156A Week 10

This Week’s Progress

• Code for the Small Scale prototype

  • Uses 5 predefined points, turns these into encoder count distances

  • Homes the tool end by locating to one post and setting corresponding values

  • Writes the motors until their individual encoder counts reach the necessary values

  • Travels up and down in Z direction through spool/unspool of each wire

  • Limitation: Motors operated sequentially (networked Arduinos in the future)

• Small Scale Prototype

  • One out of three uprights for small scale prototype

    • Arduino configuration zip tied to L-bracket

    • L-bracket to be fixated into dirt

    • Spool to be attached to motor shaft - still figuring out how to mount spool

    • Cable (nylon cord) to be wrapped around pulley and spool

      • As motor rotates, cable will be wrapped around spool with pulley as a support to add length and tension to cable

• Reaction Force Calculations

  • End Effector Masses

    • Utilized the CADs on the FarmBot website to determine the mass of each end effector

    • Heaviest end effector is best case scenario, lightest end effector is worst case scenario since that will provide the least amount of reaction force on the soil

  • Reaction Force Calculations

    • Researched depth needed to plant seeds into soil for proper cultivation of plants

    • Calculating soil density

    • Looked into soil density/reaction force research as done previously for civil/structural engineering

      • Trying to apply our soil density to these equations

• Free Body Diagrams

  • Work in progress

    • Tension on cables from end effectors

    • Torque from motor on cables between spool and pulley

• Continued Literature Review

  • Learning about end effector stabilization

Feedback from Meeting with Sponsor (12/04/2020)

12/04/2020 Meeting with Nick

• Has contacted people at FarmBot and learned about new waterjet tool they’re producing

  • We will connect with FarmBot creators for inquiries on the system we are building

  • Will not be using waterjet tool with the cable driven system due to excessive propulsion forces and vibration

• Nick has received the FarmBot - we are working to receive the technology during Week 1 of Winter Quarter

• Nick wants us to focus on more advanced FarmBot users

  • Review of FarmBot forum showed a lot of inexperienced users experiencing difficulty and frustration setting up and maintaining their system

    • Made us question whether we should even pursue cable driven system or answer already existing questions

  • Nick has confirmed that we are working to address questions raised by more advanced users since cable driven system is inherently more complex than rigid frame system

Feedback from Meeting with Instructor (12/01/2020)

12/01/2020 Meeting with Prof Qi & Week 8 - 9 Presentation

• Prof’s Biggest Concerns

  • What is the timeline for reaction force testing?

    • Team’s Response: begin calculating required reaction force for soil and compare with existing end effectors for FarmBot

    • Reaction Force = End Effector Weight + Weight of Slack Cable

  • What kind of cables are we using and how will we scale up the results of our small scale prototype?

    • Team’s Response: Selected Nylon Cable

      • Can be used for both small scale and large scale prototype so that we don’t need to account for differences in cable material

      • Nylon cable is strong, yet relatively lightweight and resistant to tears

      • Hypothesized that Nylon material will cause less wear on spools and pulley than metal or rope

  • Will we use pulleys or winches?

    • Team’s Response: Followed Tom’s suggestion from Week 8 presentation and utilized winch system

    • Continue looking into winch system requirements so far as weight/torque concerns

Current Concerns (decreasing priority)

• How should we mount the spool to the motor shaft?

  • Having difficulties with the limited resources we have

  • Preventing us from moving forward with our risk reduction

• How should we fixate posts in garden soil for a stable infrastructure?

• How should we wire the motors to arduino?

  • Given three motors and one arduino/motor driver, we were planning to wire the motors in parallel with each other.

  • We have electrical wire and we're going to solder the wire to add additional length so that it can be hooked up with arduino breadboard.

• Functionality of Motor Code (Greatest to Least Concern Below)

1. Sequence of while loops is improper for event driven code with multiple sensors (this is why Farmbot uses networked Arduinos to control all motors at once)

2. Non-stepper motors require a nonzero PWM when not in use to keep the end effector from just falling down

3. Active motor may be overwhelmed when also fighting against the tension provided by the other motors

• Determining which design for Z axis translation is best suited for this purpose

• Determining how many arduinos we will need - one for every motor?

  • Literature reviews show that each motor has an arduino and there is one Arduino mega that is connected wirelessly to the rest.

Upcoming Goals

Deliverables for Finals Week

• Draw conclusions from Risk Reduction

• Redefining Risk Reduction Question

  • Can our motor/pulley configuration drive a cable driven system for translation in 3 degrees of freedom?

    • If yes, continue with this design

    • If no, look into lead screw and linear sliders design

• Create a circuit diagram for multiple motors with one arduino

• Update BOM based on already purchased materials

• Individual Component Analysis

• Risk Reduction Presentation

Weeks 1-2 Spring Quarter

• Look into how to synchronize multiple arduinos

• Reiterate testing of motor code on existing small scale prototype

• Modify small scale prototype design

Budget: $5600

Balance as of 12/04/2020: $2600

Spent:

• 12/03/2020 - $68.40 (Small Scale Prototype Materials)

• 12/05/2020 - $26.89 (Small Scale Prototype Materials)

• 12/06/2020 - $35.24 (Small Scale Prototype Materials)

• 12/07/2020 - $39.89 (Small Scale Prototype Materials)

Balance as of 12/11/2020: $2429.58