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Old 11-16-2014, 07:50 AM   #451
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Two ways I would try and do that.

To increase mid corner steering and not upset the weight transfer balance I would shoot for more tire camber at mid corner and try to maintain the roll centre height. There are few ways to achieve this:

1) On the front shorten the length of the camber link and lower the inner ballstud or raise the outer. This will raise the front roll centre slightly and increase the camber gain. Now to get the Roll centre back where you want it remove shim from under the lower hinge pin. This will move the roll centre back down and only make a slight change to the camber gain. Now you will have more camber at mid corner and maintain the balance.

2) A more aggressive change would be to increase the front caster. A 2 deg change in caster will make a big difference in the camber angle with increasing steer angle. If you want a less aggressive change you could add a shim under the front lower hinge pin which increases kickup and adds to the caster. A .5mm shim will add around .5 deg caster.
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Old 11-16-2014, 07:46 PM   #452
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So I read the entire thread and I already learned a few things just from reading, especially about roll centers. Seems to be a really cool software, thanks for all the effort Bob! I'm a little bit confused though regarding one particular topic and I was hoping you could help me understand it.

I downloaded the trial and started measuring my TLR 22 2.0. When I wanted to measure the front suspension I missed a place to enter the kickup of the front suspension, which in my case would be 25 degrees. I remembered a statement regarding this:

Quote:
Originally Posted by BobW View Post
It's the angle of the shock relative to the arm that is important. So if the total kickup on the arm is say 20deg and the shock is laid back 20 deg the angle of the shock relative to the arm in the side view is 90 deg and no correction is needed.
At first I was fine with the answer but then I started wondering and to be honest I don't quite understand how the kickup can be irrelevant. If the entire front suspension including the shocks is angled (i.e. the shocks and therefore also the springs are not perpendicular to the ground plane) then the spring rate of any spring will not have the same effect that it would have if it were perpendicular to the ground. From what I remember from my math class the angle of 25 degrees would result in the effective spring rate of the spring mounted in the car (i.e. with kickup) being around 10% less than the nominal spring rate of the spring.

cos alpha = adjacent side / hypotenuse
cos 25 deg. = 0.906

Not sure if that is the right way to calculate it. Maybe the effect is even bigger than 10%. But one way or another, the way I see it, the suspension will be softer with kickup than without.

There is another very interesting thread regarding the topic of suspension geometry and how to properly setup an RC-car. In there Fred talks about the effect of the kickup (amongst other things):

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Originally Posted by fredswain View Post
You aren't choosing your shocks oils on the bench. You are systematically determining what to use based on how the car drives. For me when I tune 2WD buggies, the fronts always end up with a heavier weight. Why? It's due to the front end rake. The more rake you have, the more oil weight you need. If we had no front end rake we'd probably end up with the same or near the same weight front to rear.

Think of it this way. A shock that is mounted straight up and down and is getting a purely vertical load exerted on it will be utilized 100%. You are fully using the spring rate and dampening rate. Now let's say we lean that shock over 45 degrees yet keep the vertical load. Suddenly the shock is only 50% effective. Our effective spring rate and dampening rate has decreased. How do we get the effective rate back? We stiffen the spring and increase the oil weight. Remember that the front of a 2WD buggy is laid back anywhere from 20 to 30 degrees thereby lessing the effective dampening ability.

We have 2 things to understand and those are the static dampening and the effective dampening. The static dampening/spring rate is what the shock is sitting on a bench. A 4 lb spring is a 4 lb spring. 30W oil is 30W oil. The effective dampening/spring rate is what it ends up being in the real world. Let's say we install that shock directly in the middle of the a-arm. Let's say the a-arm is 2" long. With the shock being at the mid point suddenly our 4 lb spring behaves like a 2 lb spring due to the leverage the arm has on it. Our 30W oil acts like 15W. What if we lean the top of the shock over 45 degrees? Suddenly our effectively 2 lb spring acts like a 1 lb spring and our effectively 15W oil is now 7.5W. See how this works? Again, please no one get too picky about the examples. They are there to get a point across without getting overly complicated. A 2WD has far more rake than a 4WD and will have stiffer oil as a consequence.

When you drop the car on a bench, hopefully it won't bounce at all! It should just absorb the impact.
(In the above post Fred uses the term "rake" which I believe is the same as "kickup".)

----Edit----
In the above post Fred states that a 45 degree kickup reduces the effective spring rate by 50%. So my above calculation is probably wrong. With Fred's logic, the effective spring rate would be reduced by around 28% and not just 10% in case of 25 degree kickup.
----Edit end----


Now I would imagine that one could somehow either model the effect of kickup on the effective spring rate in the suspension geometry. I take it from your comment above that this was not done. Probably not so easy. But I see another possibility, which is to reduce the spring rates of all the front springs which are entered into the software by a certain percentage, depending on the kickup angle (exact formula to be determined, hopefully in this discussion). I believe that would take care of it. But in the video which shows how to use the spring rate calculator, a correction of the spring rate due to kickup is not mentioned.

Is there another way to deal with this...

...or am I totally off? Please help me understand this, thanks!

Last edited by xprainman; 11-16-2014 at 08:10 PM.
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Old 11-17-2014, 06:06 PM   #453
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Your timing is awesome. I am in the process of adding a steering module to the program that includes kickup and caster. See the screen shot below.

You are correct that there is an effect on the front stiffness due to the kickup angle. The program currently takes into consideration the effect of shock angle when viewed from the front but not the side.That's what Fred is talking about in his post. The reduction in spring rate due to laying down the shock when viewed from the front is the cosine of the angle squared so Cosine(45)^2 is approx .5. This is all accounted for in the program. Kickup will affect this calculation slightly. Likely by only a few percent. A bigger effect will be in how the kickup angle affects how the shock force is reacted to the chassis. I need to look into this further before including it in the program.

Until that happens your idea on adjusting the front spring rates to account for the kickup can't hurt. I would use the cosine of the kickup angle for now.

The primary effect kickup has is on the pitch centre which is the equivalent to the roll centre but in the fore-aft direction.You use the pitch centre to affect weight transfer much like the roll centre. Kickup (pro-dive) will increase the front weight transfer. I haven't looked into these effects much at this point but I will.

The spring rate calculator only looks at the spring itself. It doesn't take into consideration any other effects.

Regarding shock oil weights. The reason front oil weights are heavier than the rear is mainly because you run higher spring rates in the front so you need heavier oil to provide more damping to control the spring.
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Old 11-18-2014, 06:00 AM   #454
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Great, thanks for explaining! So as an interim solution I will change my spring rates and wait for the steering module to be finished. You mentioned the effect that kickup has on the pitch center. Sounds logical. Does the kickup also have an effect on the roll centre? I would imagine that it does, because if the kickup were 90 degrees, then the chassis would not be able to roll at all, at least not to the side. Not sure though how much of an effect a "moderate" kickup of 25 degrees really has on the roll centre.
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Old 11-19-2014, 04:58 AM   #455
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If you watch the video on measuring the AE B5M to shows how to account for Kickup in the Y1 and Y2 values for the front suspension.

https://www.youtube.com/watch?v=q36F39GtJUE

I'm going to borrow the B5M again and measure the front stiffness to make sure my math is correct.
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Old 11-19-2014, 09:53 PM   #456
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Thanks Bob that is very helpful.

What I would like to achieve is less mid corner steering but with equal or more turn in. I assume (based on your advice) the best setup adjustment to make would be the opposite, ie a longer camber link, less caster to reduce mid corner grip and perhaps more front toe out to increase turn in?
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Old 11-20-2014, 08:27 AM   #457
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Quote:
Originally Posted by frozenpod View Post
Thanks Bob that is very helpful.

What I would like to achieve is less mid corner steering but with equal or more turn in. I assume (based on your advice) the best setup adjustment to make would be the opposite, ie a longer camber link, less caster to reduce mid corner grip and perhaps more front toe out to increase turn in?
Yes start with adjusting the upper links to reduce camber gain, but also raise the lower arm pin to maintain your roll centre position. That way you won't affect the weight transfer balance. This change shouldn't affect turn in at all.

If that doesn't make a big enough difference then reduce your caster.

And yes if at the end of this you need more turn in then add more toe out.

I recorded another screencast video to show how to do this better than I can possibly describe in words.
How to reduce mid corner steering without affecting anything else
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Old 11-25-2014, 05:10 PM   #458
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Hi Bob,

I tried the suggested changes to camber gain which did reduce mid corner steering.

I closely monitored the tyre wear patterns and observed the following.

After the reduction in chamber gain, there was extra wear on the outside edge of the tyre as expected.

Thanks for the help.
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Old 11-25-2014, 05:40 PM   #459
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I notice some driver setups adjust the front and rear track width by using a variety methods.

A: Suspension blocks
B: Using longer arms
C: Running wider hubs / adding wheel spacers?

Why do some adjust using A instead of B, ect, ect.
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Old 11-26-2014, 05:24 AM   #460
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Quote:
Originally Posted by frozenpod View Post
Hi Bob,

I tried the suggested changes to camber gain which did reduce mid corner steering.

I closely monitored the tyre wear patterns and observed the following.

After the reduction in chamber gain, there was extra wear on the outside edge of the tyre as expected.

Thanks for the help.
That's good news. If you have any other questions or problems let me know. Science does work.

Quote:
I notice some driver setups adjust the front and rear track width by using a variety methods.

A: Suspension blocks
B: Using longer arms
C: Running wider hubs / adding wheel spacers?

Why do some adjust using A instead of B, ect, ect.
I'll assume we are trying to increase the track width which that change alone will reduce the total Weight transfer from the inside to outside wheels. This is a good thing as total grip will increase.

The different methods do have different effects on the suspension properties. They all have very minor affects on roll centre height and camber gain which are not really worth mentioning.

A: Suspension Blocks - By moving the inner hinge pin outward you not only change the track width but also the angle of the shock relative to the arm. This will soften the suspension in both compression (bump) and roll.

B:Using Longer Arms - This will have the biggest affect on the suspension properties as you are changing the lever ratio between the arm and the shock. Think of it like having longer handles on a wheel barrel. The longer the handles the easier it is to lift the load. So in our case the Load is the spring and the handles are the suspension arms. So by increasing the length of the arm and keeping the shock connection point the same we are making suspension softer. This effect is a function of the lever ratio squared so changes here have a bigger effect.

C: Wheel Offset or Spacers - In this method you are only affecting the track width the rest of the suspension properties remain the same.

So it boils down to what you want to achieve. All methods have the same affect on total weight transfer but some will have a bigger effect on suspension properties than others. So in order of effect on suspension properties from least to most it would be C: A: B:
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Old 11-27-2014, 09:01 PM   #461
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Hello Bob,

I understand now what the changes will do and how they'll affect the handling of the car.

Thank you again!
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Old 11-28-2014, 05:49 PM   #462
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Bob, what about changes in hinge pin spacing affecting the way the roll center migrates as the car rolls? Have you done any analysis of that?

-Mike
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Old 11-28-2014, 09:02 PM   #463
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Quote:
Originally Posted by grippgoat View Post
Bob, what about changes in hinge pin spacing affecting the way the roll center migrates as the car rolls? Have you done any analysis of that?

-Mike
I haven't specifically looked at that but the program will do it.

The normal trend is the further away from the ground the roll centre is the less it will move sideways. When the roll centre is below ground it move to the outside wheel. If it's above ground it will move towards the inside wheel. When its at or near ground level it will move a lot and can be well outside the wheels.

If you let me know which car and what you want to know I can certainly look into it for you.
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Old 12-23-2014, 04:46 AM   #464
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need help... I can open my program but when I click on any tabs I get an error message that says king pin and camber link arcs do not intersect change geometry. and program is locked and will not allow me to do anything..
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Old 12-23-2014, 05:20 AM   #465
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Quote:
Originally Posted by bpalmer View Post
need help... I can open my program but when I click on any tabs I get an error message that says king pin and camber link arcs do not intersect change geometry. and program is locked and will not allow me to do anything..
First what version are you running. Click >Help>About RCCrewChief on the top tool strip and let me know what version it is.

The error is due to a problem with the model geometry. So when the program opens click the "Open Car Manager" manager and then click "Export Car File" and email the file to rwdesign@kingston.net and I will try and fix it.

The problem should just be with the one model so you should be able to select a different Car from the drop down list and all will be good.
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