SV650 sidecar - homebuilt leaner

Discussion in 'Hacks' started by Turbomachine, Jul 10, 2014.

  1. Turbomachine

    Turbomachine Stirring the noodle

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    I've been (mostly) lurking here on and off for a few years, reviewing hack builds and designs. My favorite thread on the whole internet is Hacks-n-Pups, and my lab/border collie Bogart loves to ride in or on anything. We hope to post pics there soon!

    I've had a 2002 SV650 since around 2007. Its a fun, simple bike that does a lot of things well. I've only found one other reference to a hacked SV650 on the web, which looks to have used a Ural tub. The frame setup (cast aluminum, under-slung engine) isn't very conducive I guess.

    So I've been tinkering with designs for the last few years on and off, and finally cleared some space in my home projects to get it done. I'm a mechanical engineer by day, but have relatively limited metal fabricating skills. The goal was to do as much of the work myself, and work the design around available purchase parts. I have access to a welder, but didn't want to do mission-critical welding while I'm learning so I'll have a friend do that work (he builds tube frame drag racers). I can do wood and fiberglass so I'll make the body myself.

    Layout of the assembly:
    [​IMG]

    The basic design is to use a subframe made from plate and bar stock bolted to the engine casing up front and a rear mount tab. The front end of the subframe has a clevis mounted up, the rear end has one down, to give the tip-in steering effect. Both are along the bike centerline.

    [​IMG]

    The chassis is all 1-1/4 tube stock, simple ladder layout with the cross-members bent to align with the height of the clevises. The rod-ends are from QA1, pcmr8-10t, which is a 2-piece chromoly unit and has a proof strength of ~17k-lb in the radial orientation. Of course they are loaded in bending, but the nominal 1G load is about 75lb each. The chassis is designed around the Flexiride FR-550S adjustable half-axle, flipped around and upside-down in a leading link configuration. I did this to get the ride height down and the axle housing back under the seat. It will ride on a 15x4 wheel with a Firestone F560 135/15 tire.

    [​IMG]

    For basic design parameters, I set up the car to clear the bike in a 40deg right lean. The car has about 7.5" of ground clearance...one concern is that the rear / lower clevis has only about 3" (loaded). It will only be used on the street, but will be tricky around speed bumps or pot-holes. From left handlebar to fender is 74" wide with the bike vertical. The chassis is 24" long on-center, and the clevises make for a 3.75" difference between front and rear pivots.

    I've made some progress on cutting out the brackets for the subframe and notching the longitudinals for the chassis. But nothing is welded yet, and I'm open to constructive design feedback. My main concerns are the stiffness of the subframe mounts (one is through a solid part of the engine casing, the other is a boss for an exhaust mount), and the subframe ride clearance.

    More pics of the bits collected and cut so far to come later.

    Thanks
    Matt
    #1
  2. FR700

    FR700 Heckler ™©®℗

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    First off, nice bit of legible drafting :thumb

    ... didn't see any notation regarding drawn to scale, so I'm hoping that isn't your planned wheel lead :lol3



    Now, things to consider;

    Leading versus trailing arm, leading will place the fulcrum further back thus pushing more weight to the steer. The more weight in the tub, the more noticeable it will become. If the swingarm is six inches long, this, as you are aware, moves the pivot twelve inches forward from your current chosen location.

    There is nothing to stop you from fabricating a checkout in the floor to accommodate the Flexiride as it will be located under the leading edge of the seat, which in itself will not be at floor level at that point. I've done this numerous times when a lower frame ride height was desired.


    Sub-frame;

    Have you thought of using a central tube in place of the flat plate, then weld a threaded bung in the rear for the Heim, thus raising the connection point.

    Bend the tube to form an 'L' shape for your vertical separation at the front.



    [​IMG]
    #2
  3. Turbomachine

    Turbomachine Stirring the noodle

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    Thanks for your comments and questions...

    The lead is easily adjustable at this stage, but I haven't found any discussion or guidance specific to a leaner on placement of the wheel lead. So I set up the wheel reaction to roughly align with the entire rig Cg, and balanced between the fwd and rear pivots. My impression is that for a leaner the handling will be insensitive to lead.

    Since the rig can't impart any moment on the bike, all of the 15% of wheelbase or whatever # discussion is out the window. A standard rig doesn't steer the tire like this will either, which I'm hoping counters the scrub effect of being a bit more forward. I guess at some point the scrub will increase steering effort. It also will pick up a touch of camber into left turns and lose it into right turns.

    I'd like to hear more on leaner-specific wheel lead...

    I didn't follow the "more weight to the steer". You mean more to the rear? In a free-body-diagram of the sidecar, its the Cg of the load and the positions of the reactions (f/r pivots and tire) that determine the load distribution onto the bike.

    Taking this concept to the limit, the rigs which use a long trailing arm with spring and shock (or even a m/c swing arm) pivot all the way at the end of the chassis, but that doesn't change the load distribution.

    On leading vs. trailing and packaging, with it leading as drawn the axle unit sits right in the crook of the seat, so the cushion would be on the floor. The arm is 4.5" long, so it doesn't move far enough forward to clear the seat, which would then have to be ~2" higher. Not the end of the world though. If I was able to mount the axle higher it would be closer to the sweet spot, as drawn its at the upper limit for initial angle per the manufacturer, and effectively runs more stiff than rated.

    I looked into getting a higher load-rated axle and elongating the arm so I could move the axle unit wherever, but didn't really want to trust welding on that part.

    I did draw up a few of those types, but not with those specific joints. In each case the subframe itself got lower (minus the rear clevis), and I needed some more complicated brackets to mate from the bike to the tube at the front bike mount. I liked the simplicity and rigidity of the saddle type bracket. I also didn't like the pin / shoulder bolt through the heim being loaded in single shear. The rod end is loaded that way but it is quite a bit larger component.

    It could make for a more elegant design, and fix the ride height problem though. Have to think about that.
    #3
  4. Turbomachine

    Turbomachine Stirring the noodle

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    A few hardware pics. My nephew spent the weekend at our house a couple weeks back and we spent some quality time cutting and grinding things to shape.

    I was a bit surprised to find that Amazon has a great selection and pretty good pricing on steel stock. Plus free 2-day shipping with Prime. Its all 101x or A51x steel. The main subframe bar is 1/2 x 3, brackets are a mix of 5/16 and 1/4.

    [​IMG]

    [​IMG]

    [​IMG]

    Not too late to turn the bus if a better design can be found though.
    #4
  5. Feo

    Feo Commentator

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    As someone contemplating a similar fabrication project, thank you for listing steel types and sizes you're using.

    :thumb
    #5
  6. FR700

    FR700 Heckler ™©®℗

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    Extrapolate... sidecar wheel level with front axle of bike...now reverse that scenario and place the sidecar wheel level with the bikes rear axle... still think wheel lead will not play a part even on a leaner ?




    Stop and think about it... pivot wayyyy at the front... now stand on the nose of the sidecar and you'll get some compresion depending on the shock rate- now walk rearwards and watch what the suspension on the bike does.

    Put the pivot wayyy down the back and repeat the previous exercise... then get back to me.

    For reference I've got 64" WB, 10" lead. Passenger seated in tub and the front suspension does not move from its unladen ride height. If I stand on the nose of the tub, it compresses the LL 1/2". If I walk to the very rear the front extends 1/2" and the rear suspension compresses depending on what setting the compression damping and pre-load is set at.

    If you want pic's, look at the ones in my thread.






    The angle of the swingarm is a bonus for the reasons you've already mentioned.



    .
    #6
  7. Turbomachine

    Turbomachine Stirring the noodle

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    This exercise is moving the Cg of the load on the sidecar, by feet. The Cg is the biggest contributor to load distribution on the bike, in any geometric configuration.

    In a free-body-diagram of the chassis alone, the offset reaction due to position of the axle unit is cancelled by the moment created in the torsion spring. In an FBD of the chassis including axle & tire, the location of the axle unit isn't needed.

    On the other topics, I'll think about it and make some sketches. Appreciate the feedback and discussion.
    #7
  8. FR700

    FR700 Heckler ™©®℗

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    Where the pivot point is,and where and how the suspension is designed is what plays a big role.

    It's a sidecar, not a car, everything else doesn't apply.


    I'm out.

    Have fun.


    .
    #8
  9. Hiho

    Hiho Adventurer

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    Having built four leaners now for three different bikes, stick with the 15% lead. It works very well.
    The other measurement to aim for is 32inches between the heim joints and 4 1/2 inches height differance from front to rear.
    Ground clearance from the rear pivot is not to bad as it is usually close to the rear wheel.
    Bias your weight towards the rear for an even ride when cornering. You will find the front drops on left hand turns for you in the northern part of the world.
    Good luck with the build.
    #9
    CFBROWN likes this.
  10. Hellracer.nl

    Hellracer.nl What the hack???

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    :clap:clap
    Another homebuild leaner!
    Welcome to the wonderful world of the wobbly third wheel!
    :lol3
    #10
  11. Turbomachine

    Turbomachine Stirring the noodle

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    I'm trying to work through the physical mechanics of it, independent of what type of machine. I hope it doesn't come across as obstinant, I'm genuinely interested in the "why" and learning to design it deterministically.

    So these questions prompted me to go back and do some homework I should have done from the beginning. My eyeball of the FBD for the chair wasn't very good, now that I've set up a spreadsheet to work through it so I can put numbers to each load.

    In the first iteration the rear pivot(heim) load was actually negative, so it acted in the up direction. DOH! :yikes It took moving the car Cg back quite a bit to fix that. The important relationship is the contact patch to the fwd and aft heim pivot centers. The front view takes just one moment balance to find the tire and total heim load, then in side view that can be resolved to front and rear pivot loads with a single moment balance and the sum from FBD-1.

    RevA aligns with the sketches posted earlier. In other iterations I flipped the axle back to trailing, and started moving it back too. My goal is to get the loads balanced within a few lbs, preferably aft-biased.

    [​IMG]


    A few other observations that I'll come back to later:
    -Motorcycle Dynamics by Vittore Cossalter is an excellent reference for designers. Available on google books http://books.google.com/books?id=rJTQxITnkbgC&pg=PA1&source=gbs_toc_r&cad=4#v=onepage&q&f=false
    -The nominal load on the heim joints is quite low, due to the width required to have sufficient tilt angle on a right turn. I've had to guess at a few values to make this calculation but it can't be off by too far.
    -I've set up another spreadsheet to calculate the lateral scrub and hack turning angle in a few turn scenarios, which led to some interesting results
    -A leaner generates a ton of scrub just due to the height of the pivots above ground, independent of lead. The amount of lead and the height difference between pivots make this worse. I think this scrub due to lean will be much larger than that due to the turning geometry of the bike, but I have more work to do on that. I think that the turning effect due to lean mitigates the scrub, and they are directly related as a function of bike lean.
    -The amount of turning you get from the hack tire isn't direct or proportional to what you really want it to be, for a variety of turning scenarios
    #11
  12. Turbomachine

    Turbomachine Stirring the noodle

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    I don't think I could get 32 inches spacing to fit in the bike. Could probably get a little more than I have, but I already cut the base plate. In terms of turning angle, the 32/4.5 you suggest is pretty close to 24/3.75 I currently have.

    Agreed on the rear ground clearance, I was planning to put that in the layout sketch. Its far enough back it may not change the approach angle to the exhaust (now subframe) for the rear tire.

    Hmmm...hadn't considered the coriolis effect :lol3. As I've got it set up the nose will drop in both right and left turns.
    #12
  13. claude

    claude Sidecar Jockey

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    [QUOTE=Matt Gent;24595795]I'm trying to work through the physical mechanics of it, independent of what type of machine..........(MUST DELETED HERE IN ORDER TO OFFER A TIP RELATED TO WHAT IS SAID BELOW)......................................................................................

    I-ve set up another spreadsheet to calculate the lateral scrub and hack turning angle in a few turn scenarios, which led to some interesting results
    -A leaner generates a ton of scrub just due to the height of the pivots above ground, independent of lead. The amount of lead and the height difference between pivots make this worse. I think this scrub due to lean will be much larger than that due to the turning geometry of the bike, but I have more work to do on that. I think that the turning effect due to lean mitigates the scrub, and they are directly related as a function of bike lean.


    Regarding Scrub: If you really want to get into this from all angles then seriously consider
    Doing a working diagram or two viewed from the front and then from the rear. Do this with the hinge points (pivot points)located in various positions in relation to one another on various planes. I think some interesting variables will be noticed early on. You will also find that a camber curve will be generated to the sidecar wheel which is directly related to the pivot placements vertically and horizontally. There are lots of variables, some which do make a difference and some which really do not in the real world. Paper applications and seat of the pants operation can at times seem to conflict but typically will fall in line once one determines where certain data was not considered on paper. Have fun :D
    #13
  14. Turbomachine

    Turbomachine Stirring the noodle

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    This is exactly what I've done, and turned the diagrams into mass and moment balance equations. The front view and side view free body loads above are a first version, and the leaning & turning one is in progress. The lean contribution is pretty straightforward; the turning one is a bit harder since there are multiple transformations of reference frame required. I think I have it sorted for a zero-thickness front tire, but getting it right for the contact patch rolling up the side of the tire is more effort.

    I'll add the camber curve, that is pretty simple. Unfortunately it will add camber for both left and right turns, but I think the steering (toe) adjustment is more important than the camber, so I'll keep the pivots under the bike centerline.

    One other general observation:
    -For a leaner, the sidecar + rider Cg is pretty far away from the bike. This leads to the low pivot load noted above, but also contributed to needing to shift the Cg aft as mentioned by Hiho and seen in my spreadsheet. If you draw a line from the tire contact patch to the front link, the car & rider Cg needs to be behind this line, but fwd of the line to to the rear link. This becomes a pretty narrow triangle.
    #14
  15. Turbomachine

    Turbomachine Stirring the noodle

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    This was more trigonometry than I've done since college. In the end I mostly use the equations from the Cossalter book for the motorcycle side, then used that as inputs to move the sidecar chassis around.

    Now is the hard part in establishing limits for certain parameters (like scrub), or trading some against others. After working through this I'm convinced the leaner generates much more scrub than a fixed rig. Dynamically, at speed, this must be countered by the steering effect (and the time/distance over which the bike leans into a turn), but could still cause a problem in parking-lot type maneuvers.

    I don't expect anyone to digest this right away. I wish it could be checked as there are tons of sine/cosine equations and I'm sure there's an error in there somewhere. But all the numbers look reasonable compared to the Cossalter charts.

    [​IMG]

    Nomenclature for results:
    Req'd lean = simple frame angle required for equilibrium
    Frame lean = adjusted for tire width (contact patch movement) & Cg height
    Lean scrub = lateral scrub of rig due to lean component, at rig tire contact
    Lean turn angle = rotation of rig tire due to lean
    Steer scrub = lateral scrub of rig tire due to bike steering geometry
    Steer turn angle = rotation of rig tire due to bike steering geometry
    Vertical Turn = theoretical angle for a zero-rake tire to turn through prescribed radius

    The spreadsheet is set up to simulate 8 different turning scenarios at different speeds and turn radii. This generates the bike lean and handlebar turn angle which are used for the sidecar motions. Cases 1 and 7 are highlited as 1 is low lean / high turn angle and 7 is high lean / low turn angle. In addition to the scrub & turn values I was looking for, it also generated the motorcycle pitch angle and rig camber (requested by Claude).

    Then I plugged in the design revisions A, C, and E from the earlier post which have different lead % values (plus baseline 0 and 15%) and was able to populate this chart for turn cases 1, 5, and 7.

    [​IMG]

    Even a zero-lead sidecar will scrub over an inch for high lean angles, and 15% over 2", but somehow from this I need to determine where to establish a working limit.

    This could also be done for other parameters. The key ones to move would be the height of the sidecar pivots (higher = more scrub), differential height of pivots, and length between pivots. It can only calculate as of now for pivots on the bike centerline.

    I also need to make sense of the sidecar steering angle, and the difference it generates to the theoretical vertical turn angle. Any difference will generate a side load on the bike

    Last one for now, I laid in the subframe drawing on top of the rig to determine what the road clearance would look like. It clears a ~5" obstruction with a ~10deg approach angle. I think that will work fine for roads around here, and I'll just take it slow over speed bumps and humps anyways. The centerline shown runs through the pivots and intercepts the ground aft of the rear tire. Moving this intercept fwd or aft by moving pivots has a leveraging effect on the scrub and turn.

    [​IMG]

    Since I can no longer put the axle unit behind the seat, I'm considering raising the sidecar chassis up one or two adjustment angles on the trailing arm to get it more into the happy zone. I liked the look and low Cg of the earlier designs but with this axle unit it is probably not practical.
    #15
  16. Hiho

    Hiho Adventurer

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    Wow!
    I do my engineering by seat of the pants.
    I can tell you that the leaner will scrub tyres out fairly frequently. I get about 4000k out of a tyre, while getting 12000 from the bike tyres.
    I tend to really push through corners and get the bike to drift slightly, which gives some trauma to the hack tyre.
    Low speed in a car park is no problem, where you find a sgnificantly different feel is if you are trying to reverse the rig. The more turn the harder to push, so make sure you dont have to reverse too far anywhere.
    We run almost zero camber, but allow for the contour of the road, and toe in is minimal.
    You may find with the shorter distance between the heim joints that at some point you will experience head shake. It usually comes in at a low speed and you can ride through it easily. Some bikes we have done needed a steering damper, but my Roadliner is hands off at any speed.
    I will be intereste dto see how your engineering design ends up compared to how it rides.
    Good luck.
    #16
  17. cleatusj

    cleatusj Dirt floor engineer

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    I just followed what others had done and used 9" lead and setup for 40 deg. lean and could not find any fault with the way it handled at any speed up to 105 and it didn't seem to slow down acceleration. I changed over to rigid because of all the high speed gravel I ride. I could corner on pavement with most of the fast bunch except for some of the tight low speed corners because of limited lean angle. I lost about 2 1/4" of drop before the floorboards would scrub.

    [​IMG]
    #17
  18. Turbomachine

    Turbomachine Stirring the noodle

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    What kind of tire do you use on the rig? And what kind of road surface is this on?

    Well I've never designed or ridden a sidecar, leaning or otherwise, so I have nothing to compare to. Hopefully its a safe and fun way to take the dog for rides, and if it works for that maybe a person too.

    I took the geometry you provided and plugged it in with my bike's dimensions. Here's a comparison with the RevE status of mine. Top two curves are turn angle and use the right axis; bottom two curves are scrub and use the left axis.

    [​IMG]

    RevE status has about 40% more scrub than yours, and a bit higher turning angle.

    Here's a graphic on the longitudinal Cg location. I've assumed the chassis balances about the centerline of the body (that the axle & tire moment is equal to the long arms on the bike side). There's only about a 6.5" window to place the Cg, so it will be pretty sensitive to axial movement.

    [​IMG]

    I've assumed that a seated rider's Cg is about an inch in front of the belly-button, with legs extended. Couldn't find any values on this on the 'net, but I did find a graphic from a homebuilt aircraft form asking the same question. I may go sit on one of the chassis tubes in the garage and try to find my Cg. In my current state of fitness I'm sure its a bit lower and further forward than ideal :dutch

    [​IMG]
    #18
  19. Hiho

    Hiho Adventurer

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    I've tried Bridgestone 045 and shenko. Get them as hard as I can. Only running 130 wide and have used 110. The narrower the better for less drag.
    I do push hard when riding which doesn't help the life of the tyre, tend to drift it with a lot of throttle through corners.
    Maybe I should grow up? Nah.
    When I've built my chassis I tack them and go for a short ride , this gives me an idea of how it will perform. After building the first two, we knew what worked and so it has been fine tuning for each bike, and improving the look and tricking design.
    These things are addictive, but a great way to enjoy yourself.
    Cheers
    #19
  20. Isoiivari

    Isoiivari Adventurer

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    #20