2015 - Traxxas Summit
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I've had some slow-burning builds in the past, but this one takes the cake. I bought it in January 2015 and waited until September 2018 to "finish" it.
I suppose it isn't even really fair to call it a "build", per se. It's more accurate to say I bought a Summit and then, over the next 3 3/4 years, dealt with problems and inadequacies as they presented themselves. I didn't buy it with the intention of modifying it in specific, pre-planned ways -- quite the opposite, in fact. I bought it because, as I understood, it was one of the few RCs on the market that's built correctly at the factory.
That was almost true. ;) While the only parts I've ever broken were a couple 4-dollar plastic axles, a 3-dollar front skid, and a 3-dollar front bumper mount (stupid rocks!), I did manage to find a few things to improve.
I guess the first one I should talk about is visible in the picture above. (I should also mention that it's actually the last modification I made, but it's the most easily visible, so it goes first anyway.) The stock Summit lights are okay, but they use cheap LEDs and have no power regulation at all, relying instead on stringing the LEDs together in-series so the LEDs forward-voltages (aka "Vf") add up to the supply voltage of the ESC's Battery Eliminator Circuit. One of the side-effects of this is, when the BEC browns-out due to high load from the steering servo, its supply voltage drops below the LEDs' cumulative Vf, and the LEDs flicker because almost no current can get through the LEDs in that situation. (it doesn't help that each white LED's Vf is 3.2V and they're strung together in pairs for a cumulative Vf of 6.4V, while the stock ESC's BEC supply voltage was 6V -- so the LEDs are already at the limit of what the ESC can power without help.) Buuuuut, this setup is less expensive than including a power regulator so the LEDs could be powered individually without being fried, so that's what Traxxas went with.
Anyway, after I switched to a Hobbywing ESC with a lower-voltage BEC, the flickering problem got really bad, with the LEDs flickering every time the steering servo moved at all, and that's when I decided to give the lights a complete overhaul. The four white lights in the front were replaced with two better white lights (5 emitter dies per LED, if that means anything to you) and two amber lights as corner markers, and I installed four more white lights in the optional roof bar as well. Each LED is powered individually, with a resistor attached to each LED to restrict the current flow to a level the LED can handle without burning-out. (I use the same setup on all my other custom lights, though I sometimes connect amber or red LEDs in pairs if they're right next to each other.) Below is a picture of how I get power to the roof bar:
The JST connector is there because the wires pass through the body shell, a situation which is unique among all of my RCs with lights installed. With the JST connector, I can disconnect the roof bar and move it to a new body shell someday when the current one wears out, so I don't have to de-solder and re-solder the battery contacts to get the wires to fit through the hole in the body shell.
I don't have a picture of the taillights, because they're actually fine in their factory configuration. Red LEDs have a Vf of 1.6V each, and in the Summit they're wired in groups of 3 for a cumulative Vf of 4.8V, which is just below the ESC's BEC supply voltage of 5V so there was no need for any power regulation at all. (the extra 0.2V means the red LEDs are only getting 4% more current than intended, which is insignificant.) If I replace the ESC with one that has a 6V BEC someday, I'll attach resistors to the taillights at that time, but until then the factory setup will work fine.
So now the question must be asked, why did I willingly switch to an ESC with a lower BEC voltage? Well, I didn't actually want a lower BEC voltage, but I did want a LVC setting that wasn't absurdly high like it is in the stock ESC. It was quite irritating to fully-charge two full-size LiPo packs only to have the ESC go into limp mode after 15 minutes of driving. It just so happens that the Hobbywing WP860 Dual has the lower LVC setting I wanted, but also a lower BEC voltage. Gotta take the bad with the good, I guess, but it turned out to not be a problem anyway.
The Hobbywing WP860 Dual isn't the perfect ESC, but it has a LVC closer to 3.2V instead of 3.6V, so I actually get more runtime from a single ROAR-size 4S pack than I used to get from two ROAR-size 2S packs connected in-series. Being able to run on a single ROAR-size 4S pack without sacrificing usable runtime also means I'm a lot more likely to actually drive my Summit, which is obviously a good thing. (why not continue running dual packs for even more runtime? two reasons: 1) I get bored after about 30 minutes of RCing; and 2) I hate needing to charge two batteries at once before I can drive one of my RCs, for some reason.) The WP860 Dual also has double-tap reversing like the original ESC, whereas all of the Castle-Sidewinder-based ESCs have a reverse-timeout instead (and it's waaaaaay too short at only 1 second), so I don't accidentally slam the truck into reverse if I let it coast for a few seconds before braking.
Oh yeah, if you look closely at the motor in the picture above, you can see the first mod I ever made to my Summit. (unless you count hot-gluing the diff cases into the bulkheads to eliminate wobble, which I don't -- that was more of a fix than an upgrade.)
Yep, I hammered the motor apart and replaced the bushings with ceramic ball-bearings. Why didn't I just get a Kershaw DeWalt 820 motor, or better yet a 1/8-scale brushless motor? Actually, I did get a Kershaw DeWalt 820 motor, but it squeaked relentlessly. And I didn't get a 1/8-scale brushless motor partly because I didn't want to risk breaking the Summit's drivetrain, and partly because I didn't want the bother of waterproofing it before I could drive my Summit through the local creek.
Besides, the Titan 775 produces plenty of power, it just gets really hot in the process, and I wanted to see if the ball-bearings would fix that problem. Also the brushes seem to be made of concrete, because they are incredibly long-wearing, and I wanted to see how long they would last. Replacing the bushings with ball-bearings reduces friction inside the motor, reducing heat as well, and I don't have to worry about the bushings getting sloppy and letting the armature rattle-around and damage the motor as it ages, so I'll actually be able to see how long the brushes last in ideal conditions. It took an entire year just to wear-down the serrations on the brush faces, so I'm optimistic this motor will run for a very long time. :)
So did the ball-bearings fix the heat problem? Well, I was able to gear-up from the stock 14/68 to 17/65, which is a 27% increase, soooo...yes. :D
Elsewhere in the drivetrain, I replaced the center driveshafts with Traxxas' factory-upgrade sealed CVDs, which I installed when I realized the front-center plastic driveshaft was starting to twist; the sealed CVDs have never required any attention since. I also installed one transmission mod: a low-lash shift puck from Leading Edge Machining. It is by no means a unique mod -- it's probably the most widely-known transmission mod for the Summit -- but I mention it anyway because I got one and it works great. It gets rid of almost all the free-rolling "slop" that the Summit's transmission has from the factory, and it doesn't bend during hard shifts like the stock shift puck does, so it helps prevent stripped gears too. I don't have a picture of it, but "twissted" on RCCrawler.com does, so here's his picture:
To improve the Summit's "approximate" steering capabilities, I replaced the twin steering servos with a single Hitec HS-7955TG servo, which produces more torque than both of the stock servos even with the Hobbywing ESC's 5V BEC. Having all that torque on one side of the servo-saver assembly caused the input arm to flex too much, though, so STRC saved the day with their aluminum input arm for the servo-saver assembly:
Of course I have a clamping aluminum servo horn to eliminate flex in that spot as well. (on a related note, I discovered with a different monster truck that while Hitec's plastic servo horns are flexible, they are incredibly resilient against stripping the splines, so if flex weren't a concern then I could've just used a plastic servo horn. In that truck, which had no servo-saver at all, the impact from a hard cartwheel actually wrenched the servo out of its mount and broke the mounting tabs, while the splines in the servo horn were pristine. I was amazed.) I also shimmed the servo-saver spring to increase the amount of torque the servo-saver could transmit to the Summit's enormous wheels.
Those enormous wheels posed an additional problem as the truck aged -- the wheel bearings couldn't cope with the stress, and they got really notchy and wobbly, and the bearing sockets in the hubs started to loosen. I normally steer clear of aluminum hubs (excuse the pun ;)), but in this case it was a necessary upgrade. The STRC aluminum hubs also have larger outboard wheel bearings, which means the bearings will last longer before making unpleasant noises.
This picture has a lot going on in it. You can see the wires and spring-contacts I use to power the roof lights without needing to unplug connectors every time I remove the body shell; you can see the 3 tiny Blue Bird BMS-373MG servos that I replaced the original shifting and locking servos with (they have full-size 25-spline hubs just like the original servos, so the original servo-savers fit!); and you can see a couple of suspension mods.
The Summit is a chimera, in the sense that it's two different things fused into one. It's always had a dual-identity as a monster truck and a crawler, and some would say it sucks at both, but it was never supposed to be excellent at either one in the first place. But with the release of the TRX-4, which I also own, the niche that the Summit occupies has shifted. Whereas the Summit was originally supposed to be dual-purpose, now there's the TRX-4 which is a dedicated crawler that can kinda-sorta go fast sometimes, which means the Summit can focus on being a dedicated monster truck that can kinda-sorta go crawling sometimes. (or maybe just mud-bogging with locked diffs; that's good too. :)) To that end, while I had installed stiffer springs years ago to keep the Summit from wallowing in corners, I've now maxed-out the stiffness of the springs with purple-stripe in the front and blue-stripe in the rear, and I finally got around to figuring out how to fit a front swaybar. Anyone who's ever driven a Summit fast knows it has a bad tendency when cornering to tuck-and-roll the outside-front wheel, which has not become more entertaining the longer I've owned the truck. So I bought an E-Revo swaybar kit, bent the front swaybar a bit to clear the rear diff-lock linkage, and drilled an extra hole in the swaybar retainer for the front diff-lock pivot-thingy to attach. See below:
(not pictured: A stack of washers inserted under the front diff-lock pivot-thingy to raise it to the correct height.)
Because of the Summit's long-travel suspension cantilevers, the front swaybar doesn't eliminate tucking-and-rolling in corners, but it does make the problem a LOT better, making it much better-suited for its new niche as a monster truck that can kinda-sorta go crawling sometimes. Likewise, that same suspension geometry also means the front swaybar doesn't ruin the Summit's ability to articulate over difficult terrain:
So that's my Summit. I've had it for 3 years, and it's been one of the most reliable RCs I've ever owned. Tinkering on it, driving it through water deep enough to completely submerge it, and generally beating the crap out of it without consequences was a bright spot during a couple very difficult winters for me, and I think I'll keep it forever.
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