I’ve spent more than a year trying to build a helicopter that can lift a small DLSR and give clean, crisp stills and vibration-free video. I’ve built a variety of aircraft: some single rotor (with collective pitch) and several multi-rotor helicopters. I’ve also experimented with different camera mounts, and different flight control computers.
This is part 1 of a series of posts describing what I’ve found that works best and how you can build your own aerial platform (or what to buy if you want someone else to build it). This information can save you a year of trial-and-error experiments. Better, you can go straight to a solution that will work for you without wasting a lot of time or money.
First, here’s a picture of 6 rotor helicopter, a hexacopter, with a Skyrover camera mount and camera. I finished this one recently and it gives the best results for stills and videos that I’ve been able to get so far. In future posts, I plan to take you through every step of the build process. I’ll explain my choices and the reasons for them.
Here’s a view from the top.
I’ve found that multicopter configurations with 4, 6, 8 or more rotors (propellers) to be the smoothest, most stable and easiest to fly. On these multicopters the rotor has a fixed pitch. So the only way to cause the multicopter to roll, pitch or yaw is by changing the speed of the motors relative to each other. Translating the joystick movements on a remote control into speed variations of the motors is done by an on-board computer. How stable the multicopter is in flight (especially in the wind) is determined largely by the computer and the quality of its software.
I’ve found that the computers made by www.Mikrokopter.de (sold in the US by www.Mikrokopter.us and by www.quadrocopter.us) to be particularly good and probably among the best available. I’ll discuss the reasons why I think they are a good choice below.
Another contributing factor to stability and smoothness in flight seems to be the number of rotors. Having looked carefully at dozens of videos, I’ve noticed that even with the best multicopters, there’s a little bit of jerkiness, or low amplitude, short duration roll movements. I call these micro-rolls. Usually, they appear as tiny and brief (barely noticeable) jerks rolling to the right or left. These movements are most often caused by sudden stick movements by the pilot. They are also caused by wind. They are subtle and most viewers don’t notice them. But professional videographers notice them. So if you have discriminating clients, you’ll want the smoothest copter you can get.
When comparing videos, my subjective judgement is that octocopters (8 rotors) show the least of these micro-rolls. If carefully flown, you can get very smooth movement with an octocopter sometimes with no visible micro-rolls in the video. It looks like the octocopter is on a pole, not flying through the air. Hexacopters can be reasonably clean too, but they seem to be a bit jerkier. Quadcopters are usually a bit worse. The reason octocopters are immune to these movements is that there is more mass at the ends of the arms. And the arms on octocopters tend to be longer to make room for the propellers. So it takes a lot more energy to roll or pitch an octocopter.
You might think that a properly stabilized camera mount would absorb micro-rolls. I haven’t seen one yet that removes them completely. Please let me know if you find one. The camera mounts tend to be better at removing slow, large amplitude movements. So, my recommendation is that if you’re building a multicopter for aerial photography, go with a 6 or preferably an 8 rotor design.
An actively stabilized camera mount can keep your camera pointed where you want it, even when the multicopter is pitching and rolling in the wind. The camera mount should also absorb vibrations caused by the motors and rotors. The Skyrover camera mount (available at MikroKopter.us) is an inexpensive mount with active stabilization for pitch and roll. It is designed to work with the Mikrokopter computer and software.
The Skyrover doesn’t have gyros or accelerometers itself for stabilization. It comes only with servos. It relies on the Mikrokopter computer (or similar) to provide the right signals to the servos. While this is a good arrangement and works reasonably well, it is possible to improve it. The main reason it’s not perfect is that the gyros, which sense motion, are on the Mikrokopter computer board. So they’re not actually sensing the camera’s motion directly. The camera is not rigidly attached to the multicopter’s frame. There are soft rubber shock absorbers connecting the camera mount to the copter. So a better arrangement would be to have the gyros mounted on the camera mount, so they are sensing the camera’s movement directly. You can set up the Skyrover to work like this (there’s a gyro+computer product called PicLoc you can use for this), but you need to provide the extra gyros and hook them up yourself. Not difficult, but you need to decide whether the effort is worth the slight improvement.
But even with the standard arrangement of the Skyrover and Mikrokopter, the Skyrover is amazing at absorbing vibrations and stabilizing the camera. I’ve shot stills at dusk at 1/125 second and got results that were consistently tack sharp. Can’t do better even on a tripod.
For video, the results are also quite good. The Skyrover mount compensates for helicopter movement quickly, smoothly (important for video) and with lots of torque for heavier cameras. The current version of the mount will accomodate a camera body that is 5.75 inches wide. This is wide enough for most small and medium size DSLR’s. Though it’s not quite wide enough for a Canon 5DII. My understanding is that a wider carriage version of the mount will be available to handle larger cameras (Spring 2011 time frame).
Equally important, the Skyrover is mostly made of aluminum. It can withstand hard landings and outright crashes, often protecting the camera from damage. At 600 grams, you can lift it easily with an octocopter or hexacopter suitably powered (we’ll explain what this means later as well). I prefer aluminum to carbon fiber. Carbon fiber can shatter in a crash. Aluminum bends. So, you can bend the aluminum back and (hopefully) keep flying.
To be continued…