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Project: Ultimate Rustler

Phase II

With Phase I of the Ultimate Rustler project, I earned the respect of many an Associated and Losi driver at the track. I also earned such novel titles as "maniac" and "Dremel savage." It had been my first hobby-level R/C, and it had hardly seen the charge of a 1500mah pack run through it before the modifications began.

The Ultimate Rustler took the "Swiss cheese" concept to a whole new level while turning Traxxas into a force to be reckoned with in the local racing scene. However, it has been two years since those fun, early days of reckless experimentation. I've since built and run a Stampede, the Spyder and Valkyrie E-Maxxes, a 4-Tec, and many, many other R/C's. I've done modifications to and raced a 1:1 scale car. I've studied aerodynamics and the physics of racing suspensions and I've extensively practiced rally racing through a computer simulation.

After going through all of this, I finally went back to try out my old trusty Rustler, remembering the joy of powering it around the track at great speeds, passing high-end graphite racing trucks and drawing curiosity from fellow drivers. This time, though, much to my suprise, I was completely unhappy with what I saw. Without even putting it on the track, I noticed a laundry list of things that could be improved. Once I began to drive it, I was downright disgusted!

The time had come to put some of the past two years' experience to work, to shelve my old ideas and assumptions and make the Ultimate Rustler into a refined machine that I could once again be proud of.

** Be sure to click on the images below to see the large, zoomed-in versions **

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Shedding weight: The Chassis

The Phase I chassis was refreshingly lighter than stock due to the large number of holes I unscrupulously cut and drilled through it. However, I realized over time that not only could I have trimmed even more unneeded plastic, but I could have chosen my cutting paths more carefully and ended up with a stronger, more rigid frame.

Starting from a fresh set of stock parts and armed with a screaming Dremel, I attacked again, this time with careful planning. The results were both meaty and trim at the same time. As you can see in the pictures at left, I removed enormous chunks of the lower chassis tub and bored holes in more places than before, while leaving the thinnest parts significantly thicker than in Phase I. I again cut out the area behind the stock battery tray (MSC mounting area) to allow the battery to be mounted all the way back against the rear bulkhead to add rear traction. I also set up the chassis to hold the receiver and speed control as far to the rear as possible. Finally, I shaved and sanded all underside surfaces to make them as smooth as reasonably possible so that when the truck bottoms out, it won't dig into the dirt. The new Ultimate Rustler main chassis tub is 2.3oz lighter than the stock piece.

The upper chassis plate was drilled along its face, and also slimmed along the edges to take out the unnecessary angular bulge of the stock piece in favor of a functional, smooth, concave arch. Though again the skinniest sections are much more meaty than their earlier counterparts, the final piece was 0.5oz (33%) lighter than stock, 0.1oz lighter than the Phase I plate.

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Shedding weight: A-Arms

People who have seen my Phase I a-arms have been quick to say that they are too thin, that I've gone too far, and that they'll shatter into tiny fragments all too easily. I'm equally quick to point out that I ran those arms for two years and never had a problem with them.

For Phase II, I realized I could further lighten the front arms (upper left) without passing a minimum required level of strength. The trimming involved all 3 axes, but barely touched the critical areas around the suspension pins. The result was therefore a pair as strong as the hefty stock pieces, for all practical purposes. (Unfortunately the front arms were not weighed in time for this writing.)

For the rears (3rd & 4th pics, left), I decided to leave some of the crossmember material towards the outer end intact to increase rigidity in this important area. To make up for the lost weight savings here, I completely removed the relatively useless inner cross members. The result was a pair of arms that saved 0.4oz, or 25%, versus stock.

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Shedding weight: Odds & Ends

To round off the weight savings, I switched from a Pro-Line Chevy Silverado body back to a stock body, painted with a simple color scheme that used only one color overlap (to avoid heavy paint build-up), not including the quick spray of window tint. Mounting it lower also allowed me to cut out more lexan without making the truck look too odd. This body is almost 1oz lighter than the last!

I ditched the pretty RPM gear cover in favor of a trimmed & sanded stock piece, which saved about 1/5th of an ounce. On the other side of the motor plate, I cut out the motor "guard" and transmission housing as much as I could without completely exposing the motor to abuse from bad landings. I also used aluminum locknuts in a couple of places and used nylon nuts to secure the rear wheels.

Then there was the matter of cutting off half of the rear shock tower...

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Stretching Performance: The Suspension

Note that in Phase III, some of the following changes were changed again, for the better. At the end of the Phase III project, these changes will be merged together.

Weight savings are a great thing, but to continue to live up to the name of "Ultimate Rustler" and have a fair shot at toppling the supremacy of the XXX-T's at the local track, I decided to do some major, but ridiculously inexpensive changes to improve the truck's handling.

Laying the shocks down a bit (angling them inward) would contribute to increased progressiveness of the suspension action. This means that when the suspension is level, the wheels can move up & down with relative ease to "soak up" small bumps, but as the shocks are compressed, they become stiffer at an increasing rate, diminishing the tendency to bottom out over jumps.

When I tried to move the upper mounting point of the rear shocks inward, the shock bodies would rub against the chassis tub when the suspension was not compressed. Moving the mounting points down and back outward a bit would get around this, but then I ended up with far too much downtravel. I ended up switching to front shocks in the rear to solve this problem. Click the top picture on the left to see the detail. On each side, I drilled a hole through the shock tower and mounted the shock with a 3x12mm bolt and locknut, one thin plastic washer/spacer (from the parts tree that the spring preload spacers come on) and one long step-sided spacer (from the same tree -- don't know what it's called, looks like two cylinders butted end to end, one smaller in diameter than the other -- the top of the shock fits over the smaller end perfectly). This left me with a huge portion of unused shock tower, so what did I do? Cut it off to save weight, of course!

Up front I was conveniently able to reuse my rear shocks! I stole the Nitro Rustler stock front shock tower from the Ultimate Stampede to take advantage of its closed top and used the same mounting trick, though using two of the thin washer/spacers on each side this time. I then cut off the stock shock mounting posts to save a few hundredths of an ounce or so.

The end result of this suspension conversion is a significantly more agile truck that lands the jumps with much greater ease. I have much, much more suspension travel now (over 2" vertical travel at each front wheel), which also helps to smooth out the jumps by giving the shocks more of a chance to do their job on the landings.

At the front corners, I switched to Nitro Rustler caster blocks and Kyosho Ultima EP ST Type R steering knuckles with aluminum spindles. This allows me to accept standard Associated wheels with 3/16"x3/8" bearings in the wheels instead of the 5x11mm knuckle-mounted bearings and spinning stub axles I had before (the standard RPM bearing carrier upgrade). The wheels are attached with standard 4mm locknuts.

I had considered doing the full Nitro Rustler conversion with the N.Rustler's knuckles, spindles and wheels, but that would have weighed quite a bit more (solid steel 5mm spindles, bigger bearings, and slightly heavier wheels). I had to drill out the spindles & knuckles to accept the N.Rustler kingpins. Also, the N.Rustler c-hubs accept larger suspension arm pins than the E.Rustler uses. I didn't want to bore out the holes in the suspension arms to accept the larger pins as this would dramatically decrease their durability. Instead, I inserted into each knuckle a length of thin-walled 1/8" aluminum tubing (available at a general hobby shop, around where they keep either balsa or tools) that I sanded on the outside and bored on the inside with a small drill bit in a pin vice. The Kyosho knuckles are also not tall enough to fill the space in the c-hub, so I used another two plastic spacers from the shock accessories part tree (one above, one below) plus a clear Nylon washer from a stock shock rebuild kit (see the 3rd picture down, at left). For proper geometry, eliminating bump-steer, I mounted the steering linkage to the inner hole on the knuckle arm and assembled the ball end to the knuckle arm without any spacer (the Kyosho manual specifies the use of one medium spacer to raise the ball). I was left with some unused length of knuckle arm and ball end thread, so I cut those off to save precious milligrams. Finally, the outer camber link was mounted to the upper hole in the c-hub (mounting it to the lower hole would give you too much negative camber on the outer wheel in a turn).

In the rear, I mounted Associated rear wheels directly to the axles, with pins, by simply removing the hex hub. It's a snug fit and requires a bit of squeezing to get on, but it increases the rear width to a full 13", the maximum allowed by NORRCA rules.

This wheel-mounted bearing setup with immobile spindles allows easier free-wheeling than the old spinning stub axle system. This translates to less rolling resistance which means higher top speed, lower amperage draw, and faster acceleration. I also end up with far less rotating mass than before, which also contributes to more brisk acceleration. Lastly, the decreased weight of the whole assembly means less unsprung weight, allowing for more responsive suspension action.

The rear springs are Duratrax Maxximum ST progressive-rate beauties. They are medium-firm when extended, but become very firm as you compress them. This change in spring rate is the result of having the spring wound more tightly in one section at the top (see the photo at top left).

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Stretching Performance: Chassis Stiffness

I have been frequently lambasted for savagely cutting up my chassis, causing it to be weak and terribly flexible. For the past year, however, I've been running without any breakages due to my own low-tech engineering mistakes. I've also been secretly using a $0.00 hop-up part that works wonders for the stiffness of my chassis.

See the pictures at right. That plate you see bolted across the back end of my battery tub is a Dremeled-down MSC mount. This single, free piece of plastic which we normally discard when we upgrade to an ESC more than doubles the stiffness of my chassis. How could this be possible? Click on the second picture. The arrow points to an odd gap sliced into the stock Rustler chassis. I don't know what the gap is there for, but it wreaks havoc on the tortional rigidity of the truck by interrupting the critical longitudinal ridge of the battery tub on that side.


Phase II Stats-At-A-Glance

The pictures above were taken of my very first Phase II setup. As I raced it, I tweaked it, and the specifics of shock oil/spring setup changed. Here you can see what I settled on for racing before Phase III came around:

Weight 3lbs. 3.3oz.
(with everything except battery)
Motor DudeMann Extreme Racing tuned
P2K2 Pro
Gearing 20/84 (pinion/spur)
Batteries Ballistic Sanyo 3000 (gen. 1)
Servo Airtronics 94257 (0.06 sec, 110oz/in)
(note custom setup -- will not work well w/ stock suspension)
  Front Rear
Shocks Stock XL
Shock pistons 3-hole 3-hole
Shock Oil 30wt
Springs White 2.75"
Light blue 2.5"
Tires Edge M3
Hole Shot M3
Wheels One-piece T3 dish
AE T3 Dish

Summing it all up...

In these pages you have the forumulae to turn the tough, incredibly inexpensive Traxxas Rustler into a lean, mean machine that can and will win races. Please be my guest and copy and extend any of the ideas you see anywhere on this site. I don't make all of this information public because I want to keep it to myself! My only request (demand, actually) is that you don't take credit for my ideas, and don't try to sell them! Now go check out Phase III!

Now go have some fun and help me to show the world that Traxxas cars & trucks ain't just toys!

Places you see the "" icon indicate innovations & tricks first brought to you by the founders of UltimateTraxxas.com.

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