The Cart Sub-Assembly

An essential sub-assembly of the entire system is the cart.
It needs to house four actuators, remain compact and precise, while smoothly moving along the curved rail and constantly counteracting gravity.

Components of the Cart:

• 1 stepper motor — to drive the cart along the rail

• 1 linear actuator — to extend and retract the gripper

• 1 servo motor — to rotate the linear actuator

• 1 servo motor — to open and close the gripper

We use those cheap ender 3 wheels with 8mm column for our cart, the rest is 3d printed.

For the design of the cart body, we drew inspiration from these two videos:

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First prototype

This was our initial iteration: 

• This version did not include the gripper or the rotation servo for the linear actuator.
• Its main goal was to test the wheel spacing and check if the cart could move correctly along the rail.

To validate this, we also 3D printed a small section of the rail:

The tests confirmed that the cart could indeed move properly along the track

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Second Prototype

Building on our first test, we developed a second version: 

• At this stage, the gripper was still not integrated.

• We focused on figuring out a reliable way to rotate the linear actuator.

• Our first attempt was to use a gear system, where a servo drives a gear that in turn rotates a second gear connected to the actuator.

However, we were not fully satisfied with this solution. It felt too complex and introduced too much potential for failure.

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Third Prototype

We then developed a third version of the cart:

• In this version, we opted for a four-wheeled design to improve stability when moving along the rail.

• Mechanically, this iteration was similar to the second one, but we aimed to simplify the actuator rotation.

Still, the gear-based rotation system felt overly complicated.

Final Version

In our final design:

• We simplified the mechanism by having the servo motor drive the actuator directly, eliminating the need for intermediary gears.

We were finally satisfied with this design and decided to move forward with it.

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Gripper design

Designing the gripper was also a crucial step.
A poorly performing gripper would make the entire machine unreliable, as it must securely grab and release the chess pieces.

We based our initial concept on this very compact design from a reference video:

Here’s our own CAD version of the gripper:

• The gripper is shaped to fit the body of the chess pieces.

• It features a razor-like shape on each side to improve grip.

• We plan to 3D print the gripper in TPU to maximize adherence and flexibility.

• The gripper assembly includes a mounting interface at the bottom, designed to connect directly to the linear actuator.

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Final Cart Assembly

Here is the complete cart assembly : 

And here’s the cart sub-assembly integrated and moving within the final full assembly :