Taking a break from swingarm alignment issues, I decided to move ahead with choosing the rear suspension specification and layout. I had 5 different single shocks to choose from, ranging from a big-wheel pit bike through KX250 MX and finally a Huski 610 unit. I measured all the springs and calculated their spring rates.
I also created a small excel sheet with all their dimensions eg. stroke, length OA, etc.
For the first time ever, I decided to use Google's AI option, to determine which shock unit and the "best" mounting position. I was truly surprised how well this worked, sort of like having a really quick and very clever offsider in the workshop with me, to bounce ideas and do the calculations quickly.
Some of the dimensions are fixed, swingarm length, rear tyre diameter, lower shock mount rearmost position (to clear tyre) and practical height above the swing arm centre line. Estimated sprung weight of driver and Kart (200kg wet) and estimated weight distribution (60% rear). I had already chosen the swingarm pivot height, (for anti squat), the rear travel (125mm), sag (30%) ground clearance at full bounce (25mm).
It works through things quickly and raises points where it thinks their might be issues with the practical layout.
I told it that the vehicle was a tadpole trike CycleKart and it got a bit worried about the seat height & clearance above the shock top mount. I said that I am sitting in front of the firewall and referred it to the Stevenson Spec. It thanked me, and brightened up about the project. It doesn't have emotions, but does appreciate clear instructions. It says that good spelling and punctuation are useful and so are politeness and thank-you's as they let it know it is giving you a useful result.
Now that all sounds wonderfully quick and easy, but it took several sessions, as we refined various requirements. It will tend to provide the a 'correct, but very basic' result initially, unless given more specific criteria. for example, I wanted to maximise a rising spring rate, as this is a non-linkage setup (for simplicity). It also got very specific about the need for adjustable spring preload as the chosen shock was a slightly lower rate than 'Ideal'. It will calculate good initial settings. At the conclusion of the analysis it produces a workshop list of all the specs and (x,y) locations for the mounts (0,0) is the swingarm pivot. The Pro version (free, but limited use) can even prepare a dimensioned schematic sketch. Paid versions can do CNC or 3D printer files. All in all, I was very impressed.
PS. Don't let your Kids/Grand-kids waste their time & money becoming Doctors or Lawyers or Engineers. The World has changed!
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