Creating a Single Axis Wirecam for Action Filming
For our final year high school robotics project, we were approached by the art students to construct a device that could “enhance events photography and videography through aerial photos and videos”. They wanted a camera that could ‘capture intense moments of action and school chanting from aerial angles that normally would be inaccessible’. After lengthy discussions (read:arguments), we decided that due to the large amount of specifications we had to follow for it to be assessable for NCEA standards a quadcopter or plane would be too hard to try to construct in our limited timeframe. We also designed lots of different ideas, including a really long pole, a remote controlled helium balloon, and a parachute, but we found they didn’t fit enough of our specifications to be a feasible project. The main document for this can be found here..
We eventually decided on a single axis wirecam, inspired by the likes of Varavon’s wirecam. It had easy installation requirements (as opposed to a two axis ‘spidercam’) and was much safer than a drone or plane, which made our principal happy. I’ll go over how it works in a bit.
The whole year consisted of an iterative development cycle that worked the best for me and my partner - I was mainly focused on developing the software and electronics of the robot while David worked predominantly on the physical construction. We did work together on most things However.
(my end of year exam modelling report is here, I’m very proud of it. It details the whole process of modelling, designing, and working around all the competing factors that could go into a technical project like this.)
Construction
Thankfully, we had access to a lazer cutter at our school, which David and I abused. Because the structure of the robot needed to be strong, we felt that a cutting each side out of a single piece of wood instead of cutting and gluing/screwing pieces together would be the best solution. We cut out a large part of the frame to save weight, but kept it in a ‘truss’ style as it is remained strong. Most of the construction parts are outlined in my modelling report above, so I won’t go into depth here. I suggest giving it a read if you are interested. With a cheap but high-rpm motor from JayCar, we used a 1:4 gear ratio system to get the motor from 9700rpm to 2500rpm, but giving us 4x the torque (which we absolutely needed to get the wirecam moving). 2700rpm on a 2.5cm drive wheel translates to 5ms-1 linear velocity - 2500rpm is pretty close, and gets us nearly to this spec. For the gimbal, we used an EVVGC gimbal board and a gopro hero 2. It only needed to be two axis as because it is on a rope, an entire axis will be stabilised already and there was no need to add unnecessary weight. We used a continuous rotation servo attached to a gear (with a ratio of 1:10 or something) so that spinning the motor at maximum speed moves the main gear around extremely slowly and precisely. The gopro remained attached to the main gear. (see the bottom of the photo above).
Electronics
For the electronics, the vast majority of discussion is in this document. I suggest reading that! Originally, I wanted to use a pair of low powered nRF24L01+ 2.4GHz modules for the wireless communication, but we found they caused more trouble than they were worth. We eventually decided on a pre-made radio controller built for RC cars, and a single arduino nano on the robot.
The controller had three channels - the trigger, the wheel and a push button. The trigger controlled the speed of the robot down the rope while the wheel controlled the direction of the gimbal. The button was used to switch the gimbal between moving up and down or left and right. The arduino thankfully played nicely with the radio receiver and got a value between 0-1024 for each channel, which we mapped to appropriate outputs for the motor controller and the servos.
The source code to the project is here, it ended up being quite simple in the end.
