Lucky Derby - Horse Racing Machine

Lucky Derby – Horse Racing Machine

Place your bets and get ready to the horse racing game! Lucky Derby is a mechanical horse racing game where you and your friends can guess which horse will win. It’s inspired by those classic horse derby machines you’d find in old-school casinos. The internal mechanism is also inspired by pinball machines and a 1920 Gee-Wiz gaming toy. Everything is designed and modeled by me from ground up.

How It Works

The horses are powered by manually turning a wheel. Inside, a spring-loaded mechanism repeatedly compresses and releases, just like a pinball plunger. Each time the spring is released, it launches a steel ball down the track.

The ball hits the horse and pushes it forward—but the distance and timing of each push are mostly random, depending on how the ball interacts with the mechanism and the horse. This randomness keeps things fun and unpredictable. I’ve noticed that some of the horses I printed are just faster than others. For example, one horse was about 0.2mm thinner than another somehow, which reduced friction and made it move more easily. These differences can be caused by print quality and material I used. So you may want to use same material to print all the horses for a fair game!

It’s completely mechanical and doesn’t need any electronics. Just two extra parts that aren’t 3D printed. You can find them in Maker's beginner kit (link), or buy separately:

• Five 8mm Stainless Steel Balls  (link)
• and two or three 0.5x5x25 mm Helical- Compression Spring (link)

Thanks @MINDMELTERPRINT for asking. Pen spring can actually work as well. I tried a ball pen spring which is 5.4mm in diameter and 2cm length and it works too although not perfectly fit the stick and holes on the front launcher piece. 

Assembly Guide

I plan to make a YouTube video when I got more time, but for now, please refer to the GIFs for step-by-step assembly. It’s pretty straightforward!

Step 1: Assemble the Ball Launcher

Start with the launcher mechanism. It includes:

• The launcher piece
• One or more springs behind it (I use three for stronger pushes; the GIF shows just one)
• A base piece that holds the spring in place and slots into the track

Tip: The base piece connects to the back of the spring—make sure the orientation is correct. The small anchor stick should be on the upper side so that the spring is slightly pulled upward, which reduces friction.

Step 2: Install the Axle

Install the axle that repeatedly compresses the springs when you turn the wheel. There are two rollers with teeth you need to install on the axle first. Be sure the “teeth” are facing forward—this is important for the mechanism to work properly.

Step 3: Add the Gears

Attach the main gears that drive the axle. They’re designed for a tight fit, so apply a bit of pressure. If they loosen over time, a tiny dab of glue can help secure them.

Step 4: Assemble the Tracks

Snap together the two race tracks with the base. Make sure they align well—any seam or misalignment might cause the ball or horse to get stuck.

Fixes for seam issues:

• I included an optional “surface” piece in the last plate file you can print and glue over the full track, so the seam is covered.
• Or just apply tape across the seam—it works well too!
  For my own print, the seam wasn’t a big problem, but it may vary by printer.

Step 5: Add the Horses and Balls

Drop one steel ball and one horse into each track. Then add the decorative pieces such as the finish line post and numbers. Gently move the horses and balls back and forth to make sure they can slide freely.

Now give the launcher a try—see if the ball can shoot forward and roll back properly. If it doesn’t work smoothly:

• Try adjusting the number of springs
• Make sure nothing is stuck
• Reassemble if needed

If turning the wheel takes too much force, the mechanism may be jammed or a spring might be misaligned. Some small adjustments usually fix the issue.

Let me know if you find any issue with the printing file. Thanks for trying it out!