String Guide #BESTRobotics2025

Prusa Research 3D Printing National Challenge #BESTRobotics2025

School name: Central Christian Academy
Team number: 366
Team name: Cyber Lions
Hub name: Kansas BEST – Wichita State University

Model Presets:

• Tree support
• Support painting
• Wall loops: 3
• Sparse infill density: 50
• Sparse infill pattern Triangles
• Support/Raft interface:  support for pla/petg
• All other settings default in Bambu studio 
• filament used: white PLA (Bambu brand)
   

Function & Purpose of Part:

       The primary function of the string guide is to guide the string between the linear guides and prevent abrasion of the string. It prevents abrasion because instead of the string going over the sharp edge of the metal linear guide with lots of friction,  the string slides around the smooth curve down to the reel. On the other side of the linear guide, it guides the string directly down to the reel. 

How it benefits a BEST robot:

       The string guide benefits a BEST robot because it provides a simple and effective way to raise and lower a linear guide. The string guide was designed so that the string never comes in contact with the sharp edge of the linear guide, but instead glides over the smooth curvature of the guide. It was designed this way to prevent friction and abrasion which would lead to higher motor loads and more frequent string breaks. 

       The string guide was attached to the upper end of the linear guide by sliding it onto the tracks in the linear guide. Then a length of string was tied to a washer. We then fed the string between the linear guides, up and over the string guide, and down to the reel and tied it. We then mounted the arm assembly to the moving linear guide, which made it possible to reach the golden factoid.  You might notice the second “pulley” on the side of the string guide; its original purpose was to create a pulley system but this idea was scrapped because it actually made it harder for the motor to lift the arm assembly. But the “pulley” was left on the string guide because it didn’t hurt the robot and to save time and filament.

 Design Process Notes:

       The string guide was designed using a small section of the linear guide model provided in the team workflow which we used to make sure that the part would fit perfectly into the tracks of the linear guide. We then made the tolerance smaller and used it as a sturdy base for the rest of the model. The first iteration was without the smaller second “pulley”, and we had a platform out to the side of the part to mount a limit switch. After we looked at it, we decided that the platform was unnecessary because we could mount the limit switch in a different spot. When we tested it, the small motor was not strong enough to lift the arm assembly. So we tried making a pulley system (hence the second “pulley”).  At first we had the string going up between the slide bar over the large “pulley” down through an eye bolt then up to the second “pulley” then down to the reel, which was directly attached to the motor. When we tested, it still could not lift the arm assembly. We thought the problem might be that the pulley needed lubrication, so we added large amounts of lubricant but it still could not lift it. Then instead of the pulley system we decided to switch the small motor for one of the big ones on the wheels. Then it finally worked. We decided to leave the string guide version with the second pulley to save time and filament.