3 link cms question

[wingnutcrawler]

i 've already used the search function so please no flaming. i understand the the hows and whys but still have one question.. i am putting together a cms w a 3 link and panard rod . my question that i can't seem to find an answer to is does the upper link from the frame to the axle need to be centered from side to side or can it be anywhere on the axle. thanks in advance carl

[ultimate_monkey]

it can be any where, all its ther for is to stop the axle from rotating

[wingnutcrawler]

thanks ,that was my assumption as i've seen a few setups like that.

[halfcab]

Wrong answer, the panhard bar is to keep the axle centered under the chassis, when using a pan hard bar you want the drag link and panhard bar to be close in length and on the same plane...... parallel to each other within a very few degrees, if not you will end up with bump steer

[BAWLER CRAWLER]

I think he was referring to the placement of the third link, it doesn't need to be centered. Drag link and panhard same length and plane for sure.

[halfcab]

Originally Posted by ultimate_monkey

it can be any where, all its ther for is to stop the axle from rotating

Originally Posted by BAWLER CRAWLER

I think he was referring to the placement of the third link, it doesn't need to be centered. Drag link and panhard same length and plane for sure.

True enough, placement is not critical on an RC sized truck as long as you follow the basics... same length/plane, but it does nothing to prevent rotation of the axle, that is what the 3 links do, not the panhard

[ridepate]

I'm going to put this out there, remember this is my PERSONAL-OPINION......I 'm sure all the "Expert 2k-Posters" will chime in...... , they just can't help it....A pan-hard bar is un-needed and frankly ridiculous on a 10th scale-scaler with CMS that does 3MPH, 3 or 4-link.
You will never be able to feel or tell you're getting bump-steer or axle-shift. Static on the bench, you may see it ,but on the trail, you'll never know it's there. Scaling is nothing compared to comp-rigs, which it may make a difference in a comp with a true-comp rig, I can see that, but on a scaler???
You've got to be kidding.
If you're going for true 1:1 scale, I guess it does look good and is true to scale, but really needed??? NO. Just something else to fall-off.
I think the whole panhard thing has come from compers that have turned scalers.......Like I said. My opinion.

[myth619]

In response to Ridepate....I have a 3link ( wishbone and two lower links) and a CMS. While just driving around, yes you'll never feel the effects of not having a 3link and a panhard bar but where it becomes an issue is if the draglink is not perfectly parallel with the axle and the rig is fully flexed the steering can become ineffective. It happens on mine when the side of the axle that the draglink connects to is fully drooped and the other side is compressed. If/when I have a 3link and panhard this issue will go away and Ill have steering in any position.

[rckjeep]

How many times do we have to go over this panhard/bumpsteer thing. It's getting ridiculous. To the OP the upper can be anywhere on the axle. Todd I think he gets the panhard location but the upper/3 link axle side is his question.

[wingnutcrawler]

yes my original Q was just about the third link on the axle. thanks guys for all the comments. all the parts are made out of delrin and it came out great. i will test it out this coming weekend.

[ridepate]

Originally Posted by myth619

In response to Ridepate....I have a 3link ( wishbone and two lower links) and a CMS. While just driving around, yes you'll never feel the effects of not having a 3link and a panhard bar but where it becomes an issue is if the draglink is not perfectly parallel with the axle and the rig is fully flexed the steering can become ineffective. It happens on mine when the side of the axle that the draglink connects to is fully drooped and the other side is compressed. If/when I have a 3link and panhard this issue will go away and Ill have steering in any position.

Agree. But it's not hard to make a d-link that is parallel.

[War Pig]

Originally Posted by wingnutcrawler

i 've already used the search function so please no flaming. i understand the the hows and whys but still have one question.. i am putting together a cms w a 3 link and panard rod . my question that i can't seem to find an answer to is does the upper link from the frame to the axle need to be centered from side to side or can it be anywhere on the axle. thanks in advance carl

Carl, it will be best to try to get as close to center with the upper link as you can. I have found that if the upper link is too close to either side of the axle it can cause weird binding issues and can limit the flex throughout the travel.

Here is how I was going to mount my upper link on my '34. I had all kinds of issues with it.



This is where I ended up mounting the top link at the axle end. It took some fabrication and fitting but works perfectly now.



Here you can see the link and how tight the clearances are to the motor and cross member.



And here you can see how the link is centered on the axle and just inside the right frame rail on the chassis end.



Also, don't let anyone tell you that a panhard bar is unnecessary. Most scale rigs go faster than 3 mph and bump steer is obvious at just about any speed. I can see bump steer and how it effects my rig every time I drive it.....especially in the back if you have rear steer. Plus with a panhard bar you don't have to worry about worn rod ends...the axle is located side to side and it won't develop slop over time. Designing a good 3 link with panhard isn't easy, but the rewards are worth the effort.

Here is the front panhard on my '34:



And the rear:



Notice how they are level at rest? That's one of the tricks....

[wingnutcrawler]

thanks war pig. it is close to center but i could of put it on the left side and got it closer . it just looked cleaner on the right. i wish i knew how to post pics. i would like some opinions.

[heinie_21]

Originally Posted by ridepate

I'm going to put this out there, remember this is my PERSONAL-OPINION......I 'm sure all the "Expert 2k-Posters" will chime in...... , they just can't help it....A pan-hard bar is un-needed and frankly ridiculous on a 10th scale-scaler with CMS that does 3MPH, 3 or 4-link.
You will never be able to feel or tell you're getting bump-steer or axle-shift. Static on the bench, you may see it ,but on the trail, you'll never know it's there. Scaling is nothing compared to comp-rigs, which it may make a difference in a comp with a true-comp rig, I can see that, but on a scaler???
You've got to be kidding.
If you're going for true 1:1 scale, I guess it does look good and is true to scale, but really needed??? NO. Just something else to fall-off.
I think the whole panhard thing has come from compers that have turned scalers.......Like I said. My opinion.

Steering problem - YouTube

[rckjeep]

Originally Posted by heinie_21

Steering problem - YouTube

That's a great example of why a chassis mounted servo should also run a 3 link with panhard bar. Think of that happening on a climb that is slightly off camber, sloping to the drivers side. Then tell me a panhard 3 link isn't need on a RC.