I made this as an extension to my ARDUINO TIMELAPSE SHIELD.
Basically its an endless servo mounted to a skateboard wheelset.
So everytime the timelapse shield turns a step, the dolly drives 3mm.
Step 1: FRONT AXLE
the main/front axle is built from mainly skateboard parts, as there are:
2 sets of bearings
4 distance pieces, normally between the bearings of a skateboard wheel
also you will need
2 M8 bolts
4 M8 nuts
a few shims, depending on the lenght of the bolts
The front axle is screwed on to a 20x20 mm square pipe.
The main body of he dolly, is a connecting piece i had from a beamer mounting, but you can obviously use any kind of metal or plastic piece thats sturdy enough.
Step 2: THE BACKWHEEL
The driving wheel is made of a regular sized servo, that i modded to be an endless gearbox-motor.
You can do so, by open it, put the pot out and either solder in two 2.2kOHM resistors instead, or leave the pot in the circuit, but take it off of the axle.
I did the second, so i still have the pot, and can adjust mid position at any time.
Thats important because otherwise the Mid position might not be at 90 degree servo signal and you might have to find out the right mid position by trial and error, which i didnt want to do, because i already ruined a servo by trying to do so.
Anyway, lets assume you kodded the servo and midposition is at exactly 90 degree servo signal.
Also there is a small mechanical stop inside the servo that permits it from turning 360 degrees, you have to clip that or file it down till it moves freely.
There are endles instructables and how-tos about that so i will skip it for now.
The servo is mounted to a piece of stripboard, and the stripboard is mounted to the dolly with a part i got from a crashed TREX450 helicopter.
It has full ball bearings and is ideal for that job.
Watch the closeups to see how its attached
Step 3: THE STEERING MECHANISM
It can steer the dolly with a micro servo, thats attached to the timelapse shield with a nanoservo.
Also from the crashed TREX.
Scriptwise, its the same script like in the timelapse shield, but i added steps for driving and turning.
I did that by solder two servoplugs to the shield, both use the 5V from the ESC and PWM pins of the Arduino.
One is connected to PIN 3 and one to PIN 5.
As everything runs with 5V which is already the base line for the ESC to power up, i decided to let it drive, turn, and turn the gopro in dedicated steps.
That means the cycle is as following:
-take a photo
-turn the camera for 90ms
-drive for 90ms
-wait for (3000-90-90)sec
I didnt implement the possibility to turn the back to steer the dolly so far, but if i would, i would for example let it do the above lines 10 times, and then steer 1 degree.