Position of muffler in our car

[Divas]

Hi,
We are facing difficulty in placing muffler. We have routed out 3 positions as you can see through pics attached. Can anybody help us in what should be best possible placement of muffler.
Is it considered a safe practice to keep muffler in position-2?

[Jay Lawrence]

I'd use position 3. Position 2 is potentially too low (and given your sump it seems you aren't too concerned with CG height), and position 1 will probably melt your CV boot.

Who are you, which uni are you from? It's not very hard to make a signature.

Kudos for sending pictures and making an effort though.

[Freddie]

I'm agreeing with Jay, but look at angling it a bit more to make sure that it doesn't restrict suspension movement upwards. Also, why not have it forward pointing with an angled end piece?

[Claude Rouelle]

I know your topic is muffler but from the pictures I see there are serious design and manufacturing issues in your chassis and rear suspension.

Is this a car you already compete with?

And BTW who are you? Not worth to introduce your self?

[Jay Lawrence]

Forward pointing is another option, as Freddie says, but just be aware that it may not be allowed through scrutineering. There was an issue at FSAE-A recently where a scrutineer decided it was unsafe to have the muffler exit in front of the driver and teams had to modify their mufflers to suit.

Claude, it indeed looks a mess (toe control, mega rocker posts, diff poorly constrained, stock sump (!!!), lacking rear bracing, and more) but I don't think it's anything that will stop it running (the first goal). Of course I could be totally wrong

[Divas]

Thanks a lot for help.
Claude, It would be very kind of you if you point out some of the issues in our design too. We have not competed yet with this car, but going for FSG 14.

Jay, Vehicle is kept on stands, so sump height seems to be a quite higher, but in actual it is not.

Btw I am Divas Gupta, senior year Mechanical Engineering student at IIT Delhi and Team captain of AXLR8R formula Racing.

[Claude Rouelle]

Divas

Just the "punches on the face" observations from your pictures

- Lack of triangulation of the engine bay and rear bulkhead

- Forward pickup point of the rear spring/damper unit not connected to a node of the chassis

- Very weak resistance of your differential forces / torque. I can see the bottom and top tube of the rear bulkhead easily bending

- Huge bending compliance of the tube-axis of the rear rocker so far away from the chassis node.

- Rear toe link axis not passing through one of the chassi node.

- The whole thing (chassis, tools, stand, ground, walls) is dirty. It poorly reflects on the your team image and discipline.

I am in the simulation software business so I am for simulation but I am still amazed that students try to use CAD and Matlab and Adams and so on without first performing sound, simple engineering design, starting with the very basic of forces distribution (load patch as we call it) from the tire contact patch to the chassis. It seems that those basic things are not taught in classes anymore. You car looks like many FSAE / FS "Lego cars": you put things together: a wheel here, a engine there, a tube here, and a rod end there without looking at global functionality and how much compliance you will be creating.

Most of this design type end up with not only weak but also heavy chassis. Lose-lose situation

That being said you are not the only one making these mistakes. I do congratulate you for putting these pictures on the forum and daring to ask for critics. I hope you will learn from it.

[Claude Rouelle]

Divas (and other inexperienced students)

As I was focusing for the chassis design gaffes pictures, I missed the major issue: YOU STARTED TO BUILT THE CAR WHILE THE COMPLETE DESIGNS WERE NOT FINISHED. iT IS NOT NOW THAT YOU SHOULD WONDER WHERE TO PUT THE EXHAUST. iT IS AT THE TIME OF THE CONCEPT AND THE COM-PLE-TE CAR DESIGN THAT SHOULD HAVE WONDERED THIS QUESTION.

That is a typical mistake made (at different intensities) by 90 % of the FSAE/FS teams.

Too late now. Back to the drawing board. Quickly; you already lost too much time.

Good luck!

[Jay Lawrence]

Divas,

I was referring to the fact that you are running a stock sump (by the looks of it). This causes the engine to be quite a bit higher than it could be (something to rectify for next years car). For this year though, make sure you have oil pressure logged to determine how suitable that sump is for working at various g's. If it is not suitable, make sure you have a plan for a sump baffle (something like a 'cage' with holes in it that aims to retain some oil around the pickup during high acceleration loadings).

[Divas]

Thanks Claude for your feedback. This is one of the thing our team lacks during designing. These all suggestion would help in design of next year car definitely.

Jay, You are right, We are using stock sump. Thanks for helping us in this regard.

[Claude Rouelle]

Divas,

I need to understand

The car of which you showed pictures from... Is this a previous 2013 or older car or is it the car you intend to run at 2014 FSG?

[Divas]

Claude sir, We intend to run this car at FSG 2014.

[Claude Rouelle]

Divas,

I do applaud your efforts and your willingness to learn by participating to the FSG. I wish you could participate to FSI first but that that will only be in 2015.

Please take the next question as a help to you and to the community, not as finger pointing; you ask yourself where to put the exhaust now so apparently you did not ask yourself that question while you were still on the CAD software or the drawing table. Is this correct? If so why?

Next, as much as you will take risks by showing your weaknesses and expose you and your team to criticism by showing more pictures and/or design of your car, I really encourage you to so and to do it as early as possible so you can modify the car before it is too late (imagine you would have a structural weakness that you not allow you to pass technical inspection; it would be sad to do the whole trip to Germany and not participating to the event); you will learn a lot from it. You can't solve a problem unless you know you have one.

Sincerely,

[Claude Rouelle]

Divas, It is Claude. Not Claude sir. Please. Thank you.

[Divas]

Claude, Actually our team did not have precise CAD of the engine. It is very difficult here to get CAD through reverse engineering, so we made approximate model. While designing, we considered 3 possibilities as shown in pics too. According to our calculation keeping muffler in position 1(below rear bulkhead) could help in less flow losses and less weight of exhaust assembly compared to other positions, but as you know, our team does not have a very experienced feedback while designing and most of the team keep muffler in position 3 just above suspension control arms, so we wanted to take feedback from experienced ones about different position of muffler and its global compliance(like muffler can heat up drive shaft boots in one case, which is not required).

Regards,

[Divas]

Claude,
I am sharing some more pics of our car assembly. I welcome your feedback as our team definitely want to learn and grow despite the criticism faced.

[Ray19]

Hi Divas,
Like Claude said above, I think it is great that you are open to criticism about your designs. I saw a few errors in those models I would like to point out.

1. The front bulkhead of your car seems pretty low to me. I am guessing the nose cone will be even lower. Please check if your nose is going to hit the ground when you try to jack up the car from behind.

2. Main Hoop Bracing support should triangulate back to the lowest point of the main hoop according to the rules if I am not mistaken. Please check for the rules and make sure you correct it.

3.The dampers are not connected to the chassis at a node and I can't make out clearly but maybe the bellcrank isn't mounted on a node either. These are huge design errors that are frowned upon.

4. Again I can't seem to make out clearly but the differential mounts are also mounted in between a tube and not on a node. Another big design error as the tube will probably not like those bending forces on it.

My advice would be to do a thorough rule check of the CAD model and iron out any errors you can find first.


P.S.- These are solely my opinions and not of my team or my university.

Regards,

[Jonny Rochester]

Apart from what is already mentioned, this looks like a workable design (partly because it is the average of many other designs = reverse engineering).

As for the rear rocker not being on a node, I would not worry so much about that. It is on a short tube, the pivot is near a node. However your post that mounts the rear rocker is too long. That mounting post should be very short.

For your steering column, consider another support that mounts the intermediate shaft (between the 2 uni joints).

Your front shock mounting at the top is the biggest problem. It is mounting in the middle of a long tube.