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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Hello all. First time here. I have a single seater Formula Vee racing car and need help to write a simple program to work out movement of rear suspension. I have limited knowledge of Trigonometry or algebra. Can someone please give me a few pointers to how i can go about this. Rear suspension is basically a triangle fixed at two points moving in an arch. Thank your all. Can provide more information later and maybe sum examples i did in Open Office Spreadsheet.

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**jabah013.307****Member**- From: Kingdom Of Jabah013.307
- Registered: 2021-07-05
- Posts: 165
- Website

Hello Jam Racing,

Welcome to the forum!

Quote Of The Month:

'Whether it's the best of times or the worst of times, it's the only time we've got.' - Art Buchwald.

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 9,518

hi Jam Racing

Welcome to the forum.

Sounds like an interesting challenge. I need more details so I can construct a diagram. Please describe the geometry. eg. The left wheel attachment is point A. The other point B. There's a strut CD that goes from ...... etc etc.

It'll probably take a few posts for us to get to the point where we are both are talking the same problem.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Thanks Bob for replying. X = -14.96 Y = 3.05 Z = 11.22 radius rod attachment to rear of frame

X = 0 Y = 20.87 = 11.22 radius rod attachment to side shaft tube from gearbox

X = 0 Y = 26.37 = 11.22 side shaft tube at wheel end

X = 0 Y = 4.00 = 11.22 side shaft tube at gearbox end

These measurements are in inches as the Q basic program i have been trying is in imperial. But it is for a McPherson strut suspension. Does not give the correct results. Google Adam Aero Formula Vee u will see how rear suspension works. Very simple design. Using VW Beetle gearbox basically.

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

If u load the following coordinates into Interactive Cartesian Coordinates in Maths is Fun u will get an idea of radius arm attachment.

(3.05,-14.96),(4.00,0.00),(20.00,0.00) that does not account for side shaft from gearbox to wheel.

Side shaft would be (4.00,0.00),(26.00,0.00) it attaches at 4 inches form centreline of gearbox at zero to 26 inches also at zero but a high from ground at 11.22 (Z)

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Using the same graph if u entered (4.00,0.00),(26.00,0.00),(20.00,0.00) that would be side shaft from gearbox to center of wheel. The radius arm attaches at (20.00,0.00) which is third lot of numbers here in brackets.

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 9,518

hi

Thanks for the reply. This sort of car is very new to me so I'm on a steep learning curve. I was really hoping for a technical plan and elevation of the struts. Could't find that. The best view I found is this one:

I've labelled three points X Y and Z. Hopefully that makes a start towards some common ground.

My immediate thought is concerning how many dimensions we need to record the position of the key points. If everything is in the same plane then x-y will suffice but the car is three dimensional so I'm guessing the critical parts of the frame are too. You would get better structural support if the struts use three different directions to hold everything together. All in one plane and things are going to bend and break more easily.

So we may need 3-d coordinates, x y and z. That makes the sums harder but it can be done. Years ago I helped a Canadian guy who wanted to drill a slanting hole through a component which had been rotated around three axes. It took a while to get the exact description of what he was doing but we got there in the end. And he learnt how to calculate angles in 3-D along the way.

Is my picture a good one for your car? And have I labelled the right points? Finally what exactly is the problem anyway? what do you want to achieve?

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Thanks for reply. Each point of suspension will have an xyz. X is center of car out to rear or front. Y is from centre out to wheel of each side and Z is height each joint is from ground.

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Picture is perfect. My car is based on that rear suspension. Yes it has to be in 3D. What i am trying to achieve is to be able to know what the suspension is doing through its arch. The rear wheels more through an arch as any VW Beetles rear suspension does. Also how the suspension angles change and whether the wheels go in on bump or out on bump. It helps me to set wheel alignment correctly based purely on exact measurements.

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 9,518

Great! We seem to be making progress.

If you look back to your earlier posts you only gave 2-D coordinates. Please provide 3-D ones.

Question: How does the suspension work. The images I've seen show a piston and coil spring arrangement. I don't see that in the picture. As the car bounces along the suspension needs to damp the up and down movement doesn't it?

Are the wheel rods (XY) independent on each side or does that line continue as an axle right through the engine? What sort of joint movement is there at X, Y and Z? XZ looks like it might be a piston. If so what are the maximum and minimum lengths?

When I've got the coordinates I'll try to construct an end view and plan view of the end of the car. Please also say again diameter of XY and XZ.

Thanks,

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Her they are in 3D

X Y Z

-14.96 3.05 11.22 frame end

0 20.87 11.22 gearbox end

0 26.37 11.22 side shaft wheel end(outer)

0 4.00 11.22 gear box end (inner end)

Hope this helps

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 9,518

hi Jam Racing

Here's a graph with those points. As the z coordinates are all the same it's ok (for the moment) to show just the x-y plane.

I haven't shown the struts actual size ... this obviously makes a difference. I need the diameters.

I'm still confused about how the suspension works. Using A,B,C and D please say which is a suspension strut.

When the car goes over a bump, lets say 2 inch across the track, does the engine bounce up 2 inches as well. If not, where's the damping. And if just one wheel goes over a bump can the suspension work independently on each side so the whole car doesn't lurch over on the track.

And finally, what would you like to do next?

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**Jam Racing****Member**- Registered: 2021-08-03
- Posts: 8

Looking at photo u provided. The radius arms are in silver paint and the side shafts in blue paint coming out from gearbox. What happens in bump is wheels go up and wheel moves in an arch. The gearbox pivot point is 100 mm from centre of gearbox either side of centre line. The suspension does not move that much total travel of single shock/spring is about 35 mm.

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