Hey everyone! This is our first post to DIY Drones, though we've been following this community for some time and have found the depth of knowledge here amazing! For the past few months we've been working on a unique GoPro gimbal design for the 3DR Hexa. We are now at a point at which we feel like we've made enough progress to share some of the results with this community and hopefully get some feedback.
We are two guys, Jeff and David, with active careers in the broadcast industry. In addition to being enthusiasts of the UAV hobby, we see enormous potential for cost effective video production solutions. With news that the FAA will soon legislate commercial use, we've started investigating potential video production applications with our 3DR hexacopter. Read more about us here...
As many of you have experienced, we quickly ran headlong into the problem of vibration induced video distortion (better known as jello)! We tried several inexpensive gimbals on the market without much success. Obtaining a camera view that was unobstructed by the copter frame was also problematic.
So we decided to go DIY!
Once we decided to design our own gimbal, we set down the main requirements that our prototype should meet.
Vibration isolation: Since our primary application will be production quality video, our main objective is to eliminate as much vibration related video distortion as possible. The video should not require post-processing to remove distortion.
An unobstructed view: The camera’s field of view needs to be completely unobstructed by the helicopter frame. No paying client will tolerate a landing gear or props in the shot, distracting from his or her product.
Plug and Play: Our gimbal system should directly attach to the 3DR frame without the need for additional drilling or modifications.
No Tuning: The gimbal should be balanced and centered relative to the 3DR Hexa frame, resulting in smooth flight without PID adjustments.
Affordable: Through the use of select materials and efficient design, we hope to achieve a reasonable production cost relative to the cost of the 3DR Hexa Kit.
Aesthetic Design: The gimbal needs to be well designed and professional looking. Something that looks cobbled together will not inspire client confidence in the quality of the final product.
The Story So Far...
With these requirements in mind, we set out upon the rocky road of development!
As any good project should, we started with a discovery and research phase where we investigated many different options and approaches. As mentioned above, we started by looking at basic gimbals that were already available. In all cases, we found that in order to achieve an unobstructed view, the gimbal needed to be mounted out on the arms of the hexacopter. Doing so would imbalance the copter, requiring it to be tuned at the software level. This placement also introduced more vibration into the gimbal.
We decided to tackle the vibration issue first, and then design a form that would meet our requirements. As we began researching ways to dampen vibration, we discovered that the three main factors involved are:
1) the weight of the supported object
2) the disturbing frequency (RPM)
3) rigidity of the structure isolated
We started out under the assumption that our gimbal would need to be heavy enough to create a static load within the deflection material, but not so heavy that it would overstress the material. So far we've found that it’s been difficult to find a sweet spot - one that is heavy enough to provide enough compression on the isolator, but not too heavy for the copter to lift.
At higher disturbing frequencies the required minimal thickness of the isolator can be reduced. Because the helicopter operates at variable disturbing frequencies, we determined that the thickness of our isolation material should be based upon the lowest disturbance RPM. Since our motors have a KV of 850 and operate at a maximum of 12 volts, the maximum RPM should be less than 10,200. Since hovering is usually achieved under 50% throttle, the low side of motor rotation for flight should be above 4000 revolutions per minute. For this reason we chose isolators with 5/16” thickness. This should provide us with isolation efficiency of 95% or better. More on the science of vibration reduction here: http://www.easyflex.in/pdff/latest/Vibration%20Isolation%20Theory.pdf
Once we had the vibration mounts, our goals, and the dimensions of the GoPro camera, we were ready to design our gimbal frame. We decided to go with an “H” frame that would be attached to the copters center and yet hold the GoPro carriage far enough in front of the copter to obtain an unobstructed view. Given the APMs native support of servos, we decided to steer away from brushless motors for now. We placed the roll servo in the center, and the pitch servo with additional ballast weight in the back to balance everything out.
Now that we had a form in mind, we needed to work out how to mount everything together. It quickly became apparent that the gimbal carriage would need to be firmly mounted, so that it did not add vibration, while being able to spin smoothly. The meant we would need ball bearing mountings. While looking for an affordable solution, Jeff came across ServoCity.com and found exactly what we were looking for.
Once the parts arrived in the mail, we bought some ⅛” X 1” aluminium strips and started cutting and drilling in our garages. We built the entire “H” frame and assembled all of the components. The gimbal had a very smooth movement on both the roll and pitch axis. The frame was rigid and solid, and protected the GoPro very well. It gave a clear and unobstructed view from the hexacopter
It just had one major problem, it was way too heavy! This gimbal rig was approaching 4.5 pounds and there was no way the hexacopter was going to be able to get off the ground, much less fly in the controlled and stable manner needed for video production.
We decided that we needed to reduce the weight as much as possible and this was going to require a high tech solution. David devised a calculator to help us determine optimal hole placement within the frame. Once we were comfortable with our layout we sent the design off for CNC routing.
How did it all work out? Check out the video and see for yourself. Please Note: there has been no post processing of the resulting GoPro video.
As you can see our first prototype is still too heavy. The good news is that our vibration isolation method seems to be effective based upon the limited amount of video we captured. That said, there is still work to be done! We've revised the design yet again, and our Mark II version parts should be arriving in the mail shortly.
Changes to the design include a much lighter chassis built from a thinner aluminum. After a few rigidity tests we believe we can reduce weight by using a 1/16” plate. We’ll also be removing as much metal as possible. The end result should look something like a skeleton relative to our current prototype. Another change will be the incorporation of the ability to modify the weight and thus the balance of the gimbal chassis. This will allow the gimbal to work with multiple GoPro versions and accessories. We will do this by adding several weighting compartments on the chassis. We are also planning on relocating the main battery to the rear of the gimbal to contribute to the weight needed for balance. This will further reduce the overall gimbal weight.
Here is the part where we need your help!
Since we only have one hexacopter for testing purposes, any recommendations regarding payload limitations would be appreciated.
We are also interested in any additional methods you may have used for vibration isolation.
We are very determined and optimistic that we can successfully create a working system with these goals in mind (though we might have a few productive failures along the way). If you’re interested in reading more about our journey, we will be posting regularly on DIY drones and you can also follow our progress on our blog here:
-Jeff and David