4 link, pan hard, and the fms 1/10 atlas 4x4

[Minoa]

So I picked up an FMS atlas 4x4 for my son for Christmas. I've watched a ton of review and upgrade videos so I know all the major issues with the truck. My question is regarding the pan hard and 4 link set up. Everyone who mentioned this set up seemed confused by the decision made by fms to have both, but none really addressed it. Does a truck need a pan hard if it has a 4 link set up? I only own moa trucks so I have no experience with this issue. Can I just remove the pan hard and be fine?

I'm not looking for serious performance with the truck, my son is only 5 and will be trailing with it but like most here, if I can fix known issues to get the most from the truck, I'm going to do it. Any opinions would be appreciated.

 

[89Industries]

I have no first have experience with this truck but looking at the fms website it looks to have a chassis mounted steering servo and a 4 link front axle.

This set up will create bump steer.
The fix is either mount the steering servo on the axle, or add a panhard bar and remove one of the upper links.

Or your 5 year old may not notice the bump steer. Mine probably wouldn't.

Why bump steer? The 4 link suspension keeps the axle centered relative to the chassis as it travels up and down. But because the steering link is crossing from the chassis mounted servo to the axle moving up and down, the horizontal distance of the steering shaft gets longer or shorter as the axle goes up and down. To deal with this you take away one of the 4 suspension links to allow the front axle to move side to side relative to the chassis as it goes up and down, and you add a panhard bar to control that side to side motion. Ideally the panhard bar is parallel to the steering link and you get no bumpsteer because the panhard bar is moving the axle side to side the same as the steering link does as the axle travels vertically through its travel.

 

[Gula]

Are you able to post pics? It seems that this rig is the exact same as the 1/6 jeep with just a different body and "re-scaled".

Let me check mine "jeep" , as I have the body off my frame/chassis. I can take a look and "report" back what you could possibly do.

 

[Minoa]

89Industries... My 5 year old won't know the difference either. This is purely a me problem Haha. What side of the upper link should I remove, the side where the pan hard mounts or the opposite side? It would seem logical to remove the side where the pan hard is mounted but this is just a guess.

Gula, I'm not able to post pics atm. I can this evening

 

[Gula]

This is how mine looks 1/6 rochobby fms jeep willys, hope this helps:
So, all I think you need to do is remove the 4th link, but you must keep the panhard!

*EDIT That rig for sub $200 is awesome, especially for a 5 year old! Durable, and replacement parts are very cheap! Other than the alloy chubs and knuckles costing $50, me feeling that's a rip-off

 

[89Industries]

89Industries... My 5 year old won't know the difference either. This is purely a me problem Haha. What side of the upper link should I remove, the side where the pan hard mounts or the opposite side? It would seem logical to remove the side where the pan hard is mounted but this is just a guess.

Gula, I'm not able to post pics atm. I can this evening

I'm not sure if matters to much which side.

Per Gula's post above with same brand of truck, I'd take out the upper right.

Looking at the 4 trucks I have that use a panhard bar, 3 keep the right, 1 keeps the left.

Easy enough to switch sides later if it acts weird.

 

[Minoa]

Yeah I just got it during the current sale. $215 after taxes. I wanted a full 1/10 scale for him that could be upgraded. Last Christmas I got us 2 temper gen 2 crawlers. Really cool vehicles but the durability was not there. Both are sitting in my man cave broken. 1 with a snapped axle and the other a screw snapped off flush in the aluminum knuckle. Both happened with just trailing use.

 

[MAGNUMB]

I have no first have experience with this truck but looking at the fms website it looks to have a chassis mounted steering servo and a 4 link front axle.

This set up will create bump steer.
The fix is either mount the steering servo on the axle, or add a panhard bar and remove one of the upper links.

Or your 5 year old may not notice the bump steer. Mine probably wouldn't.

Why bump steer? The 4 link suspension keeps the axle centered relative to the chassis as it travels up and down. But because the steering link is crossing from the chassis mounted servo to the axle moving up and down, the horizontal distance of the steering shaft gets longer or shorter as the axle goes up and down. To deal with this you take away one of the 4 suspension links to allow the front axle to move side to side relative to the chassis as it goes up and down, and you add a panhard bar to control that side to side motion. Ideally the panhard bar is parallel to the steering link and you get no bumpsteer because the panhard bar is moving the axle side to side the same as the steering link does as the axle travels vertically through its travel.

I just tested my SCA-1E 4-link and have almost zero bump steer...had to cycle several times to even notice the slightest bit of bump steer....tbh some of my 3-links have more. This whole thing with 4-link with CMS and having tons of bump seems to be blown way of proportion

 

[Gula]

So did you try? They're identical rigs; your son's and the one i posted pics of.

 

[89Industries]

I just tested my SCA-1E 4-link and have almost zero bump steer...had to cycle several times to even notice the slightest bit of bump steer....tbh some of my 3-links have more. This whole thing with 4-link with CMS and having tons of bump seems to be blown way of proportion

You have a 4 link and chassis mounted servo? You will have bump steer. Might be minimal but it will be there. The axle is traveling straight up and down (when viewed from the front). The steering link is essentially going around in a circle around the end bolted to the servo horn so when the axle goes up, the steering link gets longer horizontally so the end at the axle has to push on the steering of the hubs. There's a chance you have a lot of slop in your pivots or a week servo which would mask some of the bump steer.

3 link with panhard bar is easy to get bumpsteer if your panhard bar and steering link from servo to axle are not parallel. Not sure all the people designing RC crawlers have realized this. Some panhard bars are adjustable(like element rc). You can also use different height servo horn to adjust the link to the panhard bar angle. Swapping the cheap plastic stock servo horn with a nice aluminum one probably causes bumper quite often since it changes the angle of the steering link without adjusting the panhard.

 

[Minoa]

Gula, I looked at it. I even took one of the upper links off. When I cycled the suspension, at full extension, the shock opposite of the pan hard bar mount would kink to the side and lock up. Probably more so because of the cheap shocks (they are the shocks off the temper gen 2). I just put the 4th link back on. My kid is only 5, he's not going to know the difference. I'm going to fab up a servo on axle mount eventually.

 

[MAGNUMB]

You have a 4 link and chassis mounted servo? You will have bump steer. Might be minimal but it will be there. The axle is traveling straight up and down (when viewed from the front). The steering link is essentially going around in a circle around the end bolted to the servo horn so when the axle goes up, the steering link gets longer horizontally so the end at the axle has to push on the steering of the hubs. There's a chance you have a lot of slop in your pivots or a week servo which would mask some of the bump steer.

3 link with panhard bar is easy to get bumpsteer if your panhard bar and steering link from servo to axle are not parallel. Not sure all the people designing RC crawlers have realized this. Some panhard bars are adjustable(like element rc). You can also use different height servo horn to adjust the link to the panhard bar angle. Swapping the cheap plastic stock servo horn with a nice aluminum one probably causes bumper quite often since it changes the angle of the steering link without adjusting the panhard.

Yes...all the carisma SCA-1E's has this setup...and i'll look again, but i don't notice any notable bump steer. Yeah it might be super minimal, but overall, this rig performs very well

 

[89Industries]

Yes...all the carisma SCA-1E's has this setup...and i'll look again, but i don't notice any notable bump steer. Yeah it might be super minimal, but overall, this rig performs very well

I just checked the sca-1e's out. So they do. Interesting choice on their part.

I hadn't checked out the carisma stuff much. I like some of their body options. Not just the normal jeeps and Toyotas.

 

[MAGNUMB]

I just checked the sca-1e's out. So they do. Interesting choice on their part.

I hadn't checked out the carisma stuff much. I like some of their body options. Not just the normal jeeps and Toyotas.

The Land Rover, Subaru Brat and pickup trucks are real good looking rigs on the trail and they shouldn't perform as well as they do. The chassis just looks kinda cheap, but it's one of the more durable rigs i have and one i tend to drive more than any of my others. For the price they are very hard to beat.