Lego Racer

Your task: create a Lego vehicle with a single motor, powered by a PicoCricket, that can carry a 1.0 kg weight as fast as possible on a 4 meter course.
On your mark, get set, GO!

One of our earlier designs with really high torque

We started with an introduction with gears and gear ratios, our main takeaway was that torque and speed are inversely proportional. Using this knowledge and the knowledge that the motors we used were high speed, we set out to first up the speed enough to carry the 1 kg weight.
This quickly proved not as easy as we thought it would be because we had to also come up with the most strategic way to also store the weight, PicoCricket, and also correctly position the motor so the gears line up. We tried really bulky designs specifically targeting holding the many parts but reasoned that there were more efficient ways to make a car and scrapped it. We also finagled with the gear and motor connection and figured that a 2 wheel drive was all that was necessary for this race.

Our first running car had a gear ratio of 1:525 because we had 4 pairs of 8:40 tooth gears and featured an inversed Lego design, meaning all the pegs for the Legos were facing down because we figured that we can more easily put the motor and the motor board on the car.

With our first working car being very slow we decided to test out other gear ratios:

1. higher speed/lower torque: 8:24+ 8:24 Gear Ratio: 1:9 Result: too weak to carry weight
2. since torque was too low lets add more gears:  8:24+8:24+8:40 GR: 1:45 Result: completes 4 m in 16 sec
3. Still a little slow, lets reduce torque: 8:24+8:24 8:24 GR: 1:27 Result: completes 4 m in 11 sec
4. let's see if we can make it faster! 8:24+8:40 GR: 1:15 Result: completes 4 m in 8 sec! Yay!

Final Design

 Our final design was very minimalist to increase the speed as much as possible. We supported the PicoCricket and the weight between between two little walls of Legos. We also found out that making the big wheels the driven wheel is an advantage because they have more distance per roll due to their large circumference.

Our final race finished in ~8 seconds despite having slight complications with the PicoCricket not cooperating for a little bit. It was interesting to look at the results because 2 other teams also had the same gear ratio but were up to 4 seconds slower, after some caparison we realized that this was because despite having the same gear ratio the other teams used more gears than we did which added friction. If we were to improve our design we would try to make the walls supporting the weight and the PicoCricket more durable because we often knocked the walls over when taking the weights on and off the car. This was a takeaway of inversing all the Legos, so to solvethis we could use thicker blocks for walls.

Well Windlass

Our project task this time was to create a delrin windlass that would span more than 12cm to lift a "bucket" (a filled 1 liter water bottle in this case) 10cm above the top of the well without shaking, buckling, or wobbling.

Brainstorm: In our initial brainstorm we came up with idea for stability: a bridge like design and a design with large triangles attached to it, ideas to increase the amount of string that was wound up per rotation: bunching up delrin rods and creating an axel

Brainstorm ideas

Our final design

Our final design took components of the "bridge" as support and integrated the axel into the side plates for extra support because we feared that if we rested all of the bottle's weight on a single delrin rod, the rod may bend and break. We also created "hubs" or inner and outer rings that were meant to keep the axel from siding out of the side plate. We quickly realized when we finished our solidworks mockups that we far exceed the material limit by trying to make as many bracing as possible so we began to cut a lot of triangles into the side plate and reduced the amount of cross bracing. 

Final overview:
While our windlass was stable and easily spun when the water bottle was not tied to it, it required a lot of force to get the water bottle up. Our idea of integrating the axel into the side plate while avoiding the problem of the bending and possible breakage of the main support rod, created too much friction when force was applied, especially since we had hub guards that held tightly on to the axel that exponentially increased the friction.
Material usage: we (shamefully) used almost all of the materials we were limited to
50cm/50cm of Delrin
499cm^2/500cm^2 of Delrin sheets used

Reflections: One of the biggest drawbacks we faced was spending too much time debating our design rather than implementing it. This was especially disadvantageous for this project because we were limited in time to cut out the pieces for the windlass. If I were to redo this project I would try to cut out our pieces as soon as possible and make as many iterations so we could spot problem areas earlier on rather than trying to brainstorm one perfect design. If we were to improve this design we would make a better handle and try to reduce the amount of friction by removing the hub guards.

Notes from other team's presentations

Mechanisms: Slotted Yoke Drive

This week we were assigned to investigate mechanisms and write about our favorite. My favorite mechanism is the ¨Slotted Yoke Drive¨, it´s my personal favorite because it at first glance almost seems counter intuitive because it uses the rotational movement and converts it to a horizontal movement.

There are two main components to the slotted yoke drive, the circular disk base with a protruding part that gets inserted to the slotted component and the slotted component with two rods at the end that causes the ¨drive¨ motion. There are two pieces that go over each rod and keeps the rods from moving out of it´s straight path.

The horizontal ¨drive¨ movement is created by the circular disk and is transferred to the slotted component via the protruding part on the edge of the circular disk. Because the disk is circular the velocity of the slotted component is constantly changing, but this circular motion is what is distinctive about the slotted yoke drive. The protruding rod on the disk spends half of it´s time on the edges of the slot where movement is maximum at the other half traveling up or down the slot, changing it´s direction giving it the trademark back and forth motion.

Optically this mechanism is really interesting because the circular motion of the disk is hidden behind the optical illusion ¨up and down motion¨ of the protruding rod in the slot but ultimately turns into a horizontal motion. The real life application of the slotted yoke drive, or the ¨scotch yoke¨ is in high pressure oil and gas pipelines or for zinc baths (pictured in the photo below)

         

Bottle Opener project

Your mission should you choose to accept it: Make a Delrin bottle opener (that works!)

For our first ENGR160 project we learned and utilized:  The Engineering Design Process, cantilever physics, solidworks experience, and basic laser cutting skills. 

Cantilever notes

In our first class we learned about cantilevers: the longer the cantilever the stronger, yet also more susceptible to bending and breakage, so we have to balance these tradeoffs. We also had the option of thickness of material which could be used to escape some of the shortcomings of length.

Then following the Engineering Design Process we brainstormed multiple ideas and made a foam model of our favorite one, which was the one that was supposed to wrap around under the cap and pull up 

Brainstorm!

Foam model for iteration 1

Trial 1: After we created the foam model we made the delrin model and tested it on the soda bottle, only to find...

Our short and thin (we chose 1/8 inch thickness) bottle opener stood no chance against the bottle, it bent out of shape majorly.

Iteration 2, The Key to Engineering Success: Our final design completely reimagined our bottle opener, rather than wrapping around half of the bottle cap we decided to focus on trying to get a small piece of delrin under the cap and use leverage to pop the bottle and made the bottle opener thicker (3/16 inch this time). We also added some aesthetic improvements by making it key shaped and engraving the words "ENGR 160" on it. Yet when we finally printed out the piece (after causing some toxic fires via burning delrin) we found that the piece supposed to go under the bottle cap was too thick, so we put some elbow grease into it and filed into a sharper edge. When we first tried it the edge chipped but eventually as we filed it down more we opened the bottle easily without chipping.

Final filed edge

 Final (Countdown) test: The final test went just as planned, our bottle opener successfully opened the bottle without breaking!

What would we change if this were to be mass manufactured: Our main fear with this design was the chipping of the sharpened edge, we would look into other materials that don't chip as easily.

Fastening and Attaching

As implied by the title this post will be about fastening and attaching. Specifically for Delrin as it's our material of choice right now, so onward march to learn about how to fasten and attach this low friction and high strength material!

Heat Staking

Heat Staking: fuzing two piece of Delrin together by melting them using a thermal press. Particularly suitable for binding smaller objects to something else.
Pro: It's permanent Con: It's permanent and limited by size/shape of machine

Slots and Pegs: creating a slot and a corresponding peg (or vice versa) in the Delrin that will later be attached much puzzle pieces. Particularly suitable for cube/box-like designs.
Pro: can fasten together Delrin of any size, less machinery work
Con: it requires very high precision and is costly (in terms of material) if done wrong
To figure out the level of accuracy needed for the slot and peg method to work we use calipers to measure the tolerances which turned out to be within +/- .1cm. We also found that the solidworks figure and the real life figure were different, due to the laser cutter's slight changes per use that depend of factors such as, the time between uses and the number of times the laser has to go over the same line to fully cut through the material. It is to be noted that for future building with the laser cutter we need to overestimate for thicker materials to be more precise.

Delrin rod data

We also explored putting bushings on Delrin rods that had fits ranging from: tight, medium, and loose. Tight bushings are more suitable for a solid and permanent attachment, medium bushings are good for modeling positions without commitment, and loose bushings are useful for spinning parts.


Piano Wire: first create holes in the two pieces of Delrin with the drill press, then cut a piece of piano wire and use arbor press to put the piano wire into the holes.


Particularly suitable for hinges.
Pro: the most flexible of the three methods because it can either be a loose hinge or a tight attachment
Con: it requires lots of time, heavy machinery work and parts

An incomplete piano wire fastening