DEX210: Alternatives for Low Roll Center/LRC

[Origineelreclamebord]

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? Or suggestions what other parts may fit?

[rcjunky]

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.

[Jonny5]

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.

[Origineelreclamebord]

Originally Posted by Jonny5

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.

[dex210Nick]

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

[Jonny5]

Originally Posted by Origineelreclamebord

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.

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.

[Origineelreclamebord]

Originally Posted by dex210Nick

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

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:


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

[dex210Nick]

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...

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.

[Jonny5]

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.

[Fabs]

Originally Posted by dex210Nick

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...

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.

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.

[dex210Nick]

Originally Posted by Fabs

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.

[Lee24h]

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

[Fabs]

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.

[dex210Nick]

Originally Posted by Fabs

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.

Here's what an actual chassis engineer has to say about it:

If you draw a free body diagram, you can see that the CG shift laterally under roll is very small, even with this super exaggerated diagram with tons of roll. Typically the weight transfer due to roll is under two percent, even in a car that rolls a lot. You are not gaining much by limiting roll. Lowering the CG and or increasing track width are much more effective means of reducing weight transfer.

And later, he even says this:

The converse is true for a short roll couple. If you have short roll couples, engineers say that you have a lot of geometric anti roll which has the same effect as stiffening the suspension, it increases weight transfer to the outside tire. This can increase over or understeer depending on what end of the car you do it to.

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.

[Fabs]

Originally Posted by dex210Nick

Here's what an actual chassis engineer has to say about it

What do you think I am?

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

[dex210Nick]

Originally Posted by Fabs

What do you think I am?

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.

[Fabs]

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

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

[fredswain]

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.

[Origineelreclamebord]

Originally Posted by Lee24h

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 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 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.

[dex210Nick]

Originally Posted by Fabs

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

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

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.