CG, TW, WB estimations - 9/2024

the damn preview isnt working… ill fix it later -

According to WSC book: determining CG TW and WB can be quite arbitrary. Finding the CG requires overall weight and wheelbase - these two things do not have an explicit method of calculation. They are typically just values estimated from pre-existing designs.

Goals:

• estimate overall new weight

• estimate CG

• estimate weight distribution across front to rear axles

• can get a rough est. of TW if the weight distribution w the assumed inputs are within our goal range of 60-70 front

I have estimated the CG and weight distribution of our new vehicle according to:

1. WSC average values

   1. gave us a range of typical WB

   2. gave us examples of calculating CG distribution

2. pre-existing daybreak weight values and dimensions - VDR

   1. battery weight - 30kg

   2. frame - ~187lbs

   3. 4.5 m length

   4. approx distance of significant masses from front axle

3. system specific goals for the new car

   1. frame weight reduction

   2. occupant cell relocation

   3. 3 wheel assemblies

4. regulations - give us a rough max and a min - regs

   1. battery - 30kg max

   2. max body length

   3. TW to WB ratio 1.5

my inputs:

MASSES (as reccomended to include by WSC):

• Driver + ballast =

• frame = 120lbs

  • daybreak = 828.74 lbs

  • goal to cut by 30% ~

  • also lines up with WSC approx. example

• battery = 30kg

  • daybreak and should stay roughly the same

  • max by regs

• “everything else” approx = 197 lbs

  • WSC

Overall weight estimation:

Distances x from the front axle / nose:

current dimensions:

WSC gives us these distances x from the front axle of all their point masses: they also use the max length of the body 5m and it is alluded that they are modeling a 3-wheel vehicle due to the increased wheelbase and their rough positions of all significant weight factors are distributed with 60-70% of weight to front axle in mind.

To compare the WSC example dimensions to daybreak to achieve the new car design: Daybreak is 4.5m and ideally it does not need to actually get longer. Because the occupancy cell will likely be moved up, cutting the front of the frame that accounts for leg room, and the trailing wheel will need to be moved behind the DB frame; assuming that also the space frame will stay moderately the same in that the crumple zone in the front should stay the same distance: then the body (frame and aeroshell) moves forward in reference to the front axle. Assume the space between the back edge of frame to the end of aeroshell stays the same - as the nose is moving up but still need to account for array surface area requirements.

The average wheelbase according to WSC is 2-2.5m. WSC uses 2.5. Because the current wheelbase is 1.5m, and move the rear axle to behind the frame to act as a trailing arm: the back wheel needs to move at least half the DB wheelbase to clear the frame.

Assume we use 2.25 for the purposes of the CG approximation.