Exercise #4 Simple Gearbox

Practice Exercises

Get ready to practice! Begin by copying the Stage 2B Exercises Document using the button below, just as you did with the Stage 2A Exercises Document. Each exercise is organized into a folder and includes a "reference" tab—a preview of the final model—as well as one or two tabs for completing the exercise.

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Exercise 4: Simple Gearbox

In this exercise, you'll be CADing and assembling a single-stage gearbox. The aim is to introduce the basics of designing a simple gear transmission. Along the way, you'll also get hands-on experience with gears, motors, bearings, c2c, gear relation, and the FTC Insert Tool.

Layout Sketches

A layout sketch captures the fundamental geometry of a design without locking in precise details. By keeping key dimensions flexible, layout sketches facilitate easy adjustments as the design evolves. Moving forward, we'll rely on layout sketches for nearly all designs.

Navigate to the "Exercise #4 Simple Gearbox" part studio tab in the copied document and follow the instructions to complete the part studio.

Create a Layout Sketch for the Gearbox

Draw pitch diameter circles for the 60-tooth and 20-tooth gears. Make them tangent to define the center-to-center distance between the gears. Then, constrain the gear centers so they align vertically.

Create a new sketch for the motor plate.

Using the layout as the reference, draw an 8mm hole for the bearing and a 14mm hole for the axle that sticks out from the motor. Note that depending on your manufacturing processes and tolerances, you may need to draw your bearing holes slightly larger or smaller.

Add four mounting holes for the motor and four bolt holes for connecting the two plates using center point rectangles. The circular pattern can also be used to duplicate the circles around the square. Make sure that these rectangles are using construction lines, so it doesn't interfere when we extrude (press q on lines to turn them into construction lines).

Finishing Bottom Plate

Using center point rectangles, sketch fillets, and 3-point arcs, outline the plate around the holes and the motor outline.

Extrude the motor plate to be 4mm thick.

Creating Spacers

Create spacers by making the inner diameter 4mm and making the outer diameter the same as the sketch fillet.

Then, extrude the spacer by 7mm.

Creating Top Plate

By using the Use tool (the cube), you can copy the geometry and holes of the motor plate. Then add a 20mm diameter circle, a line connecting both of the top mounting holes to the circle, and sketch fillets.

Then extrude by 4mm, and fillet the edges of the semi-circle by 5mm.

Countersinking Screw Mounts

Now create holes for the screws by making circle with a diameter 8mm, extruding them by 2mm, and fillet them by 0.5mm.

Creating a Gear

You can create a gear by looking up "Spur Gear" in the "Search tools" search bar. Make the gear have 60 teeth, make it 5mm deep, and make its module 0.8. You can also hide the top plate for a better view of the gear.

All GoBILDA gears have a module of 0.8mm

Then create the center REX bore by using the circumscribed polygon tool and making a 6-sided shape with a diameter of 8mm.