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Bridge

CAD

Fusion 360 Tutorial

To prepare for 3D printing week, I figured sketching another part of my project model would make sense. I followed a tutorial to make a bridge in Fusion 360.
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Converting to Drawbridge

While I had a workable bridge, I needed a drawbridge. Before I determine the mechanics, I would need to phyically split the bridge. I’ll also add a bit more detail.

  • Split bridge
  • Extrude middle column through the top

  • Cut remaining pieces in other directions
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  • Vertical mirror extrusion

  • Create plane on face at point for center of bridge

  • Mirror across plane
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  • Extrusions

  • Cut intersecting face away
  • Cut vertical columns above the face

  • Extrude top of colunms down to the same height
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  • Trim

  • Extrude down to .25 inches
  • Apply two-side extrusion horizontally
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This still needs polishing in terms of dimensions, but has proportional parts and a workable starting shape.

Adapting for Rack and Pinion

I had a ChatGPT conversation to determine the system I would use for my drawbridge. I decided to use a rack and pinion system, which moves a gear-like device along a rack with matching prongs in linear motion. I sought examples of this used in a drawbridge and found a video that demonstrates a presumably 3D printed mechanism. While I found this example very informative, the caveat was that it was not automated. I would need to add on to this design.

Since the video was more focused on the application of the mechanism than the drawbridge itself, it only lifted a wooden plank. I noticed that this design, while not suitable for a realistic golf course, did make more intuitive sense in that it was a straight line. The CAD design I had required me to make and synchronize two automated designs. While a straight line seems unchallenging, I already established that I wanted grooves.

I decided to re-create the bridge with similar base dimensions but as a flat plane.

  • Base
  • Sketch 40*120 inch rectangle
  • Extrude 5 inches
  • Sketch on top
  • Create 40*10 2-point rectangle from top left corner
  • Create rectangluar pattern for 10 total rectangles across top
  • Extrude every other rectangle -.5 inches
  • Sketch on side of base
  • Create line from top left corner to top right with the groove part outside
  • Extrude 2 inches

  • Repeat sketch and extrude on other side
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  • Railing

    • Sketch on top
    • Sketch construction line from middle of groove down to the bottom of shape
    • Sketch 3*3 center rectangle with center at the midpoint of line
    • Create rectangular pattern for 6 squares total across shape
    • Extrude all squares 20 inches
    • Sketch on right side of leftmost extruded square
    • Sketch horizontal construction line across vertical midpoint
    • Repeat for midpoint of each section
    • Delete original midpoint line
    • Create 3*3 center rectangle at midpoint of each line
    • Extrude rectangles to right side of rightmost extruded square, click join
    • Create horizontal midplane between two sides of the bridge - click the side, not the railing
    • Mirror railing across bridge
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Determining Pinion Dimensions

I looked up the measurements of a NEMA 17 stepper motor since I would fit my pinion accordingly. On the stepper motor website, I found that the shaft or cylindrical portion measures 5 mm in diameter. I decided that I would make the pinion .05 inches larger for a proper fit, considering my previous press fit calculations. I also erred on the side of caution due to the fact that the motor would spin somewhat quickly.

The NEMA 17 has a shaft length of 22 mm, so while this seems less relevant as long as it fits properly, I will base the rack width around this measurement. 5 mm would make sense, it occupies some of the shape without making contact with the faceplate.

The pinion would be 5.05 mm in diameter and 20 mm long. I will use those units for the correlating dimensions and inches for other measurements to stay consistent.

Modeling Rack and Pinion in Fusion 360

Since my bridge is not scaled, I will create this in a separate file and import it later into the bridge file. This way, my bridge dimensions will depend loosely on these. I also plan to 3D print this - not as a final design since plywood would better blend with the bridge, but as a test for the motor size and general scaling. Since I’ve never made this before, I will adhere to my measurements while following a tutorial I found.

Changing to a Pivot System

I took a break from CAD and double-checked the NEMA-17 measurements. The word “torque” stuck out to me, and upon looking more into the functions of a NEMA 17, I realized this was unnecessary. Although it would technically work if I managed to embed both sides in the foundation of the course and program it properly, I was creating extra steps.

What I could do instead is insert the programmed NEMA 17 into the bridge or use CAD to design an attachment. The only caveat is that I would likely need two to balance the movement on either side. If I program these with a Wi-Fi server, though, this is a simple fix.

Design PCB

Microcontroller Plans

I asked Mr. Dubick for some advice on the structure of the bridge and microcontroller usage. He recommended servos as opposed to steppers and a powerful microcontroller such as the ESP32 or RP2040. I’m a bit more familiar with the ESP32, so I can look into simulations and pinouts. I decided that the CAD aspect would depend on the scaling of the bridge and the course since the circuit and wires would most likely be stored underneath the bridge. I will be developing a PCB to program these servos properly with an ESP32, motor driver, and an LED for decoration. I would program the LED to light up either while the bridge rises, falls, or is on the ground.

Wokwi

Before jumping straight to KiCAD, I would simulate the ESP32-S3 (considered higher-power than the C3) on Wokwi.

KiCAD

Last update: February 26, 2025