The Arm

The design of the arm was based on the competition requirements. Two linear actuators were used to reach the required height of the 24’’ trees turned on by a 2 Module DPDT Signal Relay Board. Arduino IDE software was used to actuate these linear actuators and the servo motor placed on the gripper.

Linear Actuators

The main factor in our linear actuator choice was the length in its retracted state since one of the requirements for the competition was that it must fit within a one-foot cube.
We chose an 11" linear actuator with a 4" stroke and 4" linear actuator with a 2" stroke.
Both require 12V and pull about 0.9 A when extending/retracting at the same time.
No current passes through the linear actuators once they are fully retracted/extended because of the limit switches placed in each actuator.

ARM CAD

The “gripper holder” was created as a platform that would be attached to the end of the 11” linear actuator and hold the parts that would be composed of the gripper.
On the right side of the image, a block was designed with a hole that has a slightly larger radius than the 11” linear actuator's end-tip. This was designed as such to limit the movement of the gripper holder horizontally.
The J-Shape part attached to the block was designed in order to remain within the one-foot cubed limit required for the competition.
On the left side of the image where another screw hole is located, this is where the gripper was placed and screwed in.

The ”actuator holder” was designed to both attach to the 4” linear actuator at the bottom and hold the 11” linear actuator to lifted at the desired angle.
Enough space had to be made at the bottom for the 4” linear actuator to both fit and remain unmoved when extending/retracting.
The radius of the U-shape needed to be large enough to be able to smoothly glide along the motor of the 11” linear actuator when it is in movement.

The “actuator bracket” was designed as a holder and to act as the pivot point of the 11” linear actuator.
The bracket is attached to main platform at the bottom where the screw holes are located.
The hollow rectangle was designed large enough to fit the 11” linear actuator with a bit wiggle room.

The "actuator platform" was designed as the base of the arm.
It holds all CAD components mentioned, both linear actuators, and the gripper with its components.
The hollowed square houses the 4" linear actuator and contains a small hole in which the power cable can fit through.
The round-shape end was made to attach to the "actuator bracket" that functions as the pivot point for the 11" linear actuator.
The base of the platform contains multiple screw holes that attach to the main body of the Robot, which properly secure the entire arm in place.

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Relay

Since we needed a method that could make both linear actuators extended and retract based on a digital signal and do so at separate times if needed, we chose a 2-module relay.
The primary function of this relay is to act as a DPDT (Double-Pull Double Throw) switch for the linear actuators.

IN_A and IN_B are for the digital signal that activates the internal switches in the relay, IN_A activates RLY_A and IN_B activates RLY_B.
VDD is for the voltage source which in our case is a 12V power bank.

NO – Normally Open
NC – Normally Closed
C – Common

Proper relay wire connection is needed to have the linear actuators correctly extend and retract. On the right is an outline of the configuration we decided with:
The linear actuators are wired through the common (C) pins on the relay.
In this configuration the Robot arm is able to extend and retract through a LOW/HIGH digital signal command.

Gripper

Bracelets were placed on 21'' trees with a 6'' extension outward.
The bracelets were met when the linear actuators were extended at a 48.9 degree angle and then grabbed with the gripper.
This gripper was controlled by a servo motor moving back and forth a wheel at 180 degrees which can be seen to the right.

Gripper CAD

A gear was designed so that there would be a connection for the servo motor’s output shaft to the gear and could move it from 0 to 180 degrees through Arduino IDE.

The gear arm that would be placed on the indent of the main body of the gripper. This would go back and forth between the gear and be long enough to grab a few bracelets placed on the trees.

The arm that would be glued to the block piece on the gear arm seen in on the right side. These parts were designed separately not only for a cleaner print, but so there was room to move around if a further opening length was required. The dimensions followed the same sizing of the arm on the opposite side connected to the main body.

The main body of the gripper was designed so that it would hold all these parts together. The servo motor would be screwed in with the small level back at the bottom. This would secure the servo motor in place where there was enough room between the output shaft to the gear that could fit and be secured on the gear arm underneath. The design for the gripper did not need to be that large as its job was to just grab enough beads therefore the arm just needed to be long enough to move a great distance.

Code

Why use linear actuators to act as the base of your arm?

We utilized linear actuators because it had the easiest application method from an Electrical Engineering standpoint.

Linear actuators essentially have two settings, LOW and HIGH or retracted and extended.

The power consumption was also within scope of the battery we had at hand.

Pair this with some geometry to determine positioning and the result is a robot arm that is able to reach its target height with a single command.

Why did you move forward with a gripper for bead grabbing?

We required a solution that could grab the beads with ease, hold them, and release.

We also needed it to be small enough to placed on the end of the actuator.

Weight was also a factor since we were close to the lift limit of the 4" linear actuator. Like the linear actuators, a single digital signal was required to operate the gripper.