Atomic Carbon CR2 (mid motor XXX)

[DerbyDan]

I don't get to drive off-road very often (perhaps once a month or so), but I do really enjoy it when I do.

Last Wednesday I raced my trusty CR2 at a local indoor club meeting, I had been put in with the beginner's for the heats but qualified 3rd for the A final.... which was filmed by Matt (who runs the meetings) & posted on YouTube;

http://youtu.be/-g2-DbkSGCo

My car is the lead car until a 'grip-roll' on the penaltimate lap put me down to 3rd... which is where I finished

[fredswain]

I've got the 4 gear setup in mine now. I also built a new chassis out of carbon fiber. I lengthened the wheelbase 1/4" and wish I'd have gone slightly more. That CR2 is far too short in my opinion. At least for many US tracks it is. I now have a full sized stick pack mounted across the chassis rather than saddle packs. I have no idea why US drivers can't get mid motor to get rear traction because mine will flip over backwards from the amount of grip I have. The car is so much more nimble and forgiving than any other 2wd I have ever driven and this is regardless of track surface. The difference between rear motor and mid motor is night and day. It is so much easier to drive. Due to my chassis and battery setup I've currently got a 34f/66r weight distribution which helps with rear grip but it is all within the wheelbase which is what matters the most for drivability. No one here can seem to figure that out.

[DerbyDan]

I've got the 4 gear setup in mine now. I also built a new chassis out of carbon fiber. I lengthened the wheelbase 1/4" and wish I'd have gone slightly more. That CR2 is far too short in my opinion. At least for many US tracks it is. I now have a full sized stick pack mounted across the chassis rather than saddle packs. I have no idea why US drivers can't get mid motor to get rear traction because mine will flip over backwards from the amount of grip I have. The car is so much more nimble and forgiving than any other 2wd I have ever driven and this is regardless of track surface. The difference between rear motor and mid motor is night and day. It is so much easier to drive. Due to my chassis and battery setup I've currently got a 34f/66r weight distribution which helps with rear grip but it is all within the wheelbase which is what matters the most for drivability. No one here can seem to figure that out.

Where did you get your 4 gear casing from... I believe the PSI ones are not available now but there was someone over here in the UK that has made some... & I must say they look very nice!

I must admit there is alot talked about with set-ups - weight distributions etc etc, but for me I don't race off road enough to get too involved with it all - I just put the car on the track & drive it.. nine times out of ten so long as i've got the right tyres on it goes ok, certainly I am not practiced enough to benefit from getting the optimum set-up. One thing I would say that i've never found any Mid-motor car i've driven to feel as 'natural' to drive as I remember my old rear motored XX or XXX to be

[Mad Racer]

That looks awesome.!!

I saw some mid mounted xxx when i was over there in the U.K. Some Team driver did the conversion and Losi wasn't impressed from what i was told.

So are you saying that a Mid Mount can get good traction on a loose surface??? Just finished my 22T Truck and has jobs of steering on grass with the rear mount.

Keep in mind i think you can fit XX4 front spindels to a XXX . A team driver did it in the U.S and claimed to carry a lot more mid corner speed and since used them on the new 22 platform.

I will Try a Mid mount one day on the 22T just to see how much different it is.

Thanks for the pics

[fredswain]

Mid motor can get traction on any surface if you know what you are doing. Front to rear weight bias is what counts. On a high grip surface such as grass, asphalt, carpet, etc, having more weight up front up is a good thing. On low traction surfaces you need more weight on the rear. The 22 runs into some issues in mid motor that makes it fine for high grip tracks but not low grip. The gearbox is designed in such a way that the motor sits farther forward than it needs to. This pushes the battery farther forward as well. On top of that many people run their batteries lengthwise in the chassis. You don't really have many options in the 22 due to space. This leaves lots of weight on the front. You'll get something like 62% or so on the rear. For high grip tracks this is fine. For low grip it isn't. Many people will add all the weight they can at the back to get more weight on the rear but the problem on the 22 is where the weight is added. People add brass weights at the very back which is behind the rear axle centerline. That's a bad place to add weight. In order to run a 22 in mid motor on low traction surfaces you need to replace the chassis at a minimum to allow a different battery layout. It may or may not be enough though. The Tardis 22 conversion from Atomic Carbon is a nice one but pricey.

On my mid motor XXX I currently have 67% weight on the rear wheels and I haven't added any weight at the back at this point. I can though and if I ever need to it will be in front of the rear axle centerline rather than behind it. On my car the gearbox was designed in such a way as to allow the motor to sit as far rearward as possible and the battery up against it. I am running a full sized stick pack across the chassis like is done on the X-6 and it works very well. Some people say that having more weight on the rear wheels is completely against the point of mid motor. No it isn't. The point of mid motor is to have the weight centered more centrally within the wheelbase rather than out back. The total amount front to rear is not the greatest concern. This is merely an adjustment that you need to make for different tracks. It's where that weight is located that counts. The car is much more forgiving than rear motor and corners much harder. I can still pull the front wheels off the ground. As with anything you need to adjust your diff, slipper, and punch settings on the esc to give you the best results. I run 25% exponential on the transmitter too. I am a huge believer in mid motor now that I've driven a mid motor car. I'm not saying I'll dominate at the track with it because I can't anyways but for me mid motor is a fantastic setup regardless of track. You just have to know what you are doing and most people don't. People really don't know how to tune anymore. If the car doesn't turn hard enough, they add weight up front. If it pops wheelies, they add weight up front. If it then doesn't have enough forward traction they go with max antisquat and then add weight at the back. Just strap a concrete block to the roof if you think this is how you should tune! Adding weight is more about achieving the balance you want and only if necessary. It should be thought of as a fine tuning aid rather than a standard tuning method.

[Mad Racer]

Thanks for a great reply.

I agree 100% on what you said and it makes sense. My Drake and all other nitro Stadium Trucks are mid mounted motors and a can get plenty of traction from it.

I can tune a car well so in time i will try the mid motor layout and see how i go. I haver never used weights unless is under weight.

Once again Thank You.

[DerbyDan]

I raced the CR2 again on Tuesday (8th May) at another local indoor track, the club has swapped their carpet for some nice new astro turf, the difference between the old carpet is chalk & cheese - the old carpet gave little grip & ate the tyres, the new astro turf gives rediculous amounts of grip which took some getting used.... anyway although I was not the quickest car out there, I managed to win the A final, despite a poor start from 4th on the grid where my car snaked off the line & hit the wall!

http://www.youtube.com/watch?v=-4jedtqzrWA&feature=youtube_gdata_player

The car has very twitchy steering on the high grip surface especially at low speeds, it odd as you kind of have to maintain a certain level of speed to keep it drivable - a bit like my spool equipped touring car, & in a similar way, if the rear end starts to step out, you catch it by getting back on the power!

I think on this surface I would benefit from a slightly longer car (XX4 front hub mod?) & some experimenting with tyres to kill the 'bite'

[jamin]

The car has very twitchy steering on the high grip surface especially at low speeds, it odd as you kind of have to maintain a certain level of speed to keep it drivable - a bit like my spool equipped touring car, & in a similar way, if the rear end starts to step out, you catch it by getting back on the power!

This is what I loved about my JRXS Dan, that motor over the front gave it loads of on-power steering which meant driving the car on the throttle to keep the rear end planted, thats always been my driving style so you could say a match made in heaven!

You did well to win it though, well done! I'd move the front camber link outwards if I were you, that will help calm it down. Currently doing this mod to my 22 to reduce the 'hook' exiting the corner. Also try a stiffer front spring to reduce low speed steering - you probably know all this, but just in-case...

[fredswain]

I'm working on a new front end for mine. When I have the springs and shocks balanced I have issues with camber link settings. If I get the rear roll stiffness where it needs to be so I don't lift an inside front wheel when under power coming out of a corner, the rear will then fly around and spin the car out under hard braking. The problem is that too much weight is being transferred forwards with such a steep 30 degree front end rake. I'm going to reduce mine to about 15 initially to see how it works. If it does what I hope, this car will hold more corner speed everywhere than any other car I've ever driven as opposed to having tradeoffs.