So I've begun rebuilding a Fighter Buggy RX from my childhood...

[Lawsy 27]

I quickly repaired the upright today.

The break was very clean, therefore a perfect candidate for superglue.

Unlike my usual experience with superglue - whereby everything goes wrong, such as applying too much glue, or the pieces that mated perfectly dry simply refuse to do so when glue is applied - this came together perfectly.

To ensure there is a little strain relief, a few layers of sticky tape finished the job.

Bodged repair job: ✔

In order to reduce the stress on the repaired component, the dampers are attached to the standard gearbox mounts and less spacing at the top reduces the magnitude of any moments around the joint.

Finally, I have one of the longest collars installed inside the rear damper cylinders. This has shortened the extension and lowered the rear end to where it would have otherwise sagged to. At full throttle the centre of gravity remains below a critical point, and thus the handling remains far more friendly...

...

In all honesty, the handling is more predictable, better balanced and vastly more stable at all speeds with the standard setup (which has an almost complete lack of roll resistance). One might think some of the negative effects of the higher centre of gravity would be mitigated by adding a little anti-roll geometry, however it's actually worse! After a bit of thought I believe I have figured it out.

The additional roll from mounting a battery so high almost overwhelms the front suspension. With little roll resistance between the tub and gearbox, the rear suspension can articulate enough to allow this front end roll without lifting the inside rear wheel. If any resistance of this articulation is introduced, the front is more likely to pull the rear into rolling right along with it (rather than staying planted and assisting with roll reduction, because all that unsprung mass is trying to roll as well).

I believe that only when the effective front and rear roll centres are balanced (or the front is slightly lower than the rear), can some roll resistance between the tub and gearbox be introduced (albeit still sparingly).

That's my theory anyway; when I have a stick pack shaped LiPo, I'll test further (and then add the undertray as well). I may even find that adding roll resistance is worse, regardless of where the centre of gravity is in relation to the geometric roll centres. But we'll see...

I also need more diff locking action, but I can't find the right sized shims on eBay...

[Lawsy 27]

Broke the front upright, again...

Also, I rebuilt the dampers with medium silicon oils to see if things could be improved using the inner damper position. This certainly helps with stability, however the difference between the dampers (one feels like it's two viscosity levels lower) is exacerbated with the thicker oils, so I'm not reaping the full benefit.

One side increases it's firmness in a silky smooth manner, with great "pack", whereas the other feels like it has half the damping factor increase, and zero "pack", regardless of the viscosity increase.

Should I email Banzai about it? The problem seems to be that the cylinder of one is fractionally larger than the other. I swapped the piston's and o rings and checked the internal clearance, and it's visually obvious how much more "slop" there is within the crap one.

It's certainly outside standard tolerances, and other than ruining the good side to make them even, I'm not sure there us is anything I can do... Well, I could possibly crush the piston top slightly to increase its diameter, but that's pretty risky...

[GregM 1109]

It can't hurt to let them know about it. If that fails, you can get the CVA mini damper parts on several parts trees separately.

[Lawsy 27]

Banzai are being incredibly generous and are providing an amazing level of customer service.

They've basically offered to send me an entire CVA damper set at no charge.

I'm actually more inclined to take the "super mini II" set as it is an identical front pair, except with the multi-part piston/plunger, so I could use the 1, 2 or 3 hole piston tops (or buy even better ones instead).

Regardless of what I choose, the quality of Banzai's customer service is exemplary. It's fast, friendly and generous.

I'm very impressed.

[Lawsy 27]

Woo!

It managed, while braking from about 50 or so, to get the tail out and then roll onto its roof before much speed could be scrubbed off, and this time the front upright is not so easily repairable... It snapped off along the edge between the common horizontal base that screws into the chassis, and the right upright (my latest repair job of the top part seems to have held up however).

I'll post images if I can be bothered.

In other news.

The LiPo got held up leaving wherever in China it was coming from, and my rear tyres are almost toast because I've been driving like a dick...

Oh, those replacement on road tyres never arrived, either... So nothing is going to plan right now.

[Lawsy 27]

Ouch....

So apparently the right battery is on the way. I'll believe it when I see it... If it is though, then maybe my DT01 will finally lose its suicidal tendencies, and be fast as well.

However, it could be too little, too late.

That's a big break, and though I've glued it, I doubt it will hold for even a second of running... I'm contemplating making something, but I'm not sure how to go about it yet.

Adding to that, the hex hubs are busted in, so now there's a little binding between the hubs and gearbox if I tighten the wheels beyond just nipping them up, and both axles are bent.

This is all due to the LiPo being wrong, and NiMH being boring (and me being impatient).

Right at the beginning of the thread I said switching to brushless would result in the death of this buggy - what I wasn't expecting was a frustrating war of attrition, resulting in constant repairs and creeping misalignment of the entire front end.

Yes, it's still my fault for driving it with this battery, but my boy loves it, so I had a fatherly duty to continue! Furthermore, taking responsibility for your own actions isn't fun, so I blame the seller from eBay. The biggest accidents occurred after the second WRONG battery was sent, so it's their fault, and they're my scapegoat...

[GregM 1109]

Ouch. I wonder if aluminum or carbon sheet may help to strengthen the front damper mount next time? Although I'm not sure if the added thickness would still clear the steering assembly.

I never broke mine, but I think the big wheels of the Mad Bull played a role in protecting the car from impacts.

That reminds me I still need to cut some aluminum sheet to repair my car's upper deck.

[Lawsy 27]

Ouch. I wonder if aluminum or carbon sheet may help to strengthen the front damper mount next time? Although I'm not sure if the added thickness of the would still clear the steering assembly.

I never broke mine, but I think the big wheels of the Mad Bull played a role in protecting the car from impacts.

That reminds me I still need to cut some aluminum sheet to repair my car's upper deck.

I'm running sans upper deck, as it won't clear the ESC fan, and I'd have to perfectly cut the servo hole to make one fit.

Instead I think I'll run a beed of construction silicone (a nice thick one) around the base of the tub. It may help, it may do nothing, but currently the tub flexes like it's made from paper, so I really should at least try...

I'm also considering buying a shorter servo. If I do, then I'll be far more motivated to make an upper deck because I'll mount the servo lower, and be able to mount it further forward or further back. This will allow me to use a straight thread instead of the bent thread I'm currently using, while improving weight distribution (whichever way improves the handling).

Regarding what I'm thinking of making; it might end up looking far more like a DT03 damper mounting plate, but with a shaped horizontal base (enough to match the screw holes and the tab that inserts under the "hood"), but with more clearance over the steering crank.

I'll have multiple holes if I do make something, allowing more or less vertical damper action... We'll see though, I don't have access to either water jet cutters or CNC's (none of my mates work in machine shops), and doubt getting a precisely symmetrical cut will be an easy task by hand.

[Lawsy 27]

Well I'll be...

The right battery arrived, and the Fighter Buggy that could is now a squirming, traction limited, front wheel popping, stability challenged powerhouse.

It's still threatening to roll on medium-speed changes of direction, as well as at the end of a slide (inside rear starts to hop up), but under power the back just squats and goes. I think I need to move the ESC as far forward as possible now, the front has no weight on it at anything beyond 60% power.

It's difficult to determine what to do next though.

While coasting the front bites and tries to bring the rear around. A dab of power or opposite lock helps but then you've lost the line.

But even when using only enough power to maintain the current speed, it's understeer, understeer, understeer...

I realise this is typical 2WD buggy behavior, but this is excessive.

I'll think of something though...

[Lawsy 27]

Moving the electronics further forward has certainly improved things, I highly recommend it.

Before

Proper 3M Velcro this time.

After

It has improved stability both on and off throttle. Sadly though, the rear dirt hawgs have only half a millimetre of tread left, since the on-road tyres I was promised seem to have been lost in transit...

I'm a little concerned about what to do with the LiPo balancing leads. I really don't want to just tuck it under the body...

In other news...

The reason my fighter buggy has the torsional resistance of paper is because the internal bracing immediately behind that servo has cracked where it joins the side of the tub. I've glue the worst side, but I now think running a bead of construction adhesive/silicone around the tub and corner joints might be the best thing. It should lower the centre of gravity, and hopefully provide a strong yet flexible hold on the chassis.

PS.: With the right battery I've had zero big accidents thus far (a couple of low speed ones, but nothing even the most fragile RC couldn't handle), I don't know how I was driving this thing before...

[lentner3 281]

Try one of these for the balance lead, but you should have a low voltage alarm in there.

http://www.hobbyking.co.uk/hobbyking/store/__84283__Balance_Lead_Tidy_Saver_2S_4pcs_.html

[Lawsy 27]

Try one of these for the balance lead, but you should have a low voltage alarm in there.

http://www.hobbyking.co.uk/hobbyking/store/__84283__Balance_Lead_Tidy_Saver_2S_4pcs_.html

I'll check it out on eBay tomorrow, cheers! I knew something like that had to exist, but I was searching all the wrong key words (rather embarrassingly wrong...).

Also I've set a really conservative 3.4V cutoff per cell, resulting in the the ESC giving me plenty of warning by slowing things down at 3.5, and pulling the plug at 3.4V. I've only run this deep into a charge once. Something normally breaks, or I get bored once I've burned through about 3000mAh anyway (usually because I'm going easy on the motor at this point, and that's just no fun).

[Lawsy 27]

Still having understeer into snap over steer issues, and I'm struggling to dial this out.

I haven't had the opportunity to reinforce/ballast the chassis with construction silicone, however I'm unsure of how effective this will be for the following reasons.

1. It is not simply a live rear axle - the DT01 is essentially an unsprung power unit pushing an off balance wheel barrow. Their are two systems at work as a consequence.

2. The power train attempts to roll of its own accord, having its own centre of gravity and virtual roll centre (which cannot be easily modified)

3. The front suspension is responsible for the vast majority of roll resistance.

Number 3 is potentially the most annoying - setting up for decent turn in results in the inside rear cocking like a dog's leg. However, the front cannot be tuned stiff enough to keep the rear from misbehaving; even when the front is pushing right up until the point that it doesn't, and it rotates. Annoyingly, a well balanced car slides and the front often comes back somewhat - that doesn't happen here, at all.

Instead, under the right circumstances, it just pirouettes completely. Holding lock, winding on opposite lock, releasing the steering completely, trail brake, hard brake, power stab, coasting power - nope. It spins, or grip rolls (far less grip rolling with the new battery though, and usually only if I give it a little power at the wrong time since the DT01 is the ultimate study in anti-squat geometry... Rising under power has very few positives; sudden center of gravity increases on the verge of adhesion isn't helping in that regard).

[Nobbi1977 1793]

I think maybe you just have the wrong tool for the job. A DT-01 is what it is and like the Hornet has very little chance of being anything else. It is fun up to its limits but they are very low.

Maybe you need another tool rather than keep trying to sharpen this one?

[XV Pilot 1936]

I would tend to agree - short of a Pintopower-style Superfly-esque rework, you are unlikely to change the basic nature of the DT-01 appreciably.

It looks like you have put a great deal of effort into optimising the car within its limits, but to exceed them you'll need to either revise the suspension completely a-la Superfly, or move to a more advanced platform.

I'd be very interested to see how you get on with a DT-02 or DT-03 for example.

[GregM 1109]

I'd still suggest adding Mad Bull/Wild Willy 2 wheels and tires to get the most fun out of the DT-01 chassis. It transforms this little quirky buggy into a go-anywhere offroad monster, where you don't mind its handling shortcomings anymore.

[Lawsy 27]

I'm fully aware that I'm putting makeup on a pig - that's half the fun!

I also think I may have somehow affected the rear tyres. The fronts not only have more tread (for obvious reasons), but the rubber itself has quite a lot of "tack" still. The rear feels like I've sprayed them with silicone lube (exaggerating, but you get the point).

And I'd love a DT03, however I can't justify spending a dollar more on anything (tyres or critical spares are even a stretch)... If anyone has a spare set of the big wheels they'd like to send my way, that's fine by me

Let me lower the centre of gravity, potentially add some front ballast and then see how we go. I can't give up until I've tried everything. I also need to lock the diff at some stage, just to see what happens... One more thing on the ever growing list of ideas.

[XV Pilot 1936]

I'm not denying that it would be fun with monster wheels (and reinforced tierods to handle them) but as one who runs his Mad Bull on Star Dishes and Super Grippers, I applaud your efforts with buggy-size wheels.

The DT-01 is IMNSHO the best-handling of the Tamiya MOA buggies, and it looks like you'll soon have done pretty much all you can to improve it even further. Perhaps that is a way to better appreciate your efforts - try comparing it to a Grasshopper or Hornet, Grasshopper II or Super Hornet, or even a Rising Fighter!

[Lawsy 27]

After watching a couple of videos on YouTube to try and gain some perspective, I've come away with one overbearing opinion.

Wow is the silver can slow...

No wonder so many don't even bother with things like oil dampers or better tyres, at those speeds I wouldn't have bothered either (I went straight to a very healthy Sports Tuned and a 19T pinion for this rebuild, and then brushless). 60km/h feels slow to me now, I can't imagine how it was only going 25-30km/h back in the day.

[Lawsy 27]

Replacement dampers arrived (and I must again mention the utterly fantastic service Freya from Banzai Hobby, who generously organised this).

All four dampers are more evenly matched now and I'm much happier with the static feel of if things.

What I've done is built the new shocks with the eyelet from the other end. On the front this results in around 1mm less droop for a given spring rate, and about 2° less camber, and the rear now sits about 2mm lower. I've had to use the shorter internal limiter in the rear, and an additional bump stop (the smallest limiter) to prevent too much bottoming out.

Not expecting much change to be honest, but I just wanted to try it.

[Lawsy 27]

Slight improvement. Lowering the rear centre of gravity is definitely the right direction.

I'm also inclined to think the open differential is a bigger problem than originally thought. I'll stuff it with blu-tac later and see.

The rear dampers are definitely too stiff with a thicker oil, but I wanted to give it a go as well (need to be thorough about these things). However, since I have two sets of pistons, I'll drill a 1mm hole in one set and continue to use a thicker oil, as originally planned. This should introduce a little pack, but with the aim to make the overall damping at the rear softer.

[Lawsy 27]

It's been a while!

The Fighter Buggy held up to a lot of abuse before fitting the right Lipo, and though it's been run hard since, the abuse has certainly been reduced. I have added around 50g of weight in various nooks and crannies just under and in front of the battery (mostly from the underside), as well as some weight as low as possible under the servo, and performance was again improved, although it would grip, grip, grip, grip and then suddenly spin through medium speed turns.

So how do you (mostly) fix a DT01, about as good as it's going to get? Run a light weight lipo, and add back the same weight as low as physically possible to the tub, and lock the suspension from rising too much via internal spacers within the shocks. Other than getting the suspension dialed in with the right oil and spring rate, not much else helped to the same extent.

However, I've managed to well and truly bend the axles after a hitting a slippery patch accelerating hard up a hill (that's actually not entirely true - I was doing donuts on astroturf and the now slick wheels permanently lost a lot of grip, so after applying too much power for far too long up the hill, the road speed finally caught up to the wheel speed - at least on one side of the diff. Because my diff is a little stiff however, this resulted in the most violent side step the car has ever achieved... ******).

It spun into a gutter and slapped the rear harder than any previous hit. I'm impressed the Pro-Line wheels didn't crack or warp...

I'm now looking more seriously at a TT02B, it seems like a cheap and cheerful solution that will readily accept my brushless setup, while providing significantly better braking performance that in all honesty, has probably been one of the major contributors to the more significant impacts this DT01 has suffered through... 

I'll revive my other post regarding the TT02 vs DT03, but if anyone has more information or recommendations they would be willing to share here as well, it would certainly be appreciated. I'm also considering the DF02. I just don't know how far I want to stretch the budget at this stage.

 

Cheers.