Go Back   RCCrawler Forums > RCCrawler General Tech > General Crawlers
Loading

Notices

Thread: finding the correct suspension link length

Reply
 
LinkBack Thread Tools Display Modes
Old 10-25-2005, 01:06 AM   #1
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default finding the correct suspension link length

Ok for as often as I get pm'd or see posts about this topic. I decided to make a thread that hopefully will become a tech article or at least a sticky. So to all youu newbie's read on.

Finding the correct link length is not a hard task. In fact it's quite easy. If you know how to measure and have a little common sense. I'm going to go with a common 50/50 set up for ease of explaining it. So lets say you have a chassis in your hand.
For example my RockStar Chassis. Figure A

Now the lower link holes are 3 1/8" apart and you are looking for a 12.5" wheelbase. Now the place that most people mount their lower links to the axle is shown in figure B.

Now those links are 4" apart and the RockStar chassis is 3" wide. So you know by common sense that the lowers will be triangulated. So by looking at the picture above you measure the distance from the link mount hole center and the axle centerline. Which is roughly 5/8". And just for ease of reference the length of a standard(non short)traxxas ball end is also 5/8". So if you where to make a link using aluminum tubing with all the numbers I stated you could get the correct link length for the lower links to achieve a 12.5" wheelbase.

Here's the equation. (I'm using the decimal equivlant so you lazy arses can use a calculator)

Add the 5/8" of the (axle side) link mount to axle centerline on both front & rear.
.625" + .625" = 1.25" or 1 1/4"

Now subtract that 1 1/4" from the wheelbase of 12 1/2"
12.5" - 1.25" = 11.25

So your lower link mount holes are 11 1/4" apart.
Remember we said the lower link holes on the chassis are 3 1/8" apart? Well now you subtract that 3.125 from the 11.25. This # will give you a starting point for your lower links.

11.25" - 3.125" = 8.125" or 8 1/8" Now divide that by two. 8.125"/2 = 4. 062 or 4 1/16". There's your number 4 1/16" would be you eye to eye link length.
You also need to consider the ride height and the angle that the lower links will sit at.

If you are going to make your own links remember to also add the length of the ball ends(5/8"each, 1 1/4" together) and subtract that from your cut size on the tubing.

On my RBX the wheelbase is just about 13" with a ride height of 2 3/4" at rest and 3 1/4" without any sag. When I dropped the ride height down it gets a little longer because the links are almost flat. My lower links measure 4 1/2" eye to eye but the aluminum tubing is just 2 3/4" long because I used the longer Dubro heavy duty ends. See figure C


On to the upper links.

The upper links do a few things they set your pinion angle, which in turn sets your caster. Ideally you want to run 0* of caster for RC crawling. It gives you the best turning with a decent pinion angle. Once you have the lowers figured out, made and attached to the axle and the chassis. Set your front axle caster to zero and measure from your upper link mounting hole on the axle(now it doesn't matter which, how, or what you are using for upper link mounts) to the upper link mounting hole on the chassis.
Here in figure D you can see my front upper links are pretty short being mounted behind the servo.


Now use the info I gave you for measuring your lowers and do the same with your uppers and remember to shoot for close flat links and zero caster.

Hope this helps you guys in your building. If I should add or change anything please let me know. thanks
rckjeep is offline   Reply With Quote
Sponsored Links
Old 10-25-2005, 02:24 AM   #2
I wanna be Dave
 
DISTURBIN' tha PEACE's Avatar
 
Join Date: Jun 2005
Location: On the G-Train!!!!!
Posts: 6,081
Default

Great tutorial RCKJeep!

Just in time too. My TLT is going to be rebuilt after this weekend's comp

Thanks good info
DISTURBIN' tha PEACE is offline   Reply With Quote
Old 10-25-2005, 04:51 AM   #3
RCC Addict
 
Wild trial's Avatar
 
Join Date: May 2005
Location: the land of the midnight sun
Posts: 1,451
Default

Yup i agree, thats a great thread.
I'm building my self a chassi like that.

So tnx rckjeep.

Hopefuly someone make that a sticky some day.
Wild trial is offline   Reply With Quote
Old 10-25-2005, 07:46 AM   #4
I wanna be Dave
 
FrankyRizzo's Avatar
 
Join Date: Apr 2005
Location: Vegas
Posts: 7,172
Default

Thanks for the great post.
FrankyRizzo is offline   Reply With Quote
Old 10-25-2005, 10:29 AM   #5
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

well I'll leave it up to griz or bender to decide if it should be a sticky or not. If it helps you give me good rep. Lord knows I could use it.
rckjeep is offline   Reply With Quote
Old 10-25-2005, 11:28 AM   #6
Rock Crawler
 
Join Date: Aug 2004
Location: woods cross utah
Posts: 523
Wink

how about lesson 2? now that you have covered the basics,you mentioned that your upper links are shorter than your lower links. does that affect axle steer or have dramatic caster changes through compression? inquiring minds want to know! not that im looking into doing a tlt or anything.
chafey is offline   Reply With Quote
Old 10-25-2005, 11:39 AM   #7
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

I have no axle steer what so ever. Ideally you want them the same length but it's not always do-able. I don't know everything about 4 links but I'll teach as a I learn. In the current issue of 4 Wheel Drive & SUV (the one with an OD green TJ on the cover) there's an article on link suspensions.
rckjeep is offline   Reply With Quote
Old 10-25-2005, 01:08 PM   #8
Quarry Creeper
 
Join Date: Sep 2005
Location: Lufkin
Posts: 347
Default

I have a question. What are the pros and cons of having the chassis end of the upper and lower links mount at the same location? Should they be separated? I had my upper links mounted similar to yours (behind the servo) and then attached the links at the same hole on the chassis, but I had tons of axle steer. I don't know if it was due to the link location or not.
Rooney7783 is offline   Reply With Quote
Old 10-25-2005, 01:41 PM   #9
Quarry Creeper
 
Join Date: Jun 2005
Location: DH
Posts: 406
Default

Thanks, Great Tech article!
Kev808 is offline   Reply With Quote
Old 10-25-2005, 05:13 PM   #10
Newbie
 
Join Date: Aug 2005
Location: cherry point north carolina
Posts: 41
Default

here is a link i think would help out a lot. its a calculator just for sour link suspension. it uses microsoft excel. i found from the extreme 4x4 tv show on spike tv. hope it helps



http://www.xtreme4x4tv.com/news.aspx?iid=5023
jeepbub is offline   Reply With Quote
Old 10-25-2005, 06:35 PM   #11
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

Quote:
Originally Posted by Rooney7783
I have a question. What are the pros and cons of having the chassis end of the upper and lower links mount at the same location? Should they be separated? I had my upper links mounted similar to yours (behind the servo) and then attached the links at the same hole on the chassis, but I had tons of axle steer. I don't know if it was due to the link location or not.
I can't really tell why you had axle steer. I've noticed that rigs with poor geometry have more issues than those with good geometry. If you don't have triangulation in both the upper & lower links in opposite directions you will have some steer issue's.


uppers chassis lowers chassis
/ \ \/
axle axle

Having your upper & lowers (chassis side) mount to the same hole doesn't seem to be a hinderance in RC but if you look at the fundamentals of links suspension isn't right. I have found that having the links parallel each other gives the best results. Like on the MRV the W H O R E.


It allows each link to rotate to the max without binding an opposing link. Which as you can see equates to a lot of flex.

Last edited by rckjeep; 10-25-2005 at 06:41 PM.
rckjeep is offline   Reply With Quote
Old 10-26-2005, 06:48 AM   #12
Quarry Creeper
 
Join Date: Sep 2005
Location: Lufkin
Posts: 347
Default

I will try to make my links parallel tonight as well as opposing triangulation. Thank you for your help. I'll post and let ya know how it works. Thanks for the tips.
Rooney7783 is offline   Reply With Quote
Old 10-26-2005, 08:19 AM   #13
Quarry Creeper
 
Join Date: May 2005
Location: lost in vintage tamiya land.
Posts: 305
Default

It was to my understanding that mounting the chassis end of the links at the same point but still triangulated (like the bulu 2's are setup) eliminated torque twist but your saying it's bad for axle steer am i right? If so then why do so many people run em mounted like that?
Rockinrockcrawler is offline   Reply With Quote
Old 10-26-2005, 10:34 AM   #14
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

Quote:
Originally Posted by Rockinrockcrawler
It was to my understanding that mounting the chassis end of the links at the same point but still triangulated (like the bulu 2's are setup) eliminated torque twist but your saying it's bad for axle steer am i right? If so then why do so many people run em mounted like that?
I don't claim to know all there is to know about linked suspension but from my understanding on RC rigs it is supposed to help with torque roll. I have not tried it. The reason it doesn't get used in 1:1 is because the power to weight ratio is so different. RC's are just too lightweight for all the principles to apply.

In RC's I think axle steer is mainly caused by poor triangulation. Or loose mounting points.
rckjeep is offline   Reply With Quote
Old 10-26-2005, 09:31 PM   #15
TEAM MODERATOR
 
Reflection's Avatar
 
Join Date: May 2004
Location: Tennessee
Posts: 10,855
Default

Quote:
Originally Posted by Rockinrockcrawler
It was to my understanding that mounting the chassis end of the links at the same point but still triangulated (like the bulu 2's are setup) eliminated torque twist but your saying it's bad for axle steer am i right? If so then why do so many people run em mounted like that?
I had the opposite results in my Twin. I was running my links off the same plain at the chassis and horrible Torque twist. With that same set up I played with shock oil,springs and shock mounting locations and could get it more under control,but it was still unacceptable. I then tried changing my links mounts and it's hardly even noticeable. My links are 1 1/4" apart(verticly) at the axle and 3/4" apart at the chassis.

As far as axle steer,I think it's solely due to poor link configuration. With a double triangulated set up you can get the best results. From looking from the top of the rig my links are like this(rear axle) l\/l (front axle) l/\l. I've got a shade of axle steer but it's not really a big deal to me as of yet. Someday I will make my links like this XX front and rear,I'm confident that this will eliminate my axle steer. With the correct vertical separation and link length in the XX configuration,you can just about eliminate all axle steer.

In the RC world there are some factors and rules you can fudge on or not worry about. For one,nobodies life is at stake and like stated above,the power to weight ratio is alot different. Alot of the same principles can and still do apply. With building ANY custom suspension,regardless if it's RC or 1:1,there will be ALOT of trial and error and testing different set ups to dial it in perfect. Even if your building for 2 rigs that are very close to the same set up,there will be slight differences that will vary the results.

Best thing to do,build adjustments into your set up so you can adjust it to your likings.

Last edited by Reflection; 10-27-2005 at 08:33 PM.
Reflection is offline   Reply With Quote
Old 10-27-2005, 02:00 AM   #16
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

Raptorman great reply but please spell check that thing it's hard to read. My head hurts.
rckjeep is offline   Reply With Quote
Old 10-27-2005, 08:38 PM   #17
TEAM MODERATOR
 
Reflection's Avatar
 
Join Date: May 2004
Location: Tennessee
Posts: 10,855
Default

Quote:
Originally Posted by rckjeep
Raptorman great reply but please spell check that thing it's hard to read. My head hurts.
Sorry,I'm just a dumb bricklayer ................Spell check done
Reflection is offline   Reply With Quote
Old 10-31-2005, 12:00 AM   #18
I wanna be Dave
 
Join Date: Jun 2004
Location: San Jose
Posts: 5,207
Default

Quote:
Originally Posted by raptorman57
Sorry,I'm just a dumb bricklayer ................Spell check done
Hey, my dad's a retired tile setter. It's the same union out here. Anyway he can't spell for **** either.

Much better, it is good info.
rckjeep is offline   Reply With Quote
Old 09-21-2007, 05:17 PM   #19
I wanna be Dave
 
toy4crawlin's Avatar
 
Join Date: Feb 2006
Location: Campbell, CA 4 hrs 2Rubicon !
Posts: 2,044
Default

Quote:
Originally Posted by rckjeep View Post

Finding the correct link length is not a hard task. In fact it's quite easy. If you know how to measure and have a little common sense. I'm going to go with a common 50/50 set up for ease of explaining it. So lets say you have a chassis in your hand.
For example my RockStar Chassis. Figure A

Now the lower link holes are 3 1/8" apart and you are looking for a 12.5" wheelbase. Now the place that most people mount their lower links to the axle is shown in figure B.

Now those links are 4" apart and the RockStar chassis is 3" wide. So you know by common sense that the lowers will be triangulated. So by looking at the picture above you measure the distance from the link mount hole center and the axle centerline. Which is roughly 5/8". And just for ease of reference the length of a standard(non short)traxxas ball end is also 5/8". So if you where to make a link using aluminum tubing with all the numbers I stated you could get the correct link length for the lower links to achieve a 12.5" wheelbase.

Here's the equation. (I'm using the decimal equivlant so you lazy arses can use a calculator)

Add the 5/8" of the (axle side) link mount to axle centerline on both front & rear.
.625" + .625" = 1.25" or 1 1/4"

Now subtract that 1 1/4" from the wheelbase of 12 1/2"
12.5" - 1.25" = 11.25

So your lower link mount holes are 11 1/4" apart.
Remember we said the lower link holes on the chassis are 3 1/8" apart? Well now you subtract that 3.125 from the 11.25. This # will give you a starting point for your lower links.

11.25" - 3.125" = 8.125" or 8 1/8" Now divide that by two. 8.125"/2 = 4. 062 or 4 1/16". There's your number 4 1/16" would be you eye to eye link length.
You also need to consider the ride height and the angle that the lower links will sit at.

If you are going to make your own links remember to also add the length of the ball ends(5/8"each, 1 1/4" together) and subtract that from your cut size on the tubing.

On my RBX the wheelbase is just about 13" with a ride height of 2 3/4" at rest and 3 1/4" without any sag. When I dropped the ride height down it gets a little longer because the links are almost flat. My lower links measure 4 1/2" eye to eye but the aluminum tubing is just 2 3/4" long because I used the longer Dubro heavy duty ends. See figure C


On to the upper links.

The upper links do a few things they set your pinion angle, which in turn sets your caster. Ideally you want to run 0* of caster for RC crawling. It gives you the best turning with a decent pinion angle. Once you have the lowers figured out, made and attached to the axle and the chassis. Set your front axle caster to zero and measure from your upper link mounting hole on the axle(now it doesn't matter which, how, or what you are using for upper link mounts) to the upper link mounting hole on the chassis.
Here in figure D you can see my front upper links are pretty short being mounted behind the servo.


Now use the info I gave you for measuring your lowers and do the same with your uppers and remember to shoot for close flat links and zero caster.

Hope this helps you guys in your building. If I should add or change anything please let me know. thanks

I'd like to go over a detail if I may
This some what works for folks that allready have a Chassis .

My big Question here is Isn't there a equation for How far apart the Front lower Links are from the REAr Lower links what is the Chassis length to have proper link setup and Or hoe long should the links be
Example:
Is a chassis at 5" long that the links bolt to respond the same as a
chassis that is only 2.5" long

Last edited by toy4crawlin; 06-07-2011 at 10:25 AM.
toy4crawlin is offline   Reply With Quote
Old 02-09-2008, 03:15 AM   #20
RCC Addict
 
Join Date: Jan 2008
Location: www.rccrawler.com
Posts: 1,113
Default I wish

I wish that someone would do exactly this kinda thread for the clodbuster axles:-(
TheHeadHunter is offline   Reply With Quote
Reply



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 09:20 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO ©2011, Crawlability, Inc.
Copyright 2004-2014 RCCrawler.com