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Old 08-25-2014, 06:10 AM   #436
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Another model added to the Library Tekno EB-48.2.
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Old 09-26-2014, 06:10 PM   #437
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Another update has just been released, Some helpful new features and a sneak peak at what's in development. As usual the update will auto install when you open the program.

A couple new offroad models coming too.
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Old 09-28-2014, 09:09 AM   #438
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Two new models added, AE RC10 B5M and Mugen MBX7Teco
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Old 10-22-2014, 05:25 AM   #439
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For those of you wanting to run RC3 on a Tablet or Smart phone here is how you do it.

http://youtu.be/9Oa6mpzZ3xI
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Old 11-10-2014, 03:00 PM   #440
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Hi Bob,

When adjusting roll centers I noticed raising the front roll center on the weight transfer page, there was greater lateral weight transfer at the front of the car but less weight transfer (equal but opposite) at the rear of the car under neutral power.


I would have thought raising the front roll center would transfer less weight at the front of the car and would have had minimal effect on the weight transfer at the rear of the car under neutral power.

Can you explain why this is the case?
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Old 11-11-2014, 06:05 AM   #441
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Good question and Iíll try and keep the answer short and to the point if I am capable of doing that.

The Total Lateral Load Transfer (TLLT) from the Inside wheels to the Outside wheels is actually a very simple relationship = Car Mass x Lateral Acceleration x CG height above ground all divided by the Track Width of the Car. Note that there is no dependence on springs, ARB's or Roll Centre height in this calculation. These factors come into play in determining how the TLLT is distributed between the front and rear axles.

Two factors determine how the TLLT is distributed, mechanical roll stiffness (springs and Anti Roll bars) and roll moment (height difference between sprung mass CG and roll centre multiplied by the Sprung Mass). The roll moment is what causes the chassis to roll and the mechanical roll stiffness resists it.

So by raising the front roll centre you have reduced the front roll moment which makes the front of the car behave like it is stiffer so it will transfer more weight. A good general rule of thumb is the stiffer end of the car will transfer more weight and will have less overall grip.

The reason the front Roll Centre adjustment affects the rear as well is because the TLLT is constant for a constant Lateral Acceleration. Consider this:

Base setup - 500gm TLLT at 1g distributed 250gm front and 250gm rear.

Front roll centre raised Ė TLLT is still 500gm but the front weight transfer increases to 260 gm so the rear will now be 240gm (260+240=500)

Hope that helps.
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Old 11-12-2014, 05:36 PM   #442
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Hi Bob,

Thank you for the detailed response.

I must admit I am still a little confused.

So let me get this right, higher roll center makes the chassi stiffer and
the car rolls less, but there is more weight transfer?

How does this happen?
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Old 11-12-2014, 08:38 PM   #443
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Quote:
Originally Posted by frozenpod View Post
Hi Bob,

Thank you for the detailed response.

I must admit I am still a little confused.

So let me get this right, higher roll center makes the chassi stiffer and
the car rolls less, but there is more weight transfer?

How does this happen?
The weight transfer is the amount of weight (or pressure) put on the outside tires, not necessarily the side to side or front/rear weight balance of the overall chassis.

The extra weight may cause the tire to exceed its optimal slip angle and slide.

So, to generate the most traction at one end of the car, the trick is finding the right amount of roll to generate weight on the tires, but not too much that it overloads the outside or unloads the inside tire excessively.

Bob, feel free to correct my terminology. :-)
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Old 11-13-2014, 01:42 AM   #444
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Quote:
Originally Posted by frozenpod View Post
Hi Bob,

Thank you for the detailed response.

I must admit I am still a little confused.

So let me get this right, higher roll center makes the chassi stiffer and
the car rolls less, but there is more weight transfer?

How does this happen?
Most RC racers incorrectly think that body roll causes weight transfer. Once you erase that belief, everything else starts to make sense.

Body-roll and weight transfer are largely unrelated.

If you raise the roll-centre, body-roll will be reduced, but the same total weight transfer will still take place (in this case the load will transfer through the links and arms into the tyres). This load transfer is undamped, so too high a roll-centre will make a car very edgy, hard to drive, and prone to grip-roll.
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Old 11-13-2014, 05:47 AM   #445
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To answer this question would require getting deep into the physics which will likely just put everyone to sleep. A simpler way to look at Roll Centre changes is to think of the effect in terms of what Anti-Roll Bars do.

Raising the Roll Centre is similar to adding a stiffer Anti-Roll Bar. If you
add a stiffer front bar you have less chassis roll and more front weight
transfer which reduces grip. Raising the roll centre reduces roll and for
that end increases weight transfer and decreases relative grip. So if you
think of roll centre changes in terms of Anti-Roll Bars it is easier to
relate as you make changes.

Raising the roll centre is similar to changing to a stiffer bar. Grip at
that end due to weight transfer will decrease.

Lowering the roll centre is similar to changing to a softer bar. Grip at
that end due to weight transfer will increase.

If you want to truly delve into the equations I will scan a few pages from "Race Car Vehicle Dynamics" and post them. That is the main reference used in developing RC3.
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Old 11-13-2014, 06:15 AM   #446
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Quote:
Originally Posted by daleburr View Post
Most RC racers incorrectly think that body roll causes weight transfer. Once you erase that belief, everything else starts to make sense.

Body-roll and weight transfer are largely unrelated.

If you raise the roll-centre, body-roll will be reduced, but the same total weight transfer will still take place (in this case the load will transfer through the links and arms into the tyres). This load transfer is undamped, so too high a roll-centre will make a car very edgy, hard to drive, and prone to grip-roll.
This is completely true. What increasing body roll does is reduce how quickly the chassis responds to changes. More roll slower response, less roll faster. More roll is easier to drive as is gives us drivers who don't have our butts in the seat time to react to what we see is happening to the car. The total weight transfer from the inside wheels to the outside would be very similar between the two.
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Old 11-13-2014, 10:08 AM   #447
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Quote:
Originally Posted by daleburr View Post
Most RC racers incorrectly think that body roll causes weight transfer. Once you erase that belief, everything else starts to make sense.

Body-roll and weight transfer are largely unrelated.

If you raise the roll-centre, body-roll will be reduced, but the same total weight transfer will still take place (in this case the load will transfer through the links and arms into the tyres). This load transfer is undamped, so too high a roll-centre will make a car very edgy, hard to drive, and prone to grip-roll.
Yea, well put. Though I think the practical implications vary depending on track surface. On most asphalt tracks, that are low to mid-high, I find that the higher roll center does indeed make the car react quicker, but doesn't necessarily go as far as grip rolling. I found it instead will overload that tire and cause a slide as the tire is pushed past what it can produce as far as traction.
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Old 11-13-2014, 03:10 PM   #448
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Traction Rolling now there is a subject with lots of debate. Here are a couple things related to roll centre changes that are relevant to Traction Rolling.

If you raise the Roll centre so it is above ground level there is a jacking force that will raise the chassis upwards in roll. This can be a very bad thing and lead to Traction (Grip) roll. When the Roll centre is below ground the jacking force is downward which is good. In all the TC's I have looked at you generally don't see Roll centres above ground so jacking up should not be a major cause of traction roll.

The other thing most don't consider when making roll centre changes is the effect it has on Camber Gain. Raising the Roll centre will increase the camber gain as you are changing the angle of one or both of the suspension arms. These two effects generally oppose each other. Raising the roll centre will reduce grip due to weight transfer but more camber gain can and does increase grip. In a lot of cases the camber effect will over power the roll centre change and you will actually end up with more grip. In severe cases this can lead to Traction Roll. So when making roll centre changes sometimes you may need to reduce static camber as well.
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Old 11-14-2014, 07:39 AM   #449
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Thought this whole issue with Roll Centres and Camber Gain was worthy of a video to show the relationship.

Effect of Roll Centre on Camber and Camber Gain
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Old 11-15-2014, 04:18 PM   #450
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Quote:
Originally Posted by BobW View Post
To answer this question would require getting deep into the physics which will likely just put everyone to sleep. A simpler way to look at Roll Centre changes is to think of the effect in terms of what Anti-Roll Bars do.

Raising the Roll Centre is similar to adding a stiffer Anti-Roll Bar. If you
add a stiffer front bar you have less chassis roll and more front weight
transfer which reduces grip. Raising the roll centre reduces roll and for
that end increases weight transfer and decreases relative grip. So if you
think of roll centre changes in terms of Anti-Roll Bars it is easier to
relate as you make changes.

Raising the roll centre is similar to changing to a stiffer bar. Grip at
that end due to weight transfer will decrease.

Lowering the roll centre is similar to changing to a softer bar. Grip at
that end due to weight transfer will increase.

If you want to truly delve into the equations I will scan a few pages from "Race Car Vehicle Dynamics" and post them. That is the main reference used in developing RC3.
Hi Bob, brilliant program btw.

Thank you for the detailed response and the analogy, but how would I use this at the track?

For example if I was trying to increase or reduce mid corner steering how could I adjust the front or rear roll center to achieve this?
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