LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently March 29, 2024, 1:50 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: September 8, 2020, 1:55 am 
Offline

Joined: June 28, 2019, 7:54 pm
Posts: 114
I was curious if a control arm's design when it comes to the angle the tubes are notched or how wide it is has anything to do suspension geometry? What does it affect other than looks and clearance?


I know the height of the suspension pickups as a whole compared to the lower/upper and frame influence the suspension geometry, roll center, but what about the actual control arm width or angle of the notched tubes?

Example:
Image


In the example above, the arm in red is much wider and moves the pickup on the right by 2" or so and widens everything. The design in black and white is much narrow and angled inwards.

The black/white design has an arm that's angled inwards which I already found out is a problem if you want to adjust camber so I was working out different designs and wanted to ask this question. Been wondering about that for a while..

The design in red is much wider so what are some considerations when it comes to the control arm width and pickup widths? If it's too wide, does it weaken the design or something? If one were to go with the design in red, that would provide more clearance, ability to adjust camber correctly and generally is a better design objectively speaking?

Mostly out of curiosity

_________________
Location: LA/OC in SoCal
David


Top
 Profile  
Reply with quote  
PostPosted: September 8, 2020, 2:08 am 
Offline

Joined: June 28, 2019, 7:54 pm
Posts: 114
As a follow up question, what are the functional differences/downsides/upsides of the two control arms below?

Image

The one on the right is pulled back to allow more clearance within the center but the tubing is notched at a closer to 90deg angle than the other designs. I can already see that as you approach a more perpendicular angle, there is less welding surface area and there's probably more lateral forces (?) applied. At what point is this a detriment to the arm? Is there a specific rule to follow?

What if there is a top plate welded on top to reinforce both left/right tubes together with the bracket?

_________________
Location: LA/OC in SoCal
David


Top
 Profile  
Reply with quote  
PostPosted: September 8, 2020, 3:39 am 
Offline

Joined: February 20, 2015, 12:04 pm
Posts: 307
Location: Norfolk - UK
If the wishbones are designed right (those in your diagrams aren't great) they offer more stiffness under acceleration and particularly under braking.

You're aiming for perfect triangulation of the forces that you're feeding into the chassis pickups. The example on the left isn't great. The example on the right is worse.

The rear brakes obviously do a lot less work than the fronts but even so, with wide modern tyres there can be enough flex in the wishbones to cause brake judder (kind of an 'anti-tramping' effect) or changes to the toe alignment.


Top
 Profile  
Reply with quote  
PostPosted: September 8, 2020, 4:38 am 
Offline

Joined: June 28, 2019, 7:54 pm
Posts: 114
Sam_68 wrote:
If the wishbones are designed right (those in your diagrams aren't great) they offer more stiffness under acceleration and particularly under braking.

You're aiming for perfect triangulation of the forces that you're feeding into the chassis pickups. The example on the left isn't great. The example on the right is worse.

The rear brakes obviously do a lot less work than the fronts but even so, with wide modern tyres there can be enough flex in the wishbones to cause brake judder (kind of an 'anti-tramping' effect) or changes to the toe alignment.


Makes sense. I'm actually not going to build the left or right arms but I was wondering what kind of things to consider when using extreme examples like that.

Currently the arms are built like the black/white ones in the background pictures above, much tighter and narrower. Just don't like the angled tube on the left that messes with camber adjustment.

I think I'm just going to simplify it and go with the vodoo arm design. If clearance for tighter arms isn't an issue, and narrower distance between the two pickups do not affect actual e geometry and only stiffness/strength, then maybe these will be better:
Image

_________________
Location: LA/OC in SoCal
David


Top
 Profile  
Reply with quote  
PostPosted: September 8, 2020, 9:14 am 
Offline
User avatar

Joined: October 19, 2012, 9:25 pm
Posts: 3365
Location: Summerville, SC
pancake wrote:
As a follow up question, what are the functional differences/downsides/upsides of the two control arms below?

Image

The one on the right is pulled back to allow more clearance within the center but the tubing is notched at a closer to 90deg angle than the other designs. I can already see that as you approach a more perpendicular angle, there is less welding surface area and there's probably more lateral forces (?) applied. At what point is this a detriment to the arm? Is there a specific rule to follow?

What if there is a top plate welded on top to reinforce both left/right tubes together with the bracket?


The biggest issue I have with both of these designs is where the angled tubes meet the vertical tubes. The farther away from the heim joint, the greater the bending moment. Move those tubes in closer to the heims and you get closer to being a triangle.

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


Top
 Profile  
Reply with quote  
PostPosted: September 8, 2020, 11:44 am 
Offline
User avatar

Joined: January 11, 2017, 11:06 pm
Posts: 187
Location: Alberta
I suppose creative use of some 1/8" plate could also help stiffen it up without too much interference?


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 22 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
POWERED_BY