Some CR2 mods

[V-Rossi]

The Atomic Carbon CR2 is an excellent piece of kit but nothing is perfect. Here are some modifications to the car, at this moment solely tested on astroturf (high and medium grip) but each of them being a big improvement on the handling of the CR2.


1) XXX rear end:

Those who are familiar with the Losi Forum and/or have ever inspected the car of the Mighty Chris Doughty might have seen this mod already. The rear XXX-CR suspension (pivot block - wishbone - hub) is replaced by parts of the XXX and XXX-T MF2. It looks like this:



and



The CR pivot block is very wide, which is good for rough tracks. Its predecessor, the BK2, was extremely narrow. And the XXX one is in between. So from narrow to wide: BK2 < XXX < CR.
This creates an imbalance front and rear, which can be solved by fitting the XXX block. The following image illustrates this:



The block on the right is the standard CR one, as you can see it is a lot wider than the one in the middle (XXX). On the left we have the front Losi pivot block (same on XXX, CR and I think BK2 as well). Notice the same width of the XXX front and XXX rear pivot block => balance.

On the first images you can see which hubs I used: XXX-T MF2 ones. You can use the standard CR ones but their bigger offset makes the car a few millimeters wider, which isn't the goal of this mod. The standard XXX or BK2 hubs have the perfect offset, but! have lower camber link mounting holes than the MF2 hubs have. I strongly suggest using the MF2 hubs (middle hole).

Part numbers:
- Pivot block: LOSA4126 (plastic) or LOSA4149 (aluminium)
- Wishbones: LOSA9800 (BK2 graphite) or XXX
- Hubs: LOSA2128

Both pivot blocks are good but the plastic ones are prone to excessive play. If you don't want to spend your earnings on an expensive alu one, simply use some spacers, cheap and perfect as well
Wishbones then. If you use the BK2 ones, use the short VLA hole. This has about the same length as the standard hingepin hole of a XXX wishbone.

Our findings? The Atomic Carbon team in Belgium tested it during a club race and National @ Kampenhout, and found this rear end to be a big improvement. It gives the car more steering while maintaining a lot of rear end grip. The car's suspension reacts in a more balanced way as well. So far we haven't noticed any downsides to this mod.


2) Front wheelbase mod:

This is a very simple one. The idea is to extend the wheelbase of the car on its front end. So dremel about 1,5mm off the front side of the hub (1,5mm is about the thickness of a wheelbase spacer at the back) and move the hubs forward. This will increase the total wheelbase, but that isn't the only goal.
When placing your front and rear hubs forward (so front long and rear medium wheelbase) you don't make the car any longer, but maintain the wheelbase. The only difference is that more weight is shifted to the rear end of the car. Simply moving the rear hub forward does the same thing, but the CR2 is already a short car, so with this mod you don't make it any shorter and you'll still be able to get more weight to the back. Here is an example:






The effect? I used both front and rear long wheelbase, this made the car a lot more stable. It gives you a little less steering, but most people will hardly notice it. And while not being really faster over a single lap, it does make it a lot easier to be fast on a consistent base. Again we are all using it (with great effect, the CR2s had 1st, 5th and 7th place at the National) as it makes the car a lot easier and more fun to drive.


3) Battery bar - 'the Northy strap'

This is a picture of Jonathan's car (I hope he doesn't mind ):



As you can see it has only 1 battery bar, which makes it a lot easier to change batteries. You can make it yourself out of a B4 battery brace but JC will make them himself as well, and they look brilliant!

Secondly, the link going from the top of the gearbox to the battery brace is an anti-flex link. This way you don't need the brass gearbox brace anymore. Only difference is that we made a small plate on top of the gearbox with a hole in the middle, to have the link more in the center line of the car instead of having to choose one of the (non-centered) holes.


4) Extra hole in rear wishbone:

We did it on the S2, and we did it on the CR2: drilling an extra inner hole in the rear wishbones. Both on the CR and XXX rear end this helps rotate the car faster and enables a bigger or faster throttle input when riding bumps. In fact on the XXX rear end the extra inner hole is the standard one at the moment. From center of standard inner hole to center of newly drilled hole it should be around 4-5mm. Note that you should adjust your dampening to this new position. I'm using 2,5wt-5wt thicker oil and a smaller piston with the new hole.

I hope this helps

[V-Rossi]

Picture problem fixed

[Razer]

How did you mount the rear end? The bottom of the chassis rubs the arms if you put on the aluminum pivot block and a9800 arms, and there isn't much material to remove either... I use this mod on my regular CR, and it works great, but I'd like to try it on the CR2 as well.

[V-Rossi]

Take a bit of material off with a dremel or file, you don't have to remove that much as it is quite close.
And of course you will have to do this with the T-plate as well, as the hingepins are closer to each other on the XXX block.

[Razer]

Originally Posted by V-Rossi

Take a bit of material off with a dremel or file, you don't have to remove that much as it is quite close.
And of course you will have to do this with the T-plate as well, as the hingepins are closer to each other on the XXX block.

So you take away material both from the arms and the t-plate? I took away some material on the t-plate in front of the pivotblock - it feels bad to take away much from a place were there's little to begin with

I'm nearly always faster with my CR than with my CR2, so I need to try it all

[V-Rossi]

No off the chassis and T-plate, sorry

The T-plate (I'm using the Rudebits one) needs quite a lot of dremeling/filing.

On which surface are you struggling with the CR2?

[Razer]

Originally Posted by V-Rossi

No off the chassis and T-plate, sorry

The T-plate (I'm using the Rudebits one) needs quite a lot of dremeling/filing.

On which surface are you struggling with the CR2?

What other rudebits are people using? (Saw there was a lot of options...)

I like the CR2 quite well on carpet, but I have been just as quick with the regular CR. Last weekend at the first Norwegian Cup race, running on astro, I also ended up with the CR. It shall be said that it was cold and moist, so that the grip wasn't all there.

I'm by no means a top level racer by european standards, but I can easily run 5 minutes without mistakes and push the car quite well, so I feel that the CR2 hasn't been quite up to the task.

I think playing around with weights and setup should help a lot, I'm just a bit lost on what to do...

[V-Rossi]

Send me your set-up in a pm please

I'm using the brass T-plate from Rudebits only, as that is by far the most important upgrade to have.

[Thomas P]

Rossi, what can you do with my S4 =)?...are you a magician :P

Top notch tip...

/T

[V-Rossi]

Originally Posted by Thomas P

Rossi, what can you do with my S4 =)?...are you a magician :P

Top notch tip...

/T

Hmm yes sort of, but my sword swallowing isn't first class just yet

I don't know that much about 4wd cars I'm afraid

[Stumpz]

Hi Rossi,

Do you know if you can fit RC10b4 Axles on the CR2 and would they work as i have an S2 at the moment and thinking of changing to the CR2 but still have a lot of new tyres on B4 Rims.

Many Thanks.

[DaSloth]

rear ones should be fine, but front wouldnt work i dont think. I swapped the hubs around so i could use b4 front wheels for a dirt event and seemed ok, but there was alot of slop

[V-Rossi]

It works! A fellow CR2 driver did this mod in his car and there is no problem with it, same track width and everything. And it doesn't change the suspension geometry or something.
I'll ask him to take some pictures and then put them (with some info) in this topic

[V-Rossi]

Added a 4th item to the original post.


P.S.: I updated my set-up for astro tracks (rather flat, not bumpy like UK ones: http://picasaweb.google.com/bnkoffro...48501900709746). Stagger front and Mini Pin/Spike rear, both work with this one. If needed, send a pm.

[Legacy555]

Having a crap problem and someone on oople forums must have the answer.....

I've fitted the XXX (old style) rear end to my CR2, and am pretty happy with it. However, I'm having a small problem and I just wanted to see has anyone got a solution - ie. a part number

With the alloy XXX-T pivot, BK2 arms (outside VLA hole removed) and XXX 1 degree hubs, the XXX-CR CVDs are slightly too short and the end of the shaft almost comes out of the diff outdrive at full droop. So I fitted BK2 CVDs (as they were in the pit box) and they are a pinch too long and are hitting the diff nut at full suspension travel.

So I'm assuming that there is CVD shorter than the BK2 one and longer than the XXX-CR one. Losi manual says I need part # A-9923 - but a google search for this shows it's for XXX and XXX-CR...... not good!

Anyone encounter this? Anyone got a part number for the correct "middle" length CVDs or even just the CVD dogbone?

[V-Rossi]

Have you dremeled the Losi wheel spacer or replaced it with a B4 one? If you do that and put some shims on the inside of the hub, the axle is placed further towards the outdrive. Works very well, even when using the extra hole on the wishbone.

[Legacy555]

Thanks Jorg,

Is there a drive shaft available that is between a XXX-Cr and BK2 in length?

[V-Rossi]

Don't know actually, as the CR is the only Losi car I ever used

Elvo might know this though, send him a pm.

[tom plumb]

I have a cr2 but this is my first year racing i love the car do these mods make a brillant car even better and would a beginner like my self realy benefit from these mods cheers

[V-Rossi]

Not one of the mentioned mods to the CR2 makes it harder to drive, they are mainly suspension geometry improvements, which make it more balanced.

Of the above I think the only thing you should definitely have is the horizontal battery strap which replaces the two standard ones. This is more a security option than a performance increasing option though.

The XXX rear end is being used by an increasing amount of drivers, all of them liking it. The only situation where you could benefit from using the CR rear end (the standard one) is when the track is very rough. Like grass tracks at times.

You will notice the big difference when you use the XXX rear end and after a few weeks/months put the CR one back on to test