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Project: Ultimate Rustler

Phase III

Alright folks, I'm going to start off with something I do a lot of offline, but rarely share with the public -- self-criticism. Yes, there were a number of things about the Phase II Ultimate Rustler that I didn't like. For one thing, Associated wheels on the rear didn't leave enough stub axle exposed to get a really solid grip with the wheel nuts. I did end up losing a wheel on two occasions as a result of this. I could stick with the simple solution of using thinner wheel nuts, but there's another problem: the rear track was just a hair over the ROAR maximum of 13". I'll do my best to fix this mess in Phase III-X.

Next up, the front track. I allocated a certain degree of effort & modification for Phase II, and bringing the front width up to spec with the rear didn't make the cut. As a result, I'm losing a bit of steering and frontal stability on loose surfaces. I'll do my best to fix this mess in Phase III-X.

I never applied the slick aluminum motor plate insert trick from the Ultimate Bandit to the Ultimate Rustler. There's too much caster. The unbeatable amount of front suspension downtravel is impressive to look at (picture at left), but isn't necessarily good for racing. Also, how come the Ultimate Bandit and other manufacturers' stadium trucks get rear toe-in and the Rusler doesn't? And there's got to be some more plastic that I can Jangify, I mean, Dremel away. You guessed it, all of these messes will be fixed in Phase III-X.

Unlike the transition from Phase I to Phase II, the move to Phase III-X will fully build upon the previous base truck, not starting with a new chassis. Enjoy the ride, but hang onto your seat -- this is gonna be the big one.

Modifications: Phase III-X

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

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Nitro Rustler caster block & spindle conversion

In Phase II, I had put together a quaint hybrid front end conversion that used modified Nitro Rustler caster blocks and kingpins with Kyosho Ultima ST Type R steering knuckles and spindles. For Phase III, I've removed the Kyosho parts and gone with a simpler, decidedly more Traxxas-centric setup.

The parts used are #2536 steering blocks & spindles, #2634R caster blocks (note that these are 25-degree vs. the stock N.Rustler's 30-degree blocks, a better setup for the electric truck), and #2636 kingpins. You'll also need adjustable turnbuckles for camber links.

To minimize bump-steer (changing of a wheel's toe as the suspension is compressed & extended), you will need to raise the inner mounts of the steering linkages. This is a very important step, so do not skip it. Refer to the arrow in the first picture at left -- I used three 1mm spacers from the Traxxas shock parts tree, directly beneath the rod end. You can use any form of spacers you like, as long as the total thickness is 3mm. Note that you'll also need to use 3-4mm longer screws to secure the linkages to the bellcranks.

You'll need to mount front wheels made for the Nitro Rustler or Nitro Stampede. I chose Traxxas lightweight dish rims, but you can just as easily use Traxxas chrome 5-spoke wheels as I used on the Phase II Ultimate Stampede, Pro-Line Agitators, or any of the appropriate RPM wheels (list here). These use 5x11 bearings in the wheels, 2 apiece. Also, for a bit of extra width, add about 2mm of spacers (two Traxxas #3685's work perfectly) over each stub axle before installing the wheels.

This setup, with bearings in the wheels, gives far less rolling resistance than the stock Rustler's live stub axle system. Less rolling resistance equals more speed and longer runtimes. The Nitro Rustler kingpins are also significantly thicker and more durable than the frail stockers.

Another big advantage of running this conversion is the increased steering throw. In the pictures at left (click to zoom in, as usual), I've laid the Ultimate Rustler directly over a stock Rustler, both at full lock left steering. The photo angles are not scientifically precise, but the pictures do show how noticeable the difference in wheel angle is. The Ultimate Rustler's inside tire is turned in about 10 degrees more than stock, and the outside tire is turned in 3 degrees more.

In addition, the added width (nearly 1/4") will further contribute to increased steering while simultaneously enhancing the truck's poise over rough terrain.

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Front suspension rework

One day in February '03 I found myself marveling over the new Team Associated RC10 B4, er, I mean, studying it for design flaws, and one particular feature caught my eye. They moved the shock tower forward a tad, and moved the shocks behind the tower. This lowers the center of gravity! Think about it -- the shock tower is raked towards the rear, with the shocks in front of and above it. Swap their positions and you actually lower the heavier shocks in relation to the chassis. I looked at my Rustler and said, "Hey, I can do that."

Take a SRT fiberglass or graphite shock tower and cut out most of the lower center section so that it will fit over the tip of your upper deck and onto the front of your front bulkhead. Click the first picture at left for clarification. Also shave off about 1/8" from the outermost corners, where the camber links mount, to prevent rubbing. Remove your old tower assembly and screw the new one in from the front.

Next, with a 1/8th" bit, drill clear through the shock mounting holes on each a-arm. With a high-speed cutting bit, completely Dremel out the thin web of plastic behind where the shock originally mounted. Note that I have switched back to standard length "XL" (extra long) front shocks instead of the "XXL" set (rears) that I used in up front in Phase II. I've also slipped a 3/16" piece of fuel tubing over each front shock to limit uptravel. Affix your shocks to the rear of the shock tower with the help of some fancy big-brand, big-bucks shock standoffs, or just use the free ones that come with all Traxxas vehicles (on the parts tree with the preload spacers & extra shock pistons -- you'll recall I used these to mount the rear shocks in Phase II). You'll want to use a 3x20mm screw (make sure it doesn't have a washer head) and locknut to secure each shock. Make sure you don't overtighten -- the shock should be able to rotate around the upper mount with next to no effort.

Swap the camber links to the front as well, backing the inner ball stud or shoulder bolt with a tightly-affixed flat nut. Use the lower mounting hole on the caster block, and space your ball stud out with a 1/16" spacer from your shock parts tree (see 2nd picture at left). To keep the camber link parallel to the a-arm, you can drill a new mounting on the shock tower, below the upper hole and to the right of the lower hole.

Slip the lower eye of the shock into the new space you opened up on the a-arm and affix it with the help of a long 3mm fine-thread screw, locknut, and spacers as necessary (I used a conical single washer/spacer, the purple part in the 3rd picture at left).

There are a number of options you could use for new body mounts. The Duratrax Evader front mount would work well (also available as the Losi XXT mount, since the Evader is basically a copy of the XXT) without modification. Just line it up to the tower, mark & drill two mounting holes, and affix with bolts. To get the lowest possible body mounting position, I took a couple of basic body posts (this particular ones from an RPM RC10GT/T/T2 truck mount set) and bent them up in the center with the help of a lighter to soften the plastic. They're attached with short 3mm screws from the other side, through holes I drilled in the shock tower.

As you can see in the last picture, there's still plenty of articulation, even though I've ditched the extra-extra-long shocks.

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Adding rear toe-in

I searched for over a year for a cheap, accurate, inexpensive way to give the Rustler some rear toe-in. One night at the local hobby shop I was searching for parts to repair one of my rental 4-TECs. Lucky for me, they had exactly what I needed, part #4352, stock rear hub carriers. As I reached out to grab them, I had a nearly violent epiphany. These give 1.5 degrees of toe-in, and would fit the Rustler.

At left you can see the carriers installed. Note that you will need adjustable camber links to use these. Also be sure to pay attention to which carrier goes on which side (they're marked R & L). To properly fit the MIP CVD's I'm using, I put one 1.5mm spacer (from Traxxas part #2545) over each axle, before inserting the axle through the carrier, followed by one Traxxas #3685 1mm spacer and one wider 1mm spacer that comes with the MIP kit (alternately, you could just use two of the Traxxas spacers). If you are not using MIP CVD's, the spacing will be different, but you will still be able to make up for the gaps with the Traxxas spacer kits.

I also used a very thin metal shim (about 0.2mm) next to the carrier to take out a bit of play left over between the inner edges of the a-arm (click the picture and you'll see a bit of the shim).

IMPORTANT: For more toe-in, see "2nd Degree of X" below.

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Aluminum motor mount plate

While designing the Ultimate Bandit at the end of 2001, I was faced with a huge problem. I wanted to run the Hacker B50 8s brushless system from my Ultimate E-Maxx projects, but knew that the plastic motor mount plate would never survive the torturous torque. The solution I came up with involved Dremelling out the stock mount and inserting a custom-made aluminum prosthesis. Finally, over a year later, the Ultimate Rustler received the same treatment.

You can see more views of this mount in varous places on the Ultimate Bandit project page.

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New ultralight rear wheels

Way back in Phase I came up with a cool way to lighten stock Rustler wheels. I haven't been able to top that cutting pattern until now. Here I've used the same basic pattern, cutting out the innards of every other spoke, but I've cut closely down to the hub, and left just a bit of the outer ridge for strength. I've also added an 1/8" hole near the base of each remaining spoke, and Dremelled off the ring of material that normally surrounds the wheel nut (do this last bit only on rear wheels, not fronts!). I've also rounded all hard edges.

This cutting saved 1/3rd of an ounce off of a single pair versus either stock wheels or Pro-Line Agitator upgrade rims. Note that it's highly advisable to balance your wheels after trimming them yourself.

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Correcting rear width

The RC10 T3 rear wheels used in Phase II made the truck a smidgeon too wide for the sake of race legalities, so I've switched back to stock or stock replacement Rustler rear wheels. To maximize your width, though, be sure to use the newer, thicker hex hub adapters. Rustlers used to ship with thin ones (far left, in the picture). I haven't been able to confirm whether this has changed more recently, but 4-TECs use the wider ones, part #1654 (pictured in the center). If you can't get the wider hubs, use the thin 4-TEC hub offset spacers, part #4375. Note that TowerHobbies.com uses an incorrect image with part #4375.

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The X Factor

Why Phase III-X instead of just Phase III? The III is for 3 pounds, and "X" is the roman numeral for one-zero, in this case, 1.0 oz. This is 2 1/3rd oz. lighter than Phase II at the height of its diet.

As you can see in the bottom view image, a bit more material has been removed versus the Phase II state (as seen in this image). To do this, I first drilled out the right battery strap post hole and slotted it to mount the antenna. Off went came stock antenna mount and the entire section of lower chassis that supported it.

A new, smaller-footprint ESC was installed, specifically a Duratrax Intellispeed 8T Pro (a special gift for all the Dura-trash-talkers out there). This allowed me to trim back the chassis plate under the ESC, and I also cut back the area under the receiver. The new ESC also uses a clean 3-wire setup of which I took advantage to minimize the amount of heavy wire used on the truck.

Up front, the old fiberglass SRT shock tower gave way to a purpose-bought Traxxas carbon fiber model as soon as I became confident that the front suspension setup was final. The CF tower is noticeably stiffer, yet much thinner, and about 30% lighter. Plus, you can't deny it -- carbon fiber just looks trick.

At the rear, the transmission received more trimming. When it's out of the vehicle, it doesn't look like anything Traxxas has made since the SRT. Versus a stock Rustler setup, about half of the bulk has been removed.

I made sure to orient the DudeMann Xtreme Racing 2K2 Pro with the brush leads towards the top. I trimmed the ESC wires to fit snug (with just enough room to tune my gearing) through a hole in the shock tower, back to the respective motor terminals, soldered directly over the brush leads for the least possible resistance.

Speaking of the shock tower, I did install a new one, trimming off less material than in Phase II and mounting the shocks a bit more vertical. Racing experience on several tracks showed that the angle I had used before was a bit excessive, so I've now taken a trivial weight penalty in the name of an important geometry improvement.

Next, you've surely noticed some nice blue-anodized nuts & bolts on the truck in Phase III-X. These might look great, but they're used purely for function, not form. The blue hardware is all 3mm aluminum by General Silicones. I carefully selected screws that were just as long as they needed to be. Too short and they would strip; too long and they would add unnecessary weight. Some screws needed to remain steel, however, for strength. If you look at the photo of the bottom of the truck, you'll notice that some screws are missing, and the rest are not stock Traxxas chromed pieces. For a stock-motored truck, I'm confident the default setup is over-fastened. I've been running a reduced screw count for many months now, with no ill effects other than an occasional small clod of dirt getting stuck in a hole. The transmission normally has 16 screws holding it together. I use 10, with the top front screw hole and several of the rearmost ones removed altogether. The black screws on the truck are from Duratrax, again selected to be long enough to hold the parts together securely, without adding unneeded weight.

Finally, enough about the chassis, the Ulti.Rusty has a sleek new body! The effect of body choice on handling is often overlooked in offroad racing, but not in my workshop! Like in Phase II, I wanted to use the lightest, lowest body possible. I was leaning strongly towards the Crowd Pleazer XXX-NT shell by Pro-Line, but really hoped to find an old Traxxas SRT shell. Fortunately, at the last minute, I decided to go with the Traxxas Nitro Sport body shown here. There couldn't be a more perfect fit. The front shock tower fits up into the hood bulge with less than 1mm of clearance, and the front body mounts protrude through the front face of the hood at a perpendicular point. At the rear, the custom body mount goes through a flat open space in the body, and the rear shock tower actually slides a bit up into a raised horizontal ridge on the rear deck. Again building on lessons learned in Phase II, I went for a lightweight paint job. The lower stripe consists of two even coats of Pactra Metallic Green, with no backing. The black is a single coat. The yellow consists of two light coats backed by one quick spray of white fluorescent undercoat. The spoiler was left unpainted. The windows were left untinted, with the exception of a visor strip on the windshield. The result? This body is 0.3oz. lighter than the Phase II stock Rustler shell, which itself was 0.9oz. lighter than the Phase I Pro-Line Silverado body. The HPI Nitro Rush body I had used earlier in Phase III for dirt oval racing was 0.7oz. heavier than the current choice.

These weight-reducing measures may seem a bit over-the-top to some, but they work miraculously for me! Plus, seeing that digital scale read 3lbs. 1.0oz., the precise target weight I had set for myself nearly a month before, was the high point of my entire week. Keep an eye on the "Stats-at-a-Glance" section at the bottom of the page to watch as this weight continues to creep downward as I make further minor modifications.

Modifications: Phase III-Xb

(added 4/24/03)

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2nd degree of X

Though the updated Rustler performed quite well its first time on the track, trouncing 7 out of 8 competitors in a mixed stock/mod, buggy/truck race, there was some unwanted mid- to late-turn oversteer at the rear. To counter this, I decided to add more rear toe-in. To accomplish this, I ditched my CVD's and reinstalled the stock slider shafts, tightened down my rear camber links and installed a set of SRT/Nitro Rustler rear arms (#1955 or 2555). I'm not sure precisely how much toe-in these have, but it looks like about another 1.5-2 degrees per side, adding to the 1.5 I already have in the 4-TEC hub carriers. There was a bit of play at the inner mount when I installed these, so I fixed this with the addition of a 1mm spacer (visible in the image at left, at the lower right corner).

These new arms are much narrower than stock E-Rustler units, though, requiring the use of shallow-offset (wider) rear rims, such as stock fronts or SRT/Nitro Rustler rears.

Another nice bonus here is that the stock sliders & yokes weigh about 0.7oz. less per complete set than CVD's. Once I Dremel my new a-arms down, I should be able to dip below the 3lb. mark.

Also note that I've inverted my rear shocks to lower the center of gravity! I had tried this before, but with no luck. The problem with upside-down shocks is that they must be absolutely perfectly filled. At rest or with the suspension uncompressed, the pistons sit in the upward-facing bottoms of the shocks, right where air bubbles collect. Fortunately, I've finally gotten good at filling these shocks, with literally no detectable air, so the shock flip is now feasible. I have not done this up front yet as I change my front shock oil at the track fairly often an sometimes don't have time to do it perfectly.

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Balanced tires

If you want to go as fast as possible, as smoothly and efficiently as possible, balance your wheels. Give them a gentle spin and see where they stop. Add weight to the opposite side, and repeat. You'll be surprized at how much weight is required in some instances. Here you can see that I've put a few spare screws in a big glob of Shoe Goo on the inside of one of my front rims (yes, all of that weight was needed to achieve balance). If you use this method, be sure to add a tiny bit more weight than needed, as the Shoe Goo evaporates water and gets lighter as it dries.

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True colors

This is hardly groundbreaking, but I got my hands on RPM part #80547 to make new front body mounts in yellow. The blue was bothering me -- it just didn't feel right.

Phase III-X Ultimate Rustler Stats-At-A-Glance

(last updated 4/26/03)

General
Weight 2lbs. 13.2oz.
with everything but battery (body included in weight)
Motor DudeMann Extreme R/C Racing tuned
P2K2 Pro
Gearing 20/84 (pinion/spur)
Servo Airtronics SX 112 (0.14 sec, 56oz/in)
Suspension
(note extreme custom setup at the rear -- will not work w/ stock suspension)
  Front Rear
Shocks Stock Longs Long (fronts)
Shock pistons 2-hole 1-hole
Shock Oil 25wt
(Losi)
30wt
(Losi)
Springs Orange 2.5"
2.9lbs/in.
(Losi)
Blue 2.0"
3.8lbs/in.
(Losi)
Tires/Wheels
  Front Rear
Tires Pro-Line Edge (M3) Pro-Line Lug Nut T (M3)
or Losi T-2000 (red)
Wheels Nitro Rustler
lightweight dish
Nitro Rustler
lightweight dish
 

Stock Rustler vs. Phase III-X Ultimate Rustler

(last updated 4/26/03)

  Stock Phase III-X
Track
(width)
12 9/16" 12 7/8" - rear
12 13/16" - front
Dry weight 3lbs. 4.7oz. 2lbs. 13.2oz.
Varies by equipment. Measured with wheels/tires, motor, radio, servo, ESC installed, no body, no battery.
Toe-in,
rear
0 degrees 3 degrees/side (est)
Suspension
travel, front
1 3/4" 1 11/16"
(w/ 3/16" uptravel limiters)
Suspension
travel, rear
1 7/8" 1 1/4"
(w/ 1/4" uptravel limiters,
1/8" downtravel limiters)

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