Week 6

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

Build Stage

This stage of the build, we are constructing our PVC Go-Kart frame along with our ESC prototype (low voltage, low current BLDC). This week, we have worked on finalizing the dimensions of our Go-Kart frame, and also mounting all our various control componentes (tie rod, brakes, etc).

Additionally, I have soldered and assembled the first version of our ESC, designed for 20A of operating current and up to 50V. This will not be the final version, and is a simple version designed to prototype and understand the operating mechanics of an ESC. Further down the project, I will be designing a more resilient and higher current capacity 40A motor controller.

Progress Summary

Design

For design this week, we iterated on our brake mount. Previously, our brake mounting bracket was of the wrong size. This week, we adjusted the size to make sure that they fit properly, and had the correct dimensions.

Additionally, for electrical design, I iterated my board design to have 2 major improvements; first, the high current wires no longer run directly on the board itself (previously, this was the case in the 20A design), instead running in 12AWG wire in parallel to the plate (allowing for the required 40A capacity). Secondly, I added capacitors to the high and low sides of the half bridge drivers, which decreases the volatility and amplitude of the voltage spikes.

The next shift that is going to made is moving to gate drivers (instead of manual drivers). This should help us get smoother actuation.

Fabrication

For fabrication this week, we mounted mounted our brake, our chain guard, and modified our steering. First, we mounted our modified brake mount to the brake disk, which fits on extremely nicely.

Secondly, we also mounted the chain guard; this is an absolutely necessary component for safety, as it decreases the risk of injury, by preventing items from getting caught in the chain. This was previously identified as a risk for safety, as there have been many horrific accidents with similar carts with lack of such a protection.

Finally, we modified our steering system so that one of our universal joints is locked. This essentially creates a linked system between our steering wheel and the intermediate shaft, turning into one long, rigid, and stable shaft for steering.

For electronics, I soldered on all the components for the first PCB prototype. This includes the high current MoSFETS, the terminal blocks, the XT60 power connectors, ESP32, and my 10k resistors. This prototype does not have the added voltage correcting capacitors, the parallel high current wires, all of our control input, nor does it have a virtual neutral point for FOC control. I am also missing my control level MoSFETS (3.3v to actuate 12v), which will come in for testing next week.

Chain Guard

Custom Tie Rod

Testing

We did not do much testing this week. However, we did one small section in terms of our frame, tie rod mounts, and wheel mounts. These various tests yielded that our current tie rods are not sufficient for our current design, and that we will need to make our own tie rods in-shop.

The ESC has not yet been tested, as all the components are not yet in. Specifically, I am missing my logic level MoSFETS, which means that I am unable to test. Currently, the high current MoSFETS are not able to be actuated by the 3.3v logic voltage of the ESP-32. Thus, I require an intermediate MoSFET to actuate them at 12v. To power this, I also require a 12v converter, and also a 5v converter to power the 3.3v ESP-32 (the ESP32 has a 5v to 3.3v onboard regulator).

Challenges and Solutions

Steering Mount

One of the big challenges with this project comes in the form of the steering assembly. The steering assembly has two universal joints, one connected at the steering rack, the other connected at the steering wheel. This creates two points of universal connection: we do not need these two points, and only require one. To solve this issue, we created a rigid mounting bracket that nullified the mobility of one of the universal joints.

This 3D printed bracket unifies our latter two shafts, allowing us to have a better, more rigid, and easier mounted steering system.

Universal Joint Securer

Soldered ESC Prototype

Soldering ESC Connections

The PCB for the ESC came in this week, and one of the biggest challenges that I had in the actual construction of the ESC was soldering the mounted components. Using school solder and soldering irons, none of the solder would stick to the components or the mounting board. Secondly, there were significant issues when it came to actually melting the solder without burning all of the flux. Finally, I had issues in soldering large thru-hole components, which required robust and full soldered connections to the board.

The solution for the first issue was solved with the usage of external flux, which helped the solder stick to the board and the components. The second issue was solved again with the usage of additional flux, which rendered the burned flux irrelevant; thus, I could turn my soldering iron much higher, which allowed the solder to melt much more readily. Finally, soldering large thru-hole components was solved with the intuitive solution of using a larger soldering iron tip, which allowed for easier tinning of the pad.

Work Ethic and Collaboration

Collaboration is continuing along our designated lines. I (Charlie) am continuing to design and prototype the ESC, while Tyler and Hunter continue fabrication of the Go-Kart PVC prototype.

Next Steps

One major future electrical step is the switching of ESP-32 MOSFET (logic and high power) actuation to using actual gate drivers. This makes sense to me, and is definitely a big switch. Additionally, this will provide the necessary floating high side current for the ESC, stabilizing the voltage spikes while simultaniously providing the required bootstrap.

Next Cycle Goals

Begin metal fabrication
Cut pipes and weld together coffin frame
Weld front pipes on

Timeline

By next cycle:

Cut and prep all parts for frame
Maybe start welding and assembling

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