Week 2

Introduction

Project Goals

Construct a go-kart frame
Create a functioning ESC/motor controller
Create a functional electrical system
Integrate all systems into a full go-kart

Build Stage: Preliminary Fabrication

Go-Kart CAD design
PVC-pipe frame (preliminary design)
ESC design
ESC preliminary build

Schematic of the overall PCB design that includes all 3 half-bridges and 6-33A MOSFET. We're planning to utilize an ESP32 as our microcontroller of choice, that is being run off voltage supplied by a 48v-5v regulator.

PCB-ESC Schematic V2

While the schematic has remained relatively the same (I have not yet had a chance to test whether it works or not), there were a few important changes. First, I removed one of the components that reduce high voltage spikes - it was overcomplicating and breaking the circuit, and should also not be necessary if running off a stable battery. Second, I also simplified and corrected my switch symbol design, which was previously interfering with PCB layout (as seen in PCB-ESC V1 Design below).

PCB-ESC V1 Design (KiCAD)

First round of PCB-ESC design. I did not make a smart layout when I started the PCB-Traces. Thus, the layout is overcomplex. Additionally, the trace width for the high power lines is around an order of magnitude too small.

PCB-ESC V2 Design (KiCAD)

Second round of PCB-ESC design. I made a much better layout when I started the PCB-Traces. The layout is relatively simple, although space inefficient. The high current traces are still too small, but should function with around 10A (without overheating).

Progress Summary

Design

Completed first iteration of Go-Kart CAD
- Motor Mount
- Seat
- Steering
Completed miniaturized version of ESC controller
- Has low current capacity

Fabrication

Completed first iteration of Go-Kart PVC Frame
Started to begin practice welding
First iteration ESC-PCB has been ordered from PCBWay

Testing

Testing running lower current and lower voltage BLDC
Testing lower current capacity BLDC ESC

Problem Solving

Relatively low current capacity for our ESC-PCB
- Solution: Run high current wire parallel to PCB

Updated Go-Kart CAD

Steering assembly is being reworked at the moment. We need to make sure that our tie rod and steering rack mount properly.

Practice Welds

Photo of Tyler's practice welds.

Challenges and Solutions

PCB-Trace Calculator - Results for external layers shows that I need 5mm traces

PCB Low-Current Capacity

PCBs use copper traces to route current, but most of these traces cannot handle the 33A of continuous current that our motor requires. While it is possible to create PCB traces capable of conducting such high current (and even higher current during times of increased power draw), these traces are either extremely large and unwieldy (impossible to put on a cheaper PCB), or are extremely expensive to produce.

To navigate around this problem, the easiest solution is to simply avoid using PCB traces to conduct the high-current load. As a substitute, we have decided to use copper wire routed in parallel to the PCB for the high current circuits (Mosfet, motor, etc.). We still plan on using our PCB for our control logic circuit, as it makes directing the flow of logic extremely easy, but we plan to use the aforementioned alternative for the high current circuits.

Work Ethic and Collaboration

Go-Kart Fabrication Progress (Tyler & Hunter)

Delegations

For our Go-Kart project, we thought it would be best that we split up the necessary work by our respective interests.

I (Charlie Koh) am in charge of designing and building an ESC with Hunter. I am working on PCB design, while Hunter is focused on understanding a reconstructing the ESC controller design. These are relatively separate at the moment, but whenever Hunter comes up with an idea or discovery that he believes is useful for the PCB or greater ESC construction, he makes sure to let me know. This is primarily done over text or email.

Tyler is the one primarily working on the CAD of the Go-Kart; however, Hunter and I both have experience working with CAD, and we give our input on design and change when we believe it is applicable.

Tyler and Hunter are the ones most primarily working on the fabrication of the Go-Kart. While I do know how to use a pipe bender and tube notcher, I am not working on the immediate construction of the PVC-pipe prototype nor the final Go-Kart fabrication. If my work on the ESC is finished by the time the Go-Kart fabrication is underway, then I will assist in the fabrication; however, I expect the creation of a semi-reliable ESC to take the majority of the school year, if it is completed at all.

Time Management

Time management is a significant challenge with this project. With my specific delegation of the ESC, I believe it is going to be an extremely challenging task to complete within a school year. To properly manage my time, I have divided the completion of a closed-loop ESC into two challenging components. First, I want an ESC that is capable of general motor control, without the closed loop system in place. If I am able to complete that in a timely manner (hopefully before the start of the third quarter), then I would like to work on integrating the closed-loop control system built into the motor. While I am unsure whether I will have the time to fully complete the closed-loop controller, I will ensure that I have an ESC that is able to control the general speed of the motor by the time Engineering 4 is complete.

Next Steps

ESC Next Steps

Creating a reliable ESC is a complex and confusing topic. I've never worked the internals of an ESC before, so I'm not completely sure about the reliability of my electrical circuit. There remains a lot to be done for the ESC, such as obtaining a first low-current prototype, creating a working low-current prototype, creating a first high-current prototype, creating a working high-current prototype, creating a first high-current closed loop ESC PCB prototype, and creating a working high-current closed loop ESC PCB prototype.

Next Cycle Goals

Receive first iteration (low current) of PCB
Solder and begin to assemble first iteration (low current) of PCB
Test first iteration (low current) of PCB
Learn from the failures and successes of first iteration of PCB

Timeline

By October 1st: have a working low-current ESC PCB (<10A with a smaller BLDC)
By November 1st: have a first high-current ESC PCB prototype (capable of handling 40A on high current lines)
By December 14th: have a working high-current ESC PCB prototype (no encoder feedback yet)
By February 1st: have a first high-current closed loop ESC PCB prototype
By April 1st: have a final working high-current closed loop ESC PCB prototype

Frame Next Steps

While the first iteration of the PVC pipe frame is relatively complete, there is still much to be done with the frame. Namely, the fabrication of our steering assembly, and iteration upon our existing PVC-pipe frame. We need to make sure that our Go-kart has mounting space for all the electronics (primarily the control systems and the motor).

Next Cycle Goals

Mount motor and properly tension chain
Mount brake caliper
Have a first preliminary design for steering system
Design basic/preliminary electrical mounts - actual mounts cannot be fully designed because the electrical system is not yet complete
Designate space for control inputs

Timeline

By October 1st - mount all components onto PVC frame and begin metal fabrication

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