EV3 Robot with Shiftable Gearbox

The season’s missions required taking task attachments on and off the robot quickly between autonomous runs, while still crossing the mission field accurately and at speed. The design problem was a chassis that made attachment changes fast and repeatable without giving up driving precision.

All control ran on a single LEGO Mindstorms EV3 platform programmed in Python, using the motors and sensors that platform provides. Runs were judged on both how reliably the robot completed its missions and how quickly it moved between them, so neither accuracy nor speed could be traded away for the other.

Three chassis variants were built and compared before the box configuration was chosen. The variables evaluated across them were:

• Wheel size.
• Gear type and number of gears.
• Gear location.
• Motor placement.

The drivetrain was built around a shiftable gearbox, a gear-shifting mechanism that let the drive motors change their ratio rather than run a single fixed reduction. This let one drivetrain serve two competing demands: a faster ratio for covering ground between mission sites, and a higher-torque ratio for missions that needed more pushing force.

Motor placement and mass over the driven wheels were set to hold traction and limit slip.

Reflected-light sensors read the lines printed on the field and followed them between mission sites. This replaced dead-reckoning, which accumulates heading and distance error from wheel slip, with a line reference the robot could correct against, giving faster and more accurate travel.

The sensors were calibrated to the field’s light and dark contrast, and the chassis was reinforced so behavior stayed consistent run to run. Python was used to troubleshoot the sensors and to sequence the autonomous runs, and mission timing was rehearsed and refined through testing.