Where do you set your IC when designing a chassis?

[opek]

Looking through a ton of builds I notice the IC drifts around a bit, but mostly seems to stay in what I've read is the sweet spot. The rear IC is usually around the COG, just in front of it and above it. The front IC is usually a mirror of that, around the COG but behind it.

Is that where I want my IC? Is that going to give the good mix of anti dive and traction, and keep the rig performing consistently on a sidehill?

Right now my on my AX10 the IC lies at the forward most point of the motor - about at the motor plate, just above the motor centerline. It's just in front of and about at the height of the COG. I guess it would lie just below the normal line, as my rig still tucks the left rear up from torque twist.

Is moving the IC down to the skidplate or the bottom third of the motor going to mess up my sidehill? How about moving it back behind the motor and keeping the same height, will that be too much anti-dive for a consistent performance? What if I move the IC back behind the COG but keep the IC located on the normal line - opposite the sweet spot?

Where do you put the IC when you are designing a chassis?

Oh yeah, and how do you account for shocks or something mounted on your links, when doing the COG of the chassis?

Do shorter links make the distances between the normal line or COG and the IC have a bigger effect? Or do they just cause the IC to vary more throughout the suspension cycle?

You are all truly amazing for reading this and hopefully leaving some sweet answers so I can make a 3 or 4 chassis instead of 10.

Should I just go cut this damn thing now?

[Szczerba]

I'll take a stab at a few. These assume I know what I am talking about.

Originally Posted by opek

Looking through a ton of builds I notice the IC drifts around a bit, but mostly seems to stay in what I've read is the sweet spot. The rear IC is usually around the COG, just in front of it and above it. The front IC is usually a mirror of that, around the COG but behind it.

If on average, that is where everyone has their's, set your's there and then adjust it to your liking with link placement.

Is that where I want my IC? Is that going to give the good mix of anti dive and traction, and keep the rig performing consistently on a sidehill?

Right now my on my AX10 the IC lies at the forward most point of the motor - about at the motor plate, just above the motor centerline. It's just in front of and about at the height of the COG. I guess it would lie just below the normal line, as my rig still tucks the left rear up from torque twist.

Is moving the IC down to the skidplate or the bottom third of the motor going to mess up my sidehill?

I think that would give you more rear squat. Up to you if you want that or not. "Suck the crawler down" Movine the chassis down and wheel up.

How about moving it back behind the motor and keeping the same height, will that be too much anti-dive for a consistent performance? What if I move the IC back behind the COG but keep the IC located on the normal line - opposite the sweet spot?

That would probably get you to "Neutral" squat/anti-squat setting.

Where do you put the IC when you are designing a chassis?

I dunno, haven't thought about it til you said something.

Oh yeah, and how do you account for shocks or something mounted on your links, when doing the COG of the chassis?

Do shorter links make the distances between the normal line or COG and the IC have a bigger effect? Or do they just cause the IC to vary more throughout the suspension cycle?

You are all truly amazing for reading this and hopefully leaving some sweet answers so I can make a 3 or 4 chassis instead of 10.

Should I just go cut this damn thing now?

[opek]

Here are my current setting and two designs I'm considering.

Red and maroon are the rear IC at full droop and compression respectively, and light and dark blue are the front IC at full droop and compression. I want to try 3.5" links. The front uppers could probably benefit from being mounted up much higher on the axle, and I will probably work towards something like that in the future - but for now everything is mocked up as it would be if I bolted it on right now.

[Szczerba]

In both cases, your anti-squat lines and points (Blue lines and blue dots)where they intersect the center of the wheel hubs are above your COG lines (red lines).

So, right now both the front and rear are have a anti-squat setup. Assuming your caster's are close to vertical.

Someone correct me if I am wrong. And shouldn't you be doing this at ride height? No sure on that one.

[Szczerba]

I made this chassis, the FF-SZ. It's based on the Underground Crawlers FF-4 setup. I just raked the skid up.

Setup as of right now, the front has alot of anti-squat in it. IC, blue dot is far away from the COG line.

Setup as of right now, the rear is closer to neutral anti-squat. IC, blue dot is close to COG line.
Since the picture is skewed a bit, I roughed out the front hub line, since I run a little caster.

[frdtrkguy]

Nothing to add...

In for the tech


Actually, what do the green lines represent in the last couple of pics?

[shelljeep]

I go for a more neutral antisquat/antidive, with an emphasis on staying away from high positive values.
Edit- IC's when viewed from above the car, i.e. point of convergence of upper links compared to POC of lowers:
When you move your IC's, look at what it is doing to your roll axis and see if that really is the way you want your tires to move while articulating.
Roll center height needs to be kept in check also but it looks like you already tend to do that.
Edit- IC's when viewed from side of car(like your drawings) i.e.- where angle of uppers and angle of lowers meet in front of rear axle/behind the front axle:
If you set your IC's too far out horizontally(front/rear, not sideways)you get alot of axle steering during articulation. Think of straight uppers as an example.
If you set them too close, your roll axis becomes too steep and causes similar steering effects during articulation.
This is why there's that common range people stick with when designing 4-link suspensions.
That being said, these little cars seem much more forgiving of less than ideal suspension geometry than full size crawlers. I remember being surprised at the numbers I got when I ran my LNC through the Calc a couple years ago. I like your attention to detail though.
Good thread!

[shelljeep]

Originally Posted by Szczerba

.

Setup as of right now, the front has alot of anti-squat in it. IC, blue dot is far away from the COG line.

That's actually antidive(think braking), and might not be such a bad thing. Alot of guys like it for how it will stand the nose up on descents and suck it down on climbs.
Edit- and yes, these measurements should be taken at ride height for the average number.

Originally Posted by frdtrkguy

Nothing to add...

In for the tech


Actually, what do the green lines represent in the last couple of pics?

Green lines are his antisquat/antidive lines.

[opek]

So I'm going to assume the way to roll on an RC Crawler is to have the IC set forward of the CoG and with enough anti-squat to keep it down. Maybe this helps get tires up and over obstacles, or reduces the intensity with which wheels might fall into holes or whatnot. I I haven't read enough about jacking to really understand how this would work with or against keeping things level. But only time and experience will tell, I suppose.

Next up is roll axes, roll centers, and the vehicle roll axis. Best I can read up you want those suckers stuck somewhere close to the CoG, which seems to be par for course on many of the modern rc crawlers. All the cool crawlers seem to keep their chassis/bodies located consistently as they navigate highly variable terrain.

It seems most useful to map out the various bits of the geometry at all angles to see how things work, to keep them from moving around very much - specifically to places that will cause behavior I'm trying to avoid.

This shit gives me such a headache. But only when I don't get it!

[Manning]

I wouldn't worry about the full bump IC's. Not too many crawlers are running full droop, and crawlers don't get jumped much.

Torque twist and instant centers...... You can tune out most TT by making the IC further forward and lower on the side that lifts (which makes it harder for the axle to lift that side to lift the chassis). It's also easier to tune out with upper links that are more parallel than sharply angled. Like on Szczerba's rig.

Too much anti dive/squat up front will make the rig want to "shorten up" or "arch up" when trying to climb sharp ledges or undercuts. I do think that downhill sidehilling gets funky with very little anti dive/squat up front.

It's all a compromise. You can make the rig perform well in one area and really screw it up in another.

[MojaveMonster]

Im noob.....what is IC

[frdtrkguy]

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