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Thread: Weight distrubution mod for c1 buggy

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  1. Thumbs up Weight distrubution mod for c1 buggy 
    #1
    Join Date
    11-23-2010
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    Central Florida
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    as many apache owners know this thing is a lawn dart on huge jumps... if you don't stay on the throttle all the way through the jump ( and sometime that dose not even help) the nose come down.

    video of apache jumping - stock set-up- 
    http://m.youtube.com/watch?v=03HYV4qe4mw 

    well, i decided to redistribute the weight ( and not add to much more) since its a heavy rc but move it so moe weight is behind the center line.





    you can see in the pictures below I have relocated the batteries by creating a new tray area in the rear center of he car using a single piece  of aluminum bent to shape.. this piece  is secured in the  same spot the battery tray mounted in the front and secured to the shock tower in the back also attaching to the rear tray.








    as you can see the tray will raise the cg a little  but it moves all he battery weight backwards.  I have not decided where to put the ESC. I was thinking where the battery tray was (like the picture shows) OR MAYBE but maybe if more rear  weight is needed then I will place it in the stock location in the plastic tray.

    Also, because of the move I needed to cut some of the plastic cage and even tho I think it may not be needed I reinforced the cage/shell with a piece of aluminum. See pics below on what I cut and how it's reinforced...





    anyway i'm waiting to see if HPI will replace my motor, it looks like something broke in the motor since I can hear it turn but the car tires does not move when placed on the ground. once they let me know i will get some new jumping videos and let you know how this mod is doing.

    some more pics to help out...





    Enjoy and I will update when I have more info to post.
     

  2.  
    #2
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    08-19-2002
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    Interesting... Usually fwd rotation on a jump is due to either going too fast, bad geometry of the jump itself (too steep for the speed required), or the rear end bottoming out. Usually the easiest fix is thicker rear shock oil to keep the back end from flying up off the jump, or sometimes even some internal shock limiters. This is how I always fixed it on the track.

    Moving the weight aft is an interesting idea. Intuitively to me it seems like it would hold more rotational inertia and make the rear rotate upwards more agressively, as well as worsening the problem of the rear bottoming out.

    Wouldn't be the first time I've been wrong though! I'll be paying attention to see how it works out.

    -Eric
     

  3.  
    #3
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    12-04-2012
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    Trenton,Michigan.USA
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    what the front diff lube at?.. are the front tires slowing down way faster than rear on jumps?.. that also will cause lawndarting.. had alot of 4x4 with 1 ways upfront that like to almost back flip.. and me new EXO nose dived till i lightened front diff lube..

    Im seeing massive rolling in many turns with this setup..as CG is way above top of axle..
    Last edited by tntpoof; 03-10-2013 at 11:11 AM.
     

  4.  
    #4
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    11-23-2010
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    Central Florida
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    RC and TNT: here is some info I'm currently running that seems to be doing well on the ground running in the conditions I run...

    In shocks I don't remember size but the discs are tapered allowing for faster compression but slower recoil with 30 shock oil. I have increased the size to 112mm from the 96mm stock ( I think that was stock may have been 92mm)

    The difs are currently running 10000 in both front and rear diffs and 20000 in center. With sand I found this worked well since the power sent to each wheel was more equal acting closer to locked diffs that the thinner silicons.

    I don't remember spring compression but it was about the same as stock but theses are longer to accommodate the new 112mm shocks

    The other item I think that affected the jumps is the upgrade to the blur/tork2200 system.

    Thanks for your input , If this does not work I'm going to need to go back to playing with the suspension...

    Please keep providing ideas I can try.. I like jumping... It Jumps well but I'm sure it can do better.


    The original CRASHER : equal parts CRAwler and baSHER!
    Sent from my mobile device
     

  5.  
    #5
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    TNT: The diff fluid goes inside the diffs, affecting the differential action. It will have no affect on jumping...

    Mdlopez: I watched the video and it looks like the jump is too steep for how hard you're hitting it to me. Although if you could make it work hitting it that hard, it'd be sweet!

    I think thicker shock fluid is the way to go but I'm curious how your weight mod works out! Keep us posted!

    -Eric
     

  6.  
    #6
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    I deleted you I'm by mistake so I will post a new link on the forums I use.

    Corrected Video link:
    [ame]http://youtu.be/03HYV4qe4mw[/ame]


    The original CRASHER : equal parts CRAwler and baSHER!
    Sent from my mobile device
     

  7.  
    #7
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    12-04-2012
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    Trenton,Michigan.USA
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    ok.after watching your video.. you are lawn darting when u miss a rear wheel on the jump. or when u release the trigger..go with a lighter lube in front diff say 8000.. and keep all 4 tires on ur ramp.. thats the only issue is see besides your springs are like mush .. might try a slightly stiffer spring to soften landing.. make a more gradual ramp not a skater board ramp..
     

  8.  
    #8
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    Again, the diff fluid has no effect in the air. Springs have about 5% of the responsibility of the suspension in this case. As long as they hold the truck at ride height, the oil has the other 95% of holding the thing from bouncing the chassis off the ramp or the ground on landing.

    -Eric
     

  9.  
    #9
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    diff oil weights have alot of how a vehicle flys.. if the front tires slow in rotation then NOSE will dive..just like when he misses a wheel on takeoff that wheel is spinning faster and pulls that end side of truck UP.. its physics man..centrifugal force.. Thats 20 years of education after high school and 7 degrees and airframe and powerplant certification ..Thats all..
     

  10.  
    #10
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    Good conversation gents. I'm with rccardude on this one in one respect. Diff oil doesn't make a difference when in the air.

    May make a difference on how you come off the ramp which is what I think tntproof is saying...if you are powering up a dirt ramp face, and the center diff is way light and the fronts are pulling harder than the rears, then I could see them coming off the ramp at different speeds front and rear - that could certainly make a difference.

    But once in the air, nada. There's no force on the wheels to counteract what is coming from the axle...so it's either accelerating, braking, or something inbetween, and all 4 wheels should be doing the same. Diff oil is not a factor, or is so minimal as to be non-existant.

    Anyway, since it's a concrete ramp and a grippy jump, I would assume that the wheel speeds are the same provided you are hitting the ramp squarely and leaving it the same. So really, I think we can take that out of the equation anyway. That leaves springs, oils and technique....

    I don't have sound here at work, are you "popping" off the ramp or hitting it at full throttle? There's a rhythm to hitting ramps, I always called it popping but i'm sure there's some technical name for it. In a nutshell, leave off the throttle slightly before you get there, and then hammer it on the way up. Pop's the car off the ramp...

    MDlopez1, 1 word that would greatly improve the video....tripod.
    84 RC's and counting
     

  11.  
    #11
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    he is not popping the jump.. I call it Evel Knievel --he is smoothly accelerating off them.sometimes.. and he is letting off trigger on some and only a fe is he keeping same trigger pull as he leaves and lands and those are some what ok. basiccally dead dropping all 4 tires hitting at same time...We had a guy for weeks with same issue the guys that ran the track went thru acceleration-oils-springs this that..I said Here dropped a bottle of 120K in his lap said put this in front diff .. he did problem fixed..

    Try the lighter diff lube upfront then when it works say im wrong LOL.. TnT
     

  12.  
    #12
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    Quote Originally Posted by tntpoof View Post
    diff oil weights have alot of how a vehicle flys.. if the front tires slow in rotation then NOSE will dive..just like when he misses a wheel on takeoff that wheel is spinning faster and pulls that end side of truck UP.. its physics man..centrifugal force.. Thats 20 years of education after high school and 7 degrees and airframe and powerplant certification ..Thats all..
    "Centrifugal force" or (centripetal acceleration and momentum) also have nothing to do with the vehicle's attitude in the air. They work at right angles relative to the axis of rotation and cancel each other out to zero over each full rotation of the tire (assuming the balance isn't perfect). The phrase you are looking for is moment of inertia or inertial momentum. However, a locked differential vs one that has 10w-30 engine oil in it will decelerate at the same rate aside from the insignificant difference in moment of inertia of the fluid inside the differential. The only way the oil would affect it is if you have one side's tires spinning faster than the other side's tires. For example, the right tires spinning faster than the left tires. Then, you would see a difference in differential fluid. But it's still not going to be a whole lot.

    You're confusing "differential fluid" with "too much grease on the ring and pinion." Differential fluid changes the effort required to move the LH tire relative to the RH tire. It has nothing to do with acceleration or deceleration of the tires while they're all spinning together in the air.

    Old_School_RC: I totally agree with your driving technique assessment! What I saw in the video was too much speed and/or ramp angle. Reduce one to make it work right. That or keep playing with shock oil until you can get it to keep from bouncing. There's a point where there is literally nothing you can do to make it work though. I think your weight mod would have some promise on a HUGE jump that the car is leaving in essentially steady-state suspension mode (sitting level at ride height and not accelerating any more), since the aerodynamic drag on the front of the car would hinder its ability to fall at the same speed as the rear, which has more mass/weight to pull it down. Would be cool to see you take it off of a huge smooth jump (by huge and smooth, I mean something like the roof of a house where it's just an angled flat surface to launch off of, with enough time for the suspension to settle before leaving the surface) with the batteries in a few spots. Obviously, the consequences could be pretty harsh if that goes wrong though.

    -Eric
     

  13.  
    #13
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    Quote Originally Posted by tntpoof View Post
    he is not popping the jump.. I call it Evel Knievel --he is smoothly accelerating off them.sometimes.. and he is letting off trigger on some and only a fe is he keeping same trigger pull as he leaves and lands and those are some what ok. basiccally dead dropping all 4 tires hitting at same time...We had a guy for weeks with same issue the guys that ran the track went thru acceleration-oils-springs this that..I said Here dropped a bottle of 120K in his lap said put this in front diff .. he did problem fixed..

    Try the lighter diff lube upfront then when it works say im wrong LOL.. TnT
    The reason it fixed it probably has 90% to do with the fact that he hit the jump more squarely because the thing didn't actually turn in when he went into the corner and wasn't able to accelerate out as quickly. Would get the same effect by just slowing down.

    -Eric
     

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