Help me achieve perfection - WR450 twin Adv conversion

Discussion in 'Some Assembly Required' started by MotoPolo, Apr 22, 2016.

  1. Salsa

    Salsa Long timer

    Joined:
    Dec 12, 2006
    Oddometer:
    1,014
    Location:
    Arizona, Alaska, Kalifornia
    Don't fall into the trap "Stronger is Better".

    Remember the very stiff MotoGP bikes that were unrideable (or at least uncompetitive BECAUSE they were too stiff in some directions).

    Race cars have crushable and tearoff pieces to soften the blow to the driver. It is applicable to motorcycles too.

    I try to build my motorcycles to destroy the MC but cause less damage to me in a worst case crash. I have never tested them a worst case, and I expect the destruction of the frame in a lot lesser crash. But I light LITE !!!!!

    At 82 years young, I can't lift many street bikes.

    Don
    JagLite likes this.
  2. Son of MotoPolo

    Son of MotoPolo Yay, mountains!!

    Joined:
    May 1, 2016
    Oddometer:
    74
    Location:
    Sonoma, CA
    My sentiments exactly, I like the way you think!
  3. PHX_Joe

    PHX_Joe Adventurer

    Joined:
    Oct 11, 2016
    Oddometer:
    41
    If you install hoops and nickel plate, be prepared to be stopped and asked, "What's that?" even more than you already will. Very cool build.
  4. Son of MotoPolo

    Son of MotoPolo Yay, mountains!!

    Joined:
    May 1, 2016
    Oddometer:
    74
    Location:
    Sonoma, CA
    What's going on where these tubes cross? I think you said you got away with no cutting, but are thy contacting each other? Brazed together?

    delete this pic.PNG
    invisa-bill likes this.
  5. MotoPolo

    MotoPolo So many places, so little time

    Joined:
    Jun 4, 2015
    Oddometer:
    391
    Location:
    Portland OR
    Hey Son

    Yes they "kiss" each other and will be a full brazed joint plus "U" shaped gussets (4) forming an "X"
    JagLite likes this.
  6. MotoPolo

    MotoPolo So many places, so little time

    Joined:
    Jun 4, 2015
    Oddometer:
    391
    Location:
    Portland OR
    Well I felt a bit sheepish about the question of "to brace or not to brace", Or how I spent my weekend:

    I decided that such a question really deserved some honest engineering, so I invested about 20+ hours this last weekend in constructing a finite element model (FEM) of two frames. I found a trial version of a FEM program (CADRE Pro) that is quite capable and pretty user friendly. I've used it before but they used to limit how many nodes the trial version allowed. Now you get the full program but limited to 30 "openings" of the program on your computer (HINT: don't close the program or turn off your computer).

    For those not familiar with FEM suffice it to say that it is the standard structural analysis technique in use today and is used to design buildings, bridges, space stations, F1 cars, motorcycle frames, etc, etc. I would offer two cautions to those that might want to rely on a FEM for analysis of something like a frame: 1) Have a solid background in structural analysis before you start (or be willing to learn); and, 2) have a known solution (or truth) against which you can compare your results. I was lucky to find a paper comparing an FEM model of a motorcycle frame in torsional load against a real world test of the frame in torsion. The paper is well done and the testing was done on a high quality test rig that applied a torque load to the steering head and measured the frame deflection.

    The test frame was an aluminum motard frame with perimeter upper and a single central downtube. Measurements were made with and without the engine in place. The paper didn't say which motorcycle was tested but it looks to be a Honda 450 single.

    Capture_MC_torsion_Test.JPG

    The published test results for this frame were: 1050 NM/deg for frame only and 1320 NM/deg for frame plus engine. They also built a detailed FEM model of the frame and got 1170/1380 NM/deg. A pretty good validation of their model.

    I first made a model of my WR 450 frame. I did this to compare my model results with the paper's test results. The perimeter frame is beefy compared to the WR which is pretty much all in one plane so I expected the test frame to be much stiffer than the WR. I was looking for validation of my FEM model to see if I was in the ball park.

    Here is my model:

    Capture WR frame model.JPG

    The blue pyramid represents the "engine". My results were 573/831 NM/deg. That seemed pretty reasonable to me. So I build a model of the new frame:

    Capture MP frame with curved struts.JPG

    The results for this frame were: 470/1550 NM/deg. So the frame alone is less stiff than the WR. I believe that as the new frame only has the two tubes to resist torque at the upper rear engine mounts. The white structure forming the bottom hoops is a bolted-on 7/8" tubing which doesn't add much stiffness. With the addition of the engine the stiffness more than triples. I'm not sure how well the engine mounting is modeled but because it is a larger engine and has more mounting points, a delta increase above that of the test frame is possible.

    Well this is all interesting but really only serves to say that I have confidence that my FEM model can tell me whether "to brace or not to brace". I decided before I ran the model test that a 5% increase in torsional stiffness was worth the hassle of adding the braces. The results:

    Remove the curved braces and stiffness decreased by 6.7% . So the curved braces increased stiffness by 6.7% over no brace. Good, that justified my curved braces.

    For fun I replaced the curved braces with straight tubes - increased stiffness by 9.2%. Well we all thought that a straight tube would be better, but for a lot of reasons already mentioned that is not an option I want to pursue.

    I thought just for fun what would a short straight tube do, tangent to the apex of the curve. Warning playing with FEM models can be additive - it was now about 5 am .

    SURPRISE!! - the short tube increased stiffness by 9.8%. Just to be sure I didn't introduce something in the model I removed all braces and was back to the no brace results. The only explanation I have for why the shorter tube is stiffer than the longer tube is that it supports the downtubes about halfway between the frame crossing and the engine mount. This also happens to be where the downtubes take a bend and may stiffen up that bend.

    So in the end those nice curved braces I worked a day on will not go on the bike - just some short tubes that took half a day as I had to check that the valve cover could be removed.

    I think the prize has to go to Jays100 who said:
  7. jays100

    jays100 Been here awhile

    Joined:
    Aug 1, 2006
    Oddometer:
    125
    Location:
    CT
    Solid engineering, well done!!!!!

    And, you've not altered the geometry so handling is predictable in that it'll be similar to the donor bike. But, with CG (changed with the heavier motor) you may have a bit more body English (=mass placement) to get it into a turn. Should be more fun than a barrel'o'monkey's, I can't wait to see this thing fly!
    MotoPolo and outbacktm like this.
  8. JagLite

    JagLite Long timer

    Joined:
    Jun 17, 2010
    Oddometer:
    5,202
    Location:
    Anchorage Alaska
    Very interesting! :clap
    Excellent modeling and write up. :thumb

    I still prefer the curved tubes because they look elegant and add strength without adding a hard point mid tube.
    The straight tubes make it more rigid certainly, but some (limited) flex is good for the frame to avoid cracks at the joints.
    We design a lot of bridges where I work and we always have to keep in mind how the bending will affect the joints.
    It can be designed so it is rigid but that is never the best way for real world design so we design how we want it to flex, and how much.
    The reality is you will never need the extra strength and if you were to cartwheel it down a mountainside the braces won't make a difference when it is totaled.

    Many think "triangulate" when designing and that is very good, but really we should "pyramid" for ultimate strength.
    A 3 sided pyramid is incredibly strong when the correct material is used, but also has no give, no flex.
    It will not deform (unless the connections are designed for it), it will break.
    That's part of why beam frames are not designed as a 3 sided pyramid from the steering tube to the swingarm with either a double top tube or using the engine as the bottom of the pyramid.
    It is too stiff. (this is my opinion, worth whatever anybody will pay for it :hmmmmm)

    Whatever you do it will be excellent!
    MotoPolo and outbacktm like this.
  9. Son of MotoPolo

    Son of MotoPolo Yay, mountains!!

    Joined:
    May 1, 2016
    Oddometer:
    74
    Location:
    Sonoma, CA
    This :deal
    CitrusBobiel likes this.
  10. CitrusBobiel

    CitrusBobiel n00b

    Joined:
    May 2, 2018
    Oddometer:
    1
    Location:
    Pittsburgh,PA
    Hi everyone. Long time listener first time caller.

    I like this point.

    The curved sections should spread the energy around the structure. That engine will add enough rigidity to the frame for us mere mortals.:gdog

    Also, totally enjoying all of this great information. :beer
  11. totensiebush

    totensiebush re-tarded

    Joined:
    Feb 17, 2006
    Oddometer:
    227
    Location:
    Alameda, CA
    With the straight tubes I assume you'll be gusseting it, which can be challenging to model in FE.

    I assume you modeled the engine as rigid, is that correct?
  12. MotoPolo

    MotoPolo So many places, so little time

    Joined:
    Jun 4, 2015
    Oddometer:
    391
    Location:
    Portland OR
    Jaglite and others - Great points on structural design - it is not always or only about stiffness - a lot of factors to consider. Your pyramid example is a great one - I plan on using that again.

    So it is a toss up on curved vs straight brace and the only fair solution is to build two frames - one with each - my next frame will use the curved brace - I had already tacked in the straight ones. FE analysis is an art and the difference between the two is probably within the margin of relative error.

    The straight tubes are coped and brazed but no gussets. Yes the engine was modeled as a rigid lump.

    I am flattered that so many of you like the curved braces - they did look pretty cool - oh well next time.
    JagLite likes this.
  13. MotoPolo

    MotoPolo So many places, so little time

    Joined:
    Jun 4, 2015
    Oddometer:
    391
    Location:
    Portland OR
    Been working on the engine mounts. Got my metric reams in and made up the mount. I am using what I call a flanged shoulder bolt (full diameter just under the head, some refer to them as chassis bolts), and reamed inserts to take the slop out of bolted joint and increase stiffness. These bolts are stock Yamaha but they are hard to find, if you know of other sources let me know. The tube frame racecars and aircraft all used AN bolts which were available in any grip length needed, and had the precision non-threaded diameter. Does anyone know of a metric equivalent to AN?

    These are the front engine mounts

    IMG_2524a.jpg
    Son of MotoPolo, JagLite and nuggets like this.
  14. jays100

    jays100 Been here awhile

    Joined:
    Aug 1, 2006
    Oddometer:
    125
    Location:
    CT
    heh, heh, hardware porn.
    love it!
    will look for the hardware.
  15. jays100

    jays100 Been here awhile

    Joined:
    Aug 1, 2006
    Oddometer:
    125
    Location:
    CT
    not including links as unfortunately bolt suppliers have their own naming convention. some list by coarse or fine, others by size/pitch - so didn't do the link to any specific bolt.
    at each addy, search command as "metric flange bolt" and filter from there.
    www.asmc.net
    www.Ti64.com
    www.tyfasteners.com - these are an offshore supplier (shanghai)

    mcmaster does have flanged bolts in metric, but only in coarse thread. the picture above looks to be a M10 x 1.25 x 40mm lg?????? not in mcmasters, their M10's are all 1.5 pitch.

    i think there are other, bigger, domestic bolt suppliers in metric but they didn't come up in my initial search so obviously, didn't include.

    if you want the AN equivalent, oh boy! part of the search convention could include any variation of 12-pt, 12 point/12-point, double hex...... and, they come in at 190ksi strength so that could be a search criteria too. do you really need that (grade 12) bolt?

    conversely, the typical stainless steels will come in at 140ksi and should be good for all use except head bolts. pay attention to lubed thread/flange and preload (installation torque) - the manufacturer will publish their recommended holding torques based on installation torque (moly is recommended but motor oil, or, ATF if you don't have anything else) never, ever, dry.
  16. MotoPolo

    MotoPolo So many places, so little time

    Joined:
    Jun 4, 2015
    Oddometer:
    391
    Location:
    Portland OR
    Those TI fasteners are really hardware porn

    Didn't see what I need - may have to use Yamaha stock