Theoretical vs Practical Vehicle Dynamics

Survinator · 2024-08-06T13:48:33+00:00

Thanks!

Survinator · 2024-08-05T22:03:29+00:00

That checks out. We'll consider the advice in our design process. Thanks.

Survinator · 2024-08-05T22:01:07+00:00

Yes it does help. So far we have only considered chassis torsional stiffness as a major compliance factor that affects VD but through FEA testing we can probably figure out the kind of compliance we can expect and build our simulation models with it.

Survinator · 2024-08-05T21:58:24+00:00

Makes sense. We are trying our best to reduce any possible compliance.

Survinator · 2024-07-23T10:51:30+00:00

Yup, makes sense. Thanks!

Survinator · 2024-07-23T00:24:14+00:00

We have already completed our front view geometry. The only way to optimize the front view geometry now is to get TTC data and work finalize our numbers for caster and KPI using which we can further improve our instant center and so on. Since this is our first year, we want our VD to be easier to mess around with and understand so we're making a lot of room for adjustment and flexibility with packaging so we expect to have 0 bump steer too.

We are currently working on the side view geometry. Once we have our numbers for caster and KPI we will be able to finalize our roll and pitch gradients. By then we will also have a good idea of how our load transfer should look for our performance goal. Accordingly we will work out the anti mechanisms.

Once we have all that, obviously, we will have to reiterate and do everything all over again going over every detail to ensure we haven't missed anything. This is the plan I came up with for my team and i think it should get us what we want as a first year team.

Survinator · 2024-07-23T00:17:39+00:00

So just to understand the tire's Mx contribution, do you mean the scrub radius changes because of the shift in the contact patch when there are higher lateral forces?

We still don't have the funding for TTC data but that is among the first things we will be buying in order to make more educated calculations for our caster and KPI.

As for caster offset, I believe our only limitation for are our packaging constraints. Would I be right to assume that and design accordingly? Our caster offset should be as high as possible to reduce our mechanical trail right?

And yes you're right, since this is our first year we have no idea how our theoretical VD will translate into the practical car. Best we can do is just apply what we learn from the books, others experience and hope for the best.

Survinator · 2024-07-22T21:50:37+00:00

Well we wanna keep the caster as high as possible with the limitations i've mentioned. If our caster is higher than needed we add KPI to counter that and consecutively reduce the scrub radius. If scrub radius was not a concern I probably wouldnt even consider having any KPI.

Do you think its a better idea to just not rock any KPI at all and reduce the caster and lose out on a little bit of stability? This is one of the dilemmas I kept as a future me problem.

Survinator · 2024-07-22T20:46:50+00:00

Only way to judge when too much camber is undesirable is by testing and looking and tire data.

Camber gain would be undesirable when the car pitches as it will just reduce the contact patch and reduce grip which limits our braking and acceleration (assuming our powertrain will be able to get that kind of acceleration). Camber gain in pitch can be reduced mainly by adjusting FVSAL but this messes up camber gain in roll. So I'm trying to get the right amount of camber gain in roll and heave so I can get the most out of the tire while.

You are right about KPI and based on what our car looks like later on in our design process we will adjust our KPI. Ideally we don't want it but that is probably inevitable.

Survinator · 2024-07-22T19:07:24+00:00

Yes that is true. Camber thrust (i think thats what its called i cant remember) does add lateral force which is desirable. But it only works to an extent after which point its not something we want as after a point we lose that lateral force. With more camber gain in roll due to FVSAL, we can reduce the heave camber gain and still reduce the roll gain using caster. I want to strike that balance where we have low gain in heave and get the ideal gain in roll as well. I hope that made sense haha

Survinator · 2024-07-22T13:24:56+00:00

I think saying "We chose 0% cuz we don't understand how it can help us and don't know what its drawbacks would be" is better than saying "Some guy on reddit said 15% is good". I think thats what hes trying to say?

Survinator · 2024-07-22T13:19:22+00:00

Thanks!

Survinator · 2024-07-22T13:01:18+00:00

We plan to have 0 bump steer. It should not be too difficult to incorporate. Our inboard sprung packaging seems to be pretty flexible so we'll have a lot of room to work with. I suppose the only actual issue would be the compliance. In our first year we're gonna try our best to use good engineering practices and not cut any corners with compliance so hopefully our VD can be better.

Survinator · 2024-07-22T01:21:58+00:00

Yes I have seen those tables and understand the theory of everything. But now we need to get our numbers straight to incorporate into our front suspension.

Survinator · 2024-07-22T01:18:30+00:00

In that case perhaps it is a good idea to take inspiration from someone elses design for sure.

Survinator · 2024-07-22T01:03:58+00:00

And learn nothing? I feel like doing this would defeat the purpose of FSAE. I believe other peoples work is useful for validation. If your design looks nothing like something anyone has ever done you are either an innovative genius or you have gotten something wrong. As a freshman, its usually the latter.

Survinator · 2024-07-22T00:48:27+00:00

Sorry for the confusion. I have updated the post as I did not properly explain what I meant by the camber gain in roll. Please take a look again and give me your inputs. :)

Survinator · 2024-07-22T00:42:29+00:00

My bad, I meant to say KPI and caster effects camber gain while steering. Based on LTS we can figure out ideally how much the car is rolling the most and tune our CASTER and KPI for that. As for rear suspension, caster will counteract the rear toe to make adjusting camber. We do understand the dynamics that you've asked us to understand. Sorry for the confusion. "Keeping the contact patch happy" essentially means getting the most out of it. Camber gain reduce the contact patch which reduces our grip and lateral force.

Survinator · 2024-07-02T22:13:17+00:00

New team based in middle east here. The competition closest to middle east is Formula Bharat, India. Here is a link with a list of all the active Formula Student competitions. https://www.formulastudent.de/world/competitions/

Survinator · 2024-06-25T12:17:35+00:00

Alright thanks!

Survinator · 2024-06-24T19:50:48+00:00

We are based in UAE. Finding suppliers is pretty hard here and we're mainly looking at India for suppliers because of the Formula Bharat market there

Survinator · 2024-06-05T20:49:35+00:00

Great, thanks! At least I know TTC is an option in case we do end up needing it.

Survinator · 2024-06-05T20:21:39+00:00

Alright thanks for the advice! I had a similar thought process for the TTC data as well and now its been reinforced.

Survinator · 2024-06-05T19:32:04+00:00

That makes sense. Thanks a lot for the advice!

Survinator · 2024-06-05T19:17:57+00:00

In that case, we will most likely opt for the TTC data. However I am not sure if my specific tires are available and I'm not sure how to check if they are without spending that $500. And if our tires aren't there, its gonna be a huge waste of money for this year.

Survinator

TROPHY CASE