R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric Off-Road

Thread Tools Search this Thread
Old 06-01-2005, 03:40 PM   #1
Tech Regular
T. Thomas's Avatar
Join Date: Mar 2005
Posts: 380
Default 4wd DESIGNS

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?
T. Thomas is offline   Reply With Quote
Old 06-01-2005, 03:42 PM   #2
Tech Fanatic
Thai3g_Eclipse's Avatar
Join Date: Dec 2004
Location: Plano, TX
Posts: 879
Trader Rating: 10 (100%+)

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.
HPI Savage Flux HP | Tamiya TB-03
Thai3g_Eclipse is offline   Reply With Quote
Old 06-01-2005, 04:31 PM   #3
Tech Regular
T. Thomas's Avatar
Join Date: Mar 2005
Posts: 380

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)?
T. Thomas is offline   Reply With Quote
Old 06-01-2005, 05:22 PM   #4
Join Date: Apr 2005
Posts: 398

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
THE_REAL_FROBOY is offline   Reply With Quote
Old 06-01-2005, 06:06 PM   #5
Tech Addict
Mopar's Avatar
Join Date: Aug 2001
Location: Santee, Ca
Posts: 666

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.
Schumacher KF2se, Associated B5m CE (sold), Hot Bodies D413, Associated T5m, Axial Exo Terra, Schumacher Mi5, CRC 1/12, 3Racing FGX full suspension, Associated 18r
Mopar is offline   Reply With Quote
Old 06-01-2005, 07:28 PM   #6
Tech Regular
Nick111's Avatar
Join Date: Oct 2004
Location: Long Island, NY
Posts: 491
Send a message via AIM to Nick111

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.
Nick111 is offline   Reply With Quote
Old 06-01-2005, 10:15 PM   #7
Tech Addict
DrOlds's Avatar
Join Date: Oct 2003
Location: Kansas City
Posts: 644
Trader Rating: 4 (100%+)

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.
DrOlds is offline   Reply With Quote
Old 06-02-2005, 02:04 PM   #8
Tech Master
bender's Avatar
Join Date: May 2004
Location: Brisbane
Posts: 1,504
Trader Rating: 4 (100%+)

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.
Jason W
FIR#2 - "You can't buy this much talent"
Durango Dex410 - Schumacher Cougar SV - Top Photon
bender is offline   Reply With Quote
Old 06-03-2005, 05:04 AM   #9
Tech Addict
oople's Avatar
Join Date: Nov 2004
Posts: 586

weight at the extremes of the chassis (side to side or front to back) slow the steering.. not what you want on a 4wd..
oople is offline   Reply With Quote

Similar Threads
Thread Thread Starter Forum Replies Last Post
DG designs tcmerf Painting, Designs, Graphics and Photography 6 08-30-2009 08:51 PM
CLR DESIGNS ??????????????????????? rcnutmich Chat Lounge 2 08-09-2005 10:53 AM
CLR DESIGNS ????????????? rcnutmich Buyer/Seller dispute and Feedback discussion forum 0 08-09-2005 09:14 AM
CLR DESIGNS ???????????????? rcnutmich R/C Items: For Sale/Trade 0 08-09-2005 09:13 AM
GT designs gtrcman64 Web Links 0 05-14-2004 09:31 AM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off

All times are GMT -7. It is currently 06:24 PM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net