How to Calculate Motorcycle Girder Suspension Trajectory?

[fslflint]

hello all

I am in the midst of designing a motorcycle that I will be building. one of the things I would like to do is use a girder style front suspension with unequal length links. I am attempting to design it to have minimal variance in rake and trail, with trail being my chief concern.

a couple years ago I had to temporarily give up my pursuit of an engineering degree because of financial matters. I am learning first hand how much information is lost when you don't use it.

I sat down to try and write a simple spreadsheet program that would map the trajectory of the motorcycle suspension while still allowing me to manipulate variables such as suspension link length and spacing. I quickly hit a brick wall. now I'm drawing a blank as to where to begin.

below is a simple drawing that shows the variables I would like to use. could somebody point me in the right direction as to how to write the formulas and equations to get a graph of the trajectory of the centerline of the axle?

a few things I forgot in the drawing.
A=180mm
F=27mm

 

[fslflint]

I took a step back and took a break from it. then everything just clicked. I sat down at the computer and had everything working within a couple hours.

now I have a working spreadsheet ap that let's me change the top and bottom girder lengths, pivot distance both front and rear and the beginning angle of the lower link. it graphs the trajectory just like I wanted.

 

[oswaler]

Hello there,

It's great to see your enthusiasm for designing and building your own motorcycle. The girder suspension with unequal length links is definitely an interesting choice and I can understand your concern with minimizing variance in rake and trail.

In terms of calculating the trajectory of the suspension, there are a few key factors that you will need to consider. First, you will need to determine the forces acting on the suspension, such as the weight of the motorcycle and the rider, as well as any external forces such as bumps on the road. These forces will affect the suspension's movement and will need to be accounted for in your calculations.

Next, you will need to determine the geometry of the suspension, including the lengths and angles of the links. This will help you determine the position of the centerline of the axle as the suspension moves through its range of motion.

To calculate the trajectory of the suspension, you will need to use equations from classical mechanics, specifically those related to motion and forces. These equations will help you determine the acceleration, velocity, and position of the suspension as it moves.

I would recommend starting with a basic understanding of Newton's laws of motion and kinematics, as well as researching suspension design and dynamics. There are also many resources available online that can help you with the specific equations and calculations you will need for your design.

I hope this helps point you in the right direction. Good luck with your project!