There were two ways: to enlarge the diameter of the gear (but so I'd have also to build a longer brace between tripod and motor), or to try to make much little teeth on the same diameter. Second choice should have been impossible to make by hand, but with a laser cutter perspex plate it has become reality (thanks to Waldy which helped me).
Step 1: Laser Cutter Absolutely Needed!
I attach the dxf file with all three cogs so that you can see or utilize it to make something similar.
Step 2: The Transparent Gears
Step 3: The Metal Handy Connection
You see how the metal locking bolt pipe remains in the socket I've created in the inner circumference. There is a thin black rubber band between the tripod head and the gear, so it's tightly steady.
Step 4: Dismounting the Motor Unit
The issue is that the little nail which push the teeth has to make a shorter route because the teeth are much smaller, so closer each other than before.
On the same time I want to keep the chance to use any of my three gear sets, so I've decided to add a nail behind th exeisting one.
So let's take the motor gear apart.
Step 5: Adding a Second Nail
We also need a steel big paper clip, which is soft enough to bend, and with the help of the pliers curve it two times at 90°. The purpose is to make it reaching the back side of the existing nail, and exceed it in height, as you'll see in next pictures. After bending the clip cut it at the length of the new hole.
Step 6: Mounting Everything Back
Indeed locking the motor unit a little lower than before we obtain exactly what we wished: the new nail will push a tooth after the other, leaving the old nail under them.
Step 7: Let's Speed Up at the New Gear!
As soon the weather decides to stop pouring I'll test it and I'll upload a new image on my Gigapan page.
I hope you'll be able to make a motorized gear like this one, so let me know :-)
Step 8: [update] the Panorama
I've made a gourgeous 6 gigapixel panorama of the roof of a beautiful little city near Milan. This city is Vigevano, and it has a lovely Cathedral and a long central square. See it in detail here: Vigevano roofs.
If you then want to see an interesting 3 gigapixel panorama of the roofs of Genoa, this is also made with this gear.