djnelsen

So both mine and my son's Tamiya DF02 Chassis's broke, in the exact same place... I've read of other accounts of it happening, so clearly a design flaw... here's where they broke, right where the lower suspension arm meets the chassis:



So we ordered new chassis's, and decided to reinforce them such that they don't break again.

It seems that the problem is that the bent steel forks that reinforce the lower suspension arms are not supported by the chassis at the open end of the forks, so they really aren't very effective.

So the plan was to make the forks longer, and have the open ends of the forks extend into the chassis... thereby the chassis will support the open ends of the forks, and the whole assembly will be a heck of a lot stronger.

So first I got some 1/8" steel rod, and bent them into new forks. This took some trial and error to get the width correct, but wasn't too bad. To make the bends, I clamped them in a vice, and pounded them over with a hammer. This pic shows after the first bend was made, about to make the second bend.



Here you can see the forks for the front and rear:



Next to drill the new holes in the chassis. Using a drill bit slightly bigger than 1/8", I bored out the existing holes that support the suspension arms (they were slightly smaller than 1/8"), then continued the drill bit in until it drilled right into the chassis. Here you can see drilling into the rear of the chassis, we also did the same on the front of the chassis:



Here you can see the rear fork extending into the chassis:



Then it was just a matter of reassembling the cars. Here the car is partially reassembled, you can see the rear fork extending into the spur gear box:



So we haven't fired up the cars yet, but I feel confident that the connection between the lower suspension arms and the chassis should be WAY stronger now.

SyCo_VeNoM

Good idea actually

After you told me what happened I kinda smashed the front arm mounts off mine.

This mod should make the buggie a hell of alot stronger.

I'm gonna have to go get a rod and do it

I think the flaws are more related to the soft metal tamiya chose for its parts than the chassis though(kinda like with the shocks). I've bent that pin 5 times from it popping out [:@] I will gladly welcome a steel one

djnelsen

In the case of these forks, it's much less a matter of the grade of steel and more about simple geometry and physics... a fork is a horribly weak structure unless the open end of it is supported (in which case it's no longer a fork now is it)... even with the same low-grade metal the stock forks are made of, this mod will make the assembly way stronger.

I think this mod will also reduce the occurence of stock outdrives and dogbones popping out... might even make the DF03 universal joint shafts upgrade unnecessary (although they're so choice anyways, so much smoother)... speaking of, when reassembling the cars with the new chassis's, the spacers I told you about are no longer necessary for the DF03 shafts... points to the fact that even before the old chassis's broke, they were distorting (DF03 universal shafts were installed before the chassis's broke).

As a pointless side note, I'm sure the Tamiya engineers would have loved to have the forks extend into the chassis, but it would have meant a nearly impossible tooling issue... very complex "side actions" (aka "slides") in the injection molding tool would have been necessary to form these holes in the chassis.

If and when you do this mod, let me know how it goes.

djnelsen

Actually?

Jeez, you expect so little of me.

plasmaedge

actually i had this idea a while ago when i still had my df-02.

plasmaedge

djnelson - what setup are you running in your 02.

djnelsen

We have ezrun 12t's to to install, just haven't gotten a chance to install them. Batteries are NiMH.

I'm sure they'll be plenty fast without Lipo.

The way these things keep breaking, I'm actually hesitant to make them too much faster. We've broken chassis's and shocks, and lost a few dogbones.

plasmaedge

hahaha sounds like funive lost a few dogbones and cups on my 02, had some masive hunts for them and found them again.

plasmaedge

hey what wheels and gearing are you running??

crunchNmunch

Interesting mod, and the great thing about having true hobbyists involved in this hobby is them trying to figure out a better mousetrap and fixing what ails them on their own instead of just needlessly complaining about any specific vehicle design.
Ultimately it comes down to the fact that any reinforcing of one part transfers the inherent stress and force from impacts somewhere else in the vehicle. So while your fix might keep the highpin mounts from breaking off the diff case, chances are something else will break (as something always HAS to give). So maybe it's be a cheaper part that breaks, instead of leaving you with any entire chassis plate to replace. Personally I would have started by filling in the little voids with some sort of plastic epoxy, being as the problem really is that the hingpin brackets don't have much material holding them in place.
It'll be interesting to see if your "fix" works, but the problem(s) I see are that with the hingpins attached that too hard of a hit (which is what's snapping one side or the other of the hingpin mount) on either side of the cars will snap off the entire front end, and that I don't really see that extending the hingepins and reinforcing then with a few extra millimeters of plastic is going to help much if any.
But who knows, it could be the fix you're looking for. Keep us updated. Good luck.

djnelsen

Gotta disagree here... it's not the thickness of the wall of the chassis that's doing the supporting (the "few millimeters" you referred to)... rather, it's the length and width of the wall of the chassis that's doing the supporting... it would take a huge amount of forced for the pin to tear through the wall.

It's going to add a ton of strength to the assembly, and remove a lot of stress from the sides of the differential cases.

As I said before, the stock forks do very little to support the hingepin mounts since they're unsupported at their open ends... and if you look at how the chassis's broke, that's exactly what happened... the hingpin mounts tore out towards the open ends of the forks.

I considered filling the plastic supports with epoxy, as you suggested, or even adding additional ribs, but decided that this would do very little compared to what this mod was already doing... for the hingeipin mounts to tear out now, first the pins have to tear through the walls of the chassis.

And yes, I agree that this mod may cause breaks to happen elsewhere, but I'd rather have something else break rather than the chassis.

djnelsen

Thanks! Although I wish they hadn't broken in the first place, I find fixing them to be enjoyable.

djnelsen

HPI Racing wheels, and Dirt Hawg II tires all around.

Once we install everything, it'll be 13T ezrun brushless, with 16t pinions and stock spur gears

SyCo_VeNoM

man you can easily run the 12t in it I got a 10t with a 35A EZ-run in mine with stock gearing and HB buggy tires, and it doesn't even start to get warm.

On my buggy I'm still using the rear plastic wing mount. That rear metal mod was for my bootlegged DF-02 truck due to the way they made the body mount it introduced a extremely weak spot that didn't exist on the original(although they fixed a lot of the issues that the tamiya suffered like soft shock shafts...)

Now if your talking about the front I took a sheet of 3mm alum and traced the front alum tower on it, due to shattering the diff case mounts on it. The original way the aluminum mount would bend a little(kinda soft aluminum) and put pressure on the screws that held it on, and ultimately crack the mount off. The way I figured the added layer makes the mount more rigid so it will no longer will bend putting that force on the 2 top holes, but instead the forsce is being spread to all 4 holes.
I lifted the idea off J.D.T.'s carbon fiber/alum mount where he bolted the CF mount over the aluminum one, I went aluminum cause I had it laying around. Since I've done it the buggies taken some extremely hard launches, and landed on concrete fine without breaking the case, whereas before I did it I bent the tower from just jumping it of a curb a couple of time using the stock 27t.

You can buy swing shafts off the DF-03 and use those if you get the steel cups, and no more lost doggy bones(just might break a shaft though)


Ya the way they rip out there is really nothing you can add on to support it. Also I find epoxy (well JB weld at least) don't hold very well to this chassis. I've tried it on my current to cover the battery compartment gaps after I slightly damaged my lipo(which is proving to be a PITA to keep in) on my last chassis.

djnelsen

Another way you defintely could reinforce the chassis is if you got your hands on some MEK solvent... then you could make plastic ribs out of a number of differnet types of plastic: ABS, styrene, polycarbonate to name a few... you would then solvent bond the ribs to the chassis, which is made of ABS... solvent bonding is much more effective then gluing, as the end result is quite literally a single piece of plastic, not multiple pieces glued together.

With this technique you could go bananas reinforcing the chassis.

SyCo_VeNoM

Methyl Ethyl Ketone?

If thats it I might pick up a quart and go nuts on it

crunchNmunch

Hmmm, that's odd. But that being the case I'd have tried making some kind of hingpin support to attach at the front of the gearcase.
As my concern now is that you've changed the stress point further back in the chassis and might cause the whole gearcase to sheer off with a lesser impact.
But who knows, and that's the fun of being a true hobbyist and trying to design a fix/better mousetrap.

Good luck.

djnelsen

That's the stuff.

A quart would last you a hundred lifetimes. You only use a few drops per joint. They make small polyethylene containers with hollow needle tips that are perfect for dispensing one drop at a time.

djnelsen

Well, if the chassis breaks, it breaks... it was definitely going to break again in the same way, so if it breaks somewhere else, same result... a broken chassis is a broken chass: scrap plastic. Regardless of where it breaks.

Here's how I figure it: the more points you can make share the load, the less force each point sees. Having the hingepins supported by the chassis adds two extra points.

Having the forks pass into the spur case doesn't mean that the spur case is taking all the load. The hingepin supports are still taking some load, as are the closed ends of the fork.

I gotta shiny nickel that says something else breaks before the chassis does. And that's just fine with me. Replacing the chassis is a massive rebuild. Replacing shock towers or suspension arms isn't.

SyCo_VeNoM

My vote would be front shock tower
Rears built more sturdy


And the front sheering off I doubt would happen(unless it gets run over by a car) the front and rear are very well secured, and the points this passees through actually bear no load as of current seeing its just to enclose the sides of the chassis.
It was just the way the pin holds it in isn't the best. All the HPI's I own use a 3mm piece of aluminum between those points to prevent the issue. Due to how tamiya designed the DF-02 that really isn't an option without some decent mods(which involve a longer pin to be made either way, and if I remember right making a plate to cover the bottom).

crunchNmunch

Interesting.

Where would one get MEKfrom?

crunchNmunch

I hear where you're trying to go with your modification, it's just that part of the reason they didn't make those hingepin supports more solid (without the ribbing) is that for whatever reason other things tended to break and they designed them as such as a sort of a "sheer point", kind of like a crumple zone in an automobile. They could have made them more solid, but apparently there's a reason they didn't. It could be something simple like that by them being so solid that every little bump and jump led to a broken suspension arm, or turnbuckle, or steering knuckle, and by building some give into that area is increased the overall deflection/flex of the front end and led to less breakage.

I don't know, mere speculation on my part, but that's generally been my experience with the designs of these cars from back in my day racing for AEand Losi and working on car design.

djnelsen

Already upgraded. Next?

SyCo_VeNoM

saw it for $5 a quart on amazon



And about the design I think it was an oversight kind of like their stock shocks shafts being made of a soft metal, and prone to bending.
Honestly till I hit mine JUST right (skidding into a wall sideways at around 30mph) I didn't break it in that fashion for almost 9 months of bashing. Kinda like how toyota and the car companies are having recalls on brakes and stuff now a days for problems they didn't expect, and didn't happen till after the vehicle was on the streets.

djnelsen

I don't buy it. Why design in a weak point such that the most critical and PITA part to replace is the part that breaks? Makes no sense.

It's just an inadequately engineered part of the car. Plain and simple.

I'm sure the engineers considered extending the fork into the chassis, but it would have meant a prohibitively complex tooling condition for the chassis (complex internal slides in the tool in order to form the necessary holes).