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Old 03-09-2017, 11:36 PM   #121
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Originally Posted by Nerobro View Post
I'm not kidding. I suspect there are some ~reasons~ for this.
Ofcourse that throwing out dogbones from 4WD with no other changes won't work. But only reason of this is setup.

4WD (as FWD) are set up to transfer more weight to front axle, while for RWD you need more weight on rear - that means totally different setup.
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Old 03-10-2017, 12:15 AM   #122
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I'm hoping you put "lacking weight transfer" in quotes to point out the seemingly popular yet incorrect assumption that stiff chassis and springs don't transfer weight.
The quotes are due to a gross oversimplification of the situation. But to compensate for the soft chassis, you end up running much stiffer springs. And that leads down a long set of compromises.
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Old 03-10-2017, 12:28 AM   #123
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I'm hoping you put "lacking weight transfer" in quotes to point out the seemingly popular yet incorrect assumption that stiff chassis and springs don't transfer weight. Of course, weight transfer occurs with the same total for a given car at a given lateral acceleration regardless of spring stiffness; the springs (and dampers) just allow us to change the proportioning of weight transfer between ends of the car during cornering.
Weight transfer is an inherent and unavoidable property of having the vehicle's center of mass above the ground. Imagine invisible arrows hanging loosely and pointing straight down from every atom of the car; when the car accelerates, the arrows tilt backward and more of them point towards the rear wheels' contact patches; when the car brakes, they tilt forward; when the car turns, they tilt to the side. That is weight transfer and every vehicle does it even if there is no suspension at all.

However, soft suspension does allow the vehicle to lean and squat, which mechanically repositions the wheels relative to the center of mass, which causes an additional effect *similar* to weight transfer but not actually the same.

- - -

Anyway, I think the theoretical aspect of this topic has been beaten to death. A couple people have posted that they have RWD cars they like, so it would be great if they would actually explain what they did to make those cars handle well.
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Old 03-10-2017, 03:49 AM   #124
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Could be interesting, if the price is reasonable... Here in Switzerland, it is available for pre-order for 299CHF... ouch.
Waaah pineze!

They didn't get the point then... no-one will buy this "sub-car" at that price this will have to dip seriously below CHF200 delivered for me to start buying one for each of M. and S. so they can race it at the GeMC... 600CHf? No thanks, my old SSD-SG and T2 do the job just fine after all and are long paid for
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Old 03-10-2017, 03:54 AM   #125
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Originally Posted by Jorge T View Post
that Yokomo on asphalt with GT-R CRC tires and 17.5 w/2S.. Hmmm...handful of fun!

My RC10 DS was a blast and would keep up with the TA02 cars, but then the HPI RS4 came out...
[off-topic mode ON]

Jorge... always good to see you're still around. You have no idea how often I think about how much I enjoyed these long-gone times . You take care my friend.

[off-topic mode OFF]
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Old 03-10-2017, 06:46 AM   #126
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From the top of page 2 of this thread:
I thought I had scanned the entire thread but I obviously did not. That's a perfect answer, thank you to that author, that's very valuable info. And thank you to above for pointing it out.
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Old 03-10-2017, 02:53 PM   #127
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Originally Posted by Lonestar View Post
[off-topic mode ON]

Jorge... always good to see you're still around. You have no idea how often I think about how much I enjoyed these long-gone times . You take care my friend.

[off-topic mode OFF]
Paul... I do the same. Need to come back and visit us for the ROAR Nats in Austin.

Yeah I agree $295 is way high needs to be $195 or less.
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Old 03-10-2017, 03:39 PM   #128
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Just because it was mentioned several times now as a an advantage of 2wd:
Reducing the weight around 50grams won't do nothing in laptimes. And here you can believe me. You will have an advantage if you could reduce the weight around 150-200grams. That is the point where a 4wd tc will go faster in laptimes on tight tracks. A FF tc will react much faster to weight reduction than Rwd.
So in this 1/10 scale class and motors of 21.5t and stronger 2wd will have no advantage on tight to middle large tracks. On large flowing 1:5 tracks where traction is not the key to fast laptimes this may change.
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Old 03-11-2017, 12:16 AM   #129
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Reducing the vehicle's mass by 50 grams would still improve acceleration a little, but only if there's enough traction to actually put the motor's power to the ground. Based on my experience the motor has to be much less powerful to keep from spinning the rear tires even with moderate throttle input, and a less-powerful motor would not be competitive unless it was mandated by the rules. A high-downforce wing would improve traction at high speed, but then you'd have more drag which would counteract the benefit of lower mass, and it wouldn't help if you have to slow down a lot for corners. A less complicated drivetrain would be more efficient, so it may be possible to run a single shorty pack for a full race, with the pack pushed as far back as possible, but I don't have any firsthand experience with this setup. It works for RWD buggies, but they have bigger rear tires and therefore more traction. There may not be a solution to the traction problem without someone custom-making some extra-wide 1.9" wheels and tires.

Basically, I think a RWD touring car could excel in the same scenario that pan cars and F1 cars already excel -- high speeds, smooth pavement or carpet, and not much braking -- but it would require a LOT of hacking to make it work, whereas pan cars and F1 cars are designed and built specifically to work well with RWD on super-smooth tracks.

That being said, anything can make an interesting challenge for an RCer who just wants to try something different. That's why I did it, after all. If you like the idea of having to operate the throttle and brakes very carefully to avoid losing control of the car, RWD will definitely give you that experience. And despite already knowing the outcome, this thread makes me want to dig out my mid-rear-motor RWD touring car to experiment some more with it anyway.
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Old 03-11-2017, 08:48 AM   #130
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In the olden days, there used to be "wide" sedan tires and wheels. 24mm was the "mid-narrow" size. I think wide was 30 or 31mm. There was also super narrow, 21mm size.

I don't know if any of that stuff is still available. HPI does sell these for one of it's Sprint 2 cars, they are 34mm wide...
#109157 FALKEN AZENIS SLICK TIRE 34mm (REAR/2pcs)

There is also a 31mm version

I can tell you this about F1 cars, on high traction carpet - more rear traction is always faster. You can't launch a cannon from a canoe, as the saying goes. In my experience, I almost always find the car will be faster and more driveable if it is a little heavy. Theoretically, lighter is always faster, but since aero is vestigial atbest, and power to weight is absurd, that is not really true in a practical sense. In fact, I have lately tried a saddle pack in my F1 car and results have been positive, at 30g over the weight limit.

The first on road car I ever had was an RC10 DS that I raced in a parking lot. They ran fine with the stock tires. 3* of toe per side and weight over the rear end goes a long way, too.
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Old 03-11-2017, 12:20 PM   #131
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Basically, I think a RWD touring car could excel in the same scenario that pan cars and F1 cars already excel -- high speeds, smooth pavement or carpet, and not much braking -- but it would require a LOT of hacking to make it work, whereas pan cars and F1 cars are designed and built specifically to work well with RWD on super-smooth tracks.
That would work in case that it'd have direct drive.. From my experience, direct drive makes pretty big difference in top speed.

Btw, did you take a look on M06? It works on tiny tires, with almost non existent suspension travel and small dimensions... Which is small wonder for me

I think Tamiya's M-platform is great to analyze differences between FWD, RWD and AWD settings - they share suspension components, but every of them has different geometry.
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Old 03-11-2017, 12:27 PM   #132
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Interesting, I never heard of the RC10 DS before. How big were the tires on it, and how powerful was the motor?

I've seen the M06 before, but I've never driven one. The thing is, Tamiya still designs a lot of their vehicles to work well with stock motors and NiMH batteries, which changes things a lot. I don't even have a NiMH battery to test with my RWD touring car, but I'm sure the voltage-sag when accelerating from a stop would make the car much more manageable. Punch control on a modern ESC just doesn't seem to have the same consistent amperage-limiting effect that good old voltage-sag has.
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Old 03-11-2017, 01:17 PM   #133
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I don't even have a NiMH battery to test with my RWD touring car, but I'm sure the voltage-sag when accelerating from a stop would make the car much more manageable. Punch control on a modern ESC just doesn't seem to have the same consistent amperage-limiting effect that good old voltage-sag has.
You could emulate low current outputs of NiMH with resistor - I found 140W 0.15ohm resistor, which would limit maximum current to about 50A - as I rekember, this was maximum current of cheaper stickpacks
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Old 03-11-2017, 03:53 PM   #134
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Originally Posted by Papi View Post
That would work in case that it'd have direct drive.. From my experience, direct drive makes pretty big difference in top speed.

Btw, did you take a look on M06? It works on tiny tires, with almost non existent suspension travel and small dimensions... Which is small wonder for me

I think Tamiya's M-platform is great to analyze differences between FWD, RWD and AWD settings - they share suspension components, but every of them has different geometry.
The setup window on an M06 is pretty small. If you get setup right, the car has a lot of forward bite/acceleration and is a joy to drive. If you get setup even a little wrong, you will be swapping ends even on a high bite track. Also if you don't have the car setup perfectly, forget about even touching the brakes.

Just read through the M06 thread here on RC Tech to get an idea what it takes to make a 4 wheel independent suspension rear motor RWD car to work...

TAMIYA M-06 Thread
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Old 03-11-2017, 04:20 PM   #135
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The setup window on an M06 is pretty small. If you get setup right, the car has a lot of forward bite/acceleration and is a joy to drive. If you get setup even a little wrong, you will be swapping ends even on a high bite track. Also if you don't have the car setup perfectly, forget about even touching the brakes.

Just read through the M06 thread here on RC Tech to get an idea what it takes to make a 4 wheel independent suspension rear motor RWD car to work...

TAMIYA M-06 Thread
I'm aware of that - that's why I said it's little miracle But still, that window exists, meaning that RWD can work even as M-chassis, which isn't great in terms of handling even as FWD/AWD
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