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Thread: RC8T based large scale build

  1. #1
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    Default RC8T based large scale build

    Alright, first post here - figured I'd post up this build I've been working on and off on for the past while. I don't race and only bash an RC8T, mini revo, and a micro t and was getting a touch bored with my RC8T. So what I've got here is a stretched RC8T with a slightly shorter wheelbase than the 5b. Anyways, to the pics.

    Here's what I started with: one RC8T electric conversion, a nitro RC8T that's in pieces in the boxes, losi claw MT tires on alum beadlocks, turnigy HV300 servos, and a castle 1717.




    Here's the cardboard chassis mocked up





    Used two driveshafts for the front center shaft


    The stock RC8T axles held up fine, but wasn't sure how well they'd hold up to nearly 7'' tires on aluminum beadlocks, and a ~14lb truck. Stock CVDs are 3.5mm diameter at the shaft (top), lst2 CVDs are 5mm diameter (middle) and mgt 8.0 CVDs taper from 5mm to 4.5mm I believe (bottom).


    The mgt 8.0 cvds were the right length (barely) and the lst2s were too long, but I needed to keep the buggy/truggy style stub axles. So I stuck the mgt 8.0 bone into the lst2 stub axle and it was a perfect fit. Just a note: you can't use the mgt 4.6 cvds for this as the the joint is a touch smaller than the 8.0


    Needed to get a motor mount for the 1717 I was using....so here's a team grid mount. Needed some grinding to get the 1717 in.



    Motor mocked up in mount with center diff


    And this brings us to the chassis. The layout is kind of weak, even after bracing it, but it seems okay for now.
    Stocker cut with a section ready to be spliced in with nuts and bolts


    Bolted in place


    Wheels tossed on to see how she stands




    I don't have access to a lathe and couldn't find a proper front center shaft, so here's how I'm extending stock center shafts with an mgt 4.6 cvd (perfect mate to the stock rc8t center shaft)



    Threw on a baja 5b cage and a bar in the middle to velcro hardcase packs down with


    Chucked on the rest of the stock parts and a knock off baja body and wing, and here's how she sat after the maiden run. The stock shocks were way too soft so I doubled up the springs - it looks awful but it did okay. Ran it on two 4s packs in parallel through a HK 150a esc. It felt lethargic, probably due to gearing, and my gearing choice is REALLY limited (maybe +/- one tooth on the pinion i have now )






    I love beadlocks, even if it adds stupid amounts of rotating weight


    Since then I've been reworking it a bit. Got some 3S packs, integy RC8T diff housings, baja 5b ss front shocks, and a spare set of mgt 8.0 axles just in case



    Baja 5b shock vs big bore RC8T shock


    Diff housing bling Should also keep that area free of flex


    Rebuilt the rear diff with ~30k oil....useless pic of diff here


    Needed to make a taller rear shock tower to accommodate the longer baja shocks. Problem is, there isn't a bolt on replacement that will fit nicely where the stocker goes. So I jammed two stockers together and this is what we got. The stock one on the bottom will see larger torques/bending moments than normal, but I think it'll be okay as the truck isn't too heavy (14lb) and I don't launch off jumps.


    Here she is mounted with the new rear diff and baja shocks



    I've since removed that rear sway bar and mounted the rear end onto the truck. I really like how the 5b front shocks worked out in the rear, so I've ordered another set of baja front shocks and other goodies. Waiting for those before I tear into the front end. It's been a very slow build, started last December haha.

  2. #2
    BYT Loiterer jakel's Avatar
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    Default Re: RC8T based large scale build

    to BYT!

    You've got a lot of work done on that build so far, pretty impressive. What gearing are you at now? 5mm Mod 1 pinion?


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  3. #3
    Team BYT crash dummy NickRummy's Avatar
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    Default Re: RC8T based large scale build

    Looks sweet! You definitely have some labor into it. I like seeing these custom builds. Seems as though converting to 1/5th is really catching on.

    Are you doing anything else to brace the chassis? I'd imagine it's getting some pretty serious flex and would probably not hold up to larger jumps?

  4. #4
    Bronze Level BYT Member got nitro?'s Avatar
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    Default Re: RC8T based large scale build

    Hmmm, very good build. But i think im getting bitten by the 1/5 bug as well, we shall see. Those baja shocks should handle anything you throw at it.
    Quote Originally Posted by NickRummy View Post
    Lower the center of gravy the better the handling!

  5. #5
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    Default Re: RC8T based large scale build

    I believe the gearing is 54 spur, 13 pinion, mod 1.

    The rear of the chassis is braced with the stock chassis brace and front does have some bracing on. I'll have to get a picture of it - it's extremely ghetto. I wanted to run it so I slapped on a piece of plastic across the top. The baja roll cage also adds a bit of stiffness, but there is still flex in it. I'm really not satisfied with the chassis as it is. Ideally I wanted to use a channel alum and make a chassis from that, but then I'd have to match all the little milled pockets that are in the stock RC8T (under the diffs, the steering posts etc.) chassis and I just don't have the skills for that.

    Thanks for the welcome!

  6. #6
    Silver Level BYT Member DragsterDragons's Avatar
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    Default Re: RC8T based large scale build

    I bet that's the first ae 1/5th. . The chassis definitly would need some support like braces or something .
    You never know though
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  7. #7
    Silver Level BYT Member mrgrimm's Avatar
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    Default Re: RC8T based large scale build

    Maybe instead of just little braces, try to think of a way to make a whole upper deck. Gonna be tough if you still plan on running the buggy body though. If you ran a MT body you could cover it, but getting the mounting and locations right for durability are going to be a challenge since there isn't much to mount to. Looks like the wa yyou fabbed up the shock towers you could use the original alloy towers where the shocks were mounted as good mounting spots for the bracing/upper deck.

  8. #8
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    Default Re: RC8T based large scale build

    I really want to keep the buggy look, and you're right, it is tougher to do the full top deck. Here's how the front is braced currently. Soft 3mm plastic plate from center diff to front bearing block. Then the stock front chassis brace is modded to tie the bearing block to the front end. Just changing that plastic plate to a proper 3mm alum plate will help some I figure. I have the aluminum plate, just haven't gotten around to cutting/drilling it to fit. Besides, there's cooler parts to work on like the suspension lol

    Close up of the front tie in...don't mind the scotch tape on the driveshaft, I have collars to replace it with


    Okay, so here's where the front ends at. The problem I'm going to run into is mounting the baja shocks. I can't use the stock standoff/clevis at the bottom, and mounting to the front or rear of the arm (like in some MTs and the rear of this truck) will put a good sized offset between the shock top and the tower....so more torque around the mounts there. I really want to mount the shock flush to the tower. I'm thinking of doing a clevis style mount using two plates to sandwich the shock end above the lower arm. Should be fun making those fiddly things with a hacksaw, dremel and drillpress. Any thoughts on this approach?

    I'll also need to raise the front tower (similar method as the rear)....and if possible, I want to shorten the shock itself. Probably just use internal limiters. Ideally I should shorten the shock shaft and body, but the baja shaft has a step down from 6mm to 4mm and I'd need a lathe to recreate that


  9. #9
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    Default Re: RC8T based large scale build

    Still haven't received the goodies I ordered nearly 2 weeks ago

    But re-did some parts. Replaced the total hackjob front bearing block with a one piece design - much stiffer. Also changed out the temporary plastic brace with an aluminum one. The overall setup is SO much stiffer now and I didn't notice any flex when lifting/pushing the buggy.

    Just waiting on the baja shock set before I redo the front end and get this thing out for another test drive.

    Really wish I had a bandsaw or scroll saw when making things like this...


    Bearing block installed with aluminum top plate


  10. #10
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    Default Re: RC8T based large scale build

    Mail lady came by with some goodies....shock O-rings, diff gaskets, baja shocks, RC8T CE front tower etc. Unfortunately, I couldn't figure out a way to get the baja shocks into the front section without shortening the shocks considerably. And I can't move the lower mounting locations out much further as that quickly interferes with the front wheels when they turn. So I've given up on baja shocks on the front for the time being, and now have a spare set kicking around....backup I guess lol.

    Anyways, I was playing around with the RC8T bigbores, and using the little sleeve that comes on the baja shock plastic parts tree, it's possible to get the baja springs mated to the RC8T big bores. The stock baja black springs are quite hard since they'll be compressed a ton when put into the RC8T shocks, so I'm waiting for the soft yellow baja springs I ordered 2 weeks ago - last package I'm waiting for. Once I get that, I'll have front shocks that don't look too bad.

    So in the meanwhile, I rebuilt the front end with the integy diff housing and RC8T-CE front tower. Just waiting for my yellow springs now.

  11. #11
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    Default Re: RC8T based large scale build

    Beautiful. On the gearing, can you get the smaller RC8B spur swapped on the center diff. ? Then just get the biggest pinion that fits, probably a 16t or 17t. I'm pretty sure the RC-8T had a bigger spur than the buggy and uses the same diff. cup.
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    Default Re: RC8T based large scale build

    Thanks!
    You're right, the buggy has 44 and 46T spurs. I believe I'm running the biggest spur, 54T. When I started the build I wasn't sure what to gear, so I tried to gear down as much as possible to play it safe. I'll be running 4S and 6S setups, so once I get this thing going, I'll play around with the gearing and hopefully find one that works well with both pack sizes. Or maybe I'll ditch the 4S packs (one has a weak cell) and just get more 3S...

  13. #13
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    Default Re: RC8T based large scale build

    Got some stuff from the states....which I ordered something like 4 weeks ago now. Anywho, mashed on the soft 5b springs and collars onto the RC8T big bores - gives them a ton of preload, probably far too much. But it will do for now.


    Overalll


    I haven't figured out a proper radio box, so that stuff was just velcroed to the top deck with the antenna wire velcroed to the roll cage. I was so excited to get it running that my hands were shaking .

    No video yet, I WILL get some. Did some speed runs up and down the street and the front tires balloon too much that I'm afraid they'll just rip on me. After the run I'm already seeing pieces of rubber shredding off the tires. I couldn't really keep the throttle pegged for long. Under anything over moderate braking the rear end just locked up on the street. The truck still doesn't feel all that fast even though I'm geared for 40 or 45mph. Geared for 40mph, the original RC8T felt faster (since it was smaller?). Maybe I should gear up...the motor sure as hell can handle it Then again, that speed is useless on the dirt.

    The change from 4s to 6s added so much pep to the 1717 motor. The thing kinda jumps if you give it too much - also cogs at start. Motor temps stayed under 45C after a pack of speed runs and loops in the dirt, batteries under 30C (I LVCd to 3.3V....I think I'll up it a bit to 3.5), and ESC was under 25C. Got maybe 20 minutes of run at best. I think I'll have to order a few more 3S packs. I was thinking the set of 4s and set of 3s would keep me satisfied....but I doubt I can go back to 4S now.

    Aside from that, the only problems I had were the front center drive cvd coming loose twice and lost a wheel halfway in but bolted it back on. But the rooster tails, clouds of dirt, and scream of brushless brings a smile to my face Also brings about a LOT of interested neighbors and their kids who watch. Gotta be real careful with kids around and a 16lb land rocket. If they want to see it up close I make sure to shut the whole thing down before letting them near it. Somebody was walking their husky by....the poor thing hid behind the owners haha. Good fun today.

  14. #14
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    Default Re: RC8T based large scale build

    Just finished charging one of the 3S packs. It's a 5000mah pack, but it took 5779mah from the charger. I know packs can take more in than they're rated, but this seems like a bit much. The packs were at 3.3V/cell after the run. I haven't charged the 2nd one yet, I'll do it tomorrow. Any thoughts on this?

  15. #15
    BYT Life Member chiefmasterbeast's Avatar
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    Default Re: RC8T based large scale build

    Great looking build. As for the batteries, maybe a mis-lableing
    Nah, he didn't slam into you; he didn't bump you; he didn't nudge you; he rubbed you. And rubbin, son, is racin'. -Harry Hogge (Days of Thunder)

  16. #16
    BYT Life Member E-savage's Avatar
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    Default Re: RC8T based large scale build

    nice work man! were a bouts in Ontario are you?

  17. #17
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    Default Re: RC8T based large scale build

    Thanks guys
    Charged the other pack yesterday....took 5550mah, a little more reasonable. Thinking of converting my two 4S packs to 3S when I get the time (one of them has a weak cell anyways).

    I'm in the Kitchener-Waterloo area.

  18. #18
    BYT Life Member E-savage's Avatar
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    Default Re: RC8T based large scale build

    6s would be really good on this guy, will really make it come alive! nd a little too south for me..

  19. #19
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    Default Re: RC8T based large scale build

    Yep, 6s was definitely nicer than 4s. I'd like to give 8s a shot for fun, but don't have an esc. The mambaxl is tempting, but I think I'll wait for another revision.

  20. #20
    BYT Life Member E-savage's Avatar
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    Default Re: RC8T based large scale build

    yea there having trouble with the esc I've heard...

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