Category Archives: MECH Coursework

Fig. 1 – Solar-powered tricycle, Daisy, at Burning Man

Introduction

The Capstone project is usually done during the final year of your engineering degree. Each department get projects provided by companies related to their areas of expertise. For UBC Mechanical Engineering, the projects range from fluid dynamic pipe flow testing, biomedical knee braces, to rovers that fix wind turbine blades.

All the potential projects are presented to you in the first week of September. Then you’re allowed to rank your choice of top five projects. I was matched with my second choice, eatART Daisy Drive project, along with three other Mechanical Engineering students. The eatART (energy awareness through art) foundation is a not-for-profit foundation composed of volunteers from the STEM and art fields. Our client is the Co-Executive Director who is also a mechanical engineer and UBC alumni. Our project is to optimize the design of the electrical belt drive of the largest solar-powered tricycle in the world, Daisy.

Built approximately 20 years ago by inventor Bob Schneeveis, Daisy traveled to Burning Man, an annual festival celebrating community and art and was used to drive passengers around using purely solar power. At its maximum capacity, Daisy can carry four adults in its carriage plus a driver in the front. It is steered by a hand crank and speed-controlled by a foot pedal throttle. Due to its size and weight, Daisy has only been able to travel on flat ground, such as the desert where Burning Man takes place. Now that Daisy is in the possession of the eatART foundation in Vancouver, our aim is to improve Daisy’s climbable incline so that it fits in with the hilly terrain of Vancouver.

First Term Steps to Capstone

1. Define value for stakeholders. Establish scope of your project.

Since our team is working for a not-for-profit organization, our project’s value is in the social-good generated rather than monetary value. With an optimized drive system, Daisy can be used in Whistler village, where roads are at a slight incline. Allowing Daisy to carry visitors in Whistler allows the eatART foundation actively showcases the accessibility of renewable energy technology such as solar power.

Initially, our client mentioned that the major design issue is in the V-belt that translates the motion of the rotating motor shaft to the three meter tall front wheel. When the V-belt slips from the sheave, this means that despite the motor still turning, the wheel stays stationary. This is particularly dangerous on an inclined road, since the front wheel will start to slip backwards without braking. Even with brakes applied, Daisy remains stuck on the inclined road, and cannot move forwards at all.

Another mechanical design flaw was in the belt tensioning mechanism. This mechanism provides tension in the V belt by pulling the two sheaves apart further. This is currently done by winding up a torsion screw attached to the motor and the front frame. This tensioning system doesn’t seem to be properly designed and may be experiencing induced strains and stresses. By redesigning the tensioning mechanism, we could eliminate these stresses and eccentricity, allowing the sheaves to be correctly positioned relative to each other.

To climb a hill, a certain torque is required. Imagine changing to a smaller gear on your bike while climbing a hill. You slow down significantly, but it becomes easier to pedal. A smaller gear ratio means that speed is traded off for torque. Similarly, the current motor and gear configuration could not provide sufficient torque to climb any incline because the gear ratio was too big.

Limitations also arise from the electrical system, as the batteries only provide 24 volts, the motor controller seemed to be old and out-of-date. The motor’s torque capability sets another limit. Its peak torque (stall-torque) and power could be simply insufficient to move the large tricycle.

To sum up all the aforementioned design flaws, they include:

• V-belt slippage,
• belt tensioning device,
• low gear ratio,
• and electrical power limit.

2. Investigate the problem. Define functions of your solution.

Since Daisy was quite old, the information on its components were not recorded well. Through testing and investigation, we collected data on the electrical motor, the motor controller, and the drive.

For instance, we tested the efficiency of the motor controller. Running the motor without the V belt attachment, we measured the input current from batteries to the controller, and the output current from controller to motor. Then, the power was calculated from the simple P=IV equation. The ratio of Pin / Pout represents the controller’s efficiency. Since Daisy has a throttle, we ran test trials by varying the power draw from motor, from 17% to 100% of power draw. The controller efficiency we calculated is represented in the graph below.

Fig. 2 – Controller efficiency as power draw from battery increases

Evidently, the controller efficiency was above 60% at all times. More importantly, the controller was operating at 100% efficiency near the max power draw from motor. We concluded that a replacement for the controller was not necessary.

3. Conceptualize different solutions.

After defining the functions required to perform by your solution, create various concepts through simple sketching. Aim for quantity instead of quality. You want as many concepts for each function as you can. These become your concept fragments; they are fitted together into whole concepts through mechanical mounts.

Fig. 3 – Concept sketches; (on left) treads with timing belt; (on right) pedal chain drive

After attaining several whole concepts, you should evaluate them on a impartial basis through winnowing, Pugh chart, and a weighted decision matrix. We evaluate our concepts based on a variety of performance metrics, one of which essential to any project is cost. Even though our team had lots of different concepts involving electrical components, they did not do very well in the cost criterion of the Weighted Decision Matrix. In the end, we ended with two concepts with good potential, the chain drive and added traction on wheels. The two-stage chain drive concept we came up with would eliminate slippage and increase the effective torque translated.

Fig. 4 – Two-stage chain drive concept sketch

As opposed to a single stage chain drive, two stage would allow a much greater gear ratio while staying within the recommended roller chain to sprocket contact.

4. Create a critical functional prototype (CFP).

The critical functional prototype (CFP) is designed around a selected function that’s critical to your solution. This is a great chance to see the physical (not theoretical) feasibility of your concept without investing resources into the whole concept. The CFP also allows you to detect unexpected failure modes, undesirable defects, and incalculable performance issues.

We needed to confirm that a chain drive can sufficiently translate motion from motor to the wheel, so we built a chain drive prototype consistent of a motor, a driving sprocket and a driven sprocket. The gear ratio (# teeth driving / # teeth driven) is 17:73 or approximately 1:4. We also set up the different transverse offset to see the upper limit at which the chain starts to derail, rendering the drive useless.

Fig. 5 – Chain drive critical functional prototype test rig

The motor was running at different speeds with light shocks applied. What we found was that for commercially made sprockets (with special profiled teeth), there was almost no derailment at any transverse offset or motor speed. However, for the water-jetted sprocket, there was almost always derailment. Upon closer inspection, the aluminum plate may also have deformed while in storage, so the sprocket it made was slightly bent, leading to the chain derailing.

5. Reiterate the design

After presenting to the client once more with our CFP experiment results, the chain drive concept was deemed too risky to implement. It would increase the number of mechanical components, and due to lack of slippage, could cause irreparable harm to the motor and electrical components if the drive gets jammed.

The concept we ended up with is increased traction (through additive materials and increase wheel width) and better tensioning of the driving pulley to eliminate V belt slippage.
Through preliminary calculations, we also discovered that the batteries shifted a lot of weight to the rear of the tricycle. On a hill, this would create a lifting effect on the front wheel. By shifting the position of the batteries closer to the front wheel, we could better distribute Daisy’s weight and give it more grip on the road.

We decided, along with the clients, that a prototype wheel should be built to test different traction materials such as truck bed liner, spray-on rubber, and etching notches into the flat bar metal. We will be building a section of the wheel out of steel flat bar, attached to an electric motor at the same torque and the power level as the one on Daisy. Then we can apply the various materials onto the section and run it on a ramp. If the section successfully climbs the ramp, then it proves that the material provides sufficient power. If the section slips, then there is not enough traction. Oppositely, if the section is stuck, then there is too much traction force.

That’s all for now. The design process will resume next semester with fabrication.

If you have any questions, please comment down below. I look forward to chatting with you.

Cheers,

Kirsten

Finals can be a stressful time of year.  Now that I’m finishing up my 3rd year of Mechanical Engineering, I’ve personally had my fair share of those panicked last minute cram sessions (and have learned to avoid them at all costs).

If you’re interested in learning about how I personally get through finals nowadays, you’re in luck!  The first ever Mech Ambassadors Vlog covers just that, check it out!

Music: Bensound – Hip Jazz

Hello everyone,

I’m now back at UBC for the second term of my third year of Mechanical Engineering, which is on Term 1 of the winter session in the Co-op schedule.  Trying to explain the Co-op schedule is always complicated, so I’ve just started saying I graduate on May 2020 (assuming everything goes as planned).

I ended up taking an online course over the summer and I strongly recommend it. It didn’t feel like an extra burden on top of Co-op work since it was only one course and now I only have to take five courses this term instead of the usual six.

And the best part?

Only one course starts at 8:00am.  A dream come true.

Now, when I was first looking at this semester on paper it seemed like an easygoing semester. Only five courses? Sounds like smooth sailing to my final year. But engineering being engineering, this term is just as packed as all of my other ones. Here’s my quick student perspective off the courses this term.

MECH 325 – Mechanical Design 1

This course applies to all options of the Mechanical Engineering program (Thermofluids, Biomedical, Mechatronics, and General.  More info on those here).

You learn all about gears, pulleys and all sort of mechanical systems.  There’s tons of information and equations coming your way so get ready to soak in all types of variables.  There’s group work involved with designing components and small mechanical systems, but not every week.

MECH 327 – Thermodynamics 2

Oh boy, here we go again. Thermodynamics 2: 2 Hot 2 Handle

Only students in the General and Thermofluids options of the program have to take this one.  It’s one of the most important and applicable courses for the field I want to go into after graduation (energy).  That first midterm didn’t go so well though, so this class has been my top priority.

The second midterm is two days from the time I write this, so wish me luck.

MECH 328 – Mechanical Engineering Design Project

This one applies to all options and it’s the main design course this term.  The project this year is to design an autonomous ocean microplastic sampler.

Here’s a little information on microplastics and why they are increasingly a problem in the ocean: https://oceanservice.noaa.gov/facts/microplastics.html

The project is actually pretty neat, but it’s quite a bit of work.  We don’t have to build anything, but we do have to develop our design using engineering design principles.  This means that we have to be very thorough with our decision process and there’s tons of documentation is involved, so it’s good preparation for the engineering field.

MECH 386 – Industrial Fluid Mechanics

This course only applies to the Thermofluids option, so it is one of the more interesting courses for me.  It’s essentially a continuation of previous fluid courses, but more grounded in industry applications.  There’s a semester long project involved where you contact companies and try to solve problem they are having specific to fluid mechanics.

I did pretty well on the first midterm, so the course is currently on my good graces.  The turbulent flow midterm is just around the corner, so I’m not sure that good grace will last.

PHIL 101 – Philosophy 101

This is my non-engineering course this term.

I highly recommend taking Philosophy.  It’s a nice break from the regular engineering courses were we get smacked over the head with all of the rules that we have to follow.  The physics and math with equation after equation after equation.  I feel like this course provides a different perspective on things.

It’s nice to take a step back and go “Wait, do I even exist?” If I don’t exist neither does that grade I got on the Thermodynamics midterm.  There’s comfort in that.

__

And that’s about it. Two design courses, two regular engineering courses, and one humanities for a total of five courses.

Like I said, it looks like a pretty straightforward semester. After this it’s an 8-month Co-op and then my final year.  I just have to make it through this term first.

Now that I’m done with finals, I have some time to reflect back on the first term of my 3^rd year.

I haven’t gotten my final grades back, so I’ll have to hold on making a complete judgement, but overall I think this semester went smoother than MECH2.  If MECH 2 was a 10/10 on a difficulty scale (for the sake of argument) this semester was probably a solid 7/10.

Here’s my overall impression of my classes:

MECH305: Data Analysis and Mechanical Engineering Laboratories

The class has recently been redesigned and this year was its first run through.  It’s essentially labs and statistics.  There are five regular labs in total, which draw on concepts from other courses.  You go in, follow the procedure, and write up a lab report.  The next week you expand on one of the regular labs by setting up your own objectives, and deciding how you’ll carry the experiment out.

At the very end of the course, there was one big exploratory lab report in which we were free to explore anything we wanted using the techniques we learned throughout the semester.  My team ended up wiring strain gauges to a hockey stick in order to determine the forces applied to it during a slap shot.  We even had someone that had played hockey semi-professionally take some shots with it, shot-out to Jackson. It was pretty neat.

MECH 358 – Engineering Analysis   

This class was by far the most abstract out of all of the classes this term, since it builds on linear algebra concepts. You learn how to solve equations that can be incredibly hard/impossible to solve numerically, like the heat equation which you’ll come to know and love (here’s a quick preview of that lovely equation).  I didn’t particularly enjoy linear algebra back when I took it on 1^st year, but I actually enjoyed this class.  My biggest takeaway from the course was that even though we have large amounts of computational power, you have to be clever in how you go about computing certain problems.

Homework consists of matlab and lots of “why doesn’t my code work.”

MECH360: Mechanics of Materials

This class is a continuation of solid mechanics in MECH224.  There’s a lot of material covered, so doing the practice problems and tutorials is a must.  Luckily, there are tons of online resources.  There’s not much to say about this course except study hard for that final. I got completely blind-sided by it, and I’m still sweating about it.  Don’t let that happen to you.

MECH 375: Heat Transfer

The class is technically called heat transfer but we all referred to it as thermo.  We covered a lot of material, and in my opinion it was one of the more challenging classes this term.  There’s correlations and numeric tables all over the place.  Prepare to sprint with your hands during exams.  For the final you get a crib sheet, which is a 40 page formula packet.

Surprisingly, I enjoyed the topic as a whole.  The class was held in the MATH building and I hope for the sake of anyone reading this that you never have a class in that building.  The seating arrangement and the size of the chairs is terrible.  That classroom get a -1/10 from me.

MECH 380: Fluid Dynamics

Here’s another class that I really enjoyed.  It felt like an intro to aerodynamics.  You gain greater insight into drag/lift and learn about mach numbers and shockwaves.  The concepts can be tricky, but I found it manageable.   Engineering Analysis, Heat Transfer, and Fluid Dynamics all tie into each other, so if you understand one it can sort of help with the others.

Like I said, I’m still waiting for my final marks so I might be singing a different tune once I get them back, but this year wasn’t so bad.

Now it’s back to Co-op for the summer.

Wish me luck,

Rigoberto

Gruezi alles,

While I wait for my train to depart for Paris, nursing an espresso and thoroughly enjoying European life, I thought I’d write about the crunch time that usually happens around this time of year at UBC. If escaping to another continent isn’t an option (sorry Nick and Davey), there are a number of other strategies to get through the combination of MECH2/MECH3, and design team involvement.

For MECH2:

Like the tides, the periods of time before tests and competition deadlines roll by predictably every year. The key is to plan ahead and anticipate them from month one. This can be hard if you feel like you’re just barely able to keep your head above water, like I felt in MECH2.

While the course schedule might be unfamiliar, the MECH staff do a great job laying out the schedule as accurately as possible. Fall semester is a settling-in period, but by winter break you should be able to see your spring schedule and while your design team work may have been slow as teams ramp up, spring semester is always a rush. Make sure you take an hour or so to look through all your weeks and weekends, identify where big tests/deliverables lie, and front-load your design team work as much as possible. No one wants to be wrestling with SOLIDWORKS while attempting to absorb test material. In fact, I’d recommend pushing your team/project to reach every checkpoint as early as possible. The “unknown unknowns” that inevitably come up with design team work are always better managed the week before deadline, rather than at 5:00 am the day of.

For MECH3/3.5:

As you progress and gain a bit of experience in design teams, you’ll likely start speking to sponsors and manufacturing partners to get your parts made. Here are a few key things to know about design team manufacturing:

1. Give sponsors as much lead time as possible, for both courtesy and project management sake. Sponsors donate their time and effort (and money) to help us out, meaning real customer POs will always run first. While a simple part may take only an hour to machine out, giving many weeks of lead-time allows your sponsor to optimize their machine schedules. CNC machines aren’t cheap and need to be running near-constantly to turn profits these days. This courtesy also reflects positively on your project management skills!




2. Invariably, engineering changes will come up as certain fillets or cuts can’t be done on their equipment. You might spend weeks thinking you’ve polished your part, only to find out it’s not machinable. Try your best to consider the limitations set by your particular machinist/manufacturer at the very beginning of design; many of them post their machine capabilities and model numbers on their website. No one wants to spend hours milling out a variable-radius fillet because it “fits your aesthetic.”

Design team work has been the most memorable experiences I’ve had in MECH. The unexpected challenges might incite a bit of terror in the midst of school, but I look back on them with endearment. Sick, twisted endearment.

Next posts will be dedicated to my Coordinated International Experience in Switzerland. Trust me, you want to look into this option.

Tschuss,
Jason