2015 - ECX Ruckus
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(originally posted on UltimateRC.com on 2015-04-19)
I guess I should document this before my girlfriend's nephews get their hands on it and beat the stuffing out of it.
Last year my girlfriend's nephews had great fun driving my HPI Bullet ST over Memorial Day weekend, and it held-up to their "driving" admirably, but the only other vehicle I had with me at the time was a Savage XS, and it was just too fast for them to drive. Plus, I had both vehicles bound to my Spektrum DX4S, which meant only one could be run at a time.
This year I wanted to be prepared with more options, so I've spent the past few months building vehicles that I can take with me for them to play with, and I won't get upset if they manage to break something. This ECX 1/10 RWD Ruckus is one of those vehicles. (the other two are a spare HPI Bullet with a cheap engine, and a Traxxas Telluride configured for trailing and light crawling.) All three vehicles are bound to separate Spektrum DX2L radios, so they can be run all at once -- IF I'm crazy enough to let three kids drive RC cars in close proximity to one another. (even if I'm not that crazy, it means I can still use my DX4S radio to drive one of my nicer vehicles while the kids are playing.)
It also gave me an opportunity to see if RWD is really practical for driving off-road with any kind of precision at 1/10-scale, because my only other RWD truck is a Losi Mini Desert Truck, and it's just too small for any off-roading other than bare dirt and maybe mulch. (I've had my eye on a Pro-Line Pro-MT, but the ECX Ruckus is way less expensive.)
Since this is a budget build, I didn't go all-out with it. I just addressed the significant problems with the vehicle. I bought it used for $115 on eBay, so I had a lot of room to spend money without making the vehicle too expensive to trust kids with.
As you can see from the picture above, the stock motor has been replaced with a Traxxas Titan 12T, which has comparable top-speed and considerably more torque so it doesn't have to work as hard to move the truck through grass. Also, the stock tires were replaced with Pro-Line Trencher X 2.8" tires, which give much better grip -- enough that it can even climb over curbs fairly easily, despite having an un-powered front axle.
The stock gearing struck me as being good for speed runs, but not at all good for actual off-road driving; even with the Titan 12T's extra torque, I had to drive the truck at full-throttle pretty much constantly when it was on grass, and I knew the motor wouldn't tolerate that for long. Since the stock 48-pitch spur was already looking worse-for-wear, I decided to trash the entire stock gearing setup and switch to 32-pitch. The new spur gear is an Associated 58t gear with the center hole reamed-out slightly to fit the Ruckus' transmission input shaft, and the new pinion is a Robinson hardened-steel 10t gear. The motor-mount didn't allow me to adjust for a perfect mesh, so it's a little loose, but it's almost completely silent even at full-throttle and the spur isn't showing any premature wear, so if the truck thinks the mesh is good enough, I won't argue.
What you can't see in the picture above is that I also rebuilt the differential. It was packed full of some kind of petroleum grease, which is of course great for lubricating the metal gears inside the diff, but terrible for providing any sort of limited-slip action. Since the diff doesn't have O-rings around the outdrive holes, I packed the diff with sticky silicone grease instead of using diff oil. The silicone grease only comes in one viscosity (as far as I know), but it's a gel so it will never leak, and it provides enough limited-slip to be useful.
The stock ESC was LiPo ready, but its power output left a lot to be desired. (the "LiPo-ready" ESC is actually DYNS2211, not the DYNS2210 that is available as a separate part, and the DYNS2211 has a much lower power rating.) I had a Traxxas XL-5 ESC left-over from my Telluride build, so I just stuck that in the Ruckus, and it woke the truck up nicely. The XL-5's brakes work a lot better, too.
Having improved the power output and lowered the gearing of the truck, wheelies were now easy to achieve, and that's exactly what I was going for, because a bunch of kids will have a lot more fun with wheelies and burnouts than they will with top-speed, when they're driving around on a farm with no pavement anyway. As if in accordance with some sort of prophecy, a discontinued ECX Circuit wheelie-bar set popped-up on eBay, and I promptly snagged it. The Ruckus's rear bumper isn't designed to play nice with the wheelie-bar, but that wasn't really a problem, I just had to get creative; I cut a slot in the rear bumper for the wheelie-bar to fit through, and the displaced screw-mounts for the top of the bumper were replaced with some zip-ties. (I may go back and drill some new screw-holes into the wheelie-bar for the bumper to attach to, once I'm comfortable that I'll never want to change the angle of the wheelie bar again.)
Up at the front of the vehicle, I had to deal with the sloppy servo-saver that the ECX RWD vehicles are known for. The common solution is to replace the servo-saver with a solid bellcrank made by RPM, but I decided to try to salvage the servo-saver first. I bought two spare servo-saver kits for something like $5 apiece, removed the metal springs from the kits, and nested them together so the servo-saver would be triple-reinforced. I had to use a Dremel sanding drum to remove a bit of plastic surrounding the servo-saver on the front bulkhead before the modified servo-saver would fit, but that took about two minutes, and the reinforced servo-saver works great -- the steering is firm and accurate, even in reverse.
Also, the stock servo was replaced with a Tactic TSX45; they're a dime a dozen on eBay, because they come standard on Axial Wraiths and everyone replaces them as one of the first mods on that vehicle. But they're metal-geared and produce plenty of torque for a truck like the Ruckus, so for $12 the stock servo got upgraded to something much more effective.
After witnessing my girlfriends' nephews' "driving" skills last year, I knew I needed to do something to make the truck more controllable, otherwise they'd just spin it around in circles and never actually get it moving. So I installed a Futaba GYC430 gyro, which is total overkill for a vehicle this inexpensive, but it works great and I can put it on a more expensive vehicle when the Ruckus outlives its usefulness. (I don't like to buy cheap stuff that I know I'll have to replace.) I tuned it to provide moderate intervention, so when the back of the truck is swung side-to-side, the front wheels stay pointed straight-ahead, and that makes the truck fun while remaining almost impossible to lose control of. Perfect for kids who don't know how to adjust their steering when the vehicle transitions from one surface to another, for example from the edge of a dirt driveway onto grass.
I also made a tiny little mod to the battery-retention clips, to make them easier to use. The clips are mounted with screws that pass through the underside of the chassis and screw into the clips themselves, so the height of the clips can be adjusted to compensate for differently-sized batteries by tightening or loosening those screws. Problem is, the clips would just drop down flush against the top of the chassis, so they would have to be pulled up before they could be turned 90° to lock the battery-clamp in place. I got sick of having to do this, so I cut a couple thin pieces of fuel tubing and put them around the screws under the clips, to keep the clips in their intended position when the battery-clamp is removed. It's a little mod that makes the job of installing the battery a lot less irritating. Also, I tapered the end of the battery-clamp that slides under the ESC tray, so it would be easier to slide it into place when using a hardcase LiPo pack.
Lastly, while the shocks look stock (because they are), I found them to be woefully under-damped, filled with 20wt oil or maybe even thinner, and not even filled enough to keep from sucking bubbles through the shock pistons, which lowers the fluid's viscosity even further. So I drained them and refilled them with 45wt oil, and the damping is much better now. My standard test for damping effectiveness is to drive my vehicles at about 50% of top speed over a speedbump, and look for evidence of chassis-slap, usually indicated by the vehicle front-flipping as it comes over the speedbump. With the stock oil I saw a lot of that; with the 45wt oil I see none of that. Problem solved.
It's a good truck. It's convinced me that RWD is still a practical drivetrain, at least at 1/10-scale or larger, and my girlfriend's nephews should have a blast with it. Maybe someday I'll upgrade to a Pro-MT, but for now this will do just fine.
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