Our 2019-20 Robot: Firefly
2020 Technical Binder
After a rolling development period of 6 months, mk. VII of Firefly was finalized. Utilizing the NASA BEST continuous design process, the team created a final robot that consists of a mecanum drivebase, double ball-bearing slide vertical extension, linkage-based horizontal extension, passthrough intake-outtake system, and a quick intake.
Firefly’s drivebase consists of a four wheel mecanum drivetrain in a full body acetal enclosure. It is capable of accurate and agile maneuvers around the playing field to achieve quick cycle times, while still having adequate torque for defensive maneuvers. All subsystems stay contained within the frame perimeter when Firefly is not scoring, allowing for a full, isolated, and robust structure.
Mecanum Drivetrain - Ball-bearing based mecanum wheels - HTD5 pitch belts with exact C2C for efficient torque transfer from motor to wheels - Wheels mounted with 12mm bearings on dead-axle hex shafts directly mounted to side panels - Total approximate, loaded max speed of ~6 ft/s Motors - 4 independent 312 RPM motors - Motors geared from bare Matrix motors at a 19.2:1 ratio achieved by planetary gears Structure - Custom-manufactured and assembled structure, with laser cut and CNC-ed components - 0.25’’ acetal side, top, back, and front panels offering full protection from collisions - Robust, independent left and right side drive pods, connected via 24mm square extrusion cross members - Easily repairable superstructure with many custom mounting points - Center of mass at near center of robot
Firefly’s vertical lift consists of two motors simultaneously powering two sets of stacked, continuous slides for a smooth, low-friction, and sturdy vertical extension. Its slides are oriented to provide maximum strength, while the lift is optimally powered to achieve a quick, 0.6 second extension to maximum height, to stack up to twelve levels tall and place a capstone.
SAR230 Slides - Ball-bearing based, light aluminum drawer slides - Five continuously strung stages - Two sets of slides, inwards facing for rigidity - Custom 3d-printed mounting inserts to stack slides with a low-profile Motors - 2 independent, encoder-synced 1150 RPM motors - Motors geared from bare Matrix motors at a 5.2:1 ratio achieved by planetary gears Pulleys - Custom 3d-printed NylonX spools for string - 40mm diameter spool, with extend and retract pulleys built in one assembly - 350 lb rated kevlar string, 1mm thickness for minimal pulley overlap wrap - String wrap to slides with pulley guards
Firefly’s intake is powered by two motors with >1000 rpm loaded free speeds, and a set of compliant wheels allowing for a reliable grip to be established on the stone. Its immense speed allows for a variety of stone orientations to be quickly intaked.
Motors - 2 independent, encoder-synced 1150 RPM free-speed motors - Motors geared from bare Matrix motors at a 5.2:1 ratio achieved by planetary gears Compliancy - Two sets of two 3-inch 35A durometer compliant wheels provide a subtle amount of compression to effectively intake stones while still retaining a high tangent velocity - 1⁄4 inch delrin mounting plates for intake modules flex to allow for a spring-loading compression, further assists stone re-orientation as it enters the robot Bellypan - Custom cut and bent polycarbonate bellypan - Flexible against shock impacts, while retaining shape and shatter-resistant
Firefly’s outtake consists of a linkage based, servo powered horizontal extension, and two independent side grippers to securely grab stones by the front and back faces, while resting on the bellypan. Its linkage allows for a rotational force by the servo to be transferred into a translational motion, deploying the stone to be stacked in a fraction of a second. Two horizontal aluminum ball bearing slides are used for efficient motion of the stone, as it is transferred to be stacked. A custom laser-cut delrin structure allows for a precise placement of the stone onto the foundation when the robot is squared with the foundation, making alignment quick and simple for drivers.
Linkage - Transfers ~135° servo rotation to 8.25 into horizontal extension arm powered with one 6v goBilda 2000-series servos - Two Misumi SAR240 aluminum ball bearing drawer slides - Custom, lightweight delrin mounting structure Grippers - One 6v goBilda 2000-series servo each - Simulation and analysis tested geometry - Rubber-coated end effector for maximum grip on stone nub - Laser cut 1⁄4 in delrin gripper arms which can release the block onto a stack with clearance to drive away immediately, improving stacking times
Firefly’s foundation mover is powered by two bearing-housing reinforced angular servos, with laser-cut delrin custom foundation arms attached. Geometry design of its delrin foundation arms allow them to move in an arc to lock onto the foundation, even when the robot is not perfectly squared, allowing for a large margin of driver error.
Foundation Arms - Two independent arms powered by 6v goBilda 2000-series servos - Arc movement profile allows for sturdy grip on the foundation from a variety of alignment angles of the drivebase - Laser-cut 1⁄4 inch delrin provides durable resiliency to any possible collisions when arms are extended out of the frame perimeter