Mid Motor vs Rear motor
 

Ok, now I really want your opinions. IS it best to have a motor mounted on the rear? Or in X6 style? This is importanty, as I am ordering my carbon fibre and fret saw, and want to know which you lot prefer. Admittedly rear mounted ( less modifying of the tranmission)would be easier for me, but I'll see what you lot come up with;)

I personaly feel it is far better to have the weight infront of the rear axle, but only just in front, I don't personaly feel the motor is the right thing to be places there though.

I would say, for straight on traction, the motor should be on the back, for increased cornering speed, put in front of the raer axle...so it depends on the track and the traction of it

greez from switzerland

Maurice

Thanks Maurice I think I am going to make it a rear mounted motor, and make a carbon fibre cahssis/top deck, using saddle packs;)

I have thought so much about many layouts etc...

let me just say, EVERYTHING is a compromise, you just need to choose key things that you want your car to do that you think would generate the fastest race time.

in a simple term, if you favour power on steering, the mid-motor would be good. at loss of drive and bump riding.

if you want your car to have superb drive and rear end in between corners, then rear motor of some description would work best.

that is a very very broad example.

I like that explanatation chris, its very simple, thanks matey;) I think, firstly for simplicity, and secondly, for compatability with B4 parts( asI want to race this next year) I think rear mounted motor will simply be much easier. Secondly, I prefer a car that rides bumps better, as I am a touring car racer:D so less bumps is good:D

My thoughts are if you are running on a low grip surface then rear motor is the only way to go, if its med/high grip then mid motor (with the motor as close as poss to the diff) is the answer.

But with the B4 and CR why make you own rear motor car ? as these cars are very refined rear motor cars, but mid motor is a whole new ball game :)

Do you have idea's of how to change the weight distribution and improve the chassis?

Yes, if you are going to go mid motor, you still want weight over the rear, and I don't think the motor is the heaviest part out of components is it.....

Mmmmmm, I think me and you are on the same wavelength here DCM :D

Now only if I had some spare time to work on my 2wd car...... :cool:

G

I think a lot of people miss the point of turning the gearbox round in a 2wd.
IMO the 'standard' layouts have the weight distribution about nailed, but by having the cells down the middle and the motor hanging out at the back gives you a high polar moment of inertia. In an ideal world you want all your weight concentrated around the CG, which is what the mid motor layout gives you.

So long as you don't move the weight forward (ahem X6 :p ) I can't see how a mid motor car would have any less drive out of corners than a normal 2wd. It should feel much more planted and composed, feel more agile and suffer less pendulum effect when the back steps out.
Of course I could be taking rubbish :D I'm going to run mine for the first time tonight at Teeside so I'll have to see if it behaves how I think it will.

What have you got planned DCM? Lemmie guess, saddle cells just in front of the rear axle with the motor in the middle of the car and a belt to the back? :p

Rich, I rwally think you need totake your car to York and see how it performs on grip level changes! :o

IMHO, any car will go well at Teesside due to the huge amount of grip.

Hope it goes well though.

G

Maybe... only downside with that route, is you REALY need to go for a new chassis right away, and means a lot of machining work...... who knows...

Yeah but you already have plenty of rear end's available, Yoke BX for example.

Apart from the chassis nothing really to make either as you could use the whole rear end from the BX. If you want the B4 front end you could do like I'm planning to and screw the GT2 front sub-chassis to the main chassis and use a standard B4 front end.
You'd have to make a different motor mount though as the standard BX parts put the motor a bit far forward, and the top deck mount looks a bit high to mount straight to the GT2 sub-chassis.

yeah, once you go down that route, it gets a little complicated, but the issue I see with flipping the box round, is you tend to throw out the camber links and stuff at the rear.

Are there any detail pics of the BX rear end?

FYI of anyone that's interested,

Last night at Teeside we measured the front and rear weight distributions on some scales in a fair accurate way I think.

My X6 ready to run was 64% rear, 36% front. Rich's XXX-Cr was 67% rear, 33% front.

To note, my car had 15g on the front bulkhead, none extra at the back. Rich's CR was much modded to moe the weight forward i.e. cells forward and 40g in the front.

Rich's car ptoto car looked good I thought early doors, unfortunatly he broke a wishbone and no-body had any spares. My car was terrible early doors but came a long way and by the final was really good. I did drive like a tool though and kept hitting the same thing ALL night. Chris X6 looked pretty good all night and particularly good when being thrashed (as only Chris can) in the final.

Me?..... Thrash?...... NEVER! ;)
It paid off though! :D

:cool: Of what I can say the X - 6, is easy to drive then my Ass. B4.
Because the mid motor X - 6 style, drivers more like a 4wd then a 2wd.

Because the torque reaction from the motor pulls the weight AWAY from the rear axle now, that's why. Ideally, for a mid-motor car, you'd want 2 idler gears, and the motor spinning tht other way...
I agree 100% with the rest of your post though. Oh, and I have to give you credit in advance for an idea I'm about to steal :-D A few months ago, I made some CAD sketches of a mid-motor, saddle-pack B4, much like your contraption. But I was going to mill my own toe-in blocks. Using BJ4 toe-in blocks is way easier! They have the right geometry, too.

definately, 2 idler gears would be ace. it would get the motor 'snap' in the same direction as the wheel 'snap'

think how much control you would have in the air!

Does anyone know which way the engine spins on a gas truck? (GT2, AD2) I know they have 2 idler gears, but I think they're on the same axle :-(

Not only would the 2 'snap' in the right direction, the motor would 'snap' very, very close to the batteries and CG ===> very low polar moment of inertia ==> extreme snapage!

I think they spin the same way as elec, the last exploded diagram I looked at had the i idlers on the same shaft.

Would having two idler gears have the same result as having no idle gears??? Less weight!

yes, its the differance between an even number of gears and an odd number of gears.

but with just 2 gears (no idler) it would be pretty hard to get the right internal ratio and get the motor to meet with the spur.

I think the idler is a bit bigger than the layshaft gear, so no. But either way the spur would then hit the outdrive I think!?

Yep. No idler gear is impossible. Many have tried. Many have come to the same conclusion :-)

There is no idler gear in the slim2 :D

Im sure it could be done, no idler gear I mean. but would have to have whole new gearbox moulded.

EG. If a stock diff gear is 30teeth and layshaft is 15, that 2.0:1.
These won't meet up with no idler gear as spur would hit outdrives, motor into diff etc.

But if the diff gear was 40teeth and layshaft 20, or 60teeth and layshaft 30, that would still be 2.0:1 and create clearance, more flywheel effect perhaps, less bearings, less friction???

Chris

It also raises your outdrives too far too, you can always go like they had on the Top Cat/Couver/Cougar II and have a belt drive rear box, this would allow you to have a low outdrive height but sufficient clearance for the spur gear.

Does the idler gear effect the ratio at all? How do you work out the ratio of the box?

Belt drive is ace though! :D

G

...and a 'XXX4 syndrome' :-D

Idler has no effect whatsoever on ratio. It cancels out. Internal ratio = diff/top gear.

Thought I remembered that from Physics! :D

Whats the XXX4 syndrome? Being pants? :o

G

Having the outdrives way too high.

Ah, ok. What does that do then? :confused:

G

for starters, you will have to have longer than needed driveshafts, so that means deeper outdrive too, as the suspension compresses, it will push further in to the diff outdrive, plus there are handling implications too, but not sure as to what.

The more it moves in - the more friction there will be under power / braking so the suspension will bind up and not work as well.
maybe! haha

'maybe', lmfao! :p

That was my "I dont know what the hell I'm talking about", disclaimer! :p

IT SUCKS!

The XXX4 is basically a sled with wheels.

There's what Jimmy and DCM said. That sucks. Then there's the fact that you can't have your 'dogbones level' and have any ride height left. You can't even have the roll center anywhere near where it should be if you want any sort of decent ride height. So in any case: it sucks.