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Thread: UTAS build thread

  1. #1

    UTAS build thread





    Dear Sir, Allow me to share with you a small window into our fine (safe) workshop. Please comment and tell us how to design the complete rest of the entire car. Thankyou kind sir.

    I'm not going to tell the whole story here. But with constructive comments, more photos will follow.

    Introduction: none
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    Attached Images
    Last edited by Jonny Rochester; 03-18-2014 at 07:50 PM.
    University of Tasmania (UTAS)

  2. #2
    One comment and one question

    A chassis is just a big bracket that is supposed to
    a) respect the rules especially safety
    b) sustain the forces coming from the tires
    c) hold all the elements such as engine, diff... and driver
    d) with best possible ergonomy
    e) with the best compromise between weight, minimized compliance and manufacturing cost

    So the comment is that it is difficult to evaluate your chassis on these pictures without
    1. Seeing all the suspension pickup points
    2. Seeing the engine, diff, master cylinder, pedal box, seat belt, steering column, steering rack, radiator, wings (if you have) maybe even bodywork parts attachment, etc mounting points
    3. Having an idea of the targeted weight and torsional stiffness (at least by calculation)
    4. Knowing your targeted wheelbase, tracks, weight, engine choice and aero configuration
    5. Knowing your tire choice (at least sizes)

    I would prefer to see a design (elaborate CAD or simply a good complete sketch). Can you do that? (I hope you have not started to manufacture your car without having finished most of your car design; that is the trap in which 90 % of the students fall)

    The questions (which I remember my mechanical engineering / design teacher asked me many years ago);
    1. In your opinion what is the weakest point in the chassis? (I can already see a few even without the suspension and other elements pick up points)
    2. If you have decided not to improve this weak point (points), what is the compromise that you have made to accept such a weak point?

    I wish more students would post such pictures and drawings and ask for observations. It is courageous and helpful for the whole community.

    These are my first observations. I am sure other experienced person (I am mainly thinking of Pat Clarke and Geoff Person aka Big Bird and Tobias but also several good alumni) would come with many other valuable comments.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  3. #3
    Thankyou Claude,
    I joined the team as a student, after some other final year students had already done a chassis design (they imagining side engine). Initially I had to go along with them until I had done my own research. After visiting FSAE-A and spending the summer TIG welding this chassis for them, I have guided the team to a rear engine traditional FSAE setup. With the chassis in place, we have spent some time sitting in it, getting familiar with all the components. Design work continues in Inventor, but I like to play with the real thing. Now after measuring some stuff and looking at it, I have led the team to change the chassis design. A few weeks ago the CAD was looking like this:


    The front of the chassis will be changed to comfortably fit the 350x350 template in the leg area, with a steering rack on the floor, and the pedals on a sliding false floor. The first design was not designed around many components...

    The side intrusion section may get some extra bracing, thinking of torsional stiffness. But how stiff is stiff enough? The students here like the idea of FEA, I'm a bit old school myself.

    The engine is a single 450cc, from a BMW G450X dirtbike. Has this engine been used in FSAE before?

    Tyres will be 20" x 7"? - 13" Hoosier. Wishbones and pushrods, FSAE by the numbers as far as possible.
    Attached Images
    Last edited by Jonny Rochester; 03-18-2014 at 07:54 PM.
    University of Tasmania (UTAS)

  4. #4
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    Johnny,

    Further to what Claude says, I have two comments.
    A very common error is to build the chassis first and later adapt it to fit steering, suspension, powerplant etc. This 'adaptation' always adds complexity and weight and usually reduces stiffness and access. The chassis is a bracket to hold everything together and actually should come later in the Design process.

    Secondly, and potentially more serious.

    It appears your roll hoop has a welded joint at the top of the chassis (It might be an optical illusion). The rules require the hoop to be bent from a single tube, going from the bottom of the chassis at one side and across to the other. If your hoop is welded on top of the chassis, it will not pass tech inspection and will not be allowed to compete. :-(

    Where will you put the steering rack? remember, your chassis must pass the 'template' tests.

    Regards

    Pat
    The trick is... There is no trick

  5. #5
    The error of building the chassis was beyond my control, as I tried to say. But also, it's not such a bad thing. Consider that most teams build a mockup out of wood or PVC tubes. It only takes a bit more to build the real thing. All the better for practice welding. A grinder can cut that thing in half very very quickly. Not too hard to change... And we build workshop skills in metalwork, not woodwork!

    Another idea: Only since we built this chassis, we had a physical object that people could visualize or identify. I believe it helped assemble the team, having that physical thing. In a new workshop, you know it takes about 2 weeks just working out where the light switches are and where the tools are kept. For myself and the students (most are not tradesman) it's good to just start making something, anything.

    The main roll hoop is 1 piece.

    Steering rack is top secret.
    University of Tasmania (UTAS)

  6. #6
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    That is good news. I had visions of you having to throw it away and start again.

    Sorry I missed your earlier comment that the rack will be on the floor =]

    Pat
    The trick is... There is no trick

  7. #7

    I cut up all the wishbones from our 2002 car. We will use the same again, different dimentions. I am recycling some spherical bearings and tubes. They are 3/4" 4130 lower tubes, 1/2" 4130 upper tubes. Lower bearings are 7/16" Aurora, all 3 joints. Uppers are 5/16" bearings, all 3 joints. Bearings are held in a bucket with circlip. I have got the workshop to make new buckets on the CNC, but I will recycle some tubes with bearings still in them if I can.


    I did a test weld on new CNC buckets to check the bearing clearance after welding. It will be a small clearance fit with bearing retainer and circlip.


    I attached the front upper clevis to our new frame, saved from the old car.
    University of Tasmania (UTAS)

  8. #8
    John,

    - Again it would be nice if you can post several drawings of the whole car with steering rack, steering column, engine mounting points and engine components (inlet manifold, exhaust), differential and its attachments points on the chassis, fuel tank, seat belt anchorage points, suspension and damper brackets, etc....

    - 7/16 and 5/16 joints ...Oh my God... Are you building a truck? Is your car going to be 500 kg? How did you come to this rod end or spherical joint size choice?

    - Not sure In understand the tube between the chassis and the suspension bracket

    - Do you machine the hole for the spherical ball joint before or after the welding of your wishbone? Do you use one shoulder and one circlip or 2 circlips to hold the spherical ball joint in its housing?

    - Where in your opinion is the weakest point in your chassis? In other words in normal racing conditions and /or in case of crash / impact where would the chassis bend or twist or break? What would be the conditions in which these damage would occur? How did you come to these conclusions?
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  9. #9
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    NSW, Australia
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    Jonny,

    Just a couple of comments:
    -The front roll hoop looks pretty tall, not sure if that will make bodywork a pain/unattractive
    -Not sure what you (?) are sitting on in the first picture but you might have trouble with helmet clearance
    -Why did you build the lower chassis section as a ladder?
    -As far as I am aware, no-one has used the G450 engine. I've read they are built by Kymco in Taiwan and have regular rebuild intervals (correct me if I'm wrong)
    -Do you have experience tuning a 450 single? Many teams have struggled to get theirs working/starting reliably (although the dry sump and factory fuel injection will probably make things easier...)

    I definitely agree that it can be a massive leap forward to just build SOMETHING and go from there. Certainly a good way to get morale up and get people involved. Claude, I would argue that to a certain extent it's not a bad idea for a first year team to 'build first and design later'. If nothing else it stops people from getting trapped in the 'optimisation' loop during the design phase, and gains a very valuable practical insight.
    Jay

    UoW FSAE '07-'09

  10. #10
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    A few more comments Johnny.
    The inner location of your front wishbones will significantly compromise your suspension geometry. Have you designed your suspension (Uprights etc) yet)
    Mounting the clevises to the sheet metal extensions will materially affect the installed stiffness of the chassis.
    The bend in the upper cockpit rail will murder the beam stiffness (already marginal) of the chassis.
    Why was it necessary to add the additional bay to the rear of the chassis (first to second picture)?

    To address some earlier points.
    I agree the dashboard bulkhead is probably too high.
    We have seen the BMW engine used in Germany.
    Ultimate chassis torsional stiffness may not be as important as some might believe. 1000ft/lbs per degree might be a figure to aim for.

    Pat
    The trick is... There is no trick

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