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 http://www.nor-calrcrc.com/albums/album10/aaa.sized.jpg 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. http://www.nor-calrcrc.com/albums/M-.../aav.sized.jpg 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 http://www.nor-calrcrc.com/albums/album13/aal.sized.jpg 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. http://www.nor-calrcrc.com/albums/album13/aaq.sized.jpg 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 |
Great tutorial RCKJeep! Just in time too. My TLT is going to be rebuilt after this weekend's comp Thanks good info |
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. :) |
Thanks for the great post. |
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. |
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. |
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. |
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. |
Thanks, Great Tech article! |
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 :mrgreen: http://www.xtreme4x4tv.com/news.aspx?iid=5023 |
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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. http://www.nor-calrcrc.com/albums/album13/aag.sized.jpg 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. |
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. |
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? |
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In RC's I think axle steer is mainly caused by poor triangulation. Or loose mounting points. |
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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. |
Raptorman great reply but please spell check that thing it's hard to read. My head hurts. |
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Much better, it is good info. |
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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 :?: |
I wish I wish that someone would do exactly this kinda thread for the clodbuster axles:-( |
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