At first I had this article titled "Stepper Vs. DC motors", but I honestly couldn't think of a logical reason to defend DC motors when being used for motion control timelapse. I've been getting a ton of emails asking for advice on what motion control timelapse system I would suggest for someone to purchase. First I try to sell them my DP stage zero (still for sale!) but most of the time they have already been to my website and read my comparison review of the MX2 and the Chronotimer. Honestly though, that was a comparison of the controllers, not the entire rigs capabilities. Plus it was mostly an opinion piece to show how important a simple interface is for the less tech savvy folk (like myself) but without loosing any features. In Chronos' case, I actually gained a few. Now that there are a few more low cost systems on the market and a couple on kickstarter, I decided I should post a blog about what I think is a very important factor when it comes to a useful timelapse system.
I believe the most important factor in a good motion timelapse system(besides the controller) is the motor being used. DC motors really cannot hold up to the precision repeatability and dependability of stepper motors without the DC motor being encoded. DC motors operate on pulses, so you can make it go slower or faster be increasing the pulse rate. A capable controller can send a pulse for a constant speed for a set amount of time, then pause and expose the shot, then pulse for movement again and so on and so forth. This is referred to as a move-shoot-move mode(MSM). So when you set your controller to MSM mode, it is really only telling the motor to move for a certain amount of time, not a specific distance. Which explains why when you change from a horizontal to a vertical axis you must recalibrate and/or change the speed on the controller to get the desired travel distance. This also becomes an issue when using different loads of weight on the cart (i.e. a large lens will cause the motor to move slower).
Stepper motors on the other hand operate in "steps". A correctly calibrated controller can efficiently tell the motor to move the cart a specific distance, and it WILL move that distance! You can tell it to move a distance whether it is vertical or horizontal and have a variety of different payloads with confidence that it will move the correct distance (as long as you don't exceed that particular motor's payload capabilities).
Besides the obvious fact that your movement is predictable with stepper motors, regardless of changing payload and/or angle of the rail. One of the most important reasons to use stepper motors is REPEATABILITY. The same way that the stepper motor can move forward in precision "steps" it can also move in reverse that exact number of steps, so you can have the cart back in the original position it started from and even repeat the same routine it did previously. Below is a good demonstration of repeatability being used with a macro timelapse.
I want to add that all of this information is important in any case of motion control timelapse, not just linear motion. Emotimo has a very impressive Pan/tilt mount that uses repeatability using stepper motors and a Wii (style) controller to set keyframe points so you can plan out a movement in realtime and it will do the same routine you set when shooting timelapse . Here is another good example of how useful precision repeatability is with their rig.
Feel free to contact me on any further questions or if I have any false information!
All of the videos used in this article were embedded with the permission of the owners.