2024 PDR Notes

LHRS 2024-2026 Mechanical PDR Notes

Dynamics

Suspension - Kinematics

• Make sure to reevaluate bump steer considerations

  • Not just when wheels are pointing straight, but also at steer

• LOOK AT ZOOM COMMENTS FOR MORE DETAILS

Suspension - Bell Cranks

• Consider the pivot bearing stack up

  • Should consider running bearings over bushings - tapered or roller bearings

  • Off axis load vectors for manufacturing tolerance in Ansys

• How much misalignment can you have with the shock/bellcrank connection

  • Make sure to consider during manufacturing and making the jig

• Motion ratio looks to decrease as bump increases

  • This will cancel out the progressiveness of the shock

Suspension - Carbon Fiber Pushrod

• Be sure to consider the joints and inserts

  • Chicken pins

  • Make sure to determine the weight of the two options before going with carbon

• Combustion was doing buckling tests, didn’t have buckling tube failure, it was that the adhesive sheared and it would start to flail

  • Adhesive still matters and pure buckling of the tube will probably not be the main failure mode

  • Best bet is to do empirical testing

• CF in compression is weird

• Make sure to verify truss solver

Suspension - Rear Trailing Arm

• Need to implement method to adjust toe and camber with the trailing arm

  • Can’t rely on perfect manufacturing

  • Eccentric bolts will help with this - pushes the bolt up and down and forward and aft; pushes mounting spots up and down and in and out simultaneously (make sure Brian does not have a problem with it)

  • To measure alignment, you can use strings, have to figure out a datum for a center to alight wheel to centerline, use toe plates in the front (tells tow between the wheels, not to the centerline of the car)

• 100 thou wall thickness as a guess - the singular tube will bear all of the load of the tube, need to make sure that tube can handle torque

• There will be a significant challenge with getting the two mounting holes to be concentric with each other

• It would be good to be able to adjust the ride height at the rear

  • With coil shocks can adjust the preload

  • Same progressiveness might be a good idea between the front and rear for the pitch and roll

Suspension - Shock Selection

• Look at other comments

Suspension - Control Arms and Apexes

• Put more thought into how you will jig the control arms

• Didn’t actually have much issue with warping of the bearing bore during welding

  • Heat sinks in the bearing bore while welding

• Outsourced apexes will still require jigging

• Why mild steel over chromoly?

  • There are some issues with chromoly having loss of strength with welds but you will have a thinner tube wall thickness - chromoly is the better option

• Make sure positioning of the snap ring grooves are correct

• If you use a high misalignment spherical bearing it won’t clear the ring

  • There are specific high clearance internal snap rings but you need to be aware of the actual travel and misalignment

  • You’re going to have less misalignment than what the bearing specifies because of the snap rings and spacers

Steering - General

• How are you considering steering efforts

  • You need to know the gear ratio before designing the gearbox

• Need to reconsider why you’re using a gearbox

  • Gearbox is a whole can of worms and is difficult to implement and maintain

  • If you can find a way to use u joints

• You’re in a good position to

• Might want to consider angling the steering wheel more (like a 45 degree angle) - this will allow you reduce perceived steering effort and bring you to the range of angles where a stack of u joints is usable

• The cardan effect can help you ; end of travel doesn’t matter except at the u turn test

• Make sure the inserts are a through hole

• Brian puts emphasis on…

• Static friction makes driving more difficult

• Look at Chris’s other comments

Steering - Rack Selection

• Make sure to compare steering ratio with what you did last year to have a reference for what the steering ratio and effort are

• Steering lever length is a big factor, rack speed affects how fast you turn but you can have a combo of rack speed and steering lever length that can affect steering ratio (rack speed is not the only large)

• You can do FDB with torque at the wheel with tie rods resisting that torque to determine steering effort - everything is just a torque

  • In the past we had static friction at the wheel

Steering - Bevel Gears, bearings, and shafts

• key way depth looks pretty close to inner diameter of the tube - keyway greatly reduces strength, so you might want to reduce inner diameter of tube

• Why tapered roller bearings?

  • The tapered bearings are overkill - will also have a lot of drag in those bearings

  • All of these components might make the assembly quite heavy

• Make sure you properly characterize the loads going through this assembly

  • It seems you are designing backwards - you need to characterize the loads first and inform the design based off that

• You have a twisting force but how much of those loads are actually being transmitted to the bearings

  • Thrust bearing and washer handles the axial force

Unsprung - General

• Beware of steering compliance with outboard steering arm

• Refer to Chris’s Zoom comments

  • Actually prefer having a hub and axle so that the hub doesn’t take as much of the bending load - the axle will take all of the bending load

  • Separated the bearings axially as much as possible with the bearings on top of the contact patch

Unsprung - Hubs

• Seem difficult to manufacture

  • The lightening pattern for the brake rotor carrier will require a very long and thin end mill

  • Make sure to turn the spindle and wheel locating in the same operation

• Spindle calculation

  • Have you considered camber deflection under loads

  • Hub seems very cantilevered - will cause some issues with interferences especially with brakes

Unsprung - Uprights

• Consider having ears instead of the current caliper mount design

  • Consider just using lugs for caliper mounting

• Make sure to put more thought into the wheel cover

• The pickup should be a fairly simple part; implement the angle in the upright itself to make the pickup easier to manufacture

• Hole in steering arm will be hard to access

• Understand the drawbacks of setting camber at your outboard pickups vs inboard

Unsprung - Tire Selection

• Michelins are a good alternative

  • Michelins don’t last as long

  • The Shinkos have much more grip, very noticeable compared to the Michelins

Unsprung - Bearing Selection

• Bigger bearings are worse for rolling resistance

• Consider reamed holes and

• Double row angular contact bearings work pretty well

  • It’s just one package with two rows that are spread pretty far apart; can be relatively heavy

• Is there a reason for having the bearings so close together

  • The load sharing between the two bearings are very small

  • The reason you use two is so you’re not driving the moment on one bearing, but since the bearing is so close together it eliminates that purpose

  • Zero benefit regarding camber moment as well

• Preload sensitivity was very bad with tapered roller bearings

• First determine overall geometry of the system

  • What is bounding your problem, then determine the loads, then start thinking about geometry and bearing

Unsprung - Brakes

• Why are you not taking the max load case from the tires

  • You are designing with a level of conservation way higher than needed

• Brake FEA approach is a little simplistic

  • Contact stress from buttons with uneven load sharing between buttons

  • Need to couple this with hand calcs

• You’re going to have to waterjet the button locations undersized and then go back and precision machine

• Contact stress is greatly affected by the width - sensitive to the thou

• Manufacturing brake disc introduces a lot of challenges

  • Cast iron will probably only work if it was fully machined

• Need to consider more than yield and ultimate stress when choosing material

• Water jetting introduces a lot of micro cracks, and cast iron is very brittle

• Has had good results with 4130 or 4140 waterjetted and precision ground

• Go from the tire and understand what pad compounds; don’t over caliper yourself

Body

Frame - General

• Review Zoom comments for more

• Have you looked at tubes getting crushed because of the thinner wall thickness

  • Start with a hand calc looking at the contact area

  • Can run FEA with a split face and force being applied there - ask Jacob for more details

• Ask Nathan and Jacob for their comments, as I was not able to write most of their comments down due to a technical difficulty

• Has the truss solver been validated

• Might be helpful to have the bottom tubes be rectangular for ease of setup on the optical table

Frame - Egress

• Don’t limit yourself to a top load roll hoop. If you want weight reduction you could do so by making a more compact roll cage with forward loading

Frame - Roll Cage & Occupant Cell

• Split top roll hoop might bring up issues with Bill and Brian

• Make sure you have something keeping the head of the driver from moving side to side outside of the roll cage

Frame - Material Selection

Frame - Tabs

Frame - Simulation

Frame - Jig

• There can be a lot of slop with the jigs mounted on the vertical t bar, especially at the bolts

• How are you going to be sure that the tab placements and angles will be achieved with the jig?

  • Keep in mind that the 3D print has a tendency to warp

• Is there a reason why you’re only constraining the T bar using two L brackets?

  • There is a torsion aspect

• Two free spinning ends with a locking mechanism might help with accessibility 

Ergo - Driver Positioning

• Current driving position seems uncomfortable

• Clarify the reg about the angle of the seat back

Ergo - Steering Wheel

• Why no 3D printed components? Making a forced CF still as some challenges and touching CF is still not the most pleasant

• We might drop weight by a little, but CF can be a little finicky, so is the upside enough to outweigh the downsides?

• While the test part you made was fairly easy, complexity will increase as the contours and size increase

Ergo - Pedal Box

• Introduce a spring and mechanical stop in the middle so that on a certain regime the spring will compress which will provide force to the calipers

  • Make it position driven rather than force driven

• Keep in mind that welding will normalize the aluminum (no longer T6) and drops the yield strength by 5 times

• Make sure to be mindful of the connections so that when the driver egresses, they don’t rip them off

• Beware of the adjustability - this will lengthen the driver changes and will probably send you back to the garage instead of staying in the pit wall for the change

  • Consider just having one position and narrowing the median of drivers, at least on a yearly basis 

  • This also puts loads on the pins, not only are the pedals going to take the load. You will have to do more FEA to assure the pins won’t fail

• You should reconsider not having a belly pan under the pedal box - might not be allowable by regs too

Ergo - Belly Pan

• Be mindful of the foam compressing

• Critical fasteners for the ones fastening the belly pan - need to have a locking mechanism

Ergo - Seat

Ergo - Ballast Box

• Make sure to look at the hinge and hardware ratings to make sure that the ballast won’t fly out by a hardware failure - look at the loads and run hand calcs

• Make sure that the ballast box is accessible by the driver during the swap or accessible with the canopy open so you can swap ballast at the pit wall

  • Consider having a hole at the top of the box so officials can see what ballast is in the box; just make sure the hole is not large enough for the ballast to come through