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Pancake Printer

ECEN 361 - Fall, 2023

Ryan Whitehead, Caleb Hall, Esteban Lopez

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Project Overview

Prints designs over a griddle using pancake batter
Scope

Features

SD card reader
Fine print control
Fast print rate

Features we cut, why?

Settings
LCD touchscreen display

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Project Overview

Design Process

Hardware
Software
Challenges
Outcomes

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Hardware Design

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Hardware Design

Gantry
Movement/Control
Processing

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Gantry

Modified Ender 3 to save costs
3D printed mounts for extruder and controller board

Softwares used

Fusion 360, Cura

TINA2S 3D printer

Stepper motors move print head along X and Y axis

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Movement/Control

Positioning

Nema 17 Stepper Motors
Powered w/ 24V DC power Supply
Each pulse of the step pin rotates 0.1125 degrees
20 steps/mm - belt drive

Extrusion Valve Servo

Lifts/Lowers plunger to block/unblock batter from coming out.
Batter held in a half liter syringe
Chopstick with rubber attachment on end.
Powered w/ 5V using buck converter

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Processing

SD card reader

SPI serial connection with touchscreen LCD and SD card module

STM32L476RG MCU with Arduino compatibility
CNC Arduino shield
DRV8825 drives stepper motors
24v cooling fan

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Software Design

FreeRTOS	Interface	Movement

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FreeRTOS

Separated into:

2 tasks

Parser Task
Movement Task

2 main queues

Command Queue

Stores commands as integers

Parameter Queue

Stores additional commands parameters

Why?

RTOS allows us the ability to organize processes into task and allow the OS to worry about scheduling.
It also allows us to scale the project in the future without creating an overly messy, disorganized main loop.
Allows for constant movement

When SD reading slower than movement commands, the queue provides a buffer.
When SD reading faster, the queue fills up.

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Interface

Parser Task

translate gcode into actual movement commands for our motors
puts gcode commands into our command queue for move by move instructions to the movement task.

Interpreter Function

Pulls from the output of the SD Driver to grab organize commands into various command queues and pull vital data from the command, such as the x and y float or the speed set integer.
The command and parameters are then put into their respective queues.

SD Driver

We read lines from the only as needed, i.e. when the queue has space and the file still has lines left to be read.

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Movement

Movement Task

Gets the next command from the queue, and any parameters needed for the command
Calls the appropriate function with associated parameters in the movement driver

Movement Driver

Home - Moves to printers origin using the limit switches.
Move(X, Y) - Moves from current position to specified coordinate. Calculates how to move there in a straight line.
SetSpeed(speed) - Changes how fast stepper motors move.
Wait(ms) - Delay next command for certain amount of time.
Extruder On/Off - Calculates angle of servo needed to open and close extruder control valve.

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Additional Software Information

Main/Initialization

Initializes stepper motors
Mounts SD card
Opens file containing g-code commands
Starts tasks
Gives control to FreeRTOS to act as our scheduler

Pancake Painter

Open source software
Generates g-code files compatible with our printer

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Project Demonstration

Video (or series of videos) demonstrating the project
Show each aspect of the design, including hardware and software (and all software features)

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Challenges and Victories

Challenges

Speed Limitations
Extrusion Delay

Victories

Movement Control
SD Card implementation
Extrusion Control

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Not capable of speeds greater than 50mm/s

Cause: Delay function accuracy of 1ms prevented taking more than 1000 steps per second
Solution - Custom μs delay

Chosen because it simplified moving 2 motors together at different speeds.
While loop polling timer value
Cons:

Polling while loop prevents other tasks from running if empty, had to run useless code inside

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Problem: Extrusion Delay

Cause: Pressure build up in tube over longer distances
Solutions:

1 - Move closer to print head

Reduced tube length and pressure build up
Added valve to prevent leaking from pressure buildup
Cons:

Pressure still to great causing motor to skip and inconsistent extrusion
Valve slows flow, but still leaked to much

2 - Mount syringe directly on print head

Enlarged syringe hole for gravity
Space for less leaky valve design
Cons:

Heavy, increasing vibrations at higher speeds
Slows down as pancake batter level decreases

Takeaway:

Test before integration

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The theory of being able to extrude based on a simple input command became increasingly difficult as it was practiced

Using the syringe and a tube to push batter with a variable viscosity meant buildups in pressure with less than a consistent extrusion rate.

Luckily, moving the syringe to a horizontal setup meant better control of the pressure in the tube. We were able to get more consistent extrusion rates.

Multiple 3D printed parts were needed to put the syringe where it needed to be and to attach the motor arm for movement control

Takeaway

would have been easier and better use of time to try out the extrusion designs before attaching to device an programing code that we spent time debugging before ultimately removing. spent several hours getting extrusion motor to work at hte same time as the XY movement, to end up not using that motor

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Victories

Movement Control

We had good results building the barebones cnc controls in software and using gcode commands to make these function calls.
Within a couple weeks of starting this project we were able to get the movement sorted to some degree of satisfaction.

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Victories (Continued)

SD Card Implementation

This was almost a stretch goal for us considering how we could have hard coded designs rather than importing them, however we wanted a device that could be used without modifying the code and flashing the controller each time.

Extrusion control switched from a plunger acting as a pressure controller in order to push out batter at a set rate to a servo controlled stopper that physically blocked/opened at our extrusion point over the griddle.

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What We Learned/Takeaways

Test before integration

saves us post-integration debugging

Plan for more time to debug/organize code.

code refinement
unintended consequences of certain functionality

Meet in person as often as possible when working with hardware

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Path Forward

Where do you see this project going from here?

Creation of an to follow guide allowing others convert their Ender 3 printer into a pancake printer

If you could continue working on it, what would you do next?

Improved gantry

Improve balance allowing for quicker printing
Larger size for usage of full giddle area

Fine-tuning printing

Various variables that control the overall quality of a print

extrusion rate, movement speed, movement software delay time

Future Features

Menu interface for easily adjusting parameters affecting print quality

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Conclusion

Evolved from a simple idea into a fun project that touched many technologies
Using FreeRTOS, CNC arduino shield, motors and a good deal of other hardware/software items to create something functional

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The pancake printer was a great idea that showcases the power embedded systems skills allow for creating large projects. Our ups and downs in creating this device taught us the best ways to problem-solve as a team on an embedded systems project. Starting from clear-cut goals and due dates, we were able to work on individual parts of the hardware/software of the design to combine into a working device.

The main takeaway may be just how many ideas we were able to touch in a simple idea. Being able to construct a 3D printer type device from cheap online parts and C code, using RTOS as a scheduler shows the array of possibilities with access to a relatively small amount of tech. In this one project we dealt with reading from an SD card, controlling motors through a CNC arduino shield and other hardware.