Flip Walker Treadmill

Since building my LEGO flip walker model a couple of years ago, I’ve been thinking of ways to easily display it at public events. The fact that it continuously walks in a straight line means that it can only be demonstrated with someone there to constantly reset its position.

I finally decided to design a treadmill for it, so it can walk unattended. Of course, this came with some of its own challenges, as regulating the speed of the treadmill to match the walker was not trivial. You can see how the treadmill is constructed in the following video, or read on for some more details on how it works.

The speed of the treadmill is controlled using a LEGO Mindstorms Robot Inventor Hub, which uses two colour sensors to track the position of the walker on the treadmill.

With a fixed speed motor, it would be virtually impossible to exactly match the speed of the treadmill to the speed of the walker. Especially since the speed of the walker slightly decreases over time as its battery runs down.

Each leg of the walker has a stack of white bricks, which trigger the sensors if the walker is too close to the front or back of the treadmill.

If the walker is too close to the front, the hub will increase the treadmill speed, and if it is too close to the back, it will decrease the speed. Over time, the speed of the treadmill is constantly being adjusted to keep the walker between the sensors.

I decided to add some decorative elements as well, to liven up the display. The treadmill ‘belt’ is made up of 21 slats, and the spacing of the walker’s feet is such that it steps over every third slat. This allowed me to add some decorations directly to the belt that the walker can step over.

As a big fan of the classic space baby figs, I added a few throughout the model. I like to image the walker as some sort of exploration vehicle they use to explore an alien planet.

I’ve had this model on display at a single day event already, and I’m happy to say that it has performed quite well. The battery controlling the walker itself only lasts a couple of hours, so it can’t be left to run indefinitely, but it can be left on its own for long periods of time without issue, and is quite satisfying to watch.