2014 - Associated Mini Rival
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(originally posted on UltimateRC.com on 2014-03-13)
I finished another build last night.
I have to admit, I had my doubts about the Mini Rival at first. In stock form it was pretty slow, the gears were exposed, the outdrives were plastic, there was a weird hole under the motor for no good reason, the dogbones had a weird tendency to chatter when cornering, and even the strongest available shock springs were only barely adequate. However, I quickly discovered there were lots of upgrade options, and I went to work fixing the platform's weak points.
The first problems I tackled was the weak motor. After trying a series of different brushed motors, I gave up and converted it to a brushless system. I ended up going with a Turnigy Trackstar ESC, a Turnigy 4600KV 4-pole motor, and 2S LiPo. (I'm not sure if the motor is actually 4-pole, because it rotates with no resistance when the ESC is off, unlike most 4-pole motors, but it makes plenty of torque so I don't really care.) It went from being impotent to doing multiple standing backflips, at which point I grabbed the programming card and turned down the settings before I destroyed the drivetrain.
Because I love adjustable things, I replaced the stock fixed-length linkages with Associated's titanium turnbuckle kit. And, just for good measure, I replaced the stock suspension arms with RPM arms, sanded-down in a few spots to give the necessary clearance for the upgraded shocks.
Oh, and I replaced the wheels with RPM Spider wheels. I had hoped to score a set of Revolvers, but RPM seems to be discontinuing its mini wheel collection, and the Spiders were all that was left in-stock in black. Not a big problem, I already use Spider wheels on my Mini Desert Truck, and they look great on both vehicles. As a bonus, I discovered that Associated's mini tires are acetone-proof, unlike Losi's mini tires, so my attempt to dismount them from the stock wheels using acetone worked perfectly -- instead of resulting in a mess of stringy black goop like what happened when I tried the same thing with my Mini Desert Truck's stock tires.
The other big problem was the shocks. The stock shocks don't let the suspension move as much as it can, so the ride-height of the truck is artificially limited (these are the compromises that occur when the same platform is used for multiple types of vehicles), and the front shocks were totally inadequate. They're too short, they don't have enough leverage to provide smooth damping action, the preload collars didn't have enough range of adjustment, and even the strongest springs were too soft.
Luckily, Losi's aluminum shocks for the Mini-T saved the day yet again (I think this is the fourth mini I've installed Mini-T shocks on), and by pure luck I discovered that Dynamite offers replacement Mini-T shock housings in red or blue anodizing. Now they even match the color scheme! But more importantly, they give somewhere between 1/3" to 1/2" more suspension travel, which makes a HUGE different on such a small vehicle. As you can see in the picture below, with the new shocks, the chassis plate is actually higher than the centerline of the hubs -- something the original shocks simply couldn't do.
I opted to use green springs from the Losi Rear Spring Kit for all four shocks, which works well because the weight bias on the Mini Rival is much more neutral than it is on the Mini-T, which needs stiffer springs in the rear. I may eventually decide to try the silver springs, which are a bit softer, but overall I'm happy with the performance of the green springs.
The stock plastic steering linkage with integrated servo-saver was replaced with aluminum parts from 3Racing. The non-servo-side bellcrank has ball bearings to pivot on, which is a nice touch. Also, the 3Racing kit came with an interesting steel servo-saver spring reinforcer, which is actually designed to fit over the stock plastic spring. It turned out to work better than the replacement metal springs I had bought (which kept stretching when I actuated the servo-saver), so I decided to use the steel-reinforced-plastic spring instead.
The stock servo was replaced with a Hitec HS-5056MG metal-gear servo. I was originally sent this servo as an "upgrade" for an HS-5055MG I had ordered but was out-of-stock, and it's a different-size servo, so it couldn't fit where I originally intended to use it. However, when I got the Hitec-compatible servo-saver kit from Associated, I discovered it was designed to fit a servo like the HS-5056MG, so I chalked it up to a happy accident and installed it. It's a very good servo, good response times and plenty of torque for its size.
The differentials were rebuilt using MIP Super Diff hardened-steel outdrives, and the dogbones were replaced with MIP Shiny Drive axles. At first I was concerned about breaking the all-blue paradigm, but I eventually realized I had enough other blue parts that the shiny nickel-plated CVDs made for a nice contrast. Upgrading to CVDs also meant I could get rid of those silly little dogbone springs, which don't work very well anyway.
As usual, while I was rebuilding the axles, I went ahead and replaced the hubs and caster blocks with aluminum parts (especially useful in the front, to resist breakage in crashes), and I replaced all the bearings in the vehicle with Boca Yellow Seal ceramic bearings, so I won't have to worry about grit getting into them and destroying them -- the ceramic bearings will grind up anything that gets caught in them.
Also, you may notice some missing blue anodizing around the upper shock eyelets. That's because I had to use a cone-shaped Dremel bit to widen the outer edges of the upper eyelets on the front shocks, so they could attach to the front shock tower at a slight forward-tilting angle without binding. The rear shocks did not have this issue.
The last part I needed to finish this build (which I had to wait about a month to get) was a gear cover from Driven Productions. They are excellently constructed and very comprehensive in their protection, so I had to completely disassemble the back end of the vehicle to get the thing installed. However, it solves a glaring deficiency in the RC18 platform's design, and once I found out this part was still available, that's what changed my mind and made me decide to keep it.
One thing nobody seemed to make a pre-made part for, was the hole in the bottom of the chassis. I had zero interest in leaving it open for dirt and grass and who-knows-what to get up into the chassis during every run, so I found a suitable piece of plastic, cut it to size, drilled some holes, and screwed it into place. (I used spots of superglue to hold it in-place while I drilled the screw holes.) Thanks Ikea, for giving me useless spare parts that I could repurpose years later.
It turned out really nice. The brushless motor gives it enough speed to be entertaining and enough torque that I had to dial-down the punch control to keep the driveline safe, the Losi Mini-T shocks give it the suspension travel it should've had all along, and all the other bits do their parts to make it run well. I shall keep it.
By the way, that picture was taken without me forcibly compressing the suspension. That's how much flex it actually has.
I'm in the process of standardizing all the ESCs in my collection, and standardizing the batteries used by all my minis, so my Mini Rival got an overhaul a couple days ago.
The Trackstar ESC was replaced with a Toro ESC (same model, different brand, and slightly different firmware so it can talk to the same programming card that my bigger Toro ESCs use), the Turnigy motor was replaced with a Tacon motor, the 60t spur gear was replaced with a 55t spur gear to compensate for a slight difference in motor speed and also to provide a tiny bit of extra clearance on the underside of the chassis, and the whole freaking chassis was stripped-down so I could cut away a piece of plastic that was keeping my MERV LiPo batteries from fitting.
That was a pain to do, but at least I only have to do it once. (well, twice, including the same job on the Mini Apex.) Stripping everything off the chassis was tedious, and grinding-off the extra bit of plastic was meticulous, but the only *hard* part was reinstalling all the screws that hold the upper deck in-place, because I had to twist the chassis with my left hand and my feet while operating the screwdriver with my right hand, to counteract the chassis-tweak that occurs if I don't twist the chassis during reassembly.
I also replaced the front shock bodies, because back when I bought the blue shock bodies for the Mini-T shocks, one of them had a slightly different inner diameter and it screwed up the damping on that one shock. The Losi Mini-T aluminum shocks aren't designed to interface with the shock tower at an angle, but that's unavoidable on the front of the Mini Rival/Mini Apex platform, so I had to bevel the eyelet holes on the front shock bodies to give them room to tilt a bit. I did this the first time around with a cone-shaped Dremel bit, but since I have a wider array of tools now, I realized I could use my body-post reamer to do the same job with greater precision. It came out much cleaner this time.
So now the shocks work better, the electronics are standardized, and I only need two sizes of batteries for all my RCs: 5000mAh full-size packs for my 1/10 and 1/8-scale vehicles, and 2000mAh mini packs for my MERV and other mini vehicles. This also means I should be able to get name-brand mini packs for a long time to come, since the MERV is such a popular platform.
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