jlparsons
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| posted on 10/3/09 at 09:32 AM |
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increasing chassis stiffnes
I've heard that the 7 chassis isn't the stiffest of beasts, so I was thinking how to increase this with a bit of structural viagra. A
couple of things sprung to mind, might be rubbish, thought I'd run them by you lot!
Firstly, using the scuttle as a stiffening member, perhaps with a simple triangulated frame inside, and joining this to the transmission tunnel.
Alternatively a lighter solution would be to just use the bottom plan of the scuttle to better effect by joining the transmission tunnel to this with
a couple of small tubes.
Second, attaching a bolt-on stiffening brace over the engine, cross bracing from the top rails at the front of the scuttle, the top of the scuttle,
and the rails above the front suspension.
Anyone done similar?
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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Mr Whippy
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| posted on 10/3/09 at 09:39 AM |
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linky to some info
download it to get all the diagrams
[Edited on 10/3/09 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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smart51
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| posted on 10/3/09 at 10:08 AM |
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quote:
Originally posted by Mr Whippy
linky to some info
WOW! that's amazing. More than double the torsional stiffness and 10lbs lighter. That's well worth doing.
Edit: I also like his suggestion of using 18 guauge tubes throughout for lightweight cars. still more stiffness than the basic design but a lot
lighter.
[Edited on 10-3-2009 by smart51]
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jlparsons
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| posted on 10/3/09 at 10:15 AM |
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I've read this a while back, thanks for the link as I couldn't find it! Clearly some good suggestions here.
I'm wondering if an engine bay brace would add still further. My gut feeling is that when I look at a completed seven, and paint in my head the
picture of the underlying chassis, we have the majority of the structure for a car body three feet high contained in the first foot of that height.
Sure there's not much you can do about the cabin, unless you look at integrating a roll cage, or perhaps a T-bar with a structural windscreen
surround. But my gut is telling me there's a good amount of height and volume in the engine bay to play with, and a bolt-in x-frame might help
further for not much weight.
Just wish I had the tools to test what my gut seems to be saying!
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Mr Whippy
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| posted on 10/3/09 at 10:24 AM |
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just buy some balsa wood sticks and some super glue and build say a 1ft long chassis, then add or move 'tubes' to see the effect on the
strength. Use something like 1/4 x 1/4 sticks
this is where I get my supplies, I buy loads for
my planes 
Fame is when your old car is plastered all over the internet
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jlparsons
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| posted on 10/3/09 at 10:32 AM |
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Nice one centurion. Like it, like it. I might just have to do that.
Balsa? Check. Protractor? Check.
Check me out, I'm a scientist!
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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Paul TigerB6
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| posted on 10/3/09 at 11:41 AM |
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quote:
Originally posted by jlparsons
I'm wondering if an engine bay brace would add still further. My gut feeling is that when I look at a completed seven, and paint in my head the
picture of the underlying chassis, we have the majority of the structure for a car body three feet high contained in the first foot of that height.
Sure there's not much you can do about the cabin, unless you look at integrating a roll cage, or perhaps a T-bar with a structural windscreen
surround. But my gut is telling me there's a good amount of height and volume in the engine bay to play with, and a bolt-in x-frame might help
further for not much weight.
Just wish I had the tools to test what my gut seems to be saying!
Westfield have been doing just this for ages mate. Have a look at this MegaBlade build site - plenty of pics on there (and an interesting read).
linky
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jlparsons
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| posted on 10/3/09 at 11:52 AM |
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Spot on. Just what I was looking for!
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MikeR
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| posted on 10/3/09 at 01:06 PM |
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I used bbq skewers instead of 1/4" balsa.
Big lump of flat wood, junior hacksaw, pencil, ruler and hot glue gun. All you need.
(although i then used pizza box to simulate the floor)
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jlparsons
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| posted on 10/3/09 at 01:57 PM |
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This is all feeling like familiar territory for me. Make approximate model, bash the snot out of it, note results.
Pseudo-science rules.
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bimbleuk
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| posted on 10/3/09 at 02:05 PM |
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Without looking at the links above basic things like a full roll cage properly integrated not just bolted on top! Using the engine as a rigid member
of the chassis, so BEC more likely.
On my Striker which is fairly good to start with, a simple brace between the front suspension mounts makes a surprising difference to brake/steering
feel. The engine bay is typically a big open top box otherwise.
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cheapracer
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| posted on 10/3/09 at 02:59 PM |
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Just a note - Some people just enjoy their Locost's for Sunday type drives and stiffening will take away comfort as well as requiring stiffer
srings and shocks.
It's coming....
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smart51
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| posted on 10/3/09 at 03:33 PM |
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quote:
Originally posted by cheapracer
stiffening ... requiring stiffer srings and shocks.
Really? Why is that? I cant think of a reason why a stiffer chassis NEEDS stiffer springs or dampers.
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James
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| posted on 10/3/09 at 04:33 PM |
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The plans to look for are the ones by Cymtrics from this site.
I can't open the one's in Whippy's link from here so can't see if they Cymtrics' plans.
But they're very simple and easy to do.
------------------------------------------------------------------------------------------------------------
"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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DIY Si
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| posted on 10/3/09 at 05:42 PM |
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Having an engine bay brace will add quite a bit to the stiffness. Most of the chassis can be triangulated, except the engine bay, assuming you want to
be able to get in to it at all. Having a bolt in frame that reaches over the engine and attaches at the front near a fully boxed in front section and
reaches back to a proper scuttle bar/frame will do the job.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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mr henderson
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| posted on 10/3/09 at 06:14 PM |
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Stiffness is a matter of degree (in more than one sense).
Perhaps we should be discussing how much stiffness is needed, rather than how to achieve.
IIRC it was Einstein that proved than nothing is rigid, so it's only a question of how much rather than this is OK and that isn't.
John
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alistairolsen
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| posted on 10/3/09 at 07:24 PM |
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quote:
Originally posted by mr henderson
Stiffness is a matter of degree (in more than one sense).
Perhaps we should be discussing how much stiffness is needed, rather than how to achieve.
IIRC it was Einstein that proved than nothing is rigid, so it's only a question of how much rather than this is OK and that isn't.
John
unless youre going karting with no suspension and your only tuning is chassis compliance, then the stiffer your chassis is, the better as it gives you
a fixed reference from whcih to start. Nothing is truly rigid, but within the bounds of a small chassis with limited grip one should be able to get
pretty close to negligeable real world flex
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mr henderson
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| posted on 10/3/09 at 07:50 PM |
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quote:
Originally posted by alistairolsen
quote:
Originally posted by mr henderson
Stiffness is a matter of degree (in more than one sense).
Perhaps we should be discussing how much stiffness is needed, rather than how to achieve.
IIRC it was Einstein that proved than nothing is rigid, so it's only a question of how much rather than this is OK and that isn't.
John
unless youre going karting with no suspension and your only tuning is chassis compliance, then the stiffer your chassis is, the better as it gives you
a fixed reference from whcih to start. Nothing is truly rigid, but within the bounds of a small chassis with limited grip one should be able to get
pretty close to negligeable real world flex
But what does 'negligible' amount to in this context?
It's obvious that a stiff chassis is better than a flexible one, but the discussion is meaningless without some kind of defition as to what
'stiff' amounts to.
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alistairolsen
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| posted on 10/3/09 at 08:00 PM |
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well I guess it is logical to optimise for maximum stiffness with weight as the main constraint. A solid block of steel is stiff, but far too heavy
and no chassis at all is very light but wont control the location of the suspension mountings well.
A compromise is thus sought. I dont think it is wise to set a bound as to what is "stiff enough" but rather to work always towards the
maximum attainable stiffness given a weight constraint and construction method.
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mr henderson
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| posted on 10/3/09 at 08:13 PM |
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quote:
Originally posted by alistairolsen
A compromise is thus sought. I dont think it is wise to set a bound as to what is "stiff enough" but rather to work always towards the
maximum attainable stiffness given a weight constraint and construction method.
I would add to the list of constraints time, expense, difficulty, and intrusion into otherwise usable space
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MikeRJ
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| posted on 11/3/09 at 09:26 AM |
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quote:
Originally posted by cheapracer
Just a note - Some people just enjoy their Locost's for Sunday type drives and stiffening will take away comfort as well as requiring stiffer
srings and shocks.
I don't believe this is true. If the chassis is twisting/bending appreciably then the effective spring rate will be reduced. Stiffening the
chassis will then increase the effective spring rate so it's quite possible lower rated springs could be needed.
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l0rd
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| posted on 11/3/09 at 02:10 PM |
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I would like to add more braces when i start mine.
twisty chassis sometimes helps the car.
Look at the Peugeot 1.6 GTi.
Lift the car, open the door and it will never close back while it is lifted.
It does though handle really well.
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MikeR
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| posted on 11/3/09 at 05:35 PM |
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but how much better would it handle if you lifted one corner and for the same weight vehicle the chassis didn't twist!!!
Having said this i've wondered in the past if you had a twisty chassis on a bumpy road would it make the drive smoother?
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alistairolsen
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| posted on 11/3/09 at 05:40 PM |
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quote:
Originally posted by MikeR
but how much better would it handle if you lifted one corner and for the same weight vehicle the chassis didn't twist!!!
Having said this i've wondered in the past if you had a twisty chassis on a bumpy road would it make the drive smoother?
if you made the chassis stiff and then adjusted the springing and damping corrctly it would be better still
How much better does a 106 handle with a decent cage in it? (A LOT!)
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Liam
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| posted on 12/3/09 at 09:37 PM |
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I've done exactly what the OP is suggesting - structural scuttle and removable engine bay brace. Both make a huge difference and my FEA results
showed my design several times stiffer than my baseline model of a book chassis. Yonks ago I posted a thread with my FEA results... will try and dig
it out. Real thing in photo archive.
Liam
EDIT: Here it is
[Edited on 12/3/09 by Liam]
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