DEX210: Alternatives for Low Roll Center/LRC
 

Hi everyone,

Lately I've been looking at a low roll center modification for the DEX210 as that should aid rear traction - not a bad thing considering I drive mine in mid-motor on low bite dirt and clay. However, the parts from RDRP are very expensive though - and the ones from Tresrey and Durango don't allow for 0 degrees of anti-squat without modding the (!&@ out of an RF hanger.

So, alternative options might be:
1. A second hand set of RDRP hangers.
2. Machining 2mm off the standard Durango hangers.
3. Asking a company like Cream RC to consider producing LRC rear hangers.
4. 3D Printing a set of LRC hangers (likely not as durable as alu though).
5. Using parts off DEX210 clones.

The last one caught my interest. The Proken S1 parts might work and look as if it may indeed have a lower roll center. The Intech ER-12's rear suspension user different hangers altogether (more distance between inner rear hinge pins), which funnily enough seems to be a mod that the DEX210 proto at the Worlds has - and I recall so does the X6 line of cars (the X-6^2's I've driven had tremendous rear traction and always seem to lean on their outside rear wheel a lot - so it seems an interesting difference to try out in my situation).

So... does anyone have an Intech ER-12 and/or a Proken S1, a set of calipers and a few minutes of time to check the measurements? :D Or suggestions what other parts may fit?

The proken looks the same but from what I've seen everything is different. I think shaving the RR block and using shims there will be your best bet.

Durango has a -2mm LRC hanger available for the Type B chassis sets. I machined an original TD RR hanger to accept the new Type B motor guard quite a while ago when I received a few of the proto Type B chassis. Very helpful mod to gain rear bite and give the back end a more stable feel.

I saw that, and good to hear it helps :) However, Durango doesn't seem to offer RF hangers that can give 0 degrees of anti squat combined with the RR hanger... and I don't have any machining equipment to do an accurate job myself to make a -2mm plastic or metal RF hanger. So are you running 3 deg at all times, or have you found another way to get 0 deg. anti-squat with the LRC RR hanger?

Edit: With minor dremeling, one could also put the original RR hanger upside down, which puts the mounting point 2.5mm lower on the rear - which only leaves the RF hanger to be lowered (For a 2mm lower mount, one could do a bit of dremeling on it and shim the block upward from under the hanger). I've got an idea for a 3D printed RF hanger that might work with this to achieve proper anti-squat adjustability.

what is it about the lrc blocks that makes them better/different than adding shims under the ballstud to lower the roll center?

I have a complete set of Alum blocks, so when I machined the RR I also machined each of the RF blocks. That said, I run RM and never run 0°, though I do have the 0° installed and then shimmed up. Much easier to slide shims in and out than to change a block.

I suppose if I had read your first post a little better I would have realized that you were trying to get 0°. Oops.

A angled link (which is lower on the inside) not only adds grip, I'm told it also reduces the tendency to roll compared to a link that's parallel to the suspension arm. Also, look at this image (taken from http://users.telenet.be/elvo/) carefully, and you'll see lowering the upper link on the inside actually makes the roll center higher:
http://users.telenet.be/elvo/3/RC4.gif

As far as my understanding goes, it works like this: The roll is caused by a torque: The force caused by the shifting weight times the distance (arm) between the sprung mass and the roll center. This mass has the center of gravity (CoG), and there will be a distance between that and the roll center. The amount of distance is one of the ways to play with the amount of body roll (because it works as an arm in the torque formula).

The roll center (of most cars) seems to be lower than the center of gravity. Therefor a higher roll center (closer to CoG) will reduce body roll, and a lower one (further from CoG) will increase body roll.

Increasing body roll increases sideways bite on the car. This is beneficial in low traction conditions to make the rear end feel safe and planted, so you can floor the throttle earlier and more. In high traction conditions you don't want that much body roll, in fact you often are trying to reduce it to prevent the car's tendency to grip roll. Also, the reduced body roll may make the car respond quicker to changing direction.

If you look at the posted image again, you can see that lowering the inside pivot points of the lower suspension arm will lower the roll center. That why a LRC conversion will add rear grip to the DEX210 without playing with strange upper link positions :)

Mind you, this is my understanding of how it works. If I'm wrong please tell me :lol:

well, you certainly interpreted what I said wrong. By adding washers under the inner ball stud, you raise the ball stud thus lowering the RC.

I understand what the effects of RC location have to do with handling. What I don't understand is why you need a special block to lower the roll center when you could just as easily do it by adding washers... :confused:

Raising the RC will actually increase side bite. When you raise the RC, more weight is distributed to the outer wheel in a turn. This loads up the wheel and causes it to bite. The danger of a high RC, though, is what happens when that outside tire decides to let go. When it lets go, it's usually abrupt and not controllable.

A lower RC is the opposite. The weight is split more evenly across both tires. This is good on a low grip track because you're gonna loose traction no matter what you do, so you don't want it to be abrupt and uncontrollable when you do. A lower RC is what makes cars "rotate" in the corner. The outside tire is loaded up so the tires slide a bit.

I remember watching one of the losi videos and they discussed their RC blocks. It sounded like changing the block also changed the amount of "bind" in the suspension caused by the CVDs. I personally don't like the idea of using drive component bind to alter handling. It just sounds like using the wrong tool for the wrong job.

While I don't claim to fully understand the geometric reasons as to exactly why, here's what I've found. With the standard pivot blocks, I struggled to gain enough forward drive when traction started to drop off. I tried everything I could possibly think of- more anti squat, less anti squat, raised links, lowered links, softer springs, softer oil, long links, short links, and more combinations than I can even mention. The end result was always the same though: if I got the car to be stable on entry, forward drive suffered quite badly and there was usually an apex push. If I got the car to react nicely near the apex, then it was terribly loose on power and any point following the apex.

With the LRC blocks, I can run more anti squat to gain that forward drive, and a shorter link which also helps with that. When I tried this combo with the standard blocks, it was terribly loose on entry. With the LRC blocks corner entry is more stable, apex rotation is more controlled, and forward drive on exit is far better. For medium to low grip tracks, its the best my car has ever been. I was on the verge of offing it as I has struggled mightily, but I'm happy now.

Try the other way round mate...

Lower RC = more roll = more side to side weight transfer
Higher RC = less roll = less side to side weight transfer

And to answer your question, lowering the RC via hinge pins height is not the same as lowering it via ball stud height. What you feel with the ball stud change is mainly the effect from the difference in camber change, not in roll centre height. Whereas when you move the pins up and down it's mostly roll centre height and not very much difference in camber change.

Hope that clears it.

Not exactly. Think of it this way, if you had unlimited traction and replaced your shocks with turnbuckles, what would happen if you cornered too fast? Obviously the car rolls over. What happens when a car rolls over? The inside tire has no weight on it (because it's in the air), and the outside tire has all the weight on it.

Sure, this is an extreme example, but it shows the point. When the chassis can roll, the load on the inner and outer tires will stay relatively the same. When a car can't roll, the load decreases on the inside tire and increases on the outside tire as the car tries to tip over.

Just drive the car if you really need to change it so drastically then team durango would have changed it as they have had two years
Wait and see what the dex210 v2 has to offer

I'm not here to argue... If you think that's what's going on then that's fine by me.

And to answer the original question, if I was you I'd wait a little bit more, TD will answer your prayers. :D

Here's what an actual chassis engineer has to say about it:
And later, he even says this:
He refers to "roll couple" as the distance between the CG and RC. A short roll couple is another way of saying a high RC.

Full article, if you'd like to see all the details on why you're wrong.

What do you think I am? :lol:

Like I said not here to argue with you, only tried to be helpful.

just some guy behind a moniker on a forum trying to tell me I'm wrong without explaining why. If you can't explain "why" to me, you may as well not even be talking. Not trying to be a dick, but I've never accepted "because I said so" as an answer to anything.

I explained though... More roll = more side to side weight transfer.

AND your copy/paste said the same thing...

Weight transfer from body roll plays little role in handling since it is so small. That is a common misconception. The roll center is the coupling point between the sprung and unsprung masses. How lateral force is translated to the suspension members is what is playing the biggest role. It's not the actual change in cg. A higher rc transfers forces more through the suspension members themselves whereas a lower rc transfers more force through the springs. A lower rc actually has more chassis roll than a higher rc. You have to be careful as too high of a rc will cause jacking forces which will pick the suspension up in heavy cornering.

I wouldn't fully agree on that one - Durango seems slow at times releasing improved parts or updates.

Also, take in consideration that a design can't be best in all conditions on all tracks. I can imagine the HRC works well on high traction tracks like Blue Groove conditions or dry UK Astroturf. However, Dutch and Belgian tracks have way less bite than that and are quite bumpy. Combine that with my decision to drive the DEX210 in mid-motor in all conditions and LRC modifications start to make sense. Since the trend is that tracks are getting smoother and grippier it's not at all unlikely the DEX210 didn't see many miles on low-bite, bumpy tracks - even more so as their team drivers usually drive on high profile events with well prepared tracks.

An example where mods already worked is the amount of rear droop: It's quite limited out of the box (the shock can give much more droop than the chassis allows). After the mod it is not limited by the chassis anymore, but by the shock. It added about 6-8mm of droop I think. It helped a lot, but it's still very snappy on-power like Johny5 mentioned.

So to make it driveable I removed a lot of steering, so at least it then lacks grip on the front and rear. It's a blast drifting through every corner to get around, but it's not the way to go :lol: I know I can soften the rear end some more, but it won't be enough. The LRC will (hopefully) give the rear traction the car needs so I can (finally) make the front end more agressive.

that's not an explanation. what fred posted, that's an explanation.

I don't think you read my copy/paste. At least not the point where he said a shorter roll couple (i.e. high roll center) increases weight transfer to the outer tire. Or the part where he said body roll is less than 2% of actual weight transfer.

Hello Origineelreclamebord,

I would like to drive my Dex210 allso with MM on all tracks here in austria, and we have same conditions on our tracks, like they are bumpy and sometimes with realy less bite.
I've just bougth my dex210 and i'm interested to this rear droop mod, you told.
May you can tell me, how this mod works, or give me a link?
I'm new to 2WD, so it would be very helpful for me.


Thanks in advance

This is the mod:
http://i65.photobucket.com/albums/h2...0/IMGP9143.jpg

http://i65.photobucket.com/albums/h2...IMGP9145-2.jpg

It is pretty simple. First, you remove the droop screw (or one that doesn't stick out below) - this should already give you a few millimeters of droop. You may notice then the suspension arm is still touching the chassis plate, and if you unscrew the shock from the suspension arm you should see the eye of the shock extends further down than the mounting points on the suspension arm - so you can gain some more droop.

You can do this by getting out a Dremel and shave off material from the piece of the chassis plate which normally stops the droop screw. Alternatively, you can remove the lug alltogether: If you choose for a Low Roll Center Modification too you have to remove it anyway.

be careful with that much droop. one of my cvd's would bind at full droop when I first built the car. It was enough of a bind that it messed up the outdrive on that side of the car.

Thanks for mentioning it, I forgot an important detail! I use long ball diff outdrives - the standard outdrives are too short even without added droop (the driveshafts nearly fell out). The Gear diff outdrives are also longer than the standard ball diff outdrives, so both of these will work with the mod :)

Thanks for the quick replay and your help!
Also for the warnind, with the outdrives...

Thanks again?:thumbsup:

In addition, or as an alternative to removing the droop screw, I countersunk the hole in the arm using a drill bit and some finesse. Same result as you have shown, and you still have the droop screw should the need arise.

Nice one Jonny5 :)

By the way, I was just wondering: Does someone have an LRC conversion to confirm it's the hinging point that's 2mm lower? (And not the actual roll center that results from ALL the geometry).

I've been looking at the LRC some more, and ordered an RF Hanger (LRC) from RDRP...

It turns out the thing has exactly the same geometry as the 0 degree anti-squat one from the DEX210 kit! :thumbdown: So the LRC kit from RDRP only makes a difference when you run anti-squat.

So for anyone looking to try a low roll center: Buy a 1.5 deg or 3 deg RR hanger seperately - you don't need the RF or 0 degree RR hanger.

I've been looking into why they didn't lower the RF block. It turns out the suspension arm would rub (quite seriously) on the chassis plate. Then the question remains if it may be preferable for the car's handling if the RF hanger is lowered any further - I'll be looking into that next.

EDIT: I have been looking into this: It turns out a TRF201 has a 3mm lower roll center at the RR hanger (both cars adjust the roll center at the RF hanger). That's quite a difference. I can't measure other modern 2WDs at the moment, but I think most cars won't be around the 210's roll center, but around the one of the 201.

EDIT 2:

I've put the roll center in a CAD model. Thanks to Jimmy's nice X6/B4 comparison pictures in one of his reviews, it's easy to compare the differences:

http://i65.photobucket.com/albums/h2...e/DEX210RC.jpg

The DEX210 inner hinge pins and ball studs are about 3-4mm higher than the B4's. The X6's story is more complicated: On clay I recall the ground clearance should be the same as the way the B4 is pictured, so that'd put the hinge pins at a similar height (but further apart) and the gearbox higher up.