2014 - Traxxas Mini E-Revo
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This one's been a long time coming.
When I first got into RC and I was researching my first vehicle purchase, the Mini E-Revo was one of the vehicles that appealed most to me. In retrospect, years before when I was just reading RC magazines but wasn't rich enough to buy anything, the full-size E-Revo looked cool to me back then too. There's something about the "monster-truggy" layout that looks perfectly optimized for hard corners at high speeds, while still having enough suspension clearance to avoid smashing to bits when it runs over a crack in the pavement.
However, after reading horror story after horror story about the MERV, I decided to get something else -- a Losi Mini Desert Truck -- instead. A year and a half later, and after lots of evenings spent reading, I finally felt ready to take on the challenge of building a MERV that wouldn't suck. This is what I came up with.
Most of the horror stories I read centered around the drivetrain, so straightaway I replaced almost all the drivetrain parts -- out came all of the stock gears and driveshafts, and in went Hot Racing hardened-steel transmission gears, Hot Racing hardened-steel diffs, and Traxxas axle and center-driveshaft CVDs. Oh, and I installed bearings in the rocker-arms for the shocks and the center pivot of the steering assembly before the vehicle ever moved under its own power, because it was such a simple mod there was no reason to postpone it.
Because I wasn't looking for a vehicle that can do backflips all day long (for that I have a HPI Savage XS), I also replaced the transmission output gear with a center diff filled with 100,000wt oil, and I installed a 540 brushed mod motor with 12x2 windings. The stock copper brushes in the motor were replaced with LRP silver brushes, soldered directly to the tabs on the endbell for maximum efficiency. The Team Orion brushed motor makes such a cool sound, I love it.
There was one snag when installing my Spektrum radio, though; it absolutely refused to communicate with the Traxxas brushed ESC. A quick trip to my local hobby shop netted a Dynamite brushed ESC originally intended for the 1/10 ECX Ruckus, and conveniently the color of the heatsink matched other parts on the vehicle. It was $50 I would've rather not spent, but oh well, at least it works well.
I also read horror stories about the chassis breaking where the differential cases attach, and as complex as this vehicle is, I didn't want to have to take absolutely everything apart so I could replace the chassis. TheToyz was selling reinforcing beams that bolt to the upper shock mounts, so I decided to install a couple of those as an insurance policy.
The shocks were a problem, as everyone knows, so I rebuilt those too as soon as I decided on suitable parts. The shocks were rebuilt with Hot Racing aluminum bodies, which have screw-on lower caps so I could really cinch-down the O-rings to prevent leaks, Traxxas stanchions coated with TiN to reduce wear (the stock stanchions were already showing some polishing by the time I got around to rebuilding the shocks), blue-stripe springs and 2000wt oil in the front, and pink-stripe springs and 3000wt oil in the rear.
Somewhere around the same time, I got sick of the stock tires. I spent about 5 minutes selecting the tires (Pro-Line Trenchers) and about a week selecting the wheels, because I didn't want the Desperado or Titus wheels most people use, but other options were really hard to find. Eventually I stumbled on a version of DE Racing's Trinidad wheels which were purpose-made for the MERV, so I went with those. I think they have a nice combination of sleek and strong appearance.
Having nailed-down the drivetrain and shocks, I set about improving the durability of the suspension and steering. When I turned the stock servo back and forth, I could hear one of the gears rubbing against the inside of the case, and I knew that wouldn't last very long. I replaced the servo with a Hitec HS-5085MG, which wasn't quite a perfect fit, but the bash-guard around the servo horn is made of soft plastic, so when I tightened-down the mounting screws, the bottom of the bash-guard just conformed to the shape of the little reinforcing bits that stick up off the front surface of the servo's mounting tabs. The new servo needed a new servo horn, and Hot Racing provided yet another part I needed.
I also swapped in a set of RPM A-arms, front and rear; no idea if they're really better than the stock A-arms, but enough people complained about the stock A-arms that I decided to do it anyway. (really, most of the mods I made to this vehicle were preventative in nature.)
In stock form, the handling was very twitchy. I know the toe-alignment can be changed by adjusting both the upper and lower pillow-ball in or out at the same time, but I wanted to be able to adjust toe independent of camber, so I went ahead and bought the adjustable toe-links anyway. (I also bought the metal shock pushrods so everything would match.) After adding a bit of camber-in and toe-out to the front wheels, the handling got a lot more stable, without losing its sharpness, because the camber-in means the outside front tire will bite harder in corners.
After driving the vehicle around a bit more, I realized it was much more likely to roll-over when I turned one direction than when I turned in the other direction. After puzzling about this for a while, I realized it was probably because the chassis was unbalanced, with only a single battery on the left side. So, I weighed the battery, cut off a suitable number of chunks of lead ballast, and stuck them inside the right-side battery compartment. Between the alignment adjustments and the addition of ballast in the empty battery compartment, the vehicle suddenly felt a lot more planted.
The last upgrade the vehicle needed was new steering knuckles. The stock knuckles had varying amounts of slop, with one of them actually binding a bit, so I knew I needed something adjustable. I was originally going to get aluminum knuckles, but then I thought the better of it, because I couldn't see a way that the aluminum knuckles and the steel pillow-balls wouldn't end up grinding against each other when the knuckles were adjusted for zero slop. So instead, I got the RPM knuckles, in blue, because I figured why not show off a little bit? Now that the RPM knuckles are installed and adjusted, there is no slop anywhere in the suspension, and the vehicle handles like it's on rails.
The MERV needs a lot of work, like pretty much everyone says, but when suitably upgraded it's a great vehicle. I think this one will stay in my collection for a long time.
After driving this vehicle a bit more, I've decided that as well-tuned as the suspension is, it still needs a front swaybar. So I bought the Hot Racing kit (I ended up with a lot of Hot Racing parts on this vehicle), and bolted it up.
There was only one small snag (there's always one), which was figuring out how to properly retain the swaybar since I'm not using the stock plastic reinforcing braces to support the top eyelets on the shocks. (I have chassis braces instead, but they're not the same shape.) That problem was solved by putting two small washers under the swaybar, to keep it in the little channel it's supposed to stay in. After some quick tweaking of the leverage on the swaybar, it now works very well, and it no longer lifts the inside rear tire in sharp corners.
I did some work on my MERV yesterday, for the first time in a long time. First of all, I replaced the tires because the old ones weren't gripping very well anymore.
I actually bought these tires by mistake, thinking they were normal stadium-truck-sized tires, and while they are the correct width they're definitely not as tall as normal stadium-truck tires. I was going to send them back, but I noticed they were the same height as 1:10 buggy tires, and then I got curious. I got a set of HPI wheels and test-fit them on my MERV, and they looked great. They're made of HPI's "pro" compound, so they stick well too.
Also, since this vehicle has slowly gotten faster and heavier over the years, I decided it was time to bite the bullet and wire it for two batteries, because the single battery I was using before was getting uncomfortably hot. This rats-nest of wiring is the best I was able to do to keep the 2x2S parallel wiring under control.
Lastly, since being heavier and going faster means the *motor* has to work harder also, I decided it was time to see if I could shoehorn an endbell fan under the MERV body. I figured out I could do it if I cut off one of the corners, which was no big deal since I didn't need that corner for mounting purposes anyway.
As you can see, like everything else on this car, it just barely fits. I'll need to replace the piece of foil tape I added, which is supposed to protect the body from rubbing by the battery plug, with a piece of felt to protect it from the sharp edge of the fan instead. That's how hobbies work, right? The rabbit hole goes as deep as you want it to go.
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