Yet another Mid Engine XXX Buggy

[col1nw3bb]

Hey guys, im new on here. Been out of the RC loop for about 10yrs, recently dragged my old stuff out and am trying to get back up to speed. So i have a XXX BK2 and i normal XXX.

After reading on here about the benefits of mid motor conversions i decided to give it a go on the normal XXX. So far ive flipped the trans and trimmed the chassis. Also ive stiffend the chassis with some metal reinforcing bars and plastic weld (pro stuff thats used to hold car bumpers together).

Ok will get pics up soon but now its question time, excuse the crappy diagrams (and the fact its the wrong side) best google and my paint skills could do. Which one of the following laylouts would you say is best? The advantage to stick packs is my other XXX uses them, but then my rally weapon uses saddle.... I cant see a major difference in weight distribution from either design either...





Cheers
Colin

[Alan Reeves]

Here is a good thread
http://www.oople.com/forums/showthread.php?t=71798

[col1nw3bb]

Cheers i have seen that one before. Have also read that the mid converted cars have a tendancy to nose dive more, so i didnt want to keep the original battery layout, in order to minimise weight over the front wheels.

[peetbee]

Neither layout!
Put the esc & rx where you have them in picture 2, but use the saddle layout as per picture 1, except move them to the centreline of the chassis
And then you have a CR2!

[col1nw3bb]

Do you mean like this?

If so can you explain the benefit of this design over either of the other two for me? Like i said ive been outta the game a while and alots changed, so i dont just want an answer i want to understand the answer.

[peetbee]

I'm not in anyway technical, but I'll try!
I believe it's all about keeping the weight central to reduce roll whilst keeping it as close the rear as possible (but I'm sure someone will correct me if I'm wrong!)

The way you have it shown there is the same as in the Atomic Carbon CR2 & S2, the Centro, the X6 and the new Cougar SV2 - so there must be something good about it!

[col1nw3bb]

Ok ive decided on saddle pack in the centre. Its incredibly tight. Fortunatly i had a novak xxl from a custom xmod i made when they came out so i can make it work. Just need to make a tray for the saddle packs now and do a bit more trimming before i move on to testing.

Anyway i couldnt give up the chance to play in the snow! So i leccy taped a stick pack in and took it for a spin in the road where cars had crushed the snow down. Heres some pics of how it looks now as well.

[peetbee]

Looks good, loving the old skool electrics!
I suspect it would be worth making a brace from the top of the gearbox down to the battery retaining strap (when you make it!) to cut down on chassis flex!

[col1nw3bb]

Yup already planning it. Ive got a bit carried away actuly. The plan is once the chassis is how i want it im going to make a mold and build a carbon fibre version. Itd be alot easier to copy the cr2 design of sheet cf stacked up but i think with carefull planning i can replicate the chassis in cf. we shall see.

[fredswain]

What are you going to use for a body? With my mid motor XXX, I can't find a body that will fit over the battery without cutting holes in it for the wires.

[OldTimer]

Originally Posted by col1nw3bb

Yup already planning it. Ive got a bit carried away actuly. The plan is once the chassis is how i want it im going to make a mold and build a carbon fibre version. Itd be alot easier to copy the cr2 design of sheet cf stacked up but i think with carefull planning i can replicate the chassis in cf. we shall see.

If you plan on stacking the cf then make sure the strips over lap, and if you go down the moulded cf tub route don't make it to thick, as it will be to rigid and not flex and generate grip

[migsy]

I did the lipo across the chassis when I first tried mid, I can only decribe it as a random buggy. I think the saddle is a lot more suited to this as it is more central to the chassis.

Hope this helps.

[col1nw3bb]

BK2 body fits fine mate, check out how ive got my corraly connectors mounted in the above pics, only trimming i had to do was for the diff cover.

As a temp job im using a stick pack across the chassis held in with velcro strips. I tested it at the weekend and found it handles realy well! It didnt at first as i was lazy and just flipped the rear assembly round, resulting in toe out as seen in pics. Solved this by having the centre part of the rear arm mount as it should be and changing the outer hubs over. Now got factory toe in on the rear.

I am still planning the cf tub chassis, i will make a mould of the original chassis and pivot plate as one piece using gel coat and mould making clay. Then il laminate cf in the mould, probably around 1.2mm thick. That design will allow for saddle pack in the centre of the chassis. Luckily i have my novak xxl receiver and a novak gtx ESC as nothing else will fit, without standing the servo which i dont want to do.

However thats gonna cost about £80 in materials, so for the following reasons the project is currently on hold.
1) It handles fine in its current layout, ghetto velcro straps work, and im not competitivly racing it anyway.
2) I just blew £74 on a pair of Losi speed T trucks! one of which im converting to a off roader. So funds are low....

I will in the mean time make a brace from the diff to the front to reduce flex.

[Sheepdog]

Originally Posted by fredswain

What are you going to use for a body? With my mid motor XXX, I can't find a body that will fit over the battery without cutting holes in it for the wires.

As for the bodyshell, drop xfactor a pm, he makes a very nice bodyshell which is higher above the batteries and is the bomb!!

[adey]

i got a body off x factor. Its great. Also, why not use a stick lipo down the centre. I did and it went great.

[col1nw3bb]

Any pics of that shell im after something different.

[dodgydiy]

when i made the carbon tub for my mid 2wd i used 4 layers of carbon at the sides, 7 along the centre line and an additional two layers in the nose area for strength, came to this after a bit of experimenting and has worked very well.

[col1nw3bb]

Any pics of your tub mate?

[fredswain]

I ended up using the CR body. I just cut it lower so the sides are higher. My battery barely fits in sideways. The issue I was having was that the only lipo I have has the battery wires popping straight up on one end which requires much more body height. My nimh battery fits just fine and I'm going to buy a different lipo so that issue is taken care of.

I spent last weekend building a new chassis from carbon fiber. I used a router and hand sanded the edges smooth. It looks like something I bought. I extended the wheelbase by 1/4" since I feel the CR2 wheelbase is too short. I have the Atomic Carbon chassis btw. I replaced it so it is sitting in a box. The new chassis is just a flat chassis with no bracing or upper deck. I may change that at some point but the new chassis works really well. My biggest problem is keeping the car from doing back flips under hard acceleration. Since it doesn't happen right off the line, a small front wing may be the cure.