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Author Topic: UK Lakester build G/GL  (Read 101725 times)

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Offline ggl205

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Re: UK Lakester build G/GL
« Reply #405 on: November 05, 2019, 02:44:06 AM »
Sid:

You got me thinking about roll control (or the lack thereof) with a beam axle. Sway bars for push or pull rod suspensions can be fit inside a narrow chassis but the push rods themselves are out in the airflow. Beam axles like most of us use up front could employ sway bars but for them to work, they too would be out in the airflow. Reaching WAY back in my memory, I remember using dual-rate springs in place of linear rate, to gain a significant amount of roll control without sway bars. I wonder if this may work for our beam axles?

One remaining issue is lack of spring and damper control when my now very wide front track experiences bump on one corner but not the other. There is 20? from push rod to spindle so when just one wheel is in bump, the push rod hardly moves. One of the reasons I went with a 1.5:1 rocker ratio. I just wonder if dual-rate springs would help?

John
« Last Edit: November 05, 2019, 02:45:42 AM by ggl205 »

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #406 on: November 05, 2019, 03:46:39 AM »
Sid / John

If a watts linkage setup has the roll centre (and / or center) at the pivot bolt (centre of the axle rear case) what does the push rod arrangement do to it? Pretty much all of the performance cars using push rod have the shocks mounted high and flat - how do they counter? Is that why some push rod setups have a heave spring 'linking' the two bellcranks?

Accepting this is a solid axle (front and rear) but for reference, from what I can figure out a pull rod arrangement (rocker low down) on unequal double wishbones does not seem to affect static roll centre but a push rod (bellcrank up high) moves it vertically but I cant figure out why.

Something of a case of me monkey see monkey do - has the monkey slipped on a banana skin?  :oops:
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #407 on: November 05, 2019, 03:54:32 AM »
Plan B is single shear but only because it was enough of a mock-up to eyeball the relative (lack of) merits of the two options, not the finished article.

I will mock-up plan C this weekend. If it works it will be much easier to provide robust pivot brackets (mounted on the chassis rail). I thought the shocks were too long for this option but then I realised with the springs on they were fully extended - talk about tunnel vision. Urgh.
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline kiwi belly tank

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Re: UK Lakester build G/GL
« Reply #408 on: November 05, 2019, 12:24:05 PM »
Sid:

You got me thinking about roll control (or the lack thereof) with a beam axle. Sway bars for push or pull rod suspensions can be fit inside a narrow chassis but the push rods themselves are out in the airflow. Beam axles like most of us use up front could employ sway bars but for them to work, they too would be out in the airflow. Reaching WAY back in my memory, I remember using dual-rate springs in place of linear rate, to gain a significant amount of roll control without sway bars. I wonder if this may work for our beam axles?

One remaining issue is lack of spring and damper control when my now very wide front track experiences bump on one corner but not the other. There is 20? from push rod to spindle so when just one wheel is in bump, the push rod hardly moves. One of the reasons I went with a 1.5:1 rocker ratio. I just wonder if dual-rate springs would help?

John
There is no reason to have any part of a sway bar or anti roll bar any further out in the breeze than the suspension system.
John's system here is using a pushrod link off the axle so picking up the top of that link for anti roll is easy. If a coil-over is mounted to the axle, a linkage can be in the same location & on the same plane if necessary. If the coil-over was out in the breeze, having a linkage on the same plane ahead of that would actually help reduce the aero drag of that coil-over.
A sway bar or anti roll bar can be anything from small dia that will flex all the way up to a large dia tube that will not, depending on how much or little is desired. The largest one I've built was for a liner & it was 4" tube & 18" long.
One thing to be aware of now that the salt is resembling a plowed field is the amount of stress put on the inner axle tube at the suspension mount point & at the diff head. You have 20" there but there are lakesters with a lot more than that. All axles are at risk but banjo housings like 10 bolt & 12 bolt are a steel tube shrunk into an Iron housing & a quickchange is even weaker with an aluminum bell on the end.
Crack checking front tube axles would be desirable too & this is also why I don't like powder coating.
  Sid.

Offline ggl205

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Re: UK Lakester build G/GL
« Reply #409 on: November 05, 2019, 03:22:04 PM »
OK, but using a Watts link brings with it some degree of roll stiffness depending on where you locate the propeller pivot and may negate a need for sway bars altogether. I would guess most of us with beam axles put that pivot at or close to axle center. My question was if we think more roll control is necessary, would dual-rate springs help in place of sway bars?

John

Offline Interested Observer

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Re: UK Lakester build G/GL
« Reply #410 on: November 05, 2019, 06:38:59 PM »
In road racing an anti-roll bar is used to restrain roll motion and still allow the use of relatively soft springing.  For straight line running it is not clear why anti-roll would be useful unless a lot of steering correction (i.e., lateral loading) is an issue or if the suspension were such that it produces noticable roll-steer.

A dual-rate spring package would act like a spring with the composite rate of the two springs in series (softer than either) until the softer spring bottoms out.  Would probably be gentler at the limit than a spring and bump stop.  Whether the bi-linear nature of a dual spring setup would be ?spookier? than an essentially linear A/R bar would be up to the driver to determine.

Offline kiwi belly tank

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Re: UK Lakester build G/GL
« Reply #411 on: November 05, 2019, 07:12:23 PM »
In our application a Watts linkage is used to accurately center the axle in the chassis through the suspension travel distance using the horizontal centerline of the axle for the center pivot, this will not assist in chassis roll resistance, it will only locate the roll center. If it's above or below that centerline it will allow the axle to move sideways from center but we're not running dirt track cars that turn right to turn left so we don't need to go there.
Dual rate springs or progressive rate springs are not going to replace a sway bar. When the weight shifts to one side & loads that spring it will be unloading the other side allowing the chassis to roll. This is particularly undesirable in lakesters & liners due to the narrow wheel track & high CG's we run. It's not as critical in wider wheel track cars but can still make the difference between spinning or making a full pass. A door car that used to be twitchy & had some spins now runs like it's on rails with the only change being a sway bar off the back of a box truck.
  Sid.

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #412 on: November 07, 2019, 04:05:20 AM »
A door car that used to be twitchy & had some spins now runs like it's on rails with the only change being a sway bar off the back of a box truck.
  Sid.

Sid - you don't state which end that sway bar was fitted on the door car; my understanding is that stiffening the rear will increase over steer (reduce under steer) and so presumably the spin was over steer induced and the sway bar went up front?

Plan C of the rear shock / rocker assembly will be posted after this weekend if the weather plays and I cant do any outdoor DIY. Here's to the rain :cheers:
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline kiwi belly tank

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Re: UK Lakester build G/GL
« Reply #413 on: November 07, 2019, 10:50:29 AM »
Your understanding is correct in a normal world but we don't play there.
We're getting off track into large-barge door cars here which is somewhat of a different animal than high CG lakesters & liners but my theory on the Camaro was that it was wagging the tail & pitching the chassis. When it got too spooky he would pull his foot out of it & increasing the problem with lift-off over steer weight transfer. Some times he would catch it & lose the run & sometimes not. They were willing to try any reasonable suggestions to get it going straight. It already had a big bar on the front & that monster on the back cured it.
Lakesters & liners typically have a long wheel base to track ratio plus a high CG. If they have body roll they act more like a mono-hull boat. When they lean, that creates yaw.
The salt surface is more like snow than blacktop & can be anything from smooth (rarely now) to resembling the entry to the milking shed.
Liners & lakesters are my passion but I've helped a lot of people over the years in getting their "other stuff" stuff to behave on the salt.
  Sid.   

Offline ggl205

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Re: UK Lakester build G/GL
« Reply #414 on: November 07, 2019, 12:55:06 PM »
Sid:

You mention lakesters as as having high Cg but most small bore lakesters like John?s and mine, have relatively low Cg. In fact, my lakester uses a Hewland Mk9 gearbox turned upside down to put the engine as low in the chassis as possible. John is building a lay down car while mine is semi-lay down (normal formula car config) and as such, enjoy low Cg.

John

Offline Beef Stew

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Re: UK Lakester build G/GL
« Reply #415 on: November 07, 2019, 08:56:36 PM »
The Lotus 58 Formula car had a beam axle in front, and a De Dion Tube in the rear. Chapman wanted to have unchanging camber, for maximum mechanical grip. There should be some info available online.

Check-out the Mumford Link. https://grassrootsmotorsports.com/forum/grm/mumford-link-how-you-do-that/41677/page1/  An alternative to a Watts Link. Looks interesting, but little info available. Here's a few photos of a car using it http://texaslocost.homestead.com/Suspension.html From theses photos, it seems like you could use it on a very narrow rear axle.
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Offline ggl205

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Re: UK Lakester build G/GL
« Reply #416 on: November 07, 2019, 10:08:08 PM »
I looked closely at the Mumford Link before settling on a Watts but found I did not have room for it on my front axle. Interesting idea, however.

John

Offline kiwi belly tank

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Re: UK Lakester build G/GL
« Reply #417 on: November 07, 2019, 11:19:05 PM »
Sid:

You mention lakesters as as having high Cg but most small bore lakesters like John?s and mine, have relatively low Cg. In fact, my lakester uses a Hewland Mk9 gearbox turned upside down to put the engine as low in the chassis as possible. John is building a lay down car while mine is semi-lay down (normal formula car config) and as such, enjoy low Cg.

John
I've never been up close to your lakester John, what is the total height, track & CG when it's loaded for bear?
  Sid.

Offline ggl205

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Re: UK Lakester build G/GL
« Reply #418 on: November 08, 2019, 06:46:54 AM »
John:

Sorry for hijacking your thread. I promise not to do it again.

Sid:

I have made a front track change (wider) and some minor weight distribution readjustments but here is what I had in 2017.

Front track: 33 inches
Rear track: 52 inches
Overall height: 42 inches
Cg: 16.8 inches up and just at my seat

Front track is now 50 inches. I do plan on adding a three foot section to the rear, completing aero back there. This new section will be home to the chute tube as well.

As you can see from the image, everything sits low in the chassis. Due to my robust 6 foot, 230 pound frame (much heavier in off season), the car had to be 42 inches tall. If I had a small driver like lyn when I was building the car, it would have been 14 inches lower overall.

John
« Last Edit: November 09, 2019, 08:22:06 AM by ggl205 »

Offline Lemming Motors

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Re: UK Lakester build G/GL
« Reply #419 on: November 08, 2019, 11:25:32 AM »
John
Hijack away - it is all good info and we are in the same class (albeit sitting at the back) so its relevant. One day we might even meet.

Wow - that Texas Locost (previous post regarding Mumford and Links or is that Sons) is made out of furniture tube compared to my Lakester - maybe I am using too much steel, which leads me to Sid's questions;

1. It is a long way from bear, not even loaded for bear cubs yet so some of the answers are theoretical. Heck, kittens are pretty safe at the moment.
2. The design (again I am using the term loosely) philosophy is wide track with a rounded furry underbelly.
3. That narrowed underside constrains the space lower down so does push some items up a bit in terms of vertical cg. My engine is fairly low, fuel will be saddle tanks either side of the g'box but the radiator is quite tall so that necessitates tank mass (read water) up to and above the top of the engine head.
4. Solid front axle (heavy wall tube) with 4 bars but shocks will be high.
5. Live rear axle (4 bars, watts, shocks a few inches above the pigs head).
6. Total height from the floor to the top of the cockpit ca. 39" vs. 24" width at the shoulders. I have a somewhat upright driving position - true rooky, preferring a comfortable driving position for the sake of a couple of inches of height - I am hoping that helps with the deteriorating salt - that's my excuse and I am sticking to it. Re-attached previous pic to illustrate.
7. 5' 12.5" / 231 lb driver (assuming I can drive naked without a helmet etc) with legs above front axle a la LeMans LMP1.
8. Expecting ~ 20' end to end.
9. Rear axle 48.5" flange to flange so depending on wheel offset and drum brake etc guessing a 52 - 54 " track.
10. Slightly narrower at the front I think but haven't actually measured it. Spindle mounted wheels.
11. Theoretical total weight calculation ca. 2000 lbs.

  :oops:

John
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.