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Could Someone Please Explain This Suspension Setup


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#1 Pete649

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Posted 24 September 2021 - 05:06 PM

This car appeared in the July 2021 issue of Practical Performance Car. (Just catching up with my reading).

 

It is a Midlana which is Lotus 7 type kit car that you build from a book of general design principles that can be bought.

 

The guy building this one chose to make the front suspension rear mountings to aim along the load axis of the wishbone instead of just having the mountings in-line. He explained that this was to reduce any bending moments.

 

He is obviously happy with this setup, but I don't fully understand how it works in practise. Wouldn't this result in very limited suspension travel?

 

The spherical joints must have to twist to take up the difference in the fact that the arms are trying to operate in different planes.

 

Has anyone come across this type of setup before? Just seems a lot of trouble to go to when the mountings could be made in-line to remove any articulation problems.

 

lhaxLSY.jpg

 

 


Edited by Pete649, 24 September 2021 - 05:07 PM.


#2 nicklouse

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Posted 24 September 2021 - 05:25 PM

Not really sure why you think there would be an issue.

 

the joints are spherical so can rotate about any axis. The axis has no relation to the bolt position/angle.



#3 Pete649

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Posted 24 September 2021 - 07:26 PM

Didn't think there would be enough sideways rotation on the joints, especially as the front and rear arms are unequal lengths. I can see equal length arms working, where the hub is in the centre instead of being offset. There must be enough sideways rotation available in the rose joints for the amount of suspension travel required. Just didn't look right to me at first glance.



#4 nicklouse

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Posted 24 September 2021 - 09:39 PM

To be fair your post(s) are very general. You have not said which of the joints you are having issues with. It will be very clear in your mind but to me everything looks fine. So it is very hard to answer.  
 

remember track cars don’t need much travel. As my 3 wheeling at Stanford hall last weekend showed.



#5 r.tec

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Posted 25 September 2021 - 09:03 AM

It is a double wishbone pushrod assembly. Do not know who was the first in F1 but it might be Gordon Cuppock's McLaren M19 design of 1971.



#6 Ethel

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Posted 25 September 2021 - 01:02 PM

Do you mean because the bolts through the inner ends don't have a common axis? 

 

The upper & lower "arms" are still triangulated so they must turn on a common axis that goes through both spherical joints. The arms would do a full rotation around that axis without altering the angle of intersection of that (rotational) axis and the axis down the tubes, so no flexion.

 

You might visualise it by thinking about the Earth going round the Sun: it's tilted, giving us summer & winter, but you still extend an inaginery disc out from the Sun that slices the earth in half, touching the tropic of Cancer nearest the Sun & Capricorn farthest away. Even though the North South "bolt" is tilted we still go round on that disc same as we would without the tilt.

 

Can't quite make out the arrangement at the hub end, but it looks like it might be the same as a Mini's lower wishbone - only the arms aren't quite in the same plane, which would generate a bit of torsion in the tubes from braking & acceleration forces coming from the hub swivels

 

The Mini bottom arm, tie rod wishbone is an even more extreme example thinking about it.



#7 Pete649

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Posted 25 September 2021 - 03:11 PM

Do you mean because the bolts through the inner ends don't have a common axis?

 

Yes, although the more I looked at it I could see how it worked, as per your analogy of the Earth. (Good analogy by the way).

 

What was catching me out was, on the bottom arm in particular, the front leg is more or less perpendicular to the body with the rear leg joining at an angle of some 25 - 30 degrees. I would have thought that this would mean the rear rose joint would have to tilt quite a bit to accommodate the wishbone's rotational movement, possibly reaching the limit of off-axis travel but as Nick pointed out the amount of suspension movement is probably not that great.



#8 Ethel

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Posted 26 September 2021 - 09:39 AM

It looks to be parallel with the tube in the top wishbone to me, but longer so there'd be a bit less angular movement. That's a big web between the tubes, so it'd crank up some major internal forces if there was a lack of free movement in the spherical joints.

 

I can't get my head round the angle of pushrod for the inboard spring. I'd have expected it to be perpendicular to the wishbone axes, maybe it's just the photo.



#9 Pete649

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Posted 26 September 2021 - 02:05 PM

I saw the pushrod appeared to be angled quite a bit but wasn't going to comment as I was having enough of a problem with the rest of the setup :-)

 

As you say, though, the angle of the photo isn't the best.



#10 sonscar

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Posted 26 September 2021 - 03:56 PM

It is not rotating like a roundabout,the angular movement could be as little as 30 degrees.Looks fine by my inexpert eye.Steve..




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