2014 - ECX Smash
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(originally posted on UltimateRC.com on 2014-01-03)
I wanted a vehicle I could toss in the trunk of my car, leave there for days or weeks at a time, and pull out when I have 15 minutes to play with it on my lunch breaks. The ECX Smash looked like a good option, because it uses most of the same parts as my Losi Mini Desert Truck so I wouldn't have to stock up on a new set of spare parts, it has better ground clearance and is less finicky than my MDT, and it's small and lightweight. Also, because it shares a platform with my MDT, I won't feel like I'm missing anything if it sits in my car for weeks and I don't get to play with it, because I can just play with my MDT instead. And it cost a heck of a lot less, too -- I scored an in-store-demo model on eBay for $40.
Since I already have a lot of experience with this platform from tinkering with my MDT, I cut straight to the chase and upgraded only the parts that I knew would bring immediate benefits. I installed a hand-me-down 2.4GHz ECX receiver pulled from my ECX Mini Ruckus (which was since upgraded to a Spektrum receiver), a used Tekin B1R speed controller (I bought 3 of them for $37 on eBay), an aluminum gearbox casing to keep the gear-diff internals from stretching apart and slipping, aluminum shocks because the original shocks were complete garbage, and an aluminum steering bellcrank to get rid of slop in the steering.
The motor is a spare LOSB1218 that I had sitting in a spare-parts box, and the wheel nuts are black flanged nuts from Team Associated that I had bought for my MDT, but I had extras laying around because they came in a pack of 20. I geared this one lower than my MDT (11:61 instead of 13:60) to account for the larger tire diameter, and like my MDT, the front is ballasted with 1oz. of lead, to help keep the front wheels on the ground so it can actually turn corners while accelerating. The rear axles are a set of GPM steel universal-joint axles that I had laying around; I never used them on my MDT because I found titanium axles for that vehicle instead.
To make it a little more interesting, I decided to do something different with the wheel hubs: instead of installing ball-bearings, I installed bronze bushings instead. Why? I dunno, I guess to see if I could make them work well. To help support lateral loads while cornering, I manufactured side-races for the bushings from various thicknesses of 4x8 shims, and fit everything together so it's as tight as possible without binding. A couple drops of sewing-machine oil on each bushing finished the job.
You know, the bronze bushings actually work pretty well. After about 15 minutes of break-in, I haven't noticed any dragging at all, and the wheels roll silently. (I originally built the gearbox with bushings as well, but there was severe binding on the input shaft. It occurs to me I could probably run the input shaft with bushings in just two of the three possible locations, and I may try that if I ever decide to give bushings in the gearbox another try, just for kicks.) Admittedly they required a lot more initial prep than ball-bearings would've needed, but everything has its tradeoffs, and these bushings should be more immune to getting jammed with grit than ball-bearings are -- if they get dirty, I can just remove the wheels, clean the bushings with a Q-Tip or a rolled-up napkin, and reinstall. Time will tell how that translates to real-world reliability, I suppose.
I tuned the suspension on this one differently than I did on my MDT; the rear springs are actually softer than the front springs, both to give the front-end more resilience against running into obstacles, and to give the rear axle more compliance in corners, so both rear wheels will maintain traction when the vehicle leans. To make up for the fact that the vehicle *also* carries most of its weight in the rear, the rear preload is cranked up with a bunch of shims, and the rear shock oil is 45wt instead of 30wt to help keep the rear-end from bottoming-out after small jumps.
I may have to bump up to 60wt in the rear, but overall the odd setup seems to work quite well; one thing my Smash can do that my MDT can't do is, it can run into the sharpest part of the speedbump in front of my apartment at full speed, and clear the jump without flipping forward. So it's definitely more stable, at least in certain circumstances. It should make a good basher once the current cold weather warms up a bit.
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