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Old 06-01-2005, 02:40 PM   #1
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I have noticed that most every 4wd offroad vehicle has the motor mounted betweent he front and rear diffs. Why is this prefered ofver having the motor behind the rear diff like the 2wd has?
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Old 06-01-2005, 02:42 PM   #2
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Originally Posted by T. Thomas
I have noticed that most every 4wd offroad vehicle has the motor mounted betweent he front and rear diffs. Why is this prefered ofver having the motor behind the rear diff like the 2wd has?
Simple. Weight distribution and center of gravity. Having a motor located in the back would make the back end of the car heavy, since the rear differential and the motor is contributing to most of the weight in a R/C car. Having the motor located near the middle, such as Losi's XXX-4, enables the car to be balanced when everything else is in, such as the ESC, servo and batteries.
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Old 06-01-2005, 03:31 PM   #3
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But then why is the 2wd behind the diff? I am not a newbie, been racing for 15 years or so, just wonder why it is prefetred over just converting a 2wd into a 4wd.

If you took a 2wd(which turn very well) and then just make it a 4wd, shouldn't it turn better coming out of turns(which is really what makes a 4wd faster)?
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Old 06-01-2005, 04:22 PM   #4
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just think about the drivetrain of that kind of car it would go diff-diff- spur motor. it would be harder to do. plus either the chassis would be really long or the wheel base would be really short
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Old 06-01-2005, 05:06 PM   #5
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You must not remember the Old Kyosho Optima, chain drive off of the diff gear. It was my second car, and I still have my friends Turbo Optima in the garage. These cars were a lot better than the old Yokomo Dogfighter of the era. And they worked great untill the technology surpassed the design.
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Old 06-01-2005, 06:28 PM   #6
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One could only think what it would handle like, with the center motor, the weight is more distributed but if you moved the motor to the back of the car, the weight would be moved back thus creating more traction ( in theory ) so add to the awesome traction of 4wds and you have a car that will start to push after a while. Going back to what Tol said about converting a 2wd into a 4wd, this has potential to work very well, but with that said, how do you get the power to the front wheels from a rear based transmission you would have to make a small gear coming off the diff , ( much like the gear coming of the spur on a xxx-4) It's just, how good will this turn out with an off-center diff to accomidate (sp?) the belt to power the front. All in all I think the disadvantages outweigh the advantages, but we will nevrr know until its done.
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Old 06-01-2005, 09:15 PM   #7
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I tried to convert a XX4 to 2 wheel drive by taking the front axles and diff out for dirt oval-car handled great but just couldn't get any forward traction at all.I even tried putting truck tires on it and it just wouldn't work.Two wheel drive cars have the motor in the rear for traction-not handling.Some dirt oval cars are setup so you can flip the transmission around and run them either as a rear or mid motor.The mid motor is for high traction tracks-won't work if it's slick.

Years ago MIP made a 4 wheel drive conversion for RC10's that had a either a diff or another transmission in the front with a chain drive running forward(I've never actually seen one)-don't know if they worked or not.
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Old 06-02-2005, 01:04 PM   #8
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Weight transfer under acceleration dictates that on a rear mounted motor setup (ie 2wd) the rear wheels are getting most the grip, with the fronts getting very little - which is what is required for a 2wd.

With a 4wd you want the weight more centralized so that the front tyres are getting a more even share of the grip because they are driving wheels just like the rear wheels.

A rear motor mounted 4wd is very stable under acceleration - but is not quick through corners under power - because the front driving wheels aren't being used to their full benefit.

Part of the reason the xx4 was so successful and consistant was that it had the heaviest components (cells and motor) both placed as close as possible to each set of driving wheels, ensuring that both front and rear wheels always had similar grip levels regardless of weight transfer due to braking or acceleration.
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Old 06-03-2005, 04:04 AM   #9
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weight at the extremes of the chassis (side to side or front to back) slow the steering.. not what you want on a 4wd..
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