2017-03-25 EOT Mechanical Team Review

What races are we going to

• • Where can we test the car before competition
  • We want to make the car more modular to bring it to future competitions
  • The main differences between competitions is that WSC is older so has more defined rules. 

4 pillars of the mechanical design

• Efficiency most important
• Car that is modular and can easily be fixed/taken apart (no weird positions to remove battery box or other parts)
• Manufacturability, based on our capabilities. Try and get sponsors where necessary

Vehicle architecture

• Space frame
• Rear section is entirely for aerodynamics and to store battery box.
• Rear roof portion will lift up and the rear bottom panels will drop out for easy access to the battery box
• Have storage in the front
• The weight is currently around 500kg, but will hopefully come down to 400kg. The largest amount of the weight comes from driver/passenger but it is necessary to have a certain amount of weight due to regulations.
• Motor requirements: Reviewed parameters in power point. The battery pack should story 16kWhr and the array will produce 1kW. Values listed in slides have some idealization but also some deficiencies. The car will just barely make it up a 5% incline, but is not the absolute maximum.

Chassis

• Began by considering constraints, the main concern was the 5g impact it needs to withstand from all sides. You can do a unibody, monocoque or space frame. Steel space frame seemed more durable, easier to simulate, and easy to obtain materials. The space frame is very reliable in what the final product will look like, makes it easier to determine mounting points.
• Catamaran reduces the CDA by a significant amount.
• Design originally looked like baha but needed to be changed due to catamaran. Members were able to be removed when they were found to be redundant.
• Design is rollover protected.
• Steel was chosen such that students could weld
• Heat treating is not necessarily necessary. It would make it better, however the difference is marginal. If our safety factors come out lower, we should heat treat, but if stress is low enough we will not need too.
• Welding jig will be done ourselves, but Adam will be key guy for welding.
• Using static structural studies on Ansis for analysis. Tube thickness are smaller in simulation than they will be in reality, mostly used for seeing what is under the most stress.
• All tubes will be round except where suspension must mount.
• Looking into measurable stiffness (torsional stiffness before a driver will notice on an FSAE car: 1400Nm/degree)
• To come up with design: First looked at general shape of car, didn’t need to extend to rear. It needed to fit the right height of passenger. Then needed to spec out the hoops, then moved to the front (Where does it pinch in). Then hoops specked to fit the suspension. Next took into account catamaran. Finally looked into what would help for attaching things. Currently looking into how to reduce weight, by adding thickness and removing redundant members.

Aerobody

• Coming in on the conceptual side of things
• A lot of inspiration from sun swift
• Want to make it look more like a car than a spaceshift
• Started with surface modeling of the entire car, a lot of trouble getting nice surface
• Switched to Rhino because it is more for design.
• Built a clay model mainly to understand the side profile
• Looked into the CFD model in fluid. It is very complicated. Looking at the drag coefficients. We should be using it to model small bits at a time, don’t get too caught up in it

Suspension

• What it is: How your tire wear, makes life nice for driver.
• Goals: Want it to be functional. Good balance between driver control, how it drives and wheel life.
• Look into the camber, caster, toe and travel ratios. Because the car travels on real road ratio should be 60-40.
• A couple options for both front and rear suspension. Ideally the rear wheels give no camber.
• Front suspension: simpler to go with dual a-arm
• Went with spherical bearings because ball joints are hard to find specifics.
• Ideally the suspension should bottom out before the rod ends.
• The control arms are designed to take very little bending.
• Geometry is determined by end fittings
• Want to CNC the clevis’s here. Get the upright done professionally.
• Using QA1, race grade
• Anything that is rotating should not be a bottoming out or topping out point
• Motors are going to come with integrated brake disks Mitsuba
• To be worked on: weight reduction, twisting, add some kind of a brace
• Thought we would be able to get plastic bearings, might not work out.
• We went with 1 degree positive camber, better for corners
• Caster dictates how much the wheels inherently what to return to their original position. In a normal car they are typically extreme
• Research and Analysis: working on a handling model and finite element analysis. Looking at all of the forces using a model. There are a series of required data and inputs. Looking into steering angles. Should look into worst case scenarios.

• Objectives: How do we want the car to perform? Needs to make tight slow turns, 8 meter turning radius with a large factor of safety as well as highway steering.
• Options: Go with parallel, perfect ackerman, more than perfect ackerman, rear or front steer. Decided on the 100% ackerman, because there was no reason to do any less than that.
• Defined all geometry with trig. Notable values, is we have very long tie rods.
• Upper and lower control arms are parallel. In order to minimize bump steer tie rods should be as horizontal as possible
• Part Selection: Going all off the shelf
• Have a rack extension to shorten the tie rods, however short tie rods might not be preferable. You'd get a lot more bump steer
• The catamaran makes things difficult
• A universal joint is needed in the centre
• In order to not spear the driver, a collapsable steering column was looked into, however the universal joint might be able to be used. The collapsable column would be good for adjustability

• Objectives: To design a system to stop a car at highway speeds
• Lot of discrepancy between ASC and WSC
• What pressure is needed to stop the car, what are the parts needed to achieve that pressure
• Options 1 (chosen): Front/rear breaking
  • Calipers on all four wheels, balance bar for less pressure on rear wheels
  • Issues with line length and pressure maintenance
  • Difficult math to calculate breaking system
• Parking break needs to be operable by driver and stop car on a 20% incline
• Most parts sourced through Willwood. Break disk manufactured
• Math done. breaks are sufficient to close car.

• Must not be anything like MS XI doors
• 150 mm of compressible material inside the door
• yield at 5g impact
• designed to be structural with metal members in the door
• door will be made of multiple panels
• suggestion: interior panels attached via velcro
• Suggestion: mount doors to top chasis members
• The hinges should be mounted beside the chasis so the door does not pop into the occupant cell during a collision
• further inquiry into where the intersection point between the 150mm of compression (door) and the window most be done

• Vibrations may distrub/disrupt the already non-horizontal battery box
• a more defined latch is required
• Could be slotted horizontally as the box should only be accessed when the back suspension is in neutral position
• a Redesign of the battery pack using spot welding needs to be done
• tesla uses special fuses between modules
• spot weld leads to batteries, and solder the leads
• applying a bus-bar between each battery module
• strips to connect each battery cell, and a tag to connect a bus bar
• Two overlapping zinc tabs just coming out of each module
• Don't put bad polarities near each other. over time the plates will compress and go boom.
• DO not use 8020 as it is extremely heavy
• we hope to use teklam for the entire box

• ASC regulations say the max weight for battery box is 20kg
• Where are we going to put ballasts? Must be within 30cm of the driver’s hip. Looking at either in front of driver, or beside them (on catamaran thing). Most likely will go with front.
• The battery pack seems huge in comparison to the array, how do you charge it? At WSC you are allowed to charge overnight
• There will be steep hills at WSC, and the max hill grade found for ASC will be 7%.
• Most cruiser class vehicles drive around 80km/h. This makes most sense for energy consumption
• If you are going too slow during the competition, you will be asked to put your car in the trailer to keep up with the pack. The amount of time spent fixing the car on the side of the road will be factored into your average speed for the day. Basically you need to keep up with the back.
• We have a fire research institute we might be able to use for testing.
• Consider making a scale model and putting it into the wind tunnel. Better than the simulated model.
• Where are the main horizontal roll bars?
• There was a rule at one point that the role bar had to be separate from the chassis, is this still a regulation? – Actually need a roll cage, it should be within the 50cm regulation, because of space frame, it all gets combined into one.
• Nate believes chassis weighed less than 100 pounds on MSX (student welded)
• How does the battery pack attach, should have attachment points
• Occupancy is not a problem to fit height of a passenger but in terms of width it is cutting it a lot closer.
• Keep in mind lines of sight
• The key crush zone is the side impact
• Keep in mind, the diagonal member in the front looks great. Try to do that more. There doesn’t seem to be a lot of stiffness across the car (side to side) right now.
• Continue to think about access points and attachment points
• The goal is for the battery box to be stable at any angle.
• The reason behind having a shorter chassis is to reduce weight.
• The battery kind of only really needs to be 50% within the frame. The question is do you bolt angles to support it at a 90% angle or on a slope?
  • Don’t spend time on the fancy bits, make it work first.
  • Make sure to pay attention to seams
  • How do you attach the panels together…. Potentially just use cocking to waterproof it. Could think about cutting out teeth on each panel. Also drip tray panels
  • Having the drip tray design would add more stiffness and would make it last longer as things warp
  • Zeus fasteners are a pain to install
  • Where are the cut lines going to be because it changes the strength but also drag
  • Don’t put a seam right at the front
• Carbon fiber vs fiber glass??? Just take whatever your sponsors give you
  
  • Keep in mind hard stops
  • Think about magnetic flux
  • Don’t go with door flaps because they’re a pain in the ass. Make it as simple as possible.
  • Look into a continuous curve for the torques
  • Look into large versus small changes in the acceleration. Perhaps characterize the roughness of the road.
• Set up a gyro in the centre of the car so we can get a lot of useful data in terms of building future cars.
• Where to mount the lower and upper steering column?
• What to do about driving on the left side of the road? Egress on the left side?
• Consider angling the tie rod. S-shape?
• Where will be put all necessary signage on the car?
• asc requires the event sponsors name to be on the front
• requirements dictate we need a plate (aluminum?) for the floor of the car
• temperatures can reach 50 C in wsc
• exposed metal can become extremely hot in the cockpit, therefore it is recommended we minimize the amount of exposed chasis members