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Body adjustment

Old 02-29-2020, 09:15 PM
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Default Body adjustment

Does moving the body forward or rearward make a big difference?

I ask because im considering doing it. There are brackets for the AMX designed to move the posts forwards and rearward. I gues you also have to take into account the minimum and maximum center point for wheel arches in the body. But if its a waste of time or not allot of bang for your buck then thats what im curious about.
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Old 03-01-2020, 06:48 AM
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Moving the body forward will give you more stering. It's pretty common for most guys to mount anywhere between 0 to 6mm forward depending on your track
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Old 03-01-2020, 08:11 PM
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That makes sense. So if I mount the body forward I get more front grip. If I move it back I guess I get more rear grip. If the car oversteers and I move it back will it mellow out? How fast do i have to be going for the body to have an effect?

As I learn how to manage traction using camber, caster, toe, and weight i find that with every adjustment it changes something else. If downforce does something its pretty straightforward that it only does its thing at speed and isnt as confusing as as the 3 points of a corner and accel/deceleration. Moving the body around should be pretty easy if it worthwhile.

Thank you
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Old 03-03-2020, 11:56 AM
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Since I know you like the scientific method, do a simple test. Put a body on a gram scale and just blow on it. Top down is fine, it doesn't need to mimic actual driving. The point is to illustrate how dramatic a slight breeze can have on the body. A draft you can barely feel can add 5 grams of force to the scale. A good birthday candle blow, 40-50, or more maybe.

The point is the body affects handling at all speeds. It's just more pronounced when traveling faster. And it's also significant. A while back someone did wind tunnel testing on 1/12 bodies. At 20mph some were generating over 70 grams downforce. That's basically 10% of the vehicle weight. And that is way, way below the cars top speed.
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Old 03-03-2020, 01:21 PM
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One smaller adjustment to the body to affect balance is to mount your wing a bit further forward on the wing mounts.

Most body manufacturers have a chart to tell you the downforce balance of the body, like this one:

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Old 03-03-2020, 08:01 PM
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Originally Posted by gubbs3 View Post
Since I know you like the scientific method, do a simple test. Put a body on a gram scale and just blow on it. Top down is fine, it doesn't need to mimic actual driving. The point is to illustrate how dramatic a slight breeze can have on the body. A draft you can barely feel can add 5 grams of force to the scale. A good birthday candle blow, 40-50, or more maybe.

The point is the body affects handling at all speeds. It's just more pronounced when traveling faster. And it's also significant. A while back someone did wind tunnel testing on 1/12 bodies. At 20mph some were generating over 70 grams downforce. That's basically 10% of the vehicle weight. And that is way, way below the cars top speed.
yea, im a simple guy. Your head is in the same place as mine. I bought a wind speed sensor. Now i need a fan large enough to push air through a cardboard tunnel at 10-25mph. I have a corner scale setup so thats the other ingredient. Im hoping I can use it to see the overall downforce added as well as how moving the body around effects each corner. Now that im thinking it out Ive always thought that there should be a better way to make sure that the body is true to the traction meaning that the body being slightly off parallel to traction causing a bias to one side slightly. I picked up a force transducer for measuring shock and spring rates that i could measure a pull to the side.

I had a buddy who was going to hook me up with a cosworth guy who does aerodynamics and i didnt have the heart to keep pushing on him for it. So we will have to figure out how to evaluate downforce. Allot of people have said these chassis are too small to be effected and allot of people have said they are effected more because of the size of air in comparison to the scale of the chassis. Maybe I can figure something out.

I have to work out a method to measure the centerline of the chassis in relation to the wind i will throw at it. Any ideas? Im sure a protractor or something could do it but it would be nice to print a purpose built setup that i could use to lock the wheels down and let the suspension move while keeping track of the relative angle to the wind.
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Old 03-03-2020, 08:22 PM
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Originally Posted by Bry195 View Post

I have to work out a method to measure the centerline of the chassis in relation to the wind i will throw at it. Any ideas? Im sure a protractor or something could do it but it would be nice to print a purpose built setup that i could use to lock the wheels down and let the suspension move while keeping track of the relative angle to the wind.
I'd mount the chassis at the end of a horizontal pendulum, like a weather vane. You could secure the chassis from rolling backward with a tether of fishing line. Minimal air disturbance and won't impact any vertical chassis compliance.
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Old 03-03-2020, 08:25 PM
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Originally Posted by gubbs3 View Post
I'd mount the chassis at the end of a horizontal pendulum, like a weather vane. You could secure the chassis from rolling backward with a tether of fishing line. Minimal air disturbance and won't impact any vertical chassis compliance.
I think i will integrate that idea. Fishing line will definitely show signs of the airflow not being aligned to traction.
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Old 03-04-2020, 01:17 AM
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If you want to measure things as subtle as body symmetry, you'll need air that is travelling totally straight. A fan doesn't produce this.

You'll need flow conditioning to straighten the air up. For a small model tunnel I've seen people use a grid of straws or small diameter pipes.
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Old 03-04-2020, 08:28 PM
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Originally Posted by daleburr View Post
If you want to measure things as subtle as body symmetry, you'll need air that is travelling totally straight. A fan doesn't produce this.

You'll need flow conditioning to straighten the air up. For a small model tunnel I've seen people use a grid of straws or small diameter pipes.
Good info. Totally makes sense. Ive seen mesh or like a course screen on a MAF sensor to straighten out flow for measurement. im glad you reminded me.

I think I figured out how to index accurately. I cant believe how cheap machinist stuff is becoming.


Ordered and on the way.
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