Orbiting Gear Pendant

Goodmorning everyone,

I designed this project to improve my skills with Autodesk Fusion and exercise designing gears. This pendant serves not only as a quirky fashion statement but also as a functional fidget device, perfect for anyone interested in mechanics/design.

This Intructable documents how to design, fabricate, and assemble a gear pendant starting from CAD in Fusion, to 3D printing and construction steps.

Much of this project is 3D printed, however it does require some off the shelf components to keep things running smoothly.

Materials:

1. 3D Printing Filament
2. (3x) 3x6x2.5mm Flanged Bearing
3. (3x) 5x5mm M3 Standoff
4. (3x) 10mm M3 Bolt
5. 6mm M3 Bolt
6. M3 Washer
7. Chain/String

Tools:

1. 3D Printer
2. Hex Screwdriver
3. Computer

Software:

1. Autodesk Fusion
2. Orca Slicer

I was heavily inspired by this planetary gear necklace I found online, I appreciated how the gears were actually moveable and properly demonstrated the mechanical gear reduction. This reduction property is critical for planetary gearboxes, which are used in industry application to reduce the speed of an input and increase torque. These are commonly seen in automation and robotics, and as a enthusiast of those industries, I wanted the pendant to reflect that.

I wanted to recreate a similar design but make it more suitable for 3D printing and emphasize the fidgety nature of the spinning gears.

The most important part of the pendant is the gear interaction. I decided that 3 orbiting gears made the mechanism as simple as possible and provided visual harmony.

In Autodesk Fusion, I created a sketch to plan the gear meshing. The circles show the pitch diameter of the gears, representing the points where the teeth intersect. The large 42mm circle represents the outer ring gear that contains the three inner gears. The inner gears are shown as three 14mm circles in a circular pattern.

To start designing, sketch the basic profile of the pendant. The outer diameter is 48.5mm (It has to be larger than the ring gear's pitch diameter). This is followed by a 39.686mm circle, which is the inside of the ring gear teeth.

In the center create a 14mm disc with an undersized M3 hole (This small hole dimension will depend on your printer/setting but it must be slightly smaller than an M3 bolt.) This disc will support the gear holder and be bolted into to hold the assembly together.

Three 3mm wide spokes support the disc in the middle, reflecting the three gear which will rotate above them. Create these using a circular pattern to ensure perfect angle alignment.

Next, sketch a 5x7mm rectangle at the top to become the chain loop. Finally, extrude the profile by 6.9mm and fillet the edges to create the body of the pendant.

In order to create the ring gear teeth, start by generating a regular spur gear. You can do this easily by using Fusion's provided gear Add-in. In Fusion, select utilities and navigate to the Add-ins section and run Spur Gear.

This will open a configurable panel which defines the properties of the gear you will generate. The pitch determines the size of the teeth, for this application enter 1mm. For the number of teeth enter 42 (Which is also the pitch diameter of the ring gear). Backlash will be 0 as this gear is only used to create the ring gear. For the bore size enter 5mm, this will become the pin that the gear holder rotates around.

Select the top face of the gear and extrude it -5.9mm, this will transfer the teeth profile into the pendant housing.

Next, sketch a 17mm circle at the bottom of the pendant and extrude it by 0.2mm.

This contact point helps the gear holder rotate smoother as it provides a consistent surface to slide on above the spokes in the housing.

In order to create a loop for the chain to pass through, create a sketch on the side of the tab at the top of the housing. Sketch an arc that is tangent to all three sides, and place a circle in the center.

The diameter of the circle depending on what chain or string will be inserted, however 3-4mm seems to work well.

Finally extrude the circle and edges, cutting in both directions to not leave any material from the fillets.

To create the holder which constrains the three inner gears, start with a 5.6mm and 13mm circle in the middle.

Next sketch a 25mm and 31mm circle outside, with a circular pattern of three 3.1mm and 8mm circles around the middle. Three 3mm spokes should also be added to this circular pattern.

Extrude the sketch by 2mm to create the base of the gear holder.

In order for the bearing to run smoothly, small spacers are needed to contact the inner races and reduce friction.

Create these by sketching three 5mm circles and extruding them by 0.4mm.

This is also a good time to add 3mm fillets to all edges.

To create the inner gear, follow the same process to use the Spur Gear Add-in. However this time a few of the settings will be different.

Keep the pressure angle and module the same (20deg & 1mm), as these ensure combability with the outer gear. Set the number of teeth to 14, the root fillet to 0.25mm, gear thickness to 2.5mm, and the bore to 6.3mm.

The backlash value with determine the added clearance on the gear teeth, and will depend on your specific printer and settings. If the gears have issues meshing, this should be the first value to troubleshoot.

Once the gear has been generated, sketch a 7.6mm circle on the top face and extrude it to remove 0.6mm from the gear.

This recess will allow the flange on the bearing to sit perfectly flush with the bearing and creates a cleaner look.

To add polish to the models, create a slight chamfer on the visible edges (0.5mm).

This also makes the part feel nicer to the touch and look like a more refined product.

After finishing the models in Fusion, export them as STEP files and open the 3D printing slicer of your choice. I prefer to use Orca Slicer, but many of them work similarly.

Import all of the step files and arrange them on the digital build plate (Spare inner gear pictured in screenshot). Everything should be printed flat and does not require supports.

As for settings, these parts do not need a lot of strength so only a low infill is required (~5%). I printed with two walls as it was default, and I used precise walls to make the dimensions more accurate. Other settings are anything specific to your own printer/filament.

Click preview to slice the models and check that the output is correct. Afterwards you are ready to print.

Printing should be pretty painless as all of the parts are relatively simple. It took around 45 minutes to print all of the parts and they required very little post processing to be ready to assemble.

Optionally, you can choose to sand the front faces of your parts. This requires more manual work however it create a smooth and polished look that may make the piece look less 3D printed.

Begin the assembly by pressing the small bearings into the three inner gears. These should fit snuggly but not be too difficult to assemble.

Next, thread the standoffs onto the three 10mm M3 bolts. These will act as pegs to help spin the gears when fidgeting.

Locate the gear holder and screw the three inner gears into it using the 10mm bolts. These should thread firmly into the plastic to hold the gears on.

You may have to adject the tightness of the bolt to ensure the gear spins freely.

Next, insert the gear holder assembly into the outer gear. The peg on the housing should go through the hole in the gear holder with no interference.

Place an M3 washer on the peg and screw it down with the 6mm M3 bolt. The gear holder should still be able to spin freely, adjust screw tightness if necessary.

Finally insert the chain into the chain loop to complete the pendant and make it wearable.

You may have to use tools like tweezers to maneuver it through the hole.

This project combines aspects of fashion, design, and mechanics into a wearable showcase of engineering. The final pendant is very fun to fidget with and very satisfying to spin.

It was also very helpful in learning Fusion, as it required basic operations and using specialized gear tools.

I could not upload a gif to the Instructable, but a video of it spinning is available here: https://imgur.com/a/YBLMviI

I hope this project inspired someone to learn more about gears, 3D printing, or design in Fusion.