Based on prior flipped gearbox design collaboration with 2363 Triple Helix, this iteration for 2020 flipped two NEO motors up and over the wheels.

Previous iterations of the flipped gearbox used two or three mini-CIM motors. For 2020 we decided to move to the relatively new brushless NEO motors from Rev Robotics. Reasoning included a smaller and more powerful motor, weight savings by reducing from three to two motors per gearbox, and integrated encoders.

Why flipped?

Traditional off-the-shelf gearboxes position the motors on the interior of the robot. This takes up valuable real-estate in the center of the robot, especially as the trend towards smaller robots continues. Flipping the motors up and over the wheels to the outside of the robot frees up this space in the center of the robot. For 2020 this worked out perfectly for us as it left the perfect amount of space remaining for the ball path.

Double Reduction Design Choices

Knowing that we wanted to slim down from three mini-CIM to two NEO motors per gearbox, we utilized the ILITE Drivetrain Simulator along with the West Coast Products Gear Calculator to find a set of gear ratios that would meet our goals and have enough height when flipped that the motors would clear the 6″ pneumatic wheels.

Gearing Choice:

Stage 1: 12 : 72

Stage 2: 42 : 60

Total Reduction: 8.6 : 1

This design will work with any gear combination where the count of teeth in reduction Stage 1 = 84 and Stage 2 = 102.

Bill of Materials

PartPart #SourceQuantityUnit PriceTotal Price
.25″ Black Delrin Sheet30346-02Inventables12″x24″$113.60$113.60
NEO Brushless MotorREV-21-1650REV Robotics4$45.00$180.00
12T Steel Pinion217-3099VexPro4$9.99$39.96
72T Hex Gear217-2716VexPro2$29.99$59.98
42T Hex Gear217-3216VexPro2$12.99$25.98
60T Hex Gear217-2714VexPro2$24.99$49.98
Note: Some items on this list can be sourced with KOP vouchers.
Cost of Delrin has doubled since spring 2020. Prices updated November 2021.

Additional items required:

  • SPARK MAX Motor Controller
  • Bolts/nuts of your choice. We use black-oxide socket head cap screws.
  • 0.5″ Hex ID x 1.125″ OD bearings
  • Spacers (we 3D printed spacers of the appropriate size in team colors)
  • White lithium grease

CAD Download

View in OnShape.