AX10 Scorpion RTR turned NMRCC Trail Class Build

[Chingon]

I originally joined this forum circa 2006 as a kid and cut my teeth on the OG 1/18, and later 1/6, Nylint crawlers. They were a lot of fun for what they were, but they were fragile, lacked power, and repair/upgrade parts were not available. The 1/6 just took up too much space and it was hard to find fun terrain around the house, and I ended up breaking both of my 1/18s beyond where it was worth trying to repair them.

The Axial AX10 had come out on the scene to rave reviews on this forum as the first factory crawler; previously everyone was having to do very custom things with TLTs, Wheely Kings, Bruisers, etc. Then Axial released the RTR Scorpion version of the AX10 in March 2008 and I ended up picking mine up up around Christmas of that year as a broke-dick teenager.

Even straight out of the box, the AX10 RTR (AX90002) could literally run circles around the modded Nylints. What it lacked in finesse it more than made up with brute power and could easy bash through lines that were extremely difficult with the Nylints. However, the center of gravity was too high, as was the stock gearing, and the springs were way too stiff.

Here are some pictures of the AX10 RTR as it was straight out of the box in 2009.

The first round of upgrades I made in were the Axial 55T motor (AX24007), a 12T 48P pinion gear, 2 green "medium" 2.25 Lb/in springs (AX30215), gray aluminum link and hardware kits (AXA1432 & AXA1411). These upgrades definitely helped the crawlability, but the 12T pinion with the 55T motor lacked the wheel speed necessary for some climbs so I would often run the 20T pinion with the 55T motor. The high-clearance rear links helped a bit, but other than that the aluminum links didn't make that big of a difference. I put one green spring on the front axle, and one on the rear axle to improve articulation and keep torque twist at bay. I also ditched the foams and swapped over to some Proline Moab tires which were the shit back then. Overall, it was still very rollover prone and I am not sure the tradeoff with the 55T motor was worth it and I occasionally swapped back over to the 27T motor to be able to rip around in it.

Around this time, scalers were becoming a big thing, and I loved reading about all the scale builds on this forum. I got the idea that I wanted to build a scaler, so I got an OG SCX10 frame set (AX30525) and an HPI Bronco body. I also got a couple of sets of 7x70mm posts (AXA1431, mine were actually the red ones since gray was out of stock at the time) to use as upper links since the AX10 uppers were way too short for the SCX10 chassis. The AX10 shocks were way too long, and it sat up stupid high. The driveshaft angles were atrocious.

It looked kind of neat, but the loss of performance was unacceptable and I wasn't willing to commit to the scale thing, so I converted it back to an AX10 before long and trimmed the body a bit to deal with the tires rubbing. After wheeling it in that configuration for a while, the wishbone uppers were completely blown out on the axle end and it sat on a shelf for about 10 years collecting dust. I got out of the RC hobby since I was old enough to drive my own real 4x4 at that point, and I figured my money was better spent on upgrades for it.

 

[Chingon]

Fast forward to 2022, I was looking at my AX10 sitting on a shelf and decided to take it out and really enjoyed driving it again, so I decided to give it some love. First order of business was doing something about the blown out wishbone rod ends on the axle side that were allowing the axles to flop around while driving. I made a quickie fix for the rear with a Traxxas rod end, but there wasn't a simple way to fix the front since the servo is in the way. Just fixing the rear was enough to get it drivable enough to take it out some more, and I fell in love with RC crawling again.

This is where I started going down the rabbit hole and jumped back into the hobby with both feet and pissing money away. I found some eBay knockoffs of the old Ottsix 4 link conversion upper link mounts to remedy the shitty factory 3-link setup and ordered them up.

In hindsight I wish I went with one of the servo plate style 4-link mounts because these brackets fit like garbage, don't get the upper links mounted high enough, and are unnecessarily heavy compared to the plate-style mounts. I am stubborn though and spent way to much time sanding to make them fit. Apparently I didn't get any pictures, but the bottom surface needed heavy sanding to get it to match the contour of the axle housings and seat properly so there wasn't a gap at the screw mounting interface.

I was looking at the SCX10 belly plate and realized that it is 78mm wide vs 80mm for the AX10 belly plate, but would bolt right up to the AX10 chassis side plates. The advantage of the SCX10 belly plate is that it inboards the chassis-side lower link mounts and lowers them at the same time while also lowering the transmission and motor slightly. This helps get the lower links flat and give more clearance when turning the tires in addition to improving the flex steer and removing a major hang up point.

SCX10 belly plate top, AX10 belly plate bottom:

Next I started working on flipping the transmission. The idea here is to move the motor, which is relatively heavy, to the side of the chassis that tries to lift under torque to help combat torque twist. This also requires the belly plate to be installed in the opposite orientation of what's normal. Note the motor is on the left side when facing the spur gear as assembled from the factory.

You have to disassemble the entire tranny in order to flip the input around. The inside of the tranny looked great for never having been opened up before. I took this opportunity to add a little more grease.
Here you can also see the Axial spur gear cover (AX80078) I bought, but ended up not being able to use since I upgraded to a Kimbrough 93T 48P spur gear (141) which does not fit inside. You might be able to use a 90T spur, but even the stock 87T spur is a pretty tight fit.

You need to pop out the plug on the back side of the input gear so you can flip the input shaft around. Just pop the plug into the other case half now.

Ta-da! the motor is now on the right side when facing the spur gear.

 

[Chingon]

I also splurged and bought the Axial HD 43T/13T gear sets (AX30402) for both axles in an effort to further improve my crawl ratio, reduce torque twist, and take some stress off the drive shafts. Stock ratios are 38T/13T for reference (3.31:1 vs 2.92:1).

HD 43T/13T gears on the bottom and stock on top. Oddly, the HD gears do not have the shear pin/alignment dowels that engage the differential case.

Here's the axle re-assembled with the eBay-special 4-link truss installed. If you look closely, you can tell where it was sanded to fit. I also used some nylon nuts to bolt the axle back together since the wishbone upper link mount that the upper bolts previously treaded into no longer fits. You can see the angled RC4WD M3 Axial-width rod ends (RC4ZS0833) I replaced most of the stock Axial suspension link rod ends with now that the lowers and uppers are triangulated. These add a little bit to the overall length of the links compared to the stock Axial rod ends.

I had to take off ~1mm from each side of the upper chassis cross-members to to match the SCX10 belly plate.

I ordered a 1500 piece 304 stainless M3 SHCS assortment in lengths from 4 to 45 mm and an assortment of 7mm OD ABS spacers for M3 hardware in lengths from 3mm to 25mm which were awesome since I was reconfiguring a bunch of things on the chassis/suspension.

Here is how I set up the rear suspension. Stock, the tops of the shocks were sandwiched between the gray aluminum 55mm posts and the plastic crossmember I sanded down. I replaced the shocks with 8mm ABS spacers, and used 6mm aluminum spacers to space the tops of the shocks outboard of the chassis side plates. At the axle end, I moved the lower links to the inboard position on the axle brackets and used worn out rod ends as spacers to fill the axle brackets. I then used 3mm ABS spacers to push the lower end of the shocks even further outboard. The rear tires do not touch the springs at all despite how far everything has been pushed outboard. This spring position greatly improved stability while climbing, and along with the lower axle gears and motor relocation, has nearly eliminated any torque twist despite running the Axial red "super soft" 1.32 Lb/in springs (AX30213) at all four corners. With the red springs, I've got just a little static suspension sag so the shocks aren't completely topped out. I would like to have about the same ride height with the shocks at 50/50 or even lower so the suspension could droop out more when it gets bellied out. The inboarded position of the lower links has also helped keep them out of the rocks a lot better.

The 70mm upper links are too long using the stock mounting points with the 106mm 30º lower links and cause the pinion to roll up a lot under compression. Due to the bend, the lower links get close to binding on the upper links. This is part of the reason I wished the axle-side upper mounts were higher.

Here's how the front ended up. Initially I had them mounted outboard similar to the rear, but there was just no way to clear the tires like that. I did lose some stability having to mount the springs inboard like this, but since the front is usually light while climbing, it wasn't a huge sacrifice. I had to move the lower links to the outside of the axle brackets to keep them from interfering with the shocks. There is still adequate clearance between the tires when turned due to the chassis side now being inboarded thanks to the SCX10 belly. I also upgraded the anemic stock servo with a cheapo Chinese "FeeTech 35Kg" servo. I don't think it actually put out the advertised torque, but it is definitely a huge upgrade over stock and not bad for under $30. I had to use a plastic servo horn instead of the aluminum one it came with due to clearance issues with the front diff. The plastic horn has held up fine.

I added 1.16 Lbs of water to the front tires (total). Coming from the fullsize world water made sense and was free, and it helped stability while climbing tremendously. You wouldn't be able to get away running no foams and water in modern tires, but the rubber of the Moab carcass was thick enough to support the weight of the truck on its own.

Rear tire without water:

Front tire with water:

 

[Saltrock]

How full are the tires with water? I can’t say I’ve seen anyone rock water in their rc tires. Looking forward to your thoughts on how it works.

 

[Chingon]

Of course, one run after getting it all put back together, the receiver crapped out. I was pretty sure it was just the receiver anyway, but I decided I may as well upgrade the ESC too in case that is what was bad. I went with a FlySky GT5 transmitter and BS6 receiver combo along with a Hobbywing 1080. The Hobbywing 1080 ESC did not come with connectors on the motor wires, so I decided to solder on an XT60, since that is what it had for the battery connector, and convert my motor connectors to an XT60 as well. I just used an XT60 to Tamiya adapter for my NiMH battery pack I was still running at the time.

The AX10 might not look that different after all of these upgrades, but it was a night and day difference in performance. It was much more stable when climbing and more controllable. The lower gearing with the original 27T motor seemed to be about the perfect balance of torque/control and wheel speed. It was really nice having enough steering power to be able to hold lines and not be slipping off because I couldn't turn.

I still needed to figure out how to lower the battery in the chassis to further improve stability. I didn't like the way axle-mounted batteries look, so I was not going to do that even though that is probably the best option performance-wise. I also need to fine tune the upper link geometry. The wheelbase was sitting at ~12 7/8" with a belly height of ~2". It needed a little bigger tires and more droop to avoid hanging up on the belly as much. The new servo was also putting a hurt on the stock plastic knuckles and "C"s. I started thinking about doing the XR10 mod and upgrading the knuckles at the same time to get more strength and steering angle. I weighed it and it was sitting at 6.2 Lbs. with the 1.16 Lbs. of water in the front tires.

Even though it pretty much looks the same as it did before, here is a picture of how it sat at that point.

 

[Chingon]

How full are the tires with water? I can’t say I’ve seen anyone rock water in their rc tires. Looking forward to your thoughts on how it works.

It actually worked great, although significant changes in ambient pressure and temperature required loosening the beadlock rings to vent them. Modern tires are way too thin to work with water as I found out the hard way. I run foams now and knuckle weights, but the water gets even more weight down lower than you can with conventional brass knuckle weights.

 

[Chingon]

At this point, I was thinking the truck was hot shit and decided to try and compete with it (I had no idea how much the RC scene had changed in the last 10+ years). I found NMRCC on Facebook, and as luck would have it, they were having their season opener that next weekend. I didn't actually compete on the 2.2 Trail Class course since no one was able to get past gate 4 (there were 10 gates) and it was apparent I would point out from reverse penalties alone trying to get through the first three gates that people actually made it through even if I were able to run them clean. I played around on the 1.9 and 2.2 Trail Class courses after everyone finished, and I thought I could be competitive with a steering angle upgrade and doing something to get my battery down lower in my chassis. In order to be compliant with the trail class rules, I needed to change the chassis though. I was hooked at this point and immediately ordered all the parts I needed for an XR10 mod when I got home.

Gate 4 on the 2.2 Trail Class course no one made it through:

The AX10 parked next to the 2.2 course after screwing around on some side lines:

A picture one of the other guys got of my AX10 at the meet. He was appalled I was beating the shit out of my AX10 since they were apparently collectors items at that point.

 

[Chingon]

A few more pictures of the AX10 running in that same configuration while I was waiting for the XR mod parts to come in from RC Mart.

 

[Chingon]

It took way too long to get the XR mod finished and the truck converted back to the SCX10 chassis to make it compliant with the NMRCC trail class rules, but I finally got it back together and competed in my first comp at the San Ysidro Trials area. I also picked up an Ender 3 S1 Pro which allowed me to design and print my own parts. If you are serious about the RC hobby, you NEED a 3D printer.

First, the parts I ordered for the XR mod that snowballed the whole thing. I ordered Axial XR10 front shafts (AX30563), RC Bros 7075 "Burly tubes" to convert to Wraith/XR10 outers, the Vanquish Wraith Stage one aluminum outers (VPS06509), and Vanquish "Currie" XR10-length rear axle shafts (VPS07570). Apparently the Axial XR10 rear shafts aren't available anymore, so I took a gamble on the Vanquish "Currie" XR10 width axles and they ended up working out. Of course, you could be cheap and just run spacers in the rear to match the width of the front as well, but this setup should be a lot stronger.

I went with the RC Bros "Burly" tubes since they don't require you to hack up the stock axle housings like the other "Burly/Beef" tube options on the market do, and they cost pretty much the same amount. I did end up having to do some minor trimming on the stock plastic housings, but I do not blame RC Bros since the outer bearing support pass through for the axle shafts where the outers mount to was pretty out of round. In hindsight, I would have gone with the standard "burly" tubes to maximize screw engagement and potentially avoid having to modify the rear axle shafts by opening up the ID.

I slipped the collars that came with the Burly tubes over the housing ends and ran a 21/64" drill bit (IIRC) through by hand so that the plastic housings would seat correctly on the Burly tubes.

Here you can see this leaves the molded features inside the housing mostly intact (Most Burly/Beef tube kits require you to trim this completely out).

Now the Burly tubes seat in the housing correctly.

The next snag I ran into was that the Vanquish rear axle shafts would not fit through the Burly tubes, and neither would the stock ones for that matter. I thought about drilling out the ID of the Burly tubes, but that would make the wall thickness uncomfortably thin where the groove was machined in the OD to avoid having to trim the plastic housing. Instead, I chose to sand down the flange where the shaft engages the carrier with some 180 grit I had lying around.

 

[Chingon]

A comparison of the diameter of the stock AX10 rear shafts and the Vanquish rear shafts.

The next issue was now that I had turned down the diameter of the flange on the carrier side of the axle shafts, the axle shafts would slide too far into the carrier and the drive pin on the threaded end of the shaft would rub on the outer straight axle adapter. To fix this I used a washer (#10 or 5mm I think?) to seat the axle against the carrier.

This caused the axles to stick out slightly too far and bind on the outer bearings in the straight axle adapters. I gave the axles a calibrated tap with a hammer to "cone" the washers which worked out perfectly to seat the axles at the proper depth.

The spline engagement between the RC Bros Burly tubes and Vanquish Wraith outers was extremely tight and basically a press fit. I did some light sanding primarily to the OD of the splines on the Burly Tubes to get them to the point I could barely press them together by hand. I didn't see a need to run the bolt to clamp the Vanquish outers to the splined ends of the Burly tubes, and the hardware supplied by Vanquish didn't really work anyway. The XR10 conversion added 57g to the rear axle and over a full inch to the WMS width.

 

[Chingon]

The Axial XR10 shafts weren't quite as beefy as the Vanquish shafts I used in the rear, but still a decent upgrade over the .134" stock AX10 shaft diameter. However, the Axial XR10 shafts did not require any modification to fit through the Burly tubes.

Unfortunately at this point, I hit another snag. When I went on to the front axle, I realized that RC Bros had mixed a mod-required version of their Burly tubes in with my order. They eventually sent me the correct part, but it took them over a month to get it to me.

Once I had the right parts, the front went together pretty smoothly after the experience I had gained from doing the rear axle. The front picked up a total of 70g over stock.

 

[Chingon]

Now to mount the axles in a class-legal SCX10 chassis, I removed all of the stock cross-members, and shock hoops to be able to get the ride height as low as I wanted without any interference with the suspension components. I 3D-printed new shock hoops, a battery tray, boat-sides for electronics mounting, upper link/servo mounts, upper links, and lower coil seats for the shocks. I would have liked to get the body mounted lower so that the molded bumpers would be at the correct height in relation to the frame rails and trim the sides of the body up, but I would have had to butcher the body for tire clearance and to stick the rear shock towers through the body. I didn't think it was worth it, so I lowered the body until it was sitting on the rear shock towers and called it good.

Completed chassis:

Rear shock towers:

Front Shock Towers with integrated body mount post receivers:

Battery tray; I had to drill new holes in the chassis rails for this part (you can see where I deburred with a file):

Boat side for electronics mounting:

I ordered some 6061 aluminum and 302 Stainless 3/16" rod off Amazon to make links out of along with some Traxxas 5347 M4 and DKKY M4 offset rod ends. I ended up using the 6061 I was planning to use for upper links for the steering linkage (I ended up keeping the 3D printed upper links that I was planning on replacing with metal). The 302 stainless was a pain to work with, so I did not end up using it.

The steering angle I have after the XR10 mod. It had more to give, but I was hitting my springs and any more and the U-joint hop gets pretty bad since I was a dummy and left the outside bearings installed in the burly tubes.

I spent way too much time calculating the rates and lengths of springs I needed and ordered them from Acxess Spring, but the springs I ordered were not going to arrive before the comp. I printed up some lower spring seats that dropped the springs down and eliminated the preload on the springs with the shocks at full extension. This helped get the ride height closer to where I want it with the current Axial "Red" 14mmx90mm springs I had previously installed. The spring came loose on the shock at full droop now. My belly height ended up at about 2.5". The stock AX10 shocks have roughly 35mm of travel and are 115mm eye-eye. I was about 50% up/50% down on the front shocks and 57% up/43% down on the rear shocks.

 

[Chingon]

I also decided to upgrade to 3S LiPO from the 6S NiMH packs I was previously running, and WOW, what a difference. I had plenty of wheel speed now despite my 57:1 overall gear reduction with the stock brushed 27T motor. I went a bit overboard and got a 5200 mAh pack since it was only $1 more than the 3200 mAh pack from the same company that would have been more than enough already. The battery size definitely hurt me in the comp and was a ridiculous size, even for recreational crawling. My weight distribution ended up around 65% front and 35% rear (~6.4 Lbs total), which made it hard to pop the front up obstacles and not push when I had poor traction.

I used this stuff from Walmart to mount the electronics. It is easier to mess with than Velcro, but thinks can pop off after a hard roll.

 

[Chingon]

This was my first comp actually competing with NMRCC and it was at the San Ysidro Trials area. It was pretty cold and wet, but it was a super cool area I had not been to yet. I showed up to the comp with absolutely zero run time on the car and zero comp experience. There were 5 guys in the 2.2 trail class, and 3 courses.

I ran last on all three courses, which was nice since it let me watch the other guys and see what worked or didn't for them. It kind of sucked too though since some of the obstacles were dug out or wet and muddy by the time I ran. I had a weird issue with my servo throughout the comp where I would lose most of my steering in one direction and the neutral position was biased way over to the opposite side. At first I thought my servo horn was slipping on the the servo splines, but then after trying to tighten it, I realized it was still in the correct position when the wheels were pointed straight If I power cycled the truck and transmitter, it would usually be fixed momentarily then happen again pretty quickly. This is why you shouldn't compete with cheap Amazon servos.

I ended up getting last place, but I had a blast. I felt that my tires, battery size, shitty servo, and SCX10 chassis were holding me back. The chassis rails bottomed out on the rear axle housing and tie rod before the shocks fully bottomed out, and my ride height was still higher than I would have liked.

Here are the results of the competition:
1st: -99
2nd: -68
3rd: -42
4th: +20
Me: +82

I was super happy with the new steering angle, and it was definitely a game changer, especially for comps. I was also pleasantly surprised all the 3D-printed parts held up, especially the links. I had some fairly hard rolls, and had to get more abusive than I would have liked several times.

 

[Chingon]

After running the truck a bit more at home after the competition, the servo completely died. I tried taking it apart to see if there was something obviously wrong I could try to fix, but no cigar.

I am thinking I killed it with heat. I was working the truck pretty hard and the servo was too hot to touch at the end of the run when it died. The next time I went to run it, the servo barely moved at all and had no torque. I also found out that this servo was specified at 3.9A stall current at 7.4V and my Hobbywing 1080 only puts out 3.0A at 7.4V. That explains why the servo always seemed a bit underpowered for its rating. The new 1080 G2 can do 4.0A at 8.4V, but I felt like that money would be better spent on a direct power servo or brushless-capable ESC at that point.

I wanted the new NSDRC RS700 V2, but it was not quite available yet and it was pretty expensive. I had made plans to meet up with some co-workers the weekend after it died to do some crawling, so I needed a replacement quickly. I ended up ordering another Amazon special which showed up 34 hours after ordering it.
It was listed on Amazon as an "Injora" servo, but came in a box that was branded "SPT." It was brushless, 8.4v capable, and a little lower profile. It was definitely a lot faster than the old servo, but on 7.4V with the current limit of the HW1080, the torque seemed about the same which was a bit lacking with the really short Vanquish steering arms on my truck.

The springs from Acxess Spring showed up. I installed PN PC032-625-10.000-SST-3.407-CG-N-IN all around and my ride height ended up just about where I wanted it. The spring rate on the Acxess springs is 0.78 /Lbs./in vs 1.32 Lbs./in for the Axial red springs. I was really happy with the balance of the suspension now. The Axial red springs were way too stiff with my current setup.
Comparison with the Axial red spring:

I took it out afterwards for some practice near the house:

 

[Chingon]

The screws holding my knuckles on were constantly backing out and falling out which was no bueno. I picked up the correct Vanquish brass knuckle bushings with the flange (VPS07510) so I could properly torque the screws. The stock plastic bushings would just crush and bind up the knuckle if you tried to give them a proper torque. I also used 12mm long screws with washers and put some red thread locker this time. Even torqued as tight as I felt comfortable with, the knuckles still turn easily with no perceptible bind. No more backing out issues after that.

The last time I was running it I lost the driveshaft pin on the front driveshaft. I was just going to buy more driveshaft pins, but this Injora driveshaft was only a couple of bucks more than a pack of pins themselves, and I figured it was worth a couple of extra bucks to have a spare driveshaft. Not bad and all steel for only about $10.

I upgraded to an 11T Team Brood Ravage 5 slot motor. It was smoother and had more wheel speed than I needed which allowed me to gear the truck down some more later on.

I bought a 1400mAh 3S LiHV to cut some weight. I moved the receiver over to the passenger side boatside and mounted the battery on the driver side boatside since that got the battery a little lower than mounting on the battery plate I printed and helped balance the rig a little better. The front end was noticeably lighter now though when the truck was nearly vertical. It definitely seem\ed to steer better with the weight off the front.

I bought some J-Concepts Landmines since their tires were supposed to be the shit based on my research, and the Landmines were the shortest (5.79") of their 2.2 offerings at the time. They were way too big to run without changing a bunch of things on my build. At the time, I was still bent on running water and no foams, but the Landmines were way to thin and soft for that. I ended up selling them without ever running them. You can see my first prototype printed wheel I was using to mock them up with.

 

[Chingon]

I did a bit of prep to get the car ready for the next competition. I hadn't run the car in a few weeks, but on the last recreational run, I noticed my servo/upper link mount broke. This is the first of my 3D printed parts to fail (PLA). It lasted well enough that I added a tiny bit of thickness to the servo mounting posts; it is a tight fit between the frame rails when articulating. It never broke again.

I also found that the M3 stud between one of my rear aluminum lower links and the rod end had bent. Must have been from some of the back flips I was doing off some slab climbs. Surprisingly the RC4WD bent rod end was still useable. In hindsight, the stainless M3 set screws are a lot weaker than the black alloy steel ones.

The stock Axial plastic ball offset rod ends I was using on my upper rear links were pretty slopped out, so I finally replaced them with some of my RC4WD offset rod ends with metal balls. This required shortening the upper links 15mm which was pretty easy with my hollow printed upper links. I am actually pretty impressed with how the printed upper links had been working on the truck, and I have never had any issues with running printed links to this day.

The Injora/SPT servo was working okayish considering how much I paid for it, but it would over heat and start doing funny stuff. The splined output for the horn also had an unnerving amount of slop in it which caused/contributed to the servo shake I would get when there was little to no load on the tires. I got tired of dealing with servo issues, so I finally ponied up for a direct power servo which I should have done from the beginning. My advice for anyone wanting to get into competing is to avoid the frustration of Chinese cheapos off Amazon, and just get a good direct power servo from the get go. I had been eyeballing the NSDRC RS700V2 for a while, but it still wasn't available, so I just picked up a Holmes Hobbies SHV500LP which had pretty similar specs. I went ahead and got another Protek 1400mah 3S LiHV as well so I can swap battery packs between courses if I need to and not run the 5200mah monster pack. I had a brain fart and ordered a 12T pinion gear which brought my crawl ratio down to 66.6:1 which complimented the 11T Team Brood motor better.

I also picked up a set of 1.9 JConcepts Ruptures and some China-special aluminum beadlocks off Amazon ($11 shipped to my door for the wheels) so I could run in both the 1.9 and 2.2 trail classes NMRCC does. The Ruptures are the same diameter as my OG Moabs so I figured it should perform pretty similarly. The Ruptures are like baloney skins and don't have any support at all without foams. I tried running foams in the back and water up front, but that was a terrible idea. I immediately drained the front tires and stuffed foams back in after the first course. Of course that completely ruined the weight balance of my rig and moved my CG way up. Even with the foams, the Ruptures really wanted to fold over laterally even worse than my Moabs without foams . I needed to look into brass knuckles or something to get low slung weight on the front axle and figure out some better performing foams.

 

[Chingon]

This was my second competition with NMRCC. I ran 3 courses for each class, and this area was pretty hard on the rig. It was on an a highway berm erosion control area made of concrete and volcanic rock from the area and the courses generally worked their way up hill. Roll overs were common, and it was a long way to the bottom. I ended up bending my aluminum drag link, but the rig was still drivable after all 6 courses.

The 1.9 courses were a disaster for me. On the first course, I had water in the front Ruptures, and I punctured one after jumping the truck through the first gate monster truck style. The 11T Team Brood motor was way jumpier than I remembered. The tires were folding over all over the place and I was barely able to control the truck. I ended up pointing out at the 4th gate. I broke down the front tires, dumped the water out, and reinstalled foams before the start of the second course. I didn't have time to swap the motor out, so I struggled with control issues, a nearly 50/50 weight distribution, and higher COG. I remembered the 11T motor being kind of touchy, but that day it felt almost undrivable. I timed out at the 7th gate. I got the motor swapped out to the original Axial 27T and things were much better, but the stability was still really lacking. I don't remember where I ended on the last course, but it was my best run. I found out afterwards that I was a dummy and the throttle curve on my controller was completely screwed up.

1.9 Results:
1st: -114
2nd: -69
3rd: -20
4th: +28
5th: +61
6th: +62
Me: +92

The 2.2 course were pretty brutal. Everyone was struggling a bit on these courses. Maneuverability was killing me on these courses, and with the stock AX10 wheels and my XR10 width axles I was one of the widest rigs if not the widest. I didn't finish any of the courses, but things weren't nearly as ugly as the 1.9 courses for me. I ran out of points on the 4th gate of the first course which gave everyone grief. I had my battery pop out on the second course early on and ran with it dangling to avoid the 10 point penalty. I ended up getting to the 5th gate which I just could not get up. My battery popped out again on the final course, but I chose to take the 10 point penalty and fix it. This caused me to point out on the third gate when I killed a cone.

2.2 Results:
1st: -53
2nd: -12
3rd: +84
4th: +98
Me: +102

I needed to work on my competition nerves. My maneuverability and the tire roll situation needed improvement. I realized I needed some front overdrive and a bit more caster to improve the negative camber gain while steering. The rear upper link geometry on the SCX10 chassis causes too much antisquat, and the chassis lifts under traction rather than sucking down.

No pictures of my truck at this competition, but some pictures of the other drivers on course:

 

[Chingon]

After that competition, I ordered some eBay Chinese knock offs of the brass Dlux knuckles to try and get some front weight bias with the 1.9" wheel setup. They weigh the same but are ˜$25 vs $84 and looked nearly identical. They were also cheaper than the brass add-on weights for my Vanquish knuckles as well and got me longer steering arms in addition to weighing slightly more. 102g per knuckle for the Chilux vs 13g for the Vanquish.

I went ahead and put some red thread locker on the screws holding the upper and lower pivot plates in place (you can see some of the rough machine work in this picture).

Unfortunately, the saying that you get what you pay for is true, and they were machined incorrectly. They pulled the axle shaft out too far so that the U-joint was not in the axis of the knuckle pivot and caused some serious binding. The hardware that came with them was also pretty shitty. I rectified this by getting some "narrow" 8mm washers from my local hardware store and drilling out the wall between the inner and outer bearings. The outer bearing has a 13mm OD, so I used a 1/2"step drill to drill it out and used a Dremel with a 1/4"sanding drum to take the lip off. Unfortunately I didn't take a picture after I drilled and Dremeled.

A picture of the thin separating wall you need to drill out with a 1/2" drill:

With this mod, the axle sits pretty close to where it should for bind-free turning. I also finally removed the outer axle tube bearings at this point since they cause binding at high steering angles. I had to make some new steering links and chose to install the drag link in the shorter hole on the servo horn since that still gives me all of the steering throw I can use and helps increase steering force. Steering power was the best it had ever been up to that point, but I still felt like I could use more. It turns out, it was really the offset of the stock AX10 wheels that were putting a ton of stress on the steering.

I also reinstalled the 11T 5-slot Team Brood motor and figured out that I had the Exponential function on the GT5 transmitter adjusted 100% in the wrong way (negative instead of positive). After adjusting the "Start Punch"setting on the HW 1080 to the lowest setting and adjusting the throttle exponential setting on the GT5 to +50%, the 11T motor was extremely controllable.

 

[Chingon]

I went to my third competition, but most people bailed, so it was just the club president, me, a guy with a new 1.9" build, and his young son with a completely uncompetitive rig. Due to the low turnout, we set up a few courses mostly for fun, but the president still cleaned house like he did at the AZ state comp just prior. I finally felt like I was getting close to having a legit comp car. I still didn't have enough forward weight bias with my 1.9" wheel setup and needed to figure something out as well as some better foams since the ones that came with the J-Concepts Ruptures are way too soft and they folded over worse than my old-school 2.2" Proline Moabs with no foams. With the brass knuckles I now had too much weight on the front with the water-filled Moabs since my rear would fall off the line when I worked the steering. I felt like I did alright, but there weren't many people to compare to. I needed to get some overdrive badly, the truck was still too wide, my 2.2 tires were too small, and my chassis was still preventing me from getting the COG as low as I would like. Here are a couple of pictures: