1/10 4WD build

95PGTTech

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396
One thing I've been working on is the rear diff input - unlike the front that leaves the stub of the pinion outside the case, the rear just has a huge bearing and the pinion is a female and accepts the back of the shaft of the slipper clutch (or optional center diff). I have another front pinion, and both ring gears are identical, but the outside diameter of the pinion is 6mm and the bearing race is 18mm. My solution was to put a 6x11 bearing inside a 11x18 bearing, and sandwich them between two 18mm OD washers (I forget what the original ID was, but I drilled them out to 6mm.


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I ended up putting it back and forth together a bunch of times and I ended up adding another 6x10 shim underneath the pinion to get the R&P mesh a little tighter to where the in and out endplay of the pinion matched the front.
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I got a set of Arrma (aftermarket knockoff) diff cups and drilled them out to 6mm ID. the hole in the stock Traxxas pinion isn't big enough to accept a set screw from the Arrma diff cup, and I'd like it to sit closer to the housing than where the hole would line up, so I think I'm going to end up cutting this pinion down and just putting a new flat on it to accept a standard set screw setup. On the ground, what I have now rolls pretty smoothly. I have zero clue how much freeplay the dogbone that goes into this cup should have, I know from previously with the ECX it shouldn't be bottomed out tight.
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So the point of all that is I can now transfer power from an Arrma 116mm dogbone to the center diff setup I want to use. Once I finalize where it's going to live, I'll cut out that section of the center tunnel so I can mount it flat on the chassis. I picked this for now because it puts the motor as far forward (front left) as possible. I did some quick measurements and ordered a 102mm shaft for the front. I'll try and cornerweight it when more parts get here but I can't see a scenario where putting the longer shaft up front and moving the motor and center diff more backward actually helps me. Getting that weight forward was really the tiebreaker between going this way or doing a XO-1 style setup with a slipper/center diff right off the rear diff and the motor mounted back there. I ordered a Tekno RC big bone center shaft kit too so I can see their diff cups and if I could make them work.
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95PGTTech

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Messages
396
Front steering/subframe/diff as received from Jennys, installed, shock tower
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The old donor setup from the last version of the 4x4 Ruckus
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One question I have is this area on the front steering brace seems like it would be ideal placement for a sway bar, but the XO-1 exploded diagram does not indicate the vehicle has one. I can't really see in videos of anyone having one, anyone have any idea what this is for?
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Hung the arms, it looks like there should be plenty of suspension travel if I can get the shocks set up on it right
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Other than I can't get the inner axle shafts off the old differential (the little 1.5 allen screw the tool broke off in it on both sides!), front went together well. With the suspension at full droop, because they are a universal joint design there is some binding, so I'd really like to get away from them anyhow, but I need to get them on here at least for mockup. I'll probably just take the easy way out and go with XO-1 shafts for now, but Tekno is also an option since I have 6mm capable hubs front and rear.

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95PGTTech

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Messages
396
I weighed the old chassis with the battery, motor, motor mount, steering servo, etc. on it and put some batteries on the new one that matched the same weight to get some idea of what ride height may be when loaded. I'm not terribly upset, but it definetely gives up ground clearance over the old setup.

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The center differential is in approximately the final location, so I cut out some of the tunnel to start getting an idea on driveshaft angles and how much more cutting I'm going to need to do. The motor is going to be located in the front driver side section. Battery size and placement will be the next major hurdle. I want to begin with at least 4S on this. Clearancing for the big ring gear on the center diff is going to be needed unless I can find a smaller one. Removing this obviously introduced a slight amount of flex to the chassis, which I'm hoping will be removed with a brace between both towers and the center diff.

EDIT: Found a 46T spur, ordered it. I'd rather not have to cut the chassis to clear the spur and have it sticking out underneath. The spur was also the thing closest to the battery during mockup. I'm sure I will be able to adjust through pinion selection.

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95PGTTech

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396
Front and rear slash shock towers arrived, installed. They are MUCH thicker than the XO-1, but I need to work on the offset of the shocks in front...they hit the big camber rods. The XO-1 has huge offset spacers to clear this.
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The Arrma 46T center diff spur gear came in too. I was excited, it was 4mm less diameter around and thought it would work great...until I took it apart and realized it won't work. After much digging, I think what I was sold as a 6S BLX (regular) diff is actually a 6S EXB diff. Completely different bolt pattern, much larger output drives. The only anything I can find for an EXB diff is a 44T in China. Whatever, better than cutting up the chassis more and having the spur sticking out underneath I guess.
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The RPM rear bumper also came in today, but after going 0/2 I think I've had enough pain for one day. Oh, the joys of custom.
 
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95PGTTech

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396
102mm came in, it's pretty close to fitting just laying everything in there, so I marked out the location of the center diff and got to cutting.
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I didn't have a lot of room to miss drilling holes so I made a template. Really helped. Countersunk m4
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Used the XO-1 offsets on the Slash shock tower, best compromise I could make. Offset the bottom of the shock too to give those big camber arms a little room to work
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All in and seems good, but driveshafts feel a little tight. Don't sit all the way into the cup on the center diff but I guess it's supposed to be like that (unmodified center diff to unmodified driveshaft)
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Front and rear have maybe 2-3mm free play, didn't really sit into the diff cup all that well because of how far the Traxxas output shaft sticks out into the center of the diff cup, so pulled them out and got to work. Drilled new bosses for the set screws. Re-shimmed the rear again, when I had tightened up the case I didn't like the mesh anymore, happy now. Rolls freely without binding or noise now.
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95PGTTech

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Messages
396
RPM rear bumper went on fine except for the bottom mount (the one that holds the hinge pins in LOL). It needs to go where the XO-1 subframe is, so I'm going to need to remake the lower mount myself.
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Clearanced the left rear corner to start fitting stuff. Got the GNSS box mounted and the chassis notched a little so I can plug in to charge it without having to remove it from the vehicle. Cleranced the center tunnel a little more for the rear driveshaft.
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Just a follow up on parts that took longer to get here. EXB diff cups don't work either (out of the bag directly) they are 5mm but in a D shape so it would actually be harder to drill them out than the BLX ones I used. Tekno RC ones for the Slash won't work, they accept a 6mm dogbone not the 8mm dogbone of the arrma. It would be neat to not have to modify the slash pinion shafts like I did, but even if it did work it would be real close on driveshaft length. I did learn from them they use an o-ring which I may end up doing on the Arrma cups. Scorched makes a 6mm bore 8mm shaft cup, but its going to take a minute to get across the pond.
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95PGTTech

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Messages
396
Changed up the GNSS a tiny bit to give more clearance to other components that will need the space.
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More cutting up of the OEM chassis, this time to mount the steering servo. It was either this, or mount it outboard behind the right front tire (and to make matters worse, the wiring harness would be facing forward).

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Searched far and wide for an aluminum mount that I liked, finally found one from Redcat. It's listed as an Everest-10, I've never even heard of that model. I had to trim the servo just a tad to run this "reverse" mount. Originally I was going to cut the tunnel more and run the bracket underneath the servo to the center, but this way kept me from having to cut more and it kept the bolt holes in the meat of the chassis - mounted to the center it would have been very close to the already cut out tunnel. I have a 20kg servo on the way, my wires are too short from the old setup for this one. I'd also like to manipulate the horn a little more to get the steering arm as parallel to the chassis midline as possible. The arm I just stole from the old build - hey, an actual ECX Ruckus part! LOL! (well, actually, an aftermarket upgrade replacement of a stock ECX part, but I digress). I had to countersink the mount right out of the bag, they used button head screws that wouldn't allow the bracket to fit flat against the chassis.
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Trying to get everything neat and organized. That's a 3S battery, my 4S won't fit until the new spur arrives. It does clear, but we are talking a couple sheets of paper of clearance I don't want the battery and the spur going out on a date. 3S will be more than enough for test drives. I don't think that receiver location is going to work, I plan on running a 74mm long motor (that's a 50), but again, for a first test drive it's fine. Front driveshaft to steering servo clearance is excellent, something I didn't think of until reassembly but got lucky. On the bench, steering works well. Had to turn it down a bit with the endpoints, hence part of the reason going down to 20kg. 25kg was a little "twitchy" on test drives.
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95PGTTech

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Messages
396
Got the steering finished up and took 4x4 version 3.0 for basically the same drive I did for version 2.0 when I redesigned the suspension and driveline…like a grandma. Nothing flew off or failed catastrophically, which is a huge win. Now comes the process of looking everything over, figuring out what needs reworked, and buttoning up everything not done.


Yeah, I wanted to rip it. But I have no wheelie bar on it, no loctite on a single bolt, no fluid in the diffs, 4 axles that seem like if I look at them wrong are going to the moon, and in most cases 1 bolt where 4 are needed.

I’d be really interested in seeing if there is any differences in the drivetrain. Same battery, same tires, same motor and ESC - and see if there is any speed difference. I’ve long suspected I was losing a lot in the ECX slipper and diffs
 

95PGTTech

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Messages
396
One major problem noted from the test drive was the double bearing setup on the rear diff did not work. Not surprising. No one makes a bearing with the ID and OD necessary to run one bearing here. The outer bearing walked, which make for a lot of side to side eccentric motion as the diff cup rotated - not bad enough to cause an issue at a walking pace, but if I send this thing 50mph, it's going to shoot parts across the lawn. I changed up the shim setup to use a larger outer diameter washer to hopefully prevent this problem from occurring again.

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I have still been ordering differential cups trying to find a 6mm input shaft/8mm driveshaft setup. I think this one was from a Revo, measured 7mm on the input shaft and 10? on the driveshaft.
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20kg servo arrived. xacto knife indicating the point i was talking about needing to be removed to run this in reverse mount like i have it.
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RPM wheelie bars arrived. Still useless until I can figure out a bottom mount solution for the rear bumper
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95PGTTech

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Messages
396
one of the last major pieces that need to be fabricated was a tower-to-tower brace. the stock ECX 4wd has an upper chassis "spine" that has two bolts to each diff and a series going down the center tunnel and the driveshaft rests in between (kinda like a slash). Obviously I can't run that. On top of that, I cut a lot of strength out of the lower chassis making room for new components.

I hadn't intended on it going this way, but I just chopped up the XO-1 brace to start taking measurements and get a starting point and it evolved from there. The overlapping actually nicely accounted for the front diff being slightly taller than the rear one.
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I tried to be super cute and drill and tap the two of them together, but my HF quality m4 tap decided to break off in a hole. Just being a mockup/trial piece, I said screw it, left the broken tap in it, and through-bolted some other spots.
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One thing I really wanted to do was tie in the motor mount/center diff mount. Space is a premium, and although I'd like to, I'm not sure I'm going to have the room to run a tower-to-chassis brace at each end. By ditching the stock Arrma plastic center diff cover, I'm able to get a piece of aluminum in there to act as a diff cover and bolt to the new spine. Significant clearancing of the new piece necessary to clear the spur (smaller diameter 44T is on a boat in the Pacific somewhere).
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not sure how well you can see it, but the center diff does not have adequate bearing support/races because of changing the top plate so it moves around under power. ordered https://www.amazon.com/dp/B09MS3LWJT?psc=1&ref=ppx_yo2ov_dt_b_product_details to try and resolve this. Eventually, I'd like to use a complete billet adjustable motor mount/center support setup like the one from PPS-RC, but I've learned the value of mocking up with cheap Chinesium parts.

Regardless, even with just two bolts out of the four from the center diff/motor mount brace to the new spine/upper chassis/tower-to-tower (whatever you want to call it)...WOW...stiff. Not only took all the flex out of the two diffs at the end of the chassis, completely eliminated any of the twisting action that was so apparent after removing so much of the stock "tunnel."

I'd really like to run a complete one piece center diff support like this
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but these only seem to be available for the older kraton versions and not available in the size I'd need for a v5 exb.


next steps are to get those bearing supports in when they arrive, drill the other two holes for the center support, then blow everything apart and reassemble with proper hardware, loctite, and lubrication in preparation for an actual test drive. additional bracing and body mounts are on the fabrication list, but won't prevent moving forward at this point. front and rear bumpers as well. I'm leaving the axles be for now, I still haven't decided if I want to stay something telescoping like MIP or the XO-1, or just go all out for the Tekno fixed length dogbones - they *should* work, I'm using stock-length Slash arms.
 
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95PGTTech

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396
Vivaton 29mm (EXB) spur is here. 44T versus the 50T that was on it. 47mm OD vs 53mm OD
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One immediately noticeable problem is the pinion I have on it (I think its a 14T) isn't large enough to mesh because of the motor mount geometry. I ordered a set of bigger options.
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But it picks up the clearance that I needed, by a mile
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Those bearing races arrived (and the aluminum center support). With the top plate I have now ghetto rigged on there I have no way to bolt the supports to it, but that proved to not be a problem. They stayed in place all on their own due to how the parts are machined.
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95PGTTech

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Messages
396
Got the upper center plate thing I have rigged together drilled for all 4 bolts for the center diff support and installed. I needed to make ESC extensions for this 3674. I have a 3652 that has wires that are long enough, but I'm really trying to make an apples-apples comparison between this driveline and the last one before I do anything else. I want to try and run this on 3S and 4S with the same motor, as close to gearing as I can replicate, same tires as the last setup - my theory (my hope) is that I was still losing a significant amount of speed through the slipper clutch and the differentials I was shredding. I'm hoping it may also help me to decide what weight oils to use in the center diff and where to move the large amount of adjustable weight I have on this rig in order to make it work as best as possible, before going and adding more power. The 44T spur also required me to go to a 18T pinion to get the gear mesh I wanted. I could have stayed 17T, but it was a little too loose for my comfort. Something like a 47T maybe 48T spur would be ideal here, but one simply doesn't exist for EXB center differentials at this time. The old ECX spur was 45T, I would have to look up what I was running for a pinion. I want to say 14T off the top of my head.
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The 44T does clear the 36mm 4S battery, which was one of the space concerns for it (bottom chassis plate and spine were the others). Its hard to document, but there is roughly 3-4mm of clearance. I was able to fit two zip ties between the teeth and the battery. I monitored this clearance closely throughout the day, and there were no witness marks on the battery at the end of the day, despite a few rollovers. The battery will need better forward/rear control.
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Found the receiver its new home, zip tied some wires better to clearance the driveshafts. Set the steering endpoints (they are really short on the XO-1), and we are ready to go crawl around more.
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Adjusted the rear ride height to try and level it out a little. This is how it sits in very, very short grass
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It was raining and the lawn was freshly cut, so just took it out for five minutes or so and gave it 25% throttle. Literally trying to see what will fall off or fail catastrophically before we start sending this thing real speeds. More or less went well, was fairly easy to drive. Steering is a bit touchy for my taste. I think I'm going to give it a bunch more front grip to help with the massive oversteer and find a way to slow the steering rate down. At the end of the run when I was driving to the garage to blow off lost steering entirely, turned out to just be the bolt that holds the steering arm on backed out. Front left camber arm popped off the ball too. It did pretty well for me rolling it a few times on its lid. I have nothing to offer as far as speed or power, the Trenchers on the back aren't great on grass on a good day, let alone when it's wet. I finished driving with a smile, it's going in the right direction. Now it's time for a complete teardown and rebuild, putting correct hardware in stuff so we can actually go out and make some hits with this thing.
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95PGTTech

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396
It has been an up and down few days of testing (more ups, luckily). I had a chance to get it out much later at night the same day as the last for a second session (I didn't have enough free time to tear it down and do anything meaningful), and it did well, though the ESC got a little warm. When we took it out just to walk around our daily walk of the property that we do, it actually hit the thermal cutoff. Of all the things we weren't carefully inspecting with basically a ground up build, I never would have thought to really watch the motor and esc temps (I'm talking about fifteen minutes of 10% throttle walking speed). I pulled the motor wires out, and two of the extensions were bent really badly at the banana plug.
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I resoldered them and put new heat shrink on and ran it again, this time 5 mins or so at 25% throttle, checking often. No real change to be honest.
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You can actually see where the ESC got the wires so hot it melted some of the solder and dripped down. These are 4mm banana on a 12AWG wire, and the wires or the wire extensions do not get hot, just the ESC. I did some reading and people were saying it's the low throttle position coupled with the really tall gearing, on grass, now with the bigger front tires (I swapped to Trenchers at all 4 corners to see how it affected the handling). Previously when we had too-much-drag problems from grass, it was the motor that would get hot not the ESC. Motor is barely warm to the touch, 95F on the gun.
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Changing the gearing really isn't an option, I'm limited on both pinion and spur by space constrictions. This is about the "shortest" ratio that will fit. I decided to relocate the ESC to an area where I could completely eliminate the extensions, I put a 3S battery in it instead of the 4S, and I went out and found a nice empty parking lot to run it (less rolling resistance). I also tried to get in some higher throttle positions, internet info was saying low throttle builds ESC heat). so I just rolled into it at speed. A little barrel roll from not having enough brake ejecting a shock bolt ended the session, but I got 10 or so passes in. ESC still got to 145 on the gun, but took a lot longer to get there. I'm inclined to say the car is just overgeared for the combo in it right now. Overall though, did decently with some steering adjustments, and having a rollover at speed like that and nothing catastrophically breaking is encouraging.
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Put it back together at home, ran it on grass and basically confirmed the diagnosis. It does better for sure on 3S. At one point, hit a decent bump and the XO-1 front protrusion dug into the ground at speed, sending it cartwheeling. Other than breaking the nose, it bascially ripped the bolt that holds the front pin retainer in (it only goes into plastic in the diff) on both the front and rear). So I need to add find a solution to that, plus stiffen up the front suspension (and try and raise it).
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95PGTTech

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396
We found the missing nose piece LOL

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We also began to have an issue with the rear driveshaft popping out. What was odd is that there wasn't enough play in everything to move it back in, I had to unbolt the top chassis brace and loosen the diff from below to get it back in both times

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That's when I noticed the missing screw out of the rear tie bar and took everything apart to look. What was happening was once the rear tie bar was loose, the diff case was seperating in half allowing the pinion and the diff cup to slide backwards out of position, creating enough room for the driveshaft to slide out. This is the downside to shakedown runs when everything isn't bolted up 100%...if I had all 4 bolts in the diff housing like it should have been, it wouldn't have been relying on that one single m3 tie bar bolt at the bottom to hold it together. You can see where the diff housing took damage as the pinion, bearing, and diff cup got loose and came out of round. I threw some red grease in there while I was putting it all back together.

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Having learned my lesson and having the rear apart now, I drilled and tapped the diff housing bolt holes out to m4 so I could run one real long bolt from the bottom to sandwich the chassis plate, the diff mount, and the diff housing together. There are now 4 bolts from the underside (two for each half) and two m3 bolts at the top holding the housing together, and it hasn't been a problem since

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Despite finding these "little" issues, it's going pretty well. We managed 37 on grass, which is right around where it was on 3S and 4S on the stock style drivetrain. The damage from the rollover that broke the front nose I think knocked the front control arm pin plate out of whack too and pulled the threads out, because we would later lose it somewhere in the grass. Being that the gearing is not optimized, I would say absolutely we were losing speed on the stock style stuff because parts were clearly not holding up to the power. This is the same battery, same motor, same ESC, same tires, even same crappy axles, only difference is center diff vs slipper clutch and the front and rear driveshafts/diffs. I would suspect we are still losing something in the slop still in the center driveshafts and the terrible axles on it now. Someone is pretty pleased with our progress, we found a new big spot a few minutes away from his preschool.

IMG_5847.PNG IMG_5851.JPG


Going to do another teardown and fix some small stuff, hopefully next time out we are making full power passes.
 

95PGTTech

Well-Known Member
Messages
396
A lot has been happening lately with life and I just haven't had time to keep the thread up to date. While looking for other stuff we found a killer local deal on a max8 + 4274 2200kv combo. A few scratches on the can and a decent dent in one of the caps but appears to function fine. Made up a quick bypass for the second battery connector, just going to put it on 4S for the time being.

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I drilled out the factory Arrma motor mount to 9/16 to accommodate larger pinions. I had the slightest witness mark on it from the last one and didn't want to wait until it was a real problem before doing something.

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Fitment is pretty decent, we factored a max8 in when doing the original layout. Probably could get a 85-87 length motor in this max.

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Took it to the park where we've been doing our speed runs, 45mph and barely warm to the touch on 4S. Pretty happy with that, time to blow it all apart and finalize stuff, zip ties aren't a realistic long term fastener.

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Video of the 45mph pass
 
Last edited:

95PGTTech

Well-Known Member
Messages
396
Corner weighted the car just to get an idea of where we are at. I built in a considerable amount of "movable" mass to be able to fine tune the car. On big power, wheelies have always been the enemy of this chassis previously it lifts the front end which baloons and explodes tires and grenades the front ring and pinion. I'll probably end up ordering the SkyRC set, but mom had these two scales around anyway for baby formula/food mixing stuff in the kitchen. There is no ability on the scale to zero it, so we took some time and cut two equal pieces of wood down to the same weight. The scales measure within 1 gram of each other. Wood is 90 grams for reference.

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1948g front, 1906g rear (including the wood)

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If I move the battery back farther by removing some of the area for the old motor mount and slipper clutch, I can get it to 1930g front and 1927g rear.

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Left to right, as expected is 1919g right, 1885g left. I doubt for what we are doing this will have any factor. I'm not getting too caught up in the specific numbers, I'm just looking for a front/rear and left/right balance idea out of this. I'll run it as is, the simplest solution is add weight to the left rear.

IMG_5943.jpg
 

95PGTTech

Well-Known Member
Messages
396
Haven't updated this in a bit. We have been mostly concentrating on James 2WD car. The 4WD is under a major renovation. Most of the major architecture has been laid out to move forward, we need to pick and mount batteries and finalize the steering servo mount in order to continue moving forward. Realistically, with the weather we have here in NJ it's likely going to make its first test hits in spring with a goal of 75mph on 6S.

I did end up replacing the blown capacitor with some help from my brother who is a robotic engineer and is generally much more knowledgeable about how electronics works and how to service them (my background is all electrical). Long story short, the exact replacements for these were 2 months away in China so we found a Panasonic capacitor of the same capacitance, voltage, and diameter. It's a little longer. Very, very carefully removed the epoxy that holds it in, broke the old one free from the board, soldered in a new one, and poured new epoxy. I had to dremel away part of the outer housing to get enough room to get even my smallest pencil tip in on my Hakko.

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I don't have a vehicle currently capable of throwing this and the motor in to see if it works. I bench tested it with a motor, and it seems fine via the DVOM. I really didn't notice any problems running on 2/3 capacitors, they are really there to just stabilize the voltage going into the board it doesn't "boost" performance in any way.
 

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