2017 SAE Design meeting notes (MEETING NOTES BELOW ARE LISTED WITH MOST RECENT MEETING FIRST):
We have a student (Ben) to perform drafting and design, he has committed up 6 hours per day if we keep him busy. We need design concept sketches from participants for ideas and direction.
Some data was collected from the vehicle. Weight on front axle: 110 kg. Weight on the rear axle: 180 kg pounds. Total empty weight: 290 kg (640 pounds) It was weighed using a bathroom scale placed under each tire with a slip sheet that allowed the suspension to fully relax. It was then re-measured with the scale under the axle centerline (this should result in a sum of the two tire weights). The variation in data indicates the measurements are accurate to +/- 5.0%.
Initial thought is to get the weight under 500#. We will need to do some engineering calculations to verify the assumption that there is benefit and to quantify that benefit. Weight loss will affect; acceleration (F=MA), will affect hill climb speed (climbing is an acceleration upward, countering gravity which is an acceleration force downward), and maybe top speed if we aren’t topping out the max engine rpm and CVT gear ratio (friction or rolling resistance is a function of weight, surface texture, and contact area). We can lose some weight immediately by eliminating the redundant structure in the frame. (Ben will identify those redundant members and calculate weight loss with our current data).
Consider a hammock seat. It will save weight (how much?) and will be more ergonomic. Drivers mentioned discomfort from the hard seat.
Consider placing smaller wheels in the rear (increases torque but decreases top speed assuming we are reaching maximum rpm and CVT ratio). Increased torque will improve acceleration. Larger wheels on the front will reduce resistance when we bounce over obstacles such as rocks. Changing wheels may be a budget issue, the bolt circle is not the same for the front and rear wheels. However, one wheel is dented so…..
Steering ergonomics. The driver has to be able to reach the top of the steering wheel while wearing the wrist restraints. One full turn from center to stop (two turns from full left to full right) is probably adequate if the driver can reach the entire wheel (Ben can start an ergonomic model to identify where the steering wheel/seat should be placed). The ergonomic model should also include the 5% to 95% of persons and show how we address that.
Turning radius. Calculations indicate the existing turning radius of the inside tire is about 30 inches. The outside tire is about 72”. The team has agreed there may not be much to be gained by decreasing this. We need to verify the calculation reflects what the car was actually doing (see maintenance issues).
Maintenance issues, things to fix:
· The rear bearings still allow some wiggle.
· Kink in the front wheel brake line.
· Dented rim (from the flat tire event?)
· Steering interference. A front brake caliper protrusion seems to be impacting a suspension bolt head. It takes some force to overcome this interference. During the maneuverability event, we may have only been using partial steering capabilities.
· Investigate why our hill climbing ability (as reported by the driver) deteriorated during the endurance event. Dirty filter, slipping or overheating CVT belt, weight from mud are all possibilities that have been mentioned. Backing up during the endurance race is apparently considered an “assist” so backing up and getting a run at it is not a good idea.
The design goals continue to be:
· Lose some weight, but not so much that we lose stability.
· Improve the turning radius (possibly just fix the interference).
· Improve ergonomics (the driver has to be able to turn the steering wheel quickly from stop to stop, right now he has to do the quick shuffle).
· Sling seat design.
Adhock meeting 7/5/16
This was a basic review of the above information, as well as a discussion of our performance in the 2016 competition. In a nutshell, our performance was acceptable in the dynamic events, we did poorly in the static events. To prepare better, we will want to meet weekly. Next meeting is Thursday, 7/7, at 8:00 am in Shop 116.
Engineering. We only received 10 out of 150 points. All design decisions have to be made based on quantifiable data (better, faster, stronger, cool, are not quantifiable). If we establish goals, use quantifiable data to design to achieve those goals, build the prototype, then test to see if we achieved our goal, we will get most of the engineering points. Strength of materials, budgets, time, shop capabilities, costs, are all quantifiable should be considered when making decisions. This competition is not about how well we engineer the car, it is about the process we use.
Sales – This is a hypothetical situation, we make a professional presentation to potential investors who might buy our design. We have to tell them why they should invest in our car. We need to know our market, are manufacturing process (how do we make 2000 cars per year), the cost to manufacture and how much can we charge for a car (profit), etc. The panel is generally comprised of engineers, business representatives, and manufacturers. This is probably the only place where “cool” might get us some points.
Cost – Our car was expensive. The cheaper the better, is the way to go. Don’t use expensive materials when a cheap material will do.
Endurance race – our top speeds were up there with the leaders, our additional weight and wheel base (our car is a little bigger than most other entries) added stability on the rough course. Acceleration was probably a little slow, but once we were up to speed we had a lot of momentum to ride over bumps. A problem occurred with climbing the hills, the cars performance deteriorated and we were black flagged about half way through the race due to our slow hill climbing capability. This problem seemed to get worse as the race progressed, an investigation as to why still has to be performed. (extra weight due to mud, overheating and slipping CVT, clogged air filter, are a few of the suggestions).
Hill climb – acceptable performance, but we went slow. We were able to compete early because we passed the technical inspection on the first try, hence the hill was still fairly damp and solid. Later in the day, it dried out and got chewed up. As it was, we weren’t real fast although we ground our way up. Less weight or better gearing ratio could help with this.
Acceleration – Acceleration was acceptable. We were within 1.5 seconds of the leaders so we got points. If we lose weight, acceleration will improve. Force = Mass x acceleration. The force is given by our engine horse power, so lightening the Mass will improve acceleration.
Maneuverability – room for improvement here. We have a transmission with a reverse gear which allowed us to complete the course, but it takes time to stop and back up. Decreasing the turning radius would allow us to zip through the turns. Accelerating faster out of the turns would also help. Acceleration is a function of mass, the turning radius is a function of the steering angle of the front wheels and the length of the wheel base. Other student suggestions have included steerable rear wheels (might be interesting) and independent braking of wheels.
Suspension and traction. We did well in this event. Our heavy weight kept the car stable and gave us good traction.
Rock climb (there was no rock climb at the last event, but there might be one at the next).
The conclusion was to develop quantifiable goals for the following.
· Lose some weight, but not so much that we lose stability
· Improve the turning radius
· Improve ergonomics (the driver has to be able to turn the steering wheel quickly from stop to stop, right now he has to do the quick shuffle).
Goal for the next meeting: review these notes and goals, and assign people to come up with some quantifiable goals for the above three design improvements. How much weight should we lose, and why. What should our turning radius be, and why. How do we want to eliminate having to shuffle the steering wheel in a turn (we already know why).
SAE BAJA DESIGN and MANUFACTURING COMPETITION BACKGROUND
Any student can participate, all you need is enthusiasm and tenacity. It is still early, but we intend to design, build, and compete in the 2017 SAE Mini Baja competition (Yes, I know, this is for 2016. The 2017 information has not been published yet but it will be similar). Events in which we compete (some of these are pre-requisites to the dynamic events, but you can think of them as events that are pass fail) generally include the following:
Engine inspection (pass/fail). This is to verify there has been no tampering of the engine, and the engine is running properly. We aren’t allowed to work on the engine, so it is essentially Briggs and Stratton’s responsibility to make sure it runs properly.
Design presentation (15%). Here is where we get to show off our final product, and explain our design process, our design and performance goals, and how the final product meets those goals. It is also an appropriate place to discuss our testing procedures, describe failures or design weaknesses, and how we redesigned as a result.
Sales Presentation (5%). This is a sales presentation to an imaginary business entity to convince them to invest in our product. We must answer the question: Why should they invest in our car instead of one of the other 100+ entrants?
Cost analysis (10%). Don’t use expensive materials if the cheap materials will do the same job.
Technical Inspection (pass/fail). This can be difficult to pass if we don’t follow ALL the technical specifications for the vehicle. These requirements are published by SAE, and although sometimes vague, they are NOT open to interpretation. Don’t fall into the trap of thinking that as long as we meet the intent of the specification, or do something better, that we will pass. We don’t know the intent of the specification, so it is fool hardy to even try to guess the intent. As with any designed and manufactured product, it must meet the LETTER of the specification. If we don’t pass the technical inspection, we aren’t allowed to operate the vehicle, therefore it is imperative we pass on first inspection which gives us plenty of time to participate in the dynamic events listed below. The more time we have, the better we perform.
Hill Climb (7.5%)
Traction and Maneuverability (7.5%)
Rock Crawl (7.5%)
Endurance (40%). This is the 4 hours of the driver trying to break the car.
The above events and percentages may change from year to year.
Our tentative design schedule for the 2017 competition is as follows:
Vehicle preliminary design: Spring (2016) and Summer quarters.
Vehicle final detail design and redesign as necessary during manufacturing: Fall quarter
Vehicle manufacturing: Fall and Winter quarters
Vehicle testing and competition: Spring (2015) Quarter.
Any students interested in participating should contact one of the faculty advisors and we can make it happen. You can get as involved as you like or for as long as you like. You can design or manufacture (or both) a single part, or be involved in the entire design, manufacturing, assembly, and testing of the product.
Ron Raty – Technical Design
Al Kitchens – Welding
Guy Houser – Composites
Doug Beck – Machining
All designers and manufacturers will be responsible for knowing the rules and design specifications for the product. Failure to follow these rules will result in our team performing poorly in the competition and potentially elimination before the dynamic events. As in any design and manufacturing process, the team members have to meet the product specifications or their product is rejected, and this is no different. There is no such thing as making it up as you go along. Designing a product that meets the intent but not the letter of the specification is also unacceptable (we don’t know why some of the rules are what they are, so we as designers don’t necessarily understand the intent). We have to comply with the specifications, even if we disagree with them, or think we can do better. Compliance is mandatory. Therefore, all participants are responsible for being familiar with the rules and specifications (some participants have to know them better than others). All of these specifications can be found on this page: http://students.sae.org/cds/bajasae/rules/
We will potentially be looking for students to lead in the following tasks. Keep in mind, we don’t have to build everything. Many parts can be purchased, but we will have to design to accommodate those off-the-shelf parts.
· Vehicle concept design (establish goals and general appearance, key to the Design presentation)
· Roll cage design
· Forward Frame
· Aft Frame
· Suspension – Front
· Suspension – Back
· Engine mount and drive train
· Cockpit ergonomics (Seat design and mount, control locations)
· Electrics : brake lights
· Electrics: engine kill switches
· Body panels
· Body graphics and numbers
· Safety systems (harness and extinguishers)
· Engineering (crunching the numbers)
· Accounting (key to the cost reports, and maintaining our budget projections)
· Quality control and coordination
· Project administration (Design Document management)
· Marketing strategy (key to the Sales presentation)
· Project management (key to developing the schedule and budget, and keeping the project on track)
· Driver and backup driver (We only have 10 horse power engines, your weight and size is a factor here)
· Tool and parts management (making sure we get the parts and tools we need when they are needed, and that project tools don’t disappear).
Depending on the design goals, some of these tasks may not be necessary, and there are probably other tasks that will be identified. Students can take on the responsibility of several tasks, but don’t bite off more than you can chew. All designs must be justified quantitatively. For example, It isn’t good enough to use a material because it is stronger than what was used before, or make a change because it is better. We have to predict how much stronger, and is the additional strength really necessary, and is it worth the additional cost. And after it is built, we have to test to verify that we met the goal (prediction).
Check back frequently, this page will be updated as more information becomes available.
2016 entry. This and other photos and videos can be viewed on the common drive/Tec-D/SAEbaja