Outer Limits 4x4 Board

Just thinking ,

If you had a rig running motors in front of the front axle and behind the rear axle , other words large majority of the wieght perched at each end
rather then between the axles , how would this affect the foward -
rear cog , this would also make suspension work corner to corner
better ? (crossed up) Thoughts ?

Dozoor wrote:Just thinking ,

If you had a rig running motors in front of the front axle and behind the rear axle , other words large majority of the wieght perched at each end
rather then between the axles , how would this affect the foward -
rear cog , this would also make suspension work corner to corner
better ? (crossed up) Thoughts ?

Ask any V Dub Beetle owner...massive unpredictable oversteer.

Ask Ralph Nader....The Chevy(?) Corsair was another one, his book "Unsafe At Any Speed" should give you more than enough to think about.

In short, the front end steers, but the rear tries to go in a straight line.

All weight centered and as low as possible will do the best for the CoG. Minimises the alteration in Cog due to inclination.

Engines outside the wheelbase would tend to by leverage, give a very rocky ride, not to mention impinging on the approach/departure angles

Not an idea worth persuing.........

look at the fastest races cars around, mid - rear engines

If you want to know what it feels like whack a couple of sand bags in the back of a ute and let it get a bit tail happy and then HANG ON

isn't he talking 'bout a twin-engined vehicle? engine near or over each axle?? oversteer wouldn't be a drama...

having both would cancel out the massive understeer/oversteer tendancies i think. i'm assuming you're talking a rock crawling kind of rig, not a high-speed thing?

i think too that it'd cancel the front-rear COG issue, kinda like having a mid-engine? so long as the engines are the same weight, it shouldn't make that much difference if they were at the ends or in the middle?

would having the engines at the ends push more onto the suspension, giving more traction cos of the down pressure, with the weight being directly over the diffs?

GaryInOz wrote:Ask Ralph Nader....The Chevy(?) Corsair was another one, his book "Unsafe At Any Speed" should give you more than enough to think about.

The Corsair's biggest problem was goofy suspension design which increased positive camber as the front suspension compressed - the more weight transferred onto the outside front wheel, the more it tucked under. It's natural instinct is to roll over rather than corner.

That car was designed as a joke to put GM's pre-production QA systems to the test - and they failed massively. That's the only possible explanation for how such an appalling design could make it into production.

Just my opinion, of course.

But back to topic - the concept of keeping as much weight as possible over the axles is good. From there on, the concept sucks - two engines to keep running two gearboxes two transfer cases? and the overhang issues mentioned previously.

There's gotta be a better way - consider Bill's forced articulation, or the "diesel gen + electric motor per wheel" come to mind...

Scott

Not really related to COG, but one other issue with twin engined offroaders, unless both engines are geared together even with the throttles linked,is that when climbing steep gradients weight transfer can overload the rear unit causing it to lug down and even stall, while the lightly laden front unit will wheelspin independantly of the rear unit. Linked engine speed governors may cure this but I am not sure.
Bill.

Yep was thinking on the lines of twin engines ,And yes a rock crawler.
Independent suspension , this would help with diff to engine clearances
umm

From front , Motor transaxle frame transaxle motor.
So your engine weight is actually infront of the front axle and behind the rear axle ,, There would be no running gear between the wheels
so frame rails are only limited by driver position and the breakover angle required. could be like go cart driving position ,
Can see the probs there Bill , should be able to do somthing with electronics
Just ponderings I think with the weight in these areas it may force some more on the wheels under articulation on any sort of terrian, For instance up a steep hill where a normal stiff suspension over a lump would lift a wheel because of the weight all being behind the wheel ?



Any out of the square thoughts on configuration for the current stye of US events = big off cambers + piont n punch style ?

wanted to bump this back up cos i'm interested to see if anyone's got more to say...

GaryInOz wrote:

Dozoor wrote:Just thinking ,

If you had a rig running motors in front of the front axle and behind the rear axle , other words large majority of the wieght perched at each end
rather then between the axles , how would this affect the foward -
rear cog , this would also make suspension work corner to corner
better ? (crossed up) Thoughts ?

Ask any V Dub Beetle owner...massive unpredictable oversteer.

Ask Ralph Nader....The Chevy(?) Corsair was another one, his book "Unsafe At Any Speed" should give you more than enough to think about.

In short, the front end steers, but the rear tries to go in a straight line.

All weight centered and as low as possible will do the best for the CoG. Minimises the alteration in Cog due to inclination.

Engines outside the wheelbase would tend to by leverage, give a very rocky ride, not to mention impinging on the approach/departure angles

Not an idea worth persuing.........

It was a Chev Corvair....flat 6...popular with VW owners for conversions.

Just ponderings I think with the weight in these areas it may force some more on the wheels under articulation on any sort of terrian, For instance up a steep hill where a normal stiff suspension over a lump would lift a wheel because of the weight all being behind the wheel ?

It'd just work the same as a mid engined car with a combined engine weight of the two engines you talk about.
If you were going up a steep hill the weight of the back engine trying to lift the front would negate the weight of the front engine trying to hold the front wheels down..
I'm picturing a car with two engine/transaxles out of a small jap car, four wheel steer etc, sounds interesting enough.

How about running a mid engine powering a hydraulic pump or two, that could drive a motor on each wheel (like a scissor lift) wouldn't need axles(and therefore bugger all to get hung up), wheel motors could be supported by vertical struts, computerised drive/valving and throttle, hydraulic steer (run off of pumps) could even run hydraulic suspension with g sensors/angle sensors/load cells!!!!!!

Sounds heavy and complex but thats the sort of thing that goes on in my head...

How about a mid engine car with water that can be quickly pumped to any end of the vehicle to give a good COG as required, while driving.

The longitudinal COG depends only upon the longitudinal distribution of weight. So an engine in front of the front axle and another behind the rear axle could be made to give a longitudinal COG midway between front and rear wheels.

However this is a BAD idea. Not the position of the longitudinal COG, but the high mass moment of inertia caused by having the weight of the engines in front and behind the axles.

Mass moment of inertia is the sum of the mass of each part times the SQUARE of the distance from the neutral axis. So heavy items like an engine should be kept as close to the centre as possible.

Having a high mass moment of inertia, is bad because as a wheel goes over a bump or dip, the loads on eveything (particularly the suspension) are higher.

Where high mass moment of inertia is an advantage is when driving golf balls. The weight of a golf club is at the end that hits the ball (so the club has a high mass moment of inertia, rotating about the golfer's shoulder). The ball has no chance of stopping the swing of the club.

Likewise with an engine at both ends of a vehicle - hit a bump and the suspension has it's work cut out to control the pitching.

Even the weight of bars and winches in front of the front axle (or behind the rear axle) is detrimental.

JohnJohn wrote:How about a mid engine car with water that can be quickly pumped to any end of the vehicle to give a good COG as required, while driving.

The first & only satelite built and launch from within Australia actually used this idea to induce rotation & changes of direction.

Not that it relates to 4x4's but it is still interesting. I have specific details if anyone is interested.

So John , this means the suspension does affetivly be forced to move more for a given overal wieght? apart from the detrimental affects


intersting about the water

Dozoor wrote:So John , this means the suspension does affetivly be forced to move more for a given overal wieght? apart from the detrimental affects


intersting about the water

This is far from being a desirable feature. The suspension will move more because it will be more difficult for the springs and shocks to overcome the inertia from the pitching motion.

It can only adversely affect traction.

Furthermore the pitching wastes energy, which has to come from energy that would otherwise be used for forward motion (principle of conservation of energy/momentum in physics).

what about putting water in the tyres lke farmers on their tractors and graders. increases weight where its needed for traction and COG

AndrewPatrol wrote:what about putting water in the tyres lke farmers on their tractors and graders. increases weight where its needed for traction and COG

Aparantly been done a bit in comps , Ruff and some other have talked on this before,