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Old 05-31-2020, 08:05 PM   #126
JDwhiteWRX
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This weekend I finished the passenger side rear upper control arm which was the final control arm for this project. I had already cut and notched some of the tube whilst making the other side so it came together relatively easy.

https://i.imgur.com/EZu9uVR.jpg?1

I then installed the rear differential and rear axle to get a look at how everything has come together.

https://i.imgur.com/Ardw1kP.jpg?1

Moving forward I have some big purchases to make which may take a bit of time to save some money.

The first thing I need to do is purchase a manual transmission, adapter plate and clutch setup. At this stage I am looking at the BMW ZF 5 speed as the best option, obviously a sequential would be the ultimate but its just not in my budget. The BMW trans seems to be a strong and affordable option, whilst not being too heavy.

With the engine mated up to the trans I can then do all the fabrication around the engine mounts, front crossmember and steering rack.

I also need to get some wheels and tyres.
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Old 06-01-2020, 09:56 AM   #127
Gigs90
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Quote:
Originally Posted by JDwhiteWRX View Post
This weekend I finished the passenger side rear upper control arm which was the final control arm for this project. I had already cut and notched some of the tube whilst making the other side so it came together relatively easy.

https://i.imgur.com/EZu9uVR.jpg?1

I then installed the rear differential and rear axle to get a look at how everything has come together.

https://i.imgur.com/Ardw1kP.jpg?1

Moving forward I have some big purchases to make which may take a bit of time to save some money.

The first thing I need to do is purchase a manual transmission, adapter plate and clutch setup. At this stage I am looking at the BMW ZF 5 speed as the best option, obviously a sequential would be the ultimate but its just not in my budget. The BMW trans seems to be a strong and affordable option, whilst not being too heavy.

With the engine mated up to the trans I can then do all the fabrication around the engine mounts, front crossmember and steering rack.

I also need to get some wheels and tyres.
Have you seen what the DKG ECU guys are doing with the BMW 7AT DCT ?

It might be able to do everything you want

https://www.dkgecu.com/l/what-is-dkgecu/
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Old 06-01-2020, 11:47 PM   #128
JDwhiteWRX
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Originally Posted by Gigs90 View Post
Have you seen what the DKG ECU guys are doing with the BMW 7AT DCT ?

It might be able to do everything you want

https://www.dkgecu.com/l/what-is-dkgecu/
Thanks, I had not seen or considered this option but it does look promising! I will have to do some research.
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Old 06-03-2020, 05:24 AM   #129
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So far the only downside I can find is the weight penalty, these DCT are very heavy at about 30 - 40kg more than the other manual trans options I was considering.

At least its in the center of the car and down low, paddle shift would be really nice to drive!
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Old 06-12-2020, 07:25 PM   #130
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Saving up for a few bits at the moment but that hasn't stopped me working on the car.

Something I have been thinking about for a while is pushrod suspension but I was just not sure it was something I could do. So I figured while I'm waiting I would make a full scale mock up and see if I could get my head around it.

The main reason for doing this is to design a rising rate suspension to help with aero loads. Version 1.0 was completed last night, below is the video

https://www.instagram.com/p/CBU5x_1AjT1/

This allows me to measure the wheel travel versus the shock travel. I then put the numbers in excel and I can plot a graph showing whether the design is regressive, linear or progressive.

Version 1.0 came out regressive and it is not using all of the shock travel. So by adjusting the angles on the bellcrank and the distances between holes I will work to getting it how I want.
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Old 06-21-2020, 04:50 AM   #131
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I have finally selected the coilover shocks I will be using with the pushrod suspension in the front.

They are from a Suzuki GSXR1000 09 - 15 year models and they feature 11.6kg/mm springrates, both high and low speed compression dampening and rebound.

Now that I have exact measurements of the spring rate, eye to eye length and shock travel I can complete the bellcrank design and possibly begin fabrication. The only thing I am not sure about at this stage is the amount of rate increase I should design into the rising rate suspension. I have ordered a book to hopefully help with this.

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Old 06-22-2020, 10:16 AM   #132
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Interesting. I'd been looking at similar aged R1 dampers for my Locost project. They are also low and high speed on dampening and rebound.
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Old 06-23-2020, 03:09 AM   #133
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Originally Posted by JDwhiteWRX View Post
I have finally selected the coilover shocks I will be using with the pushrod suspension in the front.

They are from a Suzuki GSXR1000 09 - 15 year models and they feature 11.6kg/mm springrates, both high and low speed compression dampening and rebound.

Now that I have exact measurements of the spring rate, eye to eye length and shock travel I can complete the bellcrank design and possibly begin fabrication. The only thing I am not sure about at this stage is the amount of rate increase I should design into the rising rate suspension. I have ordered a book to hopefully help with this.
Nice. Looks like pretty good dampers.
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Old 06-26-2020, 04:36 AM   #134
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Well after 14 variations of my design I feel I have come up with a scale model that is at least 95% complete.

In order to complete it 100% I would need to know the final corner weights.

I wanted to write down something about how I got to this point, a few weeks ago I knew almost nothing about pushrod suspension other than there would be advantages to having it in this project.

So if I had some CAD software and knew how to use it I could have saved myself some time but I don't and there is something special about building a scale mock up, holding it in yours hands and seeing something work in real life, not on a screen.

I knew that I needed to know how much the shock would move relative to the wheels, this is the motion ratio. It does not stay constant throughout the movement of the wheel.

The next consideration is packaging. I knew I could put the shock almost anywhere it would fit but I wanted to keep it as low as possible to benefit the COG. The obvious choice was almost directly inline with the motion of the lower control arm, the only things in the way are the main chassis frame rail and the steering linkage between the steering rack and steering column.

Early mock up was done with some cardboard and a pressure can.

https://i.imgur.com/xcBHrI7.jpg?1

I knew there was a possibility to use motorcycle shocks but had no idea if it could really work on a full size car until I had figured out the motion ratios. I used the dimensions of a Suzuki Hyabusa shock found online as it was the largest size with a decent amount of springrate options.

Next I made the 3 points everything would pivot around out of some steel and minimally tack welded them into position on the car.

This is the pushrod attachment on the lower wishbone. The hole position is based on getting a 5/8" rod end as close to the outer pivot as possible.

https://i.imgur.com/otzBqgp.jpg?1

The bellcrank pivot is shown here, I ended up moving this a couple of times.

https://i.imgur.com/M9gcScU.jpg?1

All the other parts are made of some scrap aluminium extrusions I had lying around the garage. This photo shows all the bits used so far.

https://i.imgur.com/9wwsBev.jpg?1

To mimic the shock travel I made the eye to eye length match the Hyabusa shock with a ruler stuck inside the extrusion to read zero millimetres.

The whole point of using this pushrod setup is to have the springrate increase at the wheel (wheel rate) as the aero pushes down on the car at increasing speed. To do this you need a rising rate suspension.
The parameters you can play with to achieve this are all in the bellcrank design.

You have the distance to where the pushrod mounts to the bellcrank from the pivot point and the distance to where the shock mounts to the bellcrank from the pivot point.

Then you have the angle between the pushrod attachment point on the bellcrank and bellcrank pivot and the angles between the shock attachment point on the bellcrank and bellcrank pivot.

A good starting point is 90 degrees for both these angles. For progressive you set the shock angle at 90 at full bump travel and the pushrod angle to 90 at full droop.

Why 90 degrees?

As the wheels come up in bump the shock approaches 90* which is the angle at which it is pushing back most thus increasing the rate at the wheels. If it were to go past 90* then it would become easier again so this is why we set it to 90* at full bump travel.

On the pushrod side the angle is getting smaller as the wheel comes up so by setting it at 90 at full droop all the advantage is with the shock as it approaches 90.

These 90* settings give you a very progressive rate but its a good starting point and then you can adjust to lower the rate from there.

The way I got the starting 90* angles was two use to separate bits of extrusion with holes drilled in them instead of a solid bellcrank, see photo below.

https://i.imgur.com/en1i9zX.jpg

So I just set my angles in bump and droop and scribed a line in the middle so I could make a solid bellcrank. It took a few tries as the shock would hit the chassis rail at full droop or was too close to the steering linkage.

You can see in this photo I had some cardboard to show where the spring would sit and possibly hit things.

https://i.imgur.com/f0UCr1A.jpg?1

Once I had a solid bellcrank made I could then move the wheel in 10mm increments and measure the position on the shock mock up. The first few didn't work as I was not getting full shock travel or too much travel or the shock was hitting the chassis rail etc. I had to keep drilling new holes and making longer pushrods.

Once I had something that gave me full shock travel for the complete wheel travel I made a spreadsheet in excel and plotted a graph.

Motion ratio = wheel travel / shock travel

not to be confused with installation ratio which I have seen interchanged with motion ratio and this added a lot of confusion

If the motion ratio is decreasing with wheel travel then you have a progressive suspension rate.

How much progression do you need?

Well I still don't know, the last 2 books I bought didn't really have as much detail on progressive suspension rates as I would have liked. I have read that 10% is enough but that was a road car, the Carroll Smith book I have is too old but he does mention no more than 20% increasing slope if you graph the wheel rate.

The spring ratio is constant, its the wheel rate you want to know.

The wheel rate is just the spring rate / motion ratio ^2

My most recent version of bellcrank gives an 11.6% increasing wheel rate slope if you graph it but what I have done is measure the motion ratios of pushrod to bellcrank attachment points in 4 positions around a central point so I would know the exact effect of moving this attachment point in any direction. So once I know my final corner weights I can make a bellcrank exactly how I need it. I can also put multiple attachment points on the bellcrank if I require stiffer or softer wheel rates after testing.

I didn't end up using a Hyabusa shock in the end, they are only 2 way adjustable, not 3 way like the GSXR1000 shocks I bought and after working out the math I knew almost any shock could work. It's crazy how cheap they are to buy too!
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Old 06-27-2020, 09:23 AM   #135
Norm Peterson
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Couple of thoughts . . .

Motion ratio would be the reciprocal of installation ratio. So if somewhere in your math you were going to divide by either of those, it would still work by multiplying by the other. In Excel, I tend to worry less about what the parameter I'm using is called and just work the math correctly.

I think for progression you might want to start by setting some target for how much loss of ride height you're going to allow from aerodynamic downforce at some speed (probably up around your maximum speed, though I suppose you could target a specific ride height for the speed through an important high-speed corner). I'm guessing that you might not want to be sitting on the bump stops, especially considering what braking is going to do.

FWIW, I remember reading that when the upper level racing series started tinkering with rising rate suspensions to the point where rising rates were employed at both ends of the car you could have a car that was great one week on one track and terrible the next week on another.


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Last edited by Norm Peterson; 06-27-2020 at 09:28 AM.
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Old 10-17-2020, 06:53 AM   #136
JDwhiteWRX
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Just watching some videos on the HKS TRB03 and found some information on the springrates they are using.

34kg front and 60kg rear, pretty crazy!

https://i.imgur.com/owwQ5Ds.jpg?1

https://i.imgur.com/wWtmk7n.jpg?1



This project is still going, I have just been collecting some small parts and investing in new tools lately. Hopefully I can bring some updates soon.
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Old 10-17-2020, 08:55 PM   #137
speedyHAM
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This project is still going, I have just been collecting some small parts and investing in new tools lately. Hopefully I can bring some updates soon.
Good to hear, looking forward to updates.
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Old 10-19-2020, 04:31 AM   #138
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Today I picked up a set of tyres which I will need to have so I can modify the body for the new ride height and make some new panels to suit. These tyres are way past their use by date but I got them dirt cheap. No point buying new tyres unless I was planning to drive this thing some time soon.

I couldn't resist the opportunity to mock up what the car might look like with some wheels on, speaking of wheels, they will be my next purchase.

https://i.imgur.com/lvirmxj.jpg?1

https://i.imgur.com/mYQnwgg.jpg?1
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Old 10-19-2020, 07:00 PM   #139
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Yeah, when it comes to certain mock ups, resistance is futile.
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Old Yesterday, 01:53 PM   #140
Homemade WRX
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I snagged some Porsche cup car take-offs for the same reason!!
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