LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently March 29, 2024, 5:05 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 4 posts ] 
Author Message
PostPosted: December 26, 2017, 10:37 pm 
Offline

Joined: November 26, 2012, 2:29 pm
Posts: 191
Location: Rome, GA
I've been trying to figure out my bellcrank design recently and I want to make sure my excel spreadsheet for figuring this out is made correctly because it seems to give me the opposite kind of results that I want. For instance with my suspension compressed it gives e a softer spring than when it is uncompressed.

Would someone mind checking it out and give me some pointers? Maybe I could get a bit of help with the design of the bellcrank itself? I'd like to shoot for something near 80-100 CPM at static, so something around 154 lb/in spring rate right between the compressed and uncompressed values.

https://docs.google.com/spreadsheets/d/ ... sp=sharing

Attachment:
Bellcrank 2.PNG

Attachment:
Bellcrank 3.PNG


You do not have the required permissions to view the files attached to this post.

_________________
My build -> viewtopic.php?t=15585


Top
 Profile  
Reply with quote  
PostPosted: December 27, 2017, 2:00 am 
Offline
Mid-Engined Maniac

Joined: April 23, 2006, 8:26 pm
Posts: 6410
Location: SoCal
Just by eyeballing it, the rocker arm is backwards; turn it around and see where you are.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/


Top
 Profile  
Reply with quote  
PostPosted: December 27, 2017, 1:59 pm 
Offline

Joined: July 6, 2009, 11:50 pm
Posts: 177
First you should use SolidWorks to verify your spreadsheet calculation of the motion ratio. Move the wheel up an inch in the assembly and see how much the spring compresses. I can see right away that your suspension spring rate formula is wrong. The wheel rate should be spring rate/(motion ratio^2).

As for the geometry of the bellcrank, it looks like the pushrod side is gaining advantage with compression and the coilover side is loosing it. Try lifting both connection points to make the rocker arm look more triangular. You want that 68* at the coilover side to be increasing as the suspension is compressed and the 74* at the pushrod side to be decreasing (or at least increasing at a lower rate).


Top
 Profile  
Reply with quote  
PostPosted: December 27, 2017, 8:14 pm 
Offline

Joined: November 26, 2012, 2:29 pm
Posts: 191
Location: Rome, GA
Zac88GT wrote:
First you should use SolidWorks to verify your spreadsheet calculation of the motion ratio. Move the wheel up an inch in the assembly and see how much the spring compresses. I can see right away that your suspension spring rate formula is wrong. The wheel rate should be spring rate/(motion ratio^2).

As for the geometry of the bellcrank, it looks like the pushrod side is gaining advantage with compression and the coilover side is loosing it. Try lifting both connection points to make the rocker arm look more triangular. You want that 68* at the coilover side to be increasing as the suspension is compressed and the 74* at the pushrod side to be decreasing (or at least increasing at a lower rate).


Awesome. Thanks for the help. I should be able to figure it out now. It was too long of a christmas weekend and I couldn't think straight, too much eggnog probably haha.

I'll see if tonight or tomorrow I can get a better design made up.

_________________
My build -> viewtopic.php?t=15585


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 7 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