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Unread 01-26-2009, 08:06 AM   #1
Act162this
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Default question re: suspension setup

hello all!

have a quick question re: suspension setup.

my son's 2.2 crawler (using coilover shocks w/ iirc 20wt oil) is a bit tipsy. i suspect that it's due to being topheavy as well (2 7.2v battery packs wired in parallel, 3 spd tranny, etc...) all up top on a ladder frame.

when turning, even at low speeds, it lifts the inside front tire. turning in forward or reverse at anything other than a crawl results in an immediate flipover. sidehills, tree roots, rocks, etc... have to be taken head-on, or it'll tip right over.

if he tries to bump it for momentum to climb an obstacle, it goes right over backwards with no warning or hesitation. if he just floors it in 3rd gear, it'll just flip over backwards.

i lowered it on the coils by turning the nut down and removing the spacers, but if anything, the suspension got stiffer so it bounces down even a paved parking lot.

should i try removing some shock oil (do they make anything lighter than 20wt?) or should i try to find softer springs? there's almost no droop to the suspension, so traversing obstacles leads to three-wheeling a lot. with locked f/r diffs, it just pulls it right over onto it's side. i'm considering trying to only fill the shocks 1/2 way to see what will happen.

any ideas would be greatly appreciated - my son loves this truck (friend built it for him for his birthday) and takes it out every chance he gets, but it's just taking a lot of rollover damage. we only run it on grass now because it doesn't scratch up the body and paint.

thanks!
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Unread 01-26-2009, 09:00 AM   #2
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What make/model 2.2 are you working on. Also, why are you running 2 7.2 batteries. Most crawlers would run over 45 minutes on a sub C 7.2 stick packs. Try to move as much weight lower to have a better center of gravity. If you can, come out to the next HRCC comp and bring your rig. The club members have worked on almost every rig on the market and I'm sure they will have some tips for you.
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Unread 01-26-2009, 09:36 AM   #3
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Pic of the truck would be helpful if you can post some up.

Does the suspension move smoothly?

With the truck on the ground try lifting one front tire and see how high it goes before the same side rear tire lifts off the ground?

Right now I would agree with Sprint80 and trying to lower the center of gravity of the truck. And that you should be able to run the truck on just one 6 cell sub-c pack.

A thicker oil might be a better choice as this will slow down the reaction of the suspension. Maybe try some 35wt. oil.
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Unread 01-26-2009, 11:51 AM   #4
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Quote:
Originally Posted by Sprint 80
why are you running 2 7.2 batteries.
I'd have to ask that too.

Pics are the most helpful.
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Unread 01-26-2009, 01:07 PM   #5
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thanks for the help and suggestions!

my friend built the rig for my son - i'm guessing he is running 2 stick packs in parallel to extend run time (it's not a b/l or crawler-specific motor - i think it's a regular 540 can, i forget). i think it'll run off one pack just fine, i don't think it's a e-maxx or e-savvy esc for two batteries in series (14.4?).

and yes- come to think of it, the rig is quite top heavy. our friend built it up out of parts he had from other projects (kinda like how he built my son's tuber for his previous birthday, except this isn't a tuber)...

it appears to be based off a high lift or some ladder frame, with a 3 spd tranny and mostly metal drivetrain and other bits. w/o batteries, it's heavier than my son's stock e-savvy. i wish i knew how to post pictures, so you could see what it looks like.

i will definitely try removing one pack tonight and zip-tying it below the frame, instead of on top/inside where they sit now. anything to get the cg lower should make it less tipsy, no?
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Unread 01-26-2009, 01:13 PM   #6
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Yah the lower the cg the better the truck will perform.

You can use the "Manage Attachments" button that shows up in the additional options section when you are posting.

You just have to make sure the size of the pics/file is not to big. I think the file size limit is 976.6 kb. 800x600 is a good size for pics.

Last edited by Xtant3150c; 01-26-2009 at 01:17 PM.
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Unread 01-26-2009, 01:18 PM   #7
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Quote:
Originally Posted by Xtant3150c
Pic of the truck would be helpful if you can post some up.
i'm kinda clueless when it comes to things like posting pictures, etc... will take pictures and see if someone can help me figure out how to post them

Quote:
Originally Posted by Xtant3150c
Does the suspension move smoothly?
smooth, yes. but very stiff. it takes some effort to compress it if you push on it, and if you lift it up, there is very little droop. if you drop it from about four inches, it just hits and sits. his e-savvy from the same drop will sometimes bottom out (of course, the shocks/springs may be worn out from all the dukes of hazzard action we subjected it to when he was younger).

Quote:
Originally Posted by Xtant3150c
With the truck on the ground try lifting one front tire and see how high it goes before the same side rear tire lifts off the ground?
we haven't tried this yet, but in a turn (both right and left) the inside front tire will lift about an inch at low speeds. at anything faster, it will just flip over w/o warning (so we can't catch it and save it w/ countersteer).

Quote:
Originally Posted by Xtant3150c
Right now I would agree with Sprint80 and trying to lower the center of gravity of the truck. And that you should be able to run the truck on just one 6 cell sub-c pack.
we'll try this tonight - i think i can zip tie one pack to the underside of the chassis somehow so it doesn't hit the drivetrain or transmission.

if this helps, maybe the b/l + lipo conversion might be next in line. i'm assuming that a small lipo battery, placed low in the chassis, would help get the cg down (or at least reduce the topheavy weight distribution) and a goat b/l system would keep the speed down so he couldn't flip it as easily.


Quote:
Originally Posted by Xtant3150c
A thicker oil might be a better choice as this will slow down the reaction of the suspension. Maybe try some 35wt. oil.
ah, thanks. will do. i thought heavier oils would make things worse, since it'd be harder to compress and droop the suspension. looks like we're going to the LHS tonight.

thanks again for the help!
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Unread 01-26-2009, 01:27 PM   #8
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Quote:
Originally Posted by Sprint 80
What make/model 2.2 are you working on. Also, why are you running 2 7.2 batteries. Most crawlers would run over 45 minutes on a sub C 7.2 stick packs. Try to move as much weight lower to have a better center of gravity. If you can, come out to the next HRCC comp and bring your rig. The club members have worked on almost every rig on the market and I'm sure they will have some tips for you.
cool, thanks!

his crawler isn't from a kit or anything, it's sort of a home-built rig that our friend built for my son. i'm not really sure about what's in it, though.

will definitely try to run a single stick pack lower, maybe on the underside of the chassis tonight and see if we still crash and burn as much. it's not a dedicated crawler esc/motor combo, but if we can squeeze out about 15-20 min run time on a single pack, we'd be happy (by that time, he'd be bored and probably switch over to his e-savvy and terrorize that instead).

we have been meaning to check out hrcc last year - went to one out at sand island, but couldn't find you guys. we'll try to make some time this year to head out there again this year.

thanks!
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Unread 01-26-2009, 01:44 PM   #9
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Quote:
Originally Posted by Act162this
cool, thanks!

we have been meaning to check out hrcc last year - went to one out at sand island, but couldn't find you guys. we'll try to make some time this year to head out there again this year.

thanks!
HRCC is having its first comp this coming weekend Feb. 1st at the Kahalu'u pond.

Shoots..
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Unread 01-26-2009, 01:51 PM   #10
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I think it might have to do with your CG & also link/shock placement.


Get a photobucket account, it's free & simple.
www.photobucket.com
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Unread 01-26-2009, 04:25 PM   #11
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Sounds like you need softer springs as well.

You really don't need to do the drop test on a crawler

You want a spring that is pretty soft so that the suspension moves rather easily. And use either spring clips or if they are threaded shocks adjust them to set the ride height on the truck.

Adding pics here is very easy.

When you click to post a reply scroll down to the additional options section and click on Manage Attachments. Another window will open with the option to browse for pics click on browse and look for the pic on your computer. Click on the pic and then upload.
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Unread 01-26-2009, 06:31 PM   #12
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thanks... i was thinking softer springs would help out some so it would articulate more.

they are threaded shocks, so i tried spinning the mount down to lower the cg, but i think it stiffened up the springs, too. lower truck, lower cg, waaaaay less travel = more flipovers on sidehills.

thanks for the info on how to attach pictures... i thought i needed an external host. will try this later after i check on my son's homework and see how he's doing (geez - they have homework in preschool!).
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Unread 01-26-2009, 06:32 PM   #13
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Quote:
Originally Posted by DISTURBIN' tha PEACE
Get a photobucket account, it's free & simple.
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ah, thanks! can't get to that link at work - will try now that i'm at home.
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