Mechanical Design

Overview

Our primary goal while designing the robot was to create the simplest possible stacking mechanism by eliminating all linear motion. To achieve this, we came up with a two part stacking mechanism consisting of a claw mounted on a rotating arm to pick up blocks, and an enclosure mounted on the chassis to stack them.

Chassis

Solidworks model of the chassis

To fit both the arm and the enclosure in the size limits for the competition (9'' × 9'' × 12''), we designed a chassis with a pair of wheels in the middle of the robot, and casters on either side. Because of this unique design, the robot could line-follow in both directions, allowing it to pick up and stack blocks without ever having to turn around.

Wheels placed in the middle of the chassis allow the robot to tape follow forwards and backwards 

We designed the chassis in two pieces using Solidworks, and cut it out of mild steel using an OMAX waterjet cutter.

Solidworks model of the bottom piece of the chassis

Solidworks model of the top piece of the chassis

Drive System

The drive system for the robot consists of two geared Barber Coleman motors attached to a pair of 3D-printed custom wheels. The motors are attached to the middle of the chassis using motor brackets that we designed in Solidworks. Casters mounted on both sides of the motor provide improved stability when driving forward and backward.

We used a 3D-printer to create custom wheels for our robot that allowed us to achieve optimal performance.

We designed the motor bracket in Solidworks, and used a waterjet cutter to ensure that the holes were perfectly aligned.

Claw/Arm

Our aim with the claw and arm was to design an apparatus that could grab and hold blocks at any angle or orientation, and successfully lift them without the block slipping from the claw. The reason for this flexibility is that the blocks could be in any orientation while in the depot - it would be impossible to know before hand if a block was parallel to the depot wall or at an angle.

Solidworks model of our claw, with a block included for reference

Another model, this time viewed from the top

The claw was cut out of ~0.03" aluminum using the Waterjet cutter, and was actuated by two servos which were mounted on the bottom side. The plastic sensor holders were printed using the 3D printer, and the entire arm was connected together using 8-32 socket head screws. The arm was cut to a length of 5.5", and connected to the motor and chassis through a connecting ring.

Skeleton model of the claw, right after waterjetting

Full arm and claw with servos, attached to the chassis

There were a total of five sensors on the claw itself, and one on the arm (more details in electronics section). Rubber bands were found to provide the best grip out of the materials tested. The idea was to thrust in using the claw and, once a block was sensed to be in the claw's grasp, close the claw and rotate the arm upwards.

Claw with the rubber bands and sensors attached

The final claw could successfully grab a block, regardless of orientation, and could provide enough grip to transport the block from the depot to the slide.

Enclosure/Slide

We designed the enclosure/slide assembly to allow our robot to stack blocks without requiring a high level of precision in its movements. Once the robot has reached the build area, it grabs the existing block stack with the enclosure, aligning the stack. It will then rotate its arm upwards and drop the block it is trying to stack onto the slide, where it will fall into the enclosure. The robot will then open the enclosure and return to the block depot.

A block placed on the slide will fall into the enclosure, which aligns the existing stack and guides the new block into position. The slide assembly is resting on ledges attached to the enclosure shafts, and is fixed to the chassis at the bottom.

To actuate the enclosure we used a geared DC motor connected to a series of four gears we designed in Solidworks and cut out of 1/2'' Aluminum using the waterjet cutter. We made the two sides of the enclosure out of aluminum and attached them with Meccano to a pair of shafts that passed through the chassis.

A gear train attached to a DC motor allows synchronized motion of both sides of the enclosure.

The slide assembly is attached to the back of the chassis, and rests on ledges built into the enclosure shafts, allowing it to stay stationary while the sides of the enclosure move freely. The back plate of the slide assembly completes the enclosure, aligning falling blocks with the block stack while serving as a holder for the robot's motor drivers.