Drew's 4s rocketship

[Drew]

Pretty basic stuff here, but decided to start a build thread to go along with my newest round of upgrades.




Currently:

Box stock exo kit
Proline shocks with 40wt oil and stock springs
Some old trash hitec servo
MMP and old reedy 540r 6100kv 2 pole
15/52 gearing

I got bored with this real quick and ordered up a Castle 1415 2400kv, a 18t pinion and a trakpower 6800mah 70c 4s lipo. Goal of 70mph across a fairly smooth, freshly mowed field.

Last night I tore the truck down for this round of upgrades. I haven't had the problem yet but I already have heard of someone spreading the drive cups from a 4 pole motor. Back in my Baja days I used TR drive cups that had a collar welded on to the cups to keep them from spreading out.

I know Axial just released the CVD kit for these trucks but I'm not going to give up on the bones just yet. I have concerns about the small drive pin out at the wheels being able to handle a bunch of torque.

So, I made collars that press on to the drive cups, tomorrow I'll do the diffs.

I had originally planned on TIG welding the collars on so I bead blasted them to prep the surface. After machining and pressing on I no longer think this is needed. I will have to paint these now, no big deal.



Machining the collars. Since I am not marketing these nor would I be able to, I'll give out my dimensions. .625" OD, .469" ID, .300" tall with a .020 45deg chamfer on the outside to make it look pretty and to help the diff input cups clear the chassis braces.



Collars machined, one in the background installed.



And collars installed. These are tight enough I don't think they'll remove themselves, worst case I'll hear them jingling around on the bones and just stop until I can fix it. If they do seperate I'll slather everything with loctite retaining compound and put it back together. Set screws on the diff input cups are still easily accessed and should have a .020" gap between the knuckles/carriers and the cups.

[Old Ezra]

Looks good man. !!!!

[iStubz]

thats a great idea!!!
you should market them!!! (or atleast send me a set ;p)
I actually prefer the dogbones over cvds since I mainly use 2s

[Drew]

Originally Posted by iStubz

thats a great idea!!!
you should market them!!! (or atleast send me a set ;p)
I actually prefer the dogbones over cvds since I mainly use 2s

Thanks, not my idea though, just applying it to this buggy.

I'm not set up to do production stuff, but someone might pick up on the idea. Higher powered exos are going to need these and even if you go CVD you might want some for the rest of the drivetrain.

I'm planning on making some dogbones as well to handle the extra torque although I might trash a set of stock ones just to see what they'll handle. It might be nice to have something quick and easy to fix if something breaks.

[Old Ezra]

Originally Posted by iStubz

thats a great idea!!!
you should market them!!! (or atleast send me a set ;p)
I actually prefer the dogbones over cvds since I mainly use 2s

The only thing wrong with the bones is if you get a disconnect, they fly.....I've got a fix for that.....

[Drew]

Originally Posted by Old Ezra

The only thing wrong with the bones is if you get a disconnect, they fly.....I've got a fix for that.....

Only problem I had was with the rear bones. Threw in a set of front 96's and couldn't be happier.

Made a slight error on my sleeves last night and had to redo them. Measurements are now .535" OD .469"ID. The 4 at the wheels are .3" tall, the other 8 are .375" tall.

Paint is drying now, I'll assemble and upload pics in a few hours.

Battery, 1415, pinions and new steering servo shipped, should be here in a day or two.

[Drew]

Cups and sleeves painted and installed. Didn't take too many photos, yall should have a good idea of what's going on.

Time to swap center diff gears and start reassembly. New motor and stuff should be here by Friday.

I will need to slightly trim the pins on the bones to clear these cup sleeves, nothing major though, just a couple thousandths.

*EDIT* One other things I've failed to mention so far, since these press on and the cups flex a little the inside dimension I chose actually squeezes the dogbone pin slots tighter. They travel in the slot without binding and have almost no slop now. These might actually make the buggy run quieter. Also had to buzz .015 off both ends of the dog bone pins to get them to clear the new sleeves. dogbones move smoothly with almost zero slop now.

[Drew]

Motor, battery, servo and spring kits showed up today!

Got a few minutes to tinker but not much, have all day tomorrow to get it going and Sunday to break it. I did find out that with 4oz of ballast up near the radio box that the CG is about where it was with my previous setup. It is balanced left to right and about 3/4" forward of the first roll hoop on the cage.


Motor and 4s 6800mah 70c Trakpower, both of those should be cadillacing, the mmp maybe not so much.



Not quite out of space yet.



Test fitting the cage real quick. Looks like I'll have to modify the two crossmembers slightly, I'm maybe 1/8" from being able to bolt the cage down right there, everything else is golden.

[iStubz]

God damn hahah.
It's gunna be ridiculously fast...
Goodluck

[Drew]

Ran around today and picked up a few small parts to get it back together. While I was off picking up parts I stopped by the new local race track to meet the owner and check out the layout. While I was there he told me of his new plans to add a sand drag back behind the motocross style track. According to him there will only be 2 classes, electric and nitro and no rules other than that So, it looks like I'll have an option to race this if it handles like a turd.

I added a y harness to the MMP so I can easily plug in my castle link without having to disassemble the truck. I also picked up some big zip ties to use as a battery hold down.

I bent the roll cage tubing to clear the battery by slowly heating it with a heat gun and pressing with a tool handle until it cooled. It clears now and didn't distort the rest of the cage.

Wound up with 3.5oz of weight on the truck as ballast. 1.5 up front on the receiver box to account for the servo and 2 next to the esc to help get some weight on the back.

I set it back up with 70wt oil in the shocks with yellow uppers and red lowers on all 4. It sits pretty low still with 1/2" front preload and 1/4" rear, its a bit of a pig!

I wound up with 17/48 gearing for now. I'll change to 20/48 or higher after I blow up the diffs and get a chance to see what amp draw is on the controller.





10lbs of sh**

[Drew]

10 mins into 1st run with the 4s setup I tore a tire at 65+ MPH. Off to the LHS to pick up some 17mm adapters to run my DE trinidads and trenchers.

89* F ambient temp, 94* F batt, 108* F controller, 127* F motor. Need to pick a fan up for the motor.

I need to plug in the castle link and upload my graphs.

[cul8tr]

Which 17 mm adapters are you going to use? Thanks

[Drew]

Originally Posted by cul8tr

Which 17 mm adapters are you going to use? Thanks

Probably the AKA for the slash 2wd front. It should make the buggy just a little wider and might help with the occasional traction roll. I think slash 2wd rears would keep the width about the same with the 17mm trinidads.

[Theibault]

Originally Posted by Drew

10 mins into 1st run with the 4s setup I tore a tire at 65+ MPH. Off to the LHS to pick up some 17mm adapters to run my DE trinidads and trenchers.

89* F ambient temp, 94* F batt, 108* F controller, 127* F motor. Need to pick a fan up for the motor.

I need to plug in the castle link and upload my graphs.

That motor temp is fine. Castle motors perform best around 140-150f. Just keep them under 170f and you'll be fine.

[Drew]

Well, the LHS didn't have any 17mm adapters in stock, so I picked up a set of trenchers and threw them on real quick. The sand drag and mx track are still a few weeks away so I just went with standard basher tires.

Took a couple quick videos on my phone, had to run out of the house real quick before the sun went down and I forgot the camera.

Got about 35 minutes of runtime in before the motor mount slipped and I took all the teeth off the spur.

Time to order up a GCM mount and diff cups, axial HD gear sets and a hot racing 48t spur. I may try to run a 20t pinion with a fan on the motor. I hit 154* F at the end of the run.

*edit* Checked the batt after the run ~3.78v per cell all within .003v of each other. I don't think it would be unrealistic to get an hour out of this pack.

First vid is of me driving on a fairly fresh pack, 2nd vid is of my friend driving it a bit.

[Drew]

Did a minor teardown to replace the 48t spur I melted.

Found the rear facing center diff output tore the outside o-ring and puked every bit of oil all under the battery and motor, leaving the diff surprisingly spotless. Oh well, this is what I get for trying to do power wheelies constantly for 15 minutes (some of which were quite successful!).

So, used the 2 spare diff o-rings putting it back together and now have 20/50 gearing. Should be good for 75+mph wheel speeds. I might have to find a pond to run across

The stock motor mount cracked, then slipped away from the spur. Maybe I overtightened it, maybe its just too much power. I threw it back together to get some more seat time before the GCM parts arrive. I wound up taking a cue from my old gunsmithing days and slathered the dovetail and lower guide with loctite blue. This sounds weird but will help provide some extra bite to keep things in place.

Will have new (hopefully) better video tomorrow.

[Drew]

Got the exo back out today for another run, had a blast for a few minutes. I didn't have a chance to get the camera turned on before it was all over, but it now power wheelies like no other. The run was short because I keep having problems keeping the tires glued on to the rims. I might have to go with 1/8 buggy tires for high speed runs with it. Maybe I can use some beadlocks and still glue them.

I did wind up breaking the stock motor mount. I had overtightened it when I first got the kit and it had a tiny crack. Now the dovetail is in a few pieces, but what do you expect with enough power to wheelie at 50+ with 20,000 cst weight in the center diff.

[Drew]

Back together after 3 long weeks. Not giving up on the stock motor mount yet, I quite like the design of it.

New wheels and tires, m3 compound trenchers and J Concepts slash 4x4 tense wheels.
Installed castle blower to keep temps lower, didn't have any problems with this before but not reason to not have one.
Rebuilt center diff with 10,000cst oil to limit wheelies.
Going to try 22/48 gearing for somewhere around 85mph.
Had to set punch control to 30% to try to keep the front end down, its not fast if its dragging its ass.


Wound up taking off the rear body pieces, 70 mph power wheelies wound up tearing them all to hell.

Supposed to meet up with a photographer tomorrow for new pics and get some good vids.
Big thanks to LeMieux for hooking me up with some cheap takeoff parts.

[LeMieux]

looking good buddy! what wheel nuts are those? They look pretty slick. looking forward to some more vids

[Drew]

Originally Posted by LeMieux

looking good buddy! what wheel nuts are those? They look pretty slick. looking forward to some more vids

Thanks, I'm waiting for the video dude to call me back, trying to get a couple hours of vids in later today.

Those are the bolt on center caps that come with the Tense wheels. They still use standard wheel nuts behind the bolt on caps. I figure this way if for some strange reason I loose a nut it'll be retained by the cap. Really just extra insurance, I still use brand new nuts every time they get taken off and loctite blue as well. I've still seen the left side get loose after a good hour of bashing.

They also come with open caps to make it easier to change wheels and tires but being mostly a basher right now I don't need to do quick changes.