    Thanks for the info and the link.  Agree about not spending too much on experimentation.  We found a place that sells ND filter for $8 per sheet.  Will post back about blur factor.

  • T3

    In my experience, longer exposure times result in blurry images before it helps reduce rolling shutter. On a moderate vibration environment anything less than 1/500 results in image degradation due to blur. I'll even sacrifice ISO to maintain 1/500 or greater. I haven't worked with gopro on a quad so it may be worth a try - I wouldn't spend a lot of money on it until you are convinced.

    There is this guy that found ND filters got rid of visible prop aliasing.


  • Have you done any calculations of weight savings by converting it to G10? I would expect to be minimal.

    Where is it possible to get brushless gimbals motors?

  • We will definitely report back on the ND filter testing with the GoPro. We are thinking of incorporating a way to mount strips of ND film in front of the lens. This way we can quickly try different F-stop levels of filtering to see how much of a difference it will make. 

    An added side benefit of using ND filters is that we should also see richer and deeper colors in the video.

  • Curious to hear how your testing with the gopro filter goes...
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