Prototyping and fabrication
Deo A-Mutomb - Designer & Engineer
Summer 2019 (3 Weeks)
Design and prototype a cheap vehicle that is able to navigate various type of terrains and is easily steerable. The vehicle will be evaluated based on creative propulsion design, elegant mechanism, simplicity and performance.
Before setting our minds on designing an inchworm robot, we brainstormed extensively and explored multiple avenues, everything from drones, to rotating spheres, bipedal, etc...
When we came across inchwork robots, we were immediatly captivated; we saw an opportunity to create something special that appeared simple but that relied on a complex yet elegant mechanism to operate.
Inchworms have a very interesting body can be divided in three parts; true legs at the front and prolegs at the rear with a legless expanse in between. In order to move forward, inchworms take it one step at a time.
First, the rearmost part carried by prolegs moves forward, causing the legless mid-section to arch and loop up. The inchworm then proceeds to lift and extend its front-end causing it to move forward.
Step One: Moving forward
When we decided to inspire our robot from an inchworm, we had a rough idea on how to achieve the desired results based off of the research and the data we had gathered.
We came across many ideas, but the push/pull mechanism was very appealing to us due to its simplicity and the room it left us to innovate and implement our own ideas.
Our first iteration of the inchworm was a simple and non motorized prototype that used cardboard and toothpicks.
The vehicle had to be hand maneoeuvred in order to operate.
Having a physical model allowed us to explore further the moving mechanism as well as challenges we may experience along the way.
Building a physical prototype allowed us to better test our concept and visualize roadblocks.
Throughout our attempts to make the vehicle function, we noticed that the it had trouble advancing as the back wheel kept rolling backward everytime we tried to move the vehicle forward.
After doing some research on freewheels, we came up with a gear and a pawl mechnism that relied on gravity to prevent backwards rotation of the wheels.
To that effect, we designed four different Pawls each being an improvement over the previous one. We learned during the process of redesign about the importance properly locating the center of gravity on the Pawls, which, if not properly calculated, may hinder their performance.
Step Two: Turning Left and Write
After solving linear direction motion, we shifted our focus to making the vehicle multi-directional. This step was very challenging because of the lack of documentation and research on the subject.
When we put together our first motorized prototype, we tried to use a servo, but had trouble connecting it to the feather and couldn’t get the power we were after. As a result we decided to use a stepper motor instead.
Though the stepper motor provided us with the power we needed, it weight made turning challenging.
We garnered that the two front wheels need to rotate freely from one another to avoid interference which translates in one wheel that keeps the other from rotating when we attemp to turn left or right. This causes more strain on the motor and increases our energy consumption.
We also found that inching vehicle too much while turning would cause imbalances that will sometimes cause the car to tilt over on its size.
To address this problem we came up with two creative solutions that required us to reimagine our wheel system.
Tri-Wheel system
For our first solution, we created a 3 wheel system that ensured that we had wheels on ground at all times. This solution performed really well and resolved most of the imbalances issues our vehicle was facing when turning.
Having said that we knew that we needed higher wheels for our final exam parcour challenge which required us to go through a field of popcorn which we suspected might cause some trouble given how our wheels were to the ground.
Rotation control system
By limiting left and right turn within a certain range, we found out that a three-wheeled system was not necessary and that all wheels can share the same height without us having to worry that the car will tilt over on its side while turning.
Finding the sweet spot to keep the car leveled took a lot of trial and error as well as math but in the end we prevailed. After completing the design of the system, we 3D printed it and laser cut the base it was going to sit on. And just like that we had completed the last piece of our puzzle.
Inspired from Tsugite, a traditional japanese joinery, our final prototype is a beautiful and seemless vehicle that sports an industrial look. It is very easy to assemble and requires no tools. Even more, it was one of the cheapest vehicle to manufacture costing us only $17 (not including the motors and feather which were provided by the class.)
Reflecting back on our project, Hector and I are very happy with our results. We took a simple design that could only move in one direction and found a creative way to design it into a functional vehicle.
On a personal level, I learned to better appreciate the importance of quick prototyping to test out ideas and concepts as well as spot problems early on which allowed us to transition to our final prototype with more confidence.
More, working on this project made me a better at collaborating and working in a team. It also helped me improve my communication as well as interpersonal skills.
8 AA batteries $12
3 12x30 plywood $5
All motors and electrical components were provided by Chris Myers, professor of DES INV 22
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