Difference between revisions of "DEWBOT V Mechanical"

Revision as of 14:01, 31 May 2009

Beater Bar

A beater bar with curved back-plate is employed to pick up Moon Rocks.

The Beater bar is 20 in wide fabricated from 1” PVC pipe. A 1” OD x 1/16” aluminum tube inside the PVC provides rigidity and straightness. Two 1” wide wheel treads wrapped helically around the beater-bar’s exterior provide a high-friction surface to positively engage and catch the Moon Rocks.

The beater-bar is driven by a geared FisherPrice motor. This provides high torque at about 2 rev/s.

The robot chassis’ wide orientation allows a generous 19 in wide opening in the chassis front for Moon Rock entry, making Moon Rock collection easy. In Pick-up mode, the Pilot/Driver need only drive over Moon Rocks to collect them.

The Back-plate is curved at a 9 in radius and covers 68°. It is 20 in wide at bottom, tapering to 9 in wide at top. The back-plate is mounted so that curved surface is co-axial with the beater-bar, thereby maintaining constant compression on the Moon Rocks as they are lifted. Side-plates funnel Moon Rocks through a consistent opening into the bottom of the Spiral Hopper.

Back-plate and (2) side-plates are fabricated from thermally-formed 3/16” thick Tuffak® brand polycarbonate (donated by Arkema).

Beater Bar Development

Beater-bars are known technology to the Team, from 2006. The back-plate & side-plates are new for us.

The system was prototyped (using a flat back-plate) prior to design. Prototype testing provided the necessary degree of compression needed to reliably transport Moon Rocks.

Naturally, these dimensions together with the desire to make the Moon Rock opening in the front of the robot as wide as practical to make pick-up easier, had a significant impact on chassis and frame design. This had to be a early development.

(2) forms were created to accurately form the back and side-plates.

Beater Bar Specifications

• Device: Beater Bar & Back-Plate Moon Rock pick-up

• Motor: FisherPrice Motor with Gearbox

• Gearbox: 124:1 reduction

• Transmission: 1.5 in octagonal socket

• Capture Width: 19 in

Hopper

The Hopper & Spindle provide Moon Rock storage for the robot. They are integrated into the beater-bar and shooter systems.

The Hopper is a helical, up-flow magazine for Moon Rocks. The Spindle provides the necessary upward force to drive Moon Rocks to the Shooter.

The Hopper mounts on the outer ring of a 23.6 in OD aluminum turntable. This turntable allows the entire Hopper to traverse, like a turret, to aim the Shooter on top. The Hopper itself comprises a welded cylinder with (5) uprights and (2) helices: outer and inner. The outer helix, welded directly to the uprights, contains the Moon Rocks within the Hopper and provides the necessary compression (against the Spindle) to allow the Moon Rocks to be driven upwards. The inner helix, welded to stand-offs to the uprights, supports the Moon Rocks. The Pitch of both helices is 10 in. Each helix is (3) turns tall. The top of the Hopper is closed with a 5-arm, pop-riveted “Spider”. The bottom of the Hopper has a formed polycarbonate ramp to facilitate transfer of Moon Rocks onto the helix.

The open spiral design allows easy loading and unloading of Moon Rocks at the start and end of each match.

The Spindle is a 4 in PVC pipe with 2 courses of polycord on the exterior to drive the Moon Rocks. The outer course of polycord is in a spiral perpendicular to the inner helix, thereby providing force in the Hopper spiral’s direction. The Spindle possesses a 1 in x 1/16” wall internal aluminum tube, which is driven at the bottom. Wood plugs connect the aluminum tube to the PVC pipe top and bottom.

The Spindle is driven by a Nisso-Denso motor via a chain drive at 22:12 step-up gearing providing a no-load Spindle speed of 2.6 rev/s and a stall torque of 4.3 ft lbf. Chain drive includes a tensioner. There are (2) 1 in bearing races at the bottom and a ball-bearing turntable at the top of the Spindle.

In competition, the Nisso-Denso driven spindle operation was found to be inadequate. On 30-May-2009, it was replaced with a Bainbots RS-545 motor with a 64:1 P60K planetary gearbox. This drives the Spindle via a chain drive using 15:12 step-up sprockets providing a no-load Spindle speed of 5.1 rev/s and 9.9 ft lbf stall torque.

A ¾” CPVC pipe runs as a conduit through the center of the Spindle’s 1 in tube. This conduit provides safe passage for the Camera and Shooter wiring and pneumatic tubing. Since the conduit is attached to the traversing Hopper and turns with it, the conduit also provides the control system with Hopper’s angular position, via a potentiometer attached to the conduit bottom.

Hopper Development

The spiral Hopper concept was inspired by Team 694’s 2006 design, featured in Wilczynski & Slezycki, “FIRST Robots, Behind the Design”, Rockport (2007).

The Hopper and Spindle was prototyped and tested. Spindle design started as brushes (ala 694’s) but evolved with testing to the solid pipe with frictive exterior (the polycord).

While a solid cylinder was used to prototype, the decision was made to use a welded, open spiral for the final design. This decision was based primarily on weight (the hopper as-built is only about 7 lb) and secondarily on ease of manually loading and unloading Moon Rocks.

(6) forms, mandrels or jigs were created facilitate construction of the Hopper – more than half of the total used by the team in 2009.

Hopper Specifications

• Device: Spiral Hopper & Drive Spindle

• Motor: Nisso-Denso replaced by Bainbots RS-545

• Gearbox: Integral worm gear replaced by Bainbots 64:1 P60 3-stage planetary gearbox

• Transmission: Type 35 steel chain w/ tensioner; 22-tooth drive and 12-tooth driven sprockets; 22-tooth drive replaced by 15-tooth

• Capacity: 14 Moon Rocks

Shooter

category:DEWBOT V