Here’s a side view. You can see in the picture below the way the skate bearings are bolted onto the dolly tubes and sit on the rails. The 45 degree angle of the bolts into the tubes allows easy mounting onto a 3/4″ or 1″ rail. And you can always use longer bolts for thicker rails. Thicker pipes give you the possibility of longer, more stable rails. Anyone for a 10 metre time lapse rail? 😉 Seriously though, my local hardware store has 21ft gas pipes, I’m thinking about it! 🙂
And a closer look. Underneath you can see the timing belt with bearings on the left with the motor, then the box with circuits in the middle, and battery pack on the right. I used 6-pin mini-din connectors from the Pi’s GPIO, as it gave an adequate number of pins in a nice neat form factor.
Another view from underneath .Velcro is great to keep everything attached!
Here you get a look at the timing pulley in that dark cavity above the motor. That’s what pulls the dolly along the rail via the timing belt. Sending a pulse of 12v for 150ms to the motor drives the dolly about 3mm. Perfect for those slow pans. It’s important that the timing pulley is correctly matched with the timing belt. The motor is a 15RPM.
And finally, a nice low angle shot. I must clean up that Velcro. Not the prettiest solution, but it sure works nicely. You can also see the switch which I’ve used to reverse the direction of the motor. That simply reverses the polarity coming from the transistor to the motor, depending on it’s position. A motor driver (such as the one I used in the Macro Pi blog article) would allow me to switch direction in software, but the switch is OK for the moment, I don’t change direction too often.
An add-on to this project that is not detailed here is my DIY dew heater. I found that during night time shoots, the camera lens can very easily get fogged up, especially that we have such damp nights in Ireland. The dew heater wrapped around the lens brought it’s temperature up a degree or two, just enough to keep the dew from forming on the glass. The build instructions for the heater are very well documented on Steve Maddison‘s blog, at http://www.cosam.org/astronomy/equipment/dewheater.html. After a few failed attempts at a night-time lapse, I built the heater, and I was amazed at how well it worked. Zero dew on the lens in very similar conditions to the previous attempts.
Here’s a few images of the rig in operation.
In this image, you can see where I covered the viewfinder, as the sunlight entering the camera from the back was washing out the initial images.
A couple of rocks in each end of the rail to settle it down a bit. It was a bit windy that day.
I don’t mind people walking through the time-lapses much, I think it adds a bit of interest.
Sourcing the timing belt parts
Next page, the circuits.