The PolyBriX counting crab - it counts up to 99 by rotating it's left arm

This is a counting crab built with the PolyBriX construction set.

Its “eyes” count up to 99, by rotating its left arm. The right arm moves a unit for every 10 turns of the left arm.

The “eyebrows” are clickers that also show the current position for units and tens, respectively.

Kids can learn counting, basic gear transmission and they can even exercise their building skills by assembling this strange creature.

What to print

Print these files:

• the_counting_crab_body_bricks.stl
• the_counting_crab_gears_caps_shafts.stl
• the_counting_crab_addons.stl
• the_counting_crab_feet_bricks.stl

Note 1: If the standard bricks are too loose, try the ones from the_counting_crab_body_bricks_tight_tolerance.stl and the_counting_crab_feet_bricks_tight_tolerance.stl.

Note 2:  The add-ons should be printed with a different color.

The individual parts can be downloaded from the PolyBriX project.

Printing instructions:

Walls count / Perimeters: 5
Infill pattern: Zig-Zag or Rectilinear
Infill density: 10%

No supports.

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

Parts list

All the parts are displayed in the following image

They can be identified as follows:

4xB - 4 asymmetrical octagon bricks

2xG1 - 2 one tooth gears

3xG2 - 3 ten teeth gears

6xS - 6 gear shafts, 4 for the mechanism and 2 for the arms

4xC1 - 4 gear caps

2xC3 - 2 gear spacer caps

1xC2 - 1 add-on connect cap

2xC4 - 2 add-on terminal caps

1x A1 - 1 arrows gear add-on

1x A2 - 1 counter clockwise digits add-on

1x A3 - 1 clockwise digits add-on

2xK - 2 clickers

4xH1 - 4 L shaped connectors

2x H2 - 2 handles

2x C1 - 2 more gear caps for the arms (potentially printed with a different color)

Assembly instructions

Make sure to clean all the contact areas of the parts (joints, shafts).

1. First, connect all the bricks, making sure that each brick will have a socket in the “up” direction.

2. Add the gear caps (C1) to one side of the shafts(S) and insert them into the holes of the bricks. 

3. Add all the gears and the remaining parts as shown in the picture above.

Important : Some attention is required when adding the units final gear(the one from the right, as looking at the picture below, with digits going clockwise):

Notice that when “0” digit is up, the only tooth of the gear is pointing at 7. Make sure to first attach the add-on on the gear in this exact position, and then attach the gear to the whole mechanism, with 0 pointing up. When 0 is up, the tooth o the gear should be in the position that you see in the picture. 

All the other gears can be added without any positional constraints.

When adding the clickers, make sure they are placed so that they intercalate the teeth of the gears. You may need to bend them a bit it they're too tight.

Add the feet as displayed in the cover photo.

Start counting!