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Fwd chassis: Front motor vs mid motor!

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Fwd chassis: Front motor vs mid motor!

Old 01-22-2020, 05:34 AM
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Default Fwd chassis: Front motor vs mid motor!

Dear anyone, as always been Fwd cars supposed to be front motor.
Since A800FX is released, therefore has many manufacturers made conversion kit to put TC cars become mid motor FWD cars.

Could tell me difference, advantage and disadvantage about these 2 types of FWD cars, on asphalt and carpet surface, please?

Best regards
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Old 01-22-2020, 05:41 AM
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Originally Posted by mac853 View Post
Dear anyone, as always been Fwd cars supposed to be front motor.
Since A800FX is released, therefore has many manufacturers made conversion kit to put TC cars become mid motor FWD cars.

Could tell me difference, advantage and disadvantage about these 2 types of FWD cars, on asphalt and carpet surface, please?

Best regards
Its the same as with RWD:
For acceleration grip on slippery surface you want to have as much as possible weight on the powered wheels. FWD: Front motor, RWD (offroad Buggy): rear Motor.
As soon as acceleration grip is not an issue, mid motor is superior for cornering in general (e.g. carpet Buggy)

BR Erhard
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Old 01-22-2020, 02:40 PM
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Originally Posted by mac853 View Post
Dear anyone, as always been Fwd cars supposed to be front motor.
This is a false assertion. FWD says nothing about motor placement. The FF layout is what you're talking about - Front motor FWD.

There have been a few full scale mid motor FWD cars. Mid motor FWD RC cars aren't that unusual.
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Old 01-22-2020, 02:47 PM
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The only difference is the moment of inertia. Given the CG is in the same place. "where the CG" is, is independent of any other feature of the car.
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Old 01-22-2020, 09:01 PM
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Originally Posted by Nerobro View Post
The only difference is the moment of inertia. Given the CG is in the same place. "where the CG" is, is independent of any other feature of the car.
that brings up allot of great questions about the interaction of inertia with traction with front motor versus mid motor fwd in corners versus straights.
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Old 01-22-2020, 09:50 PM
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I don't know if the FWD mid motor will be realy faster..... I will test that soon I have a xray T4F and I will receive my Xray T4 fwd mid motor conversion kit from rebelion rc maybe next week !
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Old 01-22-2020, 09:51 PM
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Sure does. But the same story exists in F1, TC, and.. well all the classes really. F1 has longitudinal versus transverse. Full size, shorty, mini. TC has been doing the moving motor dance, and you can run different batteries if you're so concerned.

Geeze, 2wd off road is the craziest. Some cars have 4 different transmission configurations and they have shorty, mini, square, and full size batteries to work with.
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Old 01-22-2020, 10:00 PM
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Originally Posted by Nerobro View Post
Sure does. But the same story exists in F1, TC, and.. well all the classes really. F1 has longitudinal versus transverse. Full size, shorty, mini. TC has been doing the moving motor dance, and you can run different batteries if you're so concerned.

Geeze, 2wd off road is the craziest. Some cars have 4 different transmission configurations and they have shorty, mini, square, and full size batteries to work with.
I'm not that sure at the IIC the lap time difference between the awesomatix and the T4f was not that big .... same driver with the same electronic and bodie will be a good test
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Old 01-22-2020, 10:24 PM
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Originally Posted by Quinny45 View Post
I'm not that sure at the IIC the lap time difference between the awesomatix and the T4f was not that big .... same driver with the same electronic and bodie will be a good test
I wouldn't suspect it's a big, or even "useful" difference. :-) That said, IIC is a darned good way to make judgements. I hadn't considered it, and should go check that out.

I have a FF04 Evo, and a MST TCR. Seems like a place to start.
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Old 01-23-2020, 12:42 AM
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Originally Posted by Nerobro View Post
The only difference is the moment of inertia. Given the CG is in the same place. "where the CG" is, is independent of any other feature of the car.
Note:
It is obvious, that in reality you have limited ability to change moment of inertia without changing position of centre of gravity CG. A front motor in FF layout will result in different CG.
It will be very hard to keep the CG, when the motor is in front of the front axle. Put the battery behind the rear axle? Of course this is the opposite of centering mass and takes away agility to change from straight to a given corner radius. It will be bad for narrow slalom. But good in slippery offroad to stay straight despite of rough terrain.



To make it simple - using the same wheels front and rear a 50:50 weight distribution leads to neutral behaviour in corners but without acceleration. (Using wider rear wheels and same compound in LMP, this 50:50 weight distribution shifts - to e.g. 40:60.)
Acceleration force adds to the cornering force and take away grip for cornering, therefore we put a little more weight an the powered axis, accepting to have less traction on this axis in corners.
A rear wheel drive has the advantage, that we have a positive load shift to the rear under acceleration.
and so on and so on - endless story!

Under all aspects - the type of car (class rules) and the surface(grip level) and the track layout will shift the parameters for the best compromise.
Books are written about that with hundreds of pages. I covered only the basics and without complete explaination.

Best regards, Erhard
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Old 01-23-2020, 12:50 AM
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Originally Posted by Erhard View Post
Note:
It is obvious, that in reality you have limited ability to change moment of inertia without changing position of centre of gravity CG. A front motor in FF layout will result in different CG.
It will be very hard to keep the CG, when the motor is in front of the front axle. Put the battery behind the rear axle? Of course this is the opposite of centering mass and takes away agility to change from straight to a given corner radius. It will be bad for narrow slalom. But good in slippery offroad to stay straight despite of rough terrain.



To make it simple - using the same wheels front and rear a 50:50 weight distribution leads to neutral behaviour in corners but without acceleration. (Using wider rear wheels and same compound in LMP, this 50:50 weight distribution shifts - to e.g. 40:60.)
Acceleration force adds to the cornering force and take away grip for cornering, therefore we put a little more weight an the powered axis, accepting to have less traction on this axis in corners.
A rear wheel drive has the advantage, that we have a positive load shift to the rear under acceleration.
and so on and so on - endless story!

Under all aspects - the type of car (class rules) and the surface(grip level) and the track layout will shift the parameters for the best compromise.
Books are written about that with hundreds of pages. I covered only the basics and without complete explaination.

Best regards, Erhard
Meanwhile all the mid motor FWD layouts I've seen put a massive weight in the front bumper, roughly maintaining the CG location.
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Old 01-23-2020, 08:46 PM
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Originally Posted by Erhard View Post
Note:
It is obvious, that in reality you have limited ability to change moment of inertia without changing position of centre of gravity CG. A front motor in FF layout will result in different CG.
It will be very hard to keep the CG, when the motor is in front of the front axle. Put the battery behind the rear axle? Of course this is the opposite of centering mass and takes away agility to change from straight to a given corner radius. It will be bad for narrow slalom. But good in slippery offroad to stay straight despite of rough terrain.



To make it simple - using the same wheels front and rear a 50:50 weight distribution leads to neutral behaviour in corners but without acceleration. (Using wider rear wheels and same compound in LMP, this 50:50 weight distribution shifts - to e.g. 40:60.)
Acceleration force adds to the cornering force and take away grip for cornering, therefore we put a little more weight an the powered axis, accepting to have less traction on this axis in corners.
A rear wheel drive has the advantage, that we have a positive load shift to the rear under acceleration.
and so on and so on - endless story!

Under all aspects - the type of car (class rules) and the surface(grip level) and the track layout will shift the parameters for the best compromise.
Books are written about that with hundreds of pages. I covered only the basics and without complete explaination.

Best regards, Erhard
it would be interesting to correlate data on tech tracks versus long tracks against motor position. iíll bet mylaps could provide enough data to sort fantasy from reality.
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Old 01-23-2020, 08:58 PM
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Originally Posted by Bry195 View Post
it would be interesting to correlate data on tech tracks versus long tracks against motor position. iíll bet mylaps could provide enough data to sort fantasy from reality.
But this method is not practical, technical or not as I drive he would choose mid motor cars anyway.
I don't think someone would buy 2 cars purposely then switch between them under different circunstances.

Last edited by mac853; 01-24-2020 at 02:26 AM.
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Old 01-24-2020, 01:20 AM
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For me a Touring in 4x2 isnít a FWD and driver use real FWD with Touring bodies isnít the real FWD class
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Old 01-24-2020, 02:50 AM
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Originally Posted by mac853 View Post
Could tell me difference, advantage and disadvantage about these 2 types of FWD cars, on asphalt and carpet surface, please?

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Disadvantage of MF is, that it relies on heavy weight in front bumper to get enough traction. Most MF designs take advantage of relatively high weight limit to achieve same weight distribution as FF.

Advantage is lower CG (which is probably why awesomatix went for it, as that's important feature of their onroad), better cable routing with motor closer to ESC and battery and easier conversion from existing touring car.

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