As we explained in our photogrammetry introduction, photogrammetry fundamentally involves taking many photos of an object from multiple angles. This is pretty straightforward, but it can also be time consuming. A typical process involves a camera on a tripod, being moved slightly between each shot. An alternative is to put the object on a turntable, so the camera can remain in one place. This is still pretty fiddly though – moving a turntable slightly, taking a photo, then repeating 30 or 40 times. It also introduces opportunity for error – the camera settings might be bumped, or the object might fall over.
To us, this sounded like a great opportunity for some automation. As part of the LATIS Summer Camp 2016, we challenged ourselves to build an automated turntable, which could move a fixed amount, then trigger a camera shutter, repeating until the object had completed a full circle.
Fortunately, we weren’t the first people to have this idea, and we were able to draw upon the work of many other projects. In particular, we used the hardware design from the MIT Spin Project, along with some of the software and electrical design from Sparkfun’s Autodriver Getting Started Guide. We put the pieces together and added a bit of custom code and hardware for the camera trigger.
The first step was getting all the parts. This is our current build sheet, though we’re making some adjustments as we continue to test.
[googleapps domain=”docs” dir=”spreadsheets/d/18FVIXNNT8n3cJQVWfgfFD0G26C9ARmLLhKIKlKBOokA/pubhtml” query=”widget=true&headers=false” width=”100%” height=”500″ /]
We also had to do some fabrication, using a laser cutter and 3d printer. Fortunately, here at the University of Minnesota, we can leverage the XYZ Lab. The equipment there made short work of our acrylic, and our 3d printed gear came out beautifully.
With the parts on hand and the enclosure fabricated, it was mostly just a matter of putting it all together. We started with a basic electronics breadboard to do some testing and experimentation.
Our cameras use a standard 2.5mm “minijack” (like a headphone jack, but smaller) connector for camera control. These are very easy to work with – they just have three wires (a ground and two others). By connecting one wire to ground, you can trigger the focus function. The other wire will trigger the shutter. A single basic transistor is all that’s necessary to give our Arduino the ability to control these functions.
The basic wiring for the motor control follows the hookup guide from Sparkfun, especially the wiring diagram towards the end. The only other addition we made as a simple momentary button to start and stop the process.
Once we were confident that the equipment we working, we disassembled the whole thing and put it back together with a solder-on prototyping board and some hardware connectors. Eventually, we’d like to fabricate a PCB for this, which would be even more robust and compact. The spin project has PCB plans available, though their electronics setup is a little different. If anyone has experience laying out PCBs and wants to work on a project, let us know!
While building the first turntable was pretty time consuming, the next one could be put together in only a few hours. We’re going to continue tuning the software for this one, to find the ideal settings. If there are folks on campus who’d like to build their own, just let us know!