Demo 2

Source Code on GitHub

System Architecture | Software Design | Electrical Design | Mechanical Design

Mechanical Design

The mechanical design for this demo was created in AutoDesk Inventor. The four main components of the design are the base/shaft, boom, trolly, and gripper.

Base + Shaft

The base and shaft were constructed from wood with three large holes in the front of the base to mount the crane to the demonstraction table. The servo was mounted to the shaft via three screws through the mounting holes on the bottom of the XL-320 (where the horn is on the top-front of the servo). A 3D-printed square piece was attached to the horn of the XL-320 and additionally supported by the wooden walls of the shaft. This allows the XL-320 to apply torque while reducing the load it has to support. The downside of this design is increased friction when the boom is imbalanced and leans forward too strongly, but that can be worked around by bringing the trolley closer to the shaft before pivoting the boom.

Boom

The boom was constructed of basswood since it is light weight but still capable of supporting the weight of all the crane components. On the bottom of the boom is a 3D-printed piece which joins with the piece mounted to the XL-320 on the shaft. Also on the bottom of the boom is a perpendicular piece of wood to mount the camera on. The top of the boom is divided into two trays. The longer tray is the track the trolley travels along, while the other half is an area to place counterweights in. The counterweights are used to reduce the static torque along the horizontal axis from the trolley and gripper. The counterweights used were calibrated by placing the trolley half-way along the track and then adding weights until the boom was balanced without leaning forward onto the supports in the shaft.

Trolley

The trolley uses a chassis built from 4 3D-printed parts attached via pegs to improve sturdiness while reducing the materials and time requirements to print the parts. Inside the chassis is a single XL-320 with two wheels on the front and back. This servo is used to move the trolley in and out along the boom. Two additional XL-320s are attached to the sides of the trolley with pulleys attached to their horns. These pulleys are used to move the gripper up and down while preventing rotation relative to the trolley.

Gripper

The gripper consists of a stationary plate, a rotating arm, an XL-320 servo, and a leveling bar. The stationary plate and rotating arm are attached directly to the servo while the leveling bar is attached to the stationary plate. The leveling bar was not part of the initial design and was added in later stages when testing showed that the gripper would pull the string off the pulley tracks if the gripper was narrower than the track width between the pulleys. Had this been known when designing the parts the design of the stationary plate would have been changed to incorporate this requirement in the 3D-printed part.

Electronics Layout

The following images outline the placement of the batteries, OpenCM microcontroller, Raspberry Pi and camera on the crane.