Kraton Spare Parts Build - Kraton Krawler Trail Truck

[pomplemus]

NOTE: I lagged a bit on posting this thread and got too excited rushing forwards when building, so the truck is already complete, but I figured I would still post this log in installments.

Hey all, been here for a few years now with my original Kraton, but I figured I'd finally get a build log posted!

So, over the course of 3 years I’ve collected quite a few spare parts and retained originals when fully M2Cing out my rig. A few months ago I realized I had almost all the parts I needed to build an entire second truck. A dangerous situation I’m sure many of you have been in.

When getting other replacements from Jenny’s and the like, I also picked up the other remaining parts I needed, bit by bit. I wanted to make a “new” build utilizing as much of my original parts/spares as possible, but not just another high speed ultra-basher Kraton, since I already have one of those pretty much exactly how I want it.

I considered a road/speed build, but if I just slam my other rig and mount road crushers it pretty much fulfills that, plus many other people have already done that; I wanted to get a bit more creative. An ultralight basher (akin to @Xjeepguy 's Superleggera, awesome build) was also enticing, but would end up replacing almost all stock parts, defeating the purpose of the build.

What I have never seen before however, is a slow speed trail truck/crawler! I was initially struck by the idea when I took my Kraton with me when camping, and it actually did surprisingly well at a walking pace on some rough slopes/rocks, partially thanks to the sensored 1717. Optimizing for slow speed trail walking/crawling could be pretty cheap to execute as well, suspension tuning is mostly free and can go a long way.

Thus Kraton Kawler was conceived! It’s definitely not going to be a true “rock crawler”, since the chassis is just too far off a purpose built solid axle design, rather more focused as a slow/medium speed trail truck that can also do some light to moderate bashing. But, alliteration is fun, so I’m sticking with “Kraton Krawler” as the name.

I was further convinced of this build a little while ago when visiting my family in Slovakia, turns out one of my cousins is super into trail scalers/crawlers and there is an awesome community over there. I joined him on a couple of events and had a huge amount of fun with the trucks he let me borrow, definitely something different than high speed bashing! Its nice to get out on a walk in the woods with a truck sometimes.

Some general goals:

• It must remain 6S powered. I don’t want to invest in and more importantly lug around a whole other set of lower voltage batteries when I go bashing.
• I want to use as many of my leftover spares/original parts from my Kraton 6S V4 I bought 3 years ago. Practical application of Theseus’s ship…
• Stay on a reasonable budget. I want to stay in the spirit of bringing a bag of old/worn spares to life!
• It must have a sensored motor, sensorless is just going to be too juddery at low speed for what I want to do. This is a little at odds with the above goal since I can’t use my old BLX185, but oh well.

Anyway, the way I see it there are a few critical things to address to make this embody what I want it to:

• Suspension jacked waaaay up for maximum ground clearance/breakover angle
• Some big and soft cool looking tires for for clearance and grippiness
• Geared as low as possible for max torque/smoothness at low speeds

A while back on ebay I found an awesome deal for mojave rear shocks ($12 for a set of two!) so I went ahead and bought three sets. I figure putting rears on the front will jack that up, and I can figure out some alternate mounts for the rear

The RC4WD Mickey Thompson 40 Series Baja MTZ tires check the boxes for big (8”!), soft/grippy, and cool looking. They are pricey, but I managed to find some new ones already pre-mounted to some old Proline beadlocks from a local FB seller for a reasonable price! The bead locks will go a long way towards looking cool, but I will need to figure something out for the 23 mm hexes.

Torque/slow speed comes from both gearing and Kv. The smallest mod 1 pinion I could find for a 5 mm shaft is 11t, and I did actually find an eBay special spur slightly bigger than stock at 52t. We’ll see how it holds up.

The lowest Kv reasonably cheap (under $100) sensored motor I could find was the HobbyStar 4274 1350 Kv. I don’t think this truck needs a massive amount of power, just good torque and low speed control, so this should be alright. Between the 11/52 gearing and 1350Kv motor, but bigger 8” tires, I think this should top out around 30-35 mph, which sounds about right for a low/medium speed trail truck.

After a WTB sensored ESC post in the classifieds sections, @Sumnig66 came through with a solid price for a used Mamba Monster X 8S! Definitely overkill, but hey, it works great on my other Kraton, so it should do well here too.

The first order of business was to clean up the ESC. getting rid of the XT90s and putting on an IC5. In my experience, they simply hold up better long term and are more reliable than XT90s. I also swapped out the top case/fan mount for a 3D printed one of my own design that is much tougher, the stock Castle one tends to crack on hard landings.

Thus it begins!

More to come soon.

I'll finish off this first post by paying the cat tax, my buddy Chewie hung out on the chair next to me for most of build, the dogs couldn't be bothered and stayed buried under the blankets on the couch.

 

[RC Steve]

Just because it came from your junk bin doesn't mean it's junk. Can't wait to see it operational.
Will you be locking the diffs on this truck?

 

[pomplemus]

Haha, totally! What is it about on man's trash?

Since this will still be able to go at pretty good speed and still do some light to moderate bashing, I want some amount of give in the drivetrain to keep from trashing everything. I plan on initially "locking" the center with silicone earplugs, and putting as heavy a fluid in the front and rear I have on hand (200 or 500K) with the LSD plates set to maximum effect. Depending on how it does, I may swap more of the diffs to silicone earplugs after some testing.

 

[Xjeepguy]

Too cool! I’m looking forward to updates. Looks like Chewie is just there to supervise, keep the project on track lol

 

[pomplemus]

Thanks! Chewie is totally supervising, he's intensely curious about anything new going on in the house and is always there to check it out. He was also supervising the other day when decorating the tree.

I decided to make at least one upgrade over what I had on hand and spring for the Treal steering assembly. A soft servo saver definitely wouldn't work well in slow crawling situations, and the Treal is much stiffer and fully adjustable, should last a long time soo since it's fully 7075. I did separate the steering bar from it though and mount it on my basher Kraton to replace the broken M2C one.

I've broken two M2C steering bars over the past couple years, they seem to separate where the material is thinnest where they mount to the posts. The Treal part however, although a similar material and thickness, uses smaller diameter inserts to attach to the post, leaving a lot more material on the bar there. I expect it should hold up even better than the M2C steering bar.

Pretty impressed with the Treal parts, seem to be quite high quality and the design makes sense to me. Here's the Treal assembly mated to the stock steering bar for the Krawler, seems WAY stiffer than stock and will definitely not hold back the steering at all.

Got the diffs all assembled as well with silicone earlugs in the center, and 200K fluid front and read with the LSD plates set to maximum effect. I run open on my basher, but if LSD is going make sense anywhere, it's on a build like this!

The new outdrives for the Big Rock are noticeably beefier than the ordinal EXB outdrives, should hold up better. The best thing is they have a deeper and longer track for the pins wile still having a big chamfer on the ID with plenty of clearance, so they should help keep driveshafts from popping out while not limiting suspension travel any more.

As a mentioned previously I plan on jacking up the suspension as high as it will go, probably limited by dogbone angle in the outdrive cups. A somewhat lazy solution for the front is mounting longer rear shocks, but I needed to get a bit more creative for the rear.

I figured I could more the lower shock mount further inward for more overall travel. The spare RPM rear arms I have on hand might be able to hold up to drilling a new hole, but the material would get pretty thin and I didn't want to risk it. Instead, I designed and 3D printed a little bracket that mounts in the provided shock locaation, but extends inwards.

3D printed TPU 95A hold up really well for RC parts that don't need to be totally rigid, and it should work great here. Unfortunately there was some material on the arm further in that I didn't want to cut away, so I had to also mount the shock up on top of the arm, which will limit uptravel/compression, but I'll see how it works out, might be fine for my purposes.

With all this additional downtravel/droop the arms now bottom out on the droop ears even with no screw. I would like to keep the droop ears to still be able to fine tune that and keep from overextending the shocks, so I mounted the chassis up in a vise, grabbed them with some vise grips, and gave them a good bend.

Plenty of clearance now for some proper droop screws without limiting travel. As an added bonus, since the ears are now parallel with arms when fully extended, I can use flat heads for the screws! All the additional square contact between the screw head and chassis should limit chassis wear at that point.

Its' getting close! The axles seem to rotate fine even with the extreme angle of the suspension, this is going to have a TON of clearance.

Getting excited, I couldn't help doing a quick mock up of the wheels on my other Kraton! They really are huge on this chassis.

 

[RC Steve]

I like your travel extenders in the back, that was a clever solution.
What are your plans for a body?

 

[pomplemus]

@RCSteve Thanks, 3D printing really adds a bunch to my enjoyment of the hobby, they've been holding up great! Body pics below.

Alright @ColosTommy , thanks for giving me the kick to finally get this updated!

Been a few weeks of running and further tuning I need to document here, but first- the final part of the build showing off the body!

I ended up 3D printing some 17 to 23 mm hex adapters from ABS to get the wheels mounted. With the wheels on there, its a pretty imposing size!

This was an old 3D printed wing mount I had lying around, cut off the rear and the chassis is complete!

Rather than go with yet another truck (with bed) body, I wanted something different, so I went with a Frord Bronco body. This one is for the Revo 3.3 and the wheelbase is a little short, but it does just fit, clearing the shocks at the front and rear.

Decided to go with yellow, figured a big truck needs a color that stands out- here she is!

I only had yellow and black on hand, and since I'm going to be reinforcing the body, I needed to paint the windows. In order to keep contrast between the windows and roof I had to compromise the realism of the coloring a bit; technically the whole roof section should be grey. But in any case, I think it turned out pretty well! I used proper green painters tape this time, and the lines came out quite clean.

 

[ColosTommy]

It's looking good. You will have to upload a video of it in action next time you take it out.

Not much use to you as you've sorted your wheels, but these are som 7 inch beadlocks from an Axial sc6 that i bought and modified to fit my outcast when i was playing with the idea of turning it more into a buggy/u4 looking thing, this was back before Arrma released the fireteam, they came with 17mm hexes.

 

[pomplemus]

Will do! I'm not the greatest videographer when driving, but I think I can manage a couple clips. Got some still beauty shots incoming!

Actually, shortly after I purchased the RCAWD tires I realized SCX6 wheels and tires might work too, with some modification. I've never seen them in person, so I wasn't sure exactly what was necessary. What modifications did you have to do to get them to fit? Just hog out some material on the outside ID to get the nut to fit?

I may eventually pick up a set from a kit breaker to play around with.

 

[pomplemus]

Some beauty shots I took before the first run with the body, only going to get a nice beaten patina from here!

The suspension travel/action actually has a surprising amount of articulation. The softer Mojave rear springs on the rear and Kraton rear springs on the front work pretty well.

Side by side comparison of my MWC's basher and the Kraton Krawler with the chassis at the same height.

Between the giant tires and jacked up suspension, this has about 1.5" more clearance than a usual basher Kraton! It rolls over just about anything.

Some pretty beach shots, had a ton of fun crawling on the rocks out here. 8)

 

[pomplemus]

A promised, a couple short clips! These aren't the most impressive as I was trying to drive with one hand and hold my phone with the other, but you get the idea- please excuse my poor filming skills.

With the camera off and all of my attention on driving, the Kraton Krawler has been able to pull off some better/smoother lines, but you'll need to take my word for it, haha.

 

[ColosTommy]

Actually, shortly after I purchased the RCAWD tires I realized SCX6 wheels and tires might work too, with some modification. I've never seen them in person, so I wasn't sure exactly what was necessary. What modifications did you have to do to get them to fit? Just hog out some material on the outside ID to get the nut to fit?

So the threaded part that goes through the wheel hub is much smaller in diameter on the scx6, so first that had to be drilled out to the correct size, then as you summarised from the pic i had to remove some material on teh outside because the threaded part on an arrma 6s wasn't longer enough that it would poke through the wheel hub enough to get the wheel nut on, so some material had to be removed there,

 

[pomplemus]

Thanks for the details, I'll keep a lookout for good deals on SCX6 wheels/tires.

 

[sumguy75]

Cool build! Yeah, not a dedicated crawler, but really impressed with the things you climbed in the videos.

 

[pomplemus]

Thanks @sumguy75! I really need to have someone else come along with me sometime so I can get some getter shots, the really impressive stuff happens when I'm concentrating too much to be filming at the same time, lol!

It's been a bit sicne I've updated this thread, and there have been some changes, to say the least.

But basically, my initial requirement to keep this on a budget? Yeah... that ship has sailed sunk, and is presently decomposing.

It all started when I dumbly looked at castles website over Christmas and noticed they had the 1717 1260 Kv on sale for only $120 (!). Definitely inferior to the 1650 KV for bashing, but perfect for this sort of build. Once impulsive click later, and...

With the low gearing, the 46 mm can just barely clears enough for good mesh, but it does fit. I had noticed the Hobbystar 1350 Kv was struggling a bit under super high load at low speeds, and would overheat without a fan during an extended session. So such issues with the Castle 1717! It has WAY more torque, and can go all day without reaching 180°F.

I also added some weights to the front to increase the crawling ability. This is about 0.6 lbs of what I just had laying around the garage, and it makes a difference- with enough grip, it can scale a 52° slope now.

However, all is not rosy- the servo has become a real limiting factor. Other than my SCX24, I have pretty minimal experience crawling, so I didn't quite realize just how much higher the torque/durability requirements are for a servo like this.

After killing a couple more cheapo Amazon servos I had laying around (including stripping a franken-servo I made by kludging together the parts of half broken ones) I decided to get serious and get a ProModeler DS1155BLHV.

Unfortunately, while pretty and impressive performing, I killed it on the very first day on the rocks. Turns out ProModeler servos have no overload/current/temperature protection whatsoever, and will burn themselves out in seconds when stalled. While I can see how this would be the desired behaviors for air vehicles, for a crawler like this it's not ideal.

I'm getting it repaired, it will probably work nicely my basher Kraton since I recently killed the 729MBL in that one during a particularly exuberant skatepark session.

While continuing to look into servo options, I temporarily put in an AGF 55Kg so I could have it up and running on a trip to Arizona I had a few weeks ago, and I'm glad I did- so much RC fun to be had out in the desert!

I have all 3 diffs "locked" now with silicone earplugs, and the crawling performance has improved again. This is so versatile, I ended up crawling on some volcanic rocks outside Kofa wildlife refuge in the morning, and bashing on imperial dunes in the evening! No changes to the setup at all in between- definitely not as good a purpose built vehicle in either environment, but its still plenty fun!

Videos from the same day:

 

[ColosTommy]

Coming along nicely.

Do you plans or idea of what you want your next upgrades to be, or are you just waiting till something breaks/ shows weakness?

 

[pomplemus]

Mostly just waiting until something breaks/doesn't work right and then going from there. I always think "now its FINALLY in a good state" and then something else breaks. Oh well, figuring this out is actually the most fun I've had with RC in a while! I like these sort of out of the box challenges.

Speaking of upgrades- the old Proline bead locks, while looking cool and working well in lighter conditions, kept having the bead of the tire pull out. I 3D printed some spacers the have the rings squeeze the bead a bit more, and it worked, at least until the stress literally pulled the plastic channel on the wheel apart!

Got some nice RC4WD bead locks to match the RC4WD tires.

These feel super solid. RC4WD stuff is not cheap, but the quality shows.

One thing I didn't realize is just how much wider the offset is no these, I think they've added about 1.5" of width.

For the servo, I ended up getting an NSDRC RS800V2 4S direct power. The performance is the best I've tried so far, but the real star I think is the NSDRC 4S voltage regulator. When it says, 5A constant, it MEANS 5A constant. This is the only RC BEC/voltage regulator I've tried so far that truly seems to hold it's rated current with a stable voltage without breaking a sweat.

I threw on a fan with a remote actuated switch the help cool the servo when crawling.

With this much steering torque, the front hub/suspension setup can't quite keep up. Under steering load, the hubs torque enough to twist the arms such that the effective caster angle goes to almost 90°, and the hubs/steering lock up. Once of the rare cases I think where aluminum arms may be superior, so I threw on an Amazon special (AllinRC) set. They seem solid, but I haven't quite gotten to running them yet.

While the servo performed great, I either pushed it a bit too much or the FETs were a dud, as I also burned it up during a crawling session. :/ I'm leaning on thinking something may not have been quite up to stuff with it, and I've only hear good things about these servos in other vehicles.

A bit disappointing, since before buying NSDRC assured me their servos had thorough protections in place to keep that sort of thing from happening. On the plus side, their warranty covers this and they're making it right, so I feel pretty good about giving it another shot.

However, I need too step up the servo even more if I can, I'm seeing there's no such thing as too much steering torque in a vehicle like this.

I'm already breathing rarified air with the RS800V2, so stepping it up even more gets tricky. I could try stuffing in a 5th scale servo by relocating the ESC, but the linkage could get tricky, and it would raise the CG quite a bit.

So since I'm getting the NSDRC servo repaired anyway I decided to go a different route- can anyone guess?

 

[YourConfused]

Twin servos would be nice. Have you eliminated the servo saver or locked it somehow?

 

[pomplemus]

Update coming very soon regarding the servo(s)

Nope, not locked or eliminated. I was originally considering it, but it turns out the Treal 7075 servo saver and steering assembly is so incredibly stiff that it's unnecessary. The spring is crazy hard, possibly even too hard for regular bashing, even loosened up all the way with the washer removed.

Even outside of the truck and mounted in my bench vise, I was unable to get it to cam out until I loosened it up all the way. I've never noticed it engaging when running it, even when I purposely lock up the front wheels.

 

[pomplemus]

So I managed to fit two servos!

I have to give credit to to @arrma only fans for the idea, I came across this post of theirs during some late night googling-brainstorming how to increase steering power even more, and I couldn't shake the idea.

If you remove the receiver box and mount, there is actually plenty of space for another servo and mount if you drill the holes perfectly mirrored from the original location.

In order to drive the steering linkage, all that is needed is another steering bar/servo saver set. If the servo saver is taken apart and re-assembled with the top arm flipped 180° to mirror the orientation, everything lines up perfectly, with the the exception of a bit of grinding.

The turnbuckle rod end mounted to the steering bar will interfere with the shape of the servo saver arm, so some material will need to be ground away. I had to grind a fair bit to ensure no interference with the increased suspension travel this truck has. For this reason, I decided to go with an $20 aluminum Amazon special set to keep it strong and stiff enough.

I decided to relocate the receiver box on top of he top plate above the steering assembly- plenty of room up here, and it will make access a bit easier, as well as keep the weight over the front wheels. I 3D printed an entirely new box to make the best use of space and give me a bit more room for all the wires I want to stuff in there.

As for the servos- not just one, now twin NSDRC RS800 V2s! As far as I know, there are just about the best standard size super high torque crawler servos you can get, direct 4S powered. I don't think it would be possible to stuff more steering power into a Kraton, short of jamming in a 5th scale servo like @ColosTommy did in his 6X6 project Scylla.

I used some adjustable length steering links from a Revo (stock, cut down) to fine tune everything to get the servos synced up, and works like a dream, really flings the tires around now! These ended up being the weak link though, on the trial run the rod ends pullod off and bent. So I got some shiny aluminum ones for a Revo!

Pay no attention to the mismatched colors, it's just what was in stock that I could get my hands on quickly.

I temporarily powered the servos with an additional 4S pack, but long terms I'm going with 2X NSDRC 5A 16.8V voltage regulators to step down the 6S pack voltage, one for each servo. The 5A units seem to be more robust and keep a more stable output than the 10A model at 6S input voltage, so I figure why not go overkill on the servo power system as well.

A little messy now, still need to get everything cleaned up.

The steering so good now that the aluminum upper arms are a must, the steering block would otherwise twist all the way around under heavy steering load.