Inexpensive, easy to build, and it actually works! What's not to like?
Here's a sample video shot using my cellphone on this home-made motorized LEGO camera dolly.
Step 1: Parts
1 x Cellphone bracket $1.50
1 x 1/4-20 screw
2 x 1/4-20 nuts
1 x LEGO Battery holder
1 x LEGO Motor
4 x LEGO tires
An assortment of LEGO gears, axles, beams and bricks.
I intentionally did not list the exact LEGO parts that I used. Instead, I will share my approach in building this, so you may do the same with the parts you have at hand. You might even have better LEGO parts than I.
Step 2: Smaller to Larger Gear = Slower + Power
Rather than electronically slowing down the motor rotation, I opted to do this mechanically. This has the advantage of increasing the power (so it could carry more weight) while slowing down the movement.
Use any set of gears you have. Use smaller gear (1) on the motor and mesh that with a larger gear (2). The larger gear (2) will move slower.
On the same axle as gear (2), put another small gear(3), and mesh that with another large gear (4).
Gear 1 will move fastest, gear 2 slower, gear 4 even slower.
On my build, I used six gears. Your build might vary depending on the ratio of your gears.
Step 3: Camera Bracket
You could make the camera holder using LEGO. However, I already have the camera bracket so I mounted it on a 2x3 LEGO brick using a bolt. Use the hole to guide the drillbit. Start with a drill bit smaller than size of the middle hole at the bottom of the brick. Gradually use larger and larger drill bit until the hole is big enough for the machine screw.
Use two nuts, one to attach the bolt to the LEGO brick. The other to push up against the camera bracket.
LEGO is amazing! Even with the middle nub completely missing, the LEGO brick was still strong enough to hold the bracket and my cellphone.
Step 4: Final Tip
Originally, I thought that the weight of the battery and camera, plus some rubber bands on the wheels would be sufficient for a smooth travel. However, it still occasionally stutters. My friend Tony came up with a simple and effective solution. A rubber band to keep the wheel axle taut. As you can see in the video, it works quite well.
If you build this, I'd love to see it. Please leave links to photos/videos in the comments. Thank you!