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Old 08-07-2017, 11:10 AM   #1
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Default Doing something different on carpet - DeDion, Struts, Trailing Arms,

So lets talk alternative suspensions for a bit. Mostly with an eye towards reducing CG, as that seems to be the limiting factor at my local black carpet track.

Obviously, this is going to be mostly thought experiments, and "well that'll never happen" but hey, lets talk about something other than "buy part y because the manufacturer didn't think of it."

I got on this after considering ~just how fast~ live axle cars can be on good track surfaces. I mean, we have something like that with pan cars. But.. un-sprung weight there is ridiculous. What first came to mind, was DeDion.

DeDion

DeDion is what you get when you which amounts to a very light, rigid live axle, with the differential mounted to the chassis. DeDion when done right, is the one of the lightest and lowest cg suspension designs.

Due to the axles, you can do toe in, camber, easily on DeDion. And because you're not trying to constrain the hub carriers in three dimensions through suspension travel, you will end up with much simpler hub carriers. The through axle could be something as simple as an arrow shaft.

The net result would be a lower CG, if not necessarily lower weight. And on a prepped surface such as carpet, you'll end up with a quite sticky setup. Perhaps, even with less unsprung weight.

So.. I went and checked the rules, while USVTA doesn't care if a car has X-Y or Z suspension setup, ROAR says all corners must be independent, or a pan car. Poo.

Struts

Struts are nice as they reduce parts count. Sadly, they introduce some rather wacky geometry restrictions. There are some cars on the market that use struts, so this isn't entirely new. They require a significant superstructure to handle the upper mounts of the struts, so they do raise the CG.

Come to think of it, "conventional" pan car suspension isn't far removed from an inverted strut setup. I need to look into that more. Doing that, could lower the CG of a touring car, and reduce parts count.

Can you imagine having a car where the tallest components are the top of the diff and maybe the fan on top of your ESC? I think that could be a reality with a chassis like that.

And these would be ROAR legal. Speaking of ROAR legal...

Trailing Arms

Well this is a subject that's not been visited since the late 80's. Trailing arms need to be a bit chunky. But they also are very friendly to laydown spring setups.

Having Trailing Arms where the pivot is, or is very nearly perpendicular to the chassis centerline, would provide you with constant, or even a slight camber gain through suspension movement. By limiting downtravel, you can get around the chassis English/VW Beatle axle tuck behavior.

The downside, is that trailing arms end up being pretty chunky, as they provide all of the control for the axle, and their size means the pivot loads are high. The weight is low, but they're not as light as the other options. Still, in classes where weight is a rule, this might have a place.

Trailing arms also take up lots of space, so packaging might become a concern. As would laydown shocks.
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Old 08-07-2017, 01:32 PM   #2
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If you after suspension with lowest CG and parts count then something along the lines of the awesomatix is your best bet.

Or if the lowest CG is really the most important matter then you forgot the best one, no suspension. I'm serious. No suspension means you have to tune using flex somewhere but if that can be accounted for why not? Lowest part count, less geometry to worry about...The advantages are many.
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Old 08-07-2017, 01:38 PM   #3
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If you after suspension with lowest CG and parts count then something along the lines of the awesomatix is your best bet.

Or if the lowest CG is really the most important matter then you forgot the best one, no suspension. I'm serious. No suspension means you have to tune using flex somewhere but if that can be accounted for why not? Lowest part count, less geometry to worry about...The advantages are many.

+1, like we have been doing it for over 40 years in 1:8 2wd Pan, lol.

Another thought, dont we have a thread on this already...
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Old 08-07-2017, 01:39 PM   #4
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Years ago, in the foam tire days, there was a home built sedan with, if I remember right, 4 fiberglass arms and 1/12 style damper tubes for suspension. I only saw it once or twice. Not sure how well it worked, but I thought it raced at the US Indoor champs that year.

Unique idea.
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Old 08-07-2017, 01:45 PM   #5
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The Awesomeatix still leaves some weird tastes in my mouth. It feels a lot "well here's our magic, it works, deal." They do have a unique solution to the "lets move weight lower" thing.

Damping becomes an issue with no suspension. Tuning flex is essentially what the early pan cars did. And eventually became pretty sophisticated with it, as we got to the pre-ball pivot pan cars. One trouble with chassis flex, is dealing with power transmission across it. Another trouble, is controlling that flex, as you need to start considering how to do damping across the chassis. And then mounted components start to be part of the suspension.

Having a distinct line between sprung, and unspurng weight is a big advantage when it comes to wheel control.

has anyone tried using hingeless suspension components? like.. narrower bits of plastic that act as hinges instead of actual hinge pins? Or routed out bits of carbon? Would ROAR still see that as independent suspension?

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+1, like we have been doing it for over 40 years in 1:8 2wd Pan, lol.

Another thought, dont we have a thread on this already...
If we do, it's not active, or has a cruddy title. :-) Tell me more about suspension setup in 1/8 2wd pan?
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Old 08-07-2017, 01:47 PM   #6
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Quote is not reply... remember, quote is not reply. *beats own head in*

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if I remember right, 4 fiberglass arms and 1/12 style damper tubes for suspension. I only saw it once or twice. Not sure how well it worked, but I thought it raced at the US Indoor champs that year.

Unique idea.
I wonder if we can find anything on it. I've heard of demos of 1/12 damping rods not being very consistent when worked hard.
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Old 08-07-2017, 01:59 PM   #7
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Quote is not reply... remember, quote is not reply. *beats own head in*



I wonder if we can find anything on it. I've heard of demos of 1/12 damping rods not being very consistent when worked hard.
Probably not. It may be in a basement somewhere though....
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Old 08-07-2017, 02:06 PM   #8
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+1, like we have been doing it for over 40 years in 1:8 2wd Pan, lol.

Another thought, dont we have a thread on this already...
Exactly those early cars. One could still tune camber and caster and everything you can with independent suspension.

I also recommend to not use lubed shafts as damping control, too inconsistent. My car design uses arms like the 1990's F1 cars with 6 threaded rods per wheel (4 for A arms, 1 for steering(front only if I can make it keep rear toe in check) and another for dampening). It uses a torsion bar front and rear, a monoshock for heave and a lubed "disc" for roll with a wiper that can be exchanged for one it more or less range of motion. Could design a pull rod and then chassis mount the monoshock(or place it like the serpent 4x shock,in a chassis slot).
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Old 08-07-2017, 02:26 PM   #9
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Tell me more about suspension setup in 1/8 2wd pan?
Its all done with flex vs. shore being run. And the early days of adding dampening with horizontally mounted shocks hs passes.

...the best advice i have to give, is look back at the beginning of Pro10 and TC. So many ideas, from the Vicfor, Brimod, Delta, and PTI's "Amethyst" TC. So much was tried back then
...

Now you have greats like the Hazenbach Pro10, Awesomatix, Serpent 4x etc.
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Old 08-07-2017, 02:32 PM   #10
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Aaah, so those cars were highly dependent on the actual foam to do their chassis damping. Interesting. The transition to thinner foam must be putting a greater emphasis on suspension than there was in the past.

My Bolink 91 sport, ran around on 1/2" of foam in the back, and 1/4" up front. The stuff I seen on pan cars these days almost looks like a skim of foam tape on a plastic rim.
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Old 08-07-2017, 02:34 PM   #11
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Always love trailing arms in rc. I was thinking of using flex suspension on a tc before. When i was working on a one off fwd car for a friend. I consider using diffrent thickness g10 for the rear arm.
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Old 08-07-2017, 03:16 PM   #12
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I saw someone use a Bolink Legend at an indoor offroad track. Looked like it survived the jumps pretty well, so for flat black carpet you may be able to get away with a lot less foam.
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Old 08-08-2017, 02:47 PM   #13
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Yes the Awesomatix has an advantage CG wise over other cars, but I still think that it is not impossible to overcome with short shocktowers, unless you refuse to run a superlight body(60g-70g), and lcg pack with aluminum screws up top, etc... You don't need the lowest cg of all ; you just need to be close....
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Old 08-08-2017, 06:44 PM   #14
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Aaah, so those cars were highly dependent on the actual foam to do their chassis damping. Interesting. The transition to thinner foam must be putting a greater emphasis on suspension than there was in the past.

My Bolink 91 sport, ran around on 1/2" of foam in the back, and 1/4" up front. The stuff I seen on pan cars these days almost looks like a skim of foam tape on a plastic rim.
No it was majnly chassis flex and twist tht you can tune. if you ran a harder shore, you put in more flex, and less with softer shore.
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Old 08-10-2017, 02:54 AM   #15
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Trailing Arms

Well this is a subject that's not been visited since the late 80's. Trailing arms need to be a bit chunky. But they also are very friendly to laydown spring setups.

Having Trailing Arms where the pivot is, or is very nearly perpendicular to the chassis centerline, would provide you with constant, or even a slight camber gain through suspension movement. By limiting downtravel, you can get around the chassis English/VW Beatle axle tuck behavior.

The downside, is that trailing arms end up being pretty chunky, as they provide all of the control for the axle, and their size means the pivot loads are high. The weight is low, but they're not as light as the other options. Still, in classes where weight is a rule, this might have a place.

Trailing arms also take up lots of space, so packaging might become a concern. As would laydown shocks.
Trailing arms (or semi-trailing, to be precise) can achieve very similar, if not same, kinematics as double wishbone, while being simplier. Only downside is, that it's more complicated to change setting like camber gain or rollcentre, because change in geometry of arm and mounting is needed. Axle tuck is not issue, that's problem of swing arm suspension (that's what beetle had in rear)

I'm now experimenting with semitrailing suspension on ky rally car, as they have some advantages over double wishbone, when you need high ride height. So far it seems, that they work great



There are lot of interesting concepts in real life cars, that could be interesting in RC world. What about transverse leaf spring from corvette, which acts both as spring and anti-roll bar? Torsion spring? Using swing shaft or anti roll bar as suspension link? Possibilites are endless
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