The PolyBriX distance measuring wagon ( it works on wooden rails too )

This is a distance measuring wagon made with the PolyBriX construction kit.

It can be used to teach kids the formula of the circumference of the circle and also how that can be applied for a practical use. For example, if we carefully choose the radius of the wheels they travel 100mm for a full turn. 

Using some gears, the distance can  be measured up to 99 meters, by rolling the wheels of the wagon.

This wagon is also designed to work on the wooden rails that, probably, many kids have at home. It can be used to measure the length of a track, for example, or as a handy tool to measure distances.

What to print:

bricks_parts.stl - this file contains the 3 bricks for the body, two smaller bricks to server as wheels supports and one brick spacer for the front wheels

Note: If these bricks are too loose, try the ones from the bricks_parts_tight_tolerance.stl file.

g0_g1_parts_and_wheels.stl -  this file contains the parts required to assemble the rear wheels ( G0 group ), those that do the measuring up to 9 centimeters, and the G1 group, that measure tens of centimeters

g2_g3_parts.stl - this file contains the parts required to assemble the group that measures meters ( G2 ) and the group that measures tens of meters ( G3 )

g0_g1_addons.stl -  this file contains the digits wheels for the G0 and G1 groups and the gear clicker for the G1 group

g2_g3_addons.stl -  this file contains the digits wheels for the G2 and G3 groups and the clickers for both of them

The parts are separated this way so that the digits can be printed with a different color then the gears on which they are mounted, for contrast.

Printing instructions:

The following settings can be used to print everything

Walls count: 5
Infill pattern: Zig-Zag or Rectilinear if using the PrusaSlicer
Infill density: 10%

No supports.

I've used PETG, but PLA will probably work as well

Assembly instructions

After printing the parts, make sure to clean all the contact areas.

Assemble the wheels like in this picture:

The rear wheels are the bigger ones, they actually do the measuring and are labeled G0.

Assemble the body of the wagon like in the picture bellow:

First assemble each group completely, then connect all of them together.

Observations:

1. Note that the digit wheels go clockwise for G0 and G2 groups and counter clockwise for G1 and G3 groups. Don't interchange them. Each digit wheel is created specifically for a certain group and are coupled G0 with G1  and G2 with G3, in separate print files, so it's easy to know which is which.
2. The one tooth gears in the G1 and G2 groups should be mounted exactly in the position illustrated in the picture, when their corresponding digit wheels have the “0” up.

Usage instructions

Just roll the wagon on the floor, carped or the train track applying some down pressure. 

You can read the distance as shown in the image bellow:

So the measurement in the picture is 15 meters and 43 centimeters.

The counters can be reset starting from tens of meters and working your way down to centimeters.