Thread: 1/8 4-stroke Baja truck project (56K DEATH!)

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  1. 1/8 4-stroke Baja truck project (56K DEATH!) 
    For some reason I have failed to spam ya'll with this here project I'm working on. Seeing that I am pestering the rest of the internet with this thing, its only fair that you guys get to suffer thru it as well

    As some of you may know, this has been an on-going thing for the last 8 months; on-again off-again due to other things (like work and such), so in order to get ya'll up to speed I'll be starting off by bombarding you with all the old posts from other forums. So yeah, observe as your bandwidth screams for mercy

    OK folks, go to the bathroom first, this is gonna take a while.....

    Last edited by ThorBobRC; 05-09-2004 at 04:19 PM.

    For quite a while I have been playing with the idea of making me a Baja or "Trophy Truck" type rig; you know those beasts you see flying over dunes down in Baja. I knew that I wanted it nitro-powered, I had in fact purchased some power for it already last year, but I simply had no time to work on the idea. But now I figure its time to get cracking with it.

    The whole deal is still very much in the works, as a matter of fact it really only exsists on some scraps of paper and in my head (lottsa spare room in there ya see ). But I am now at a stage where I am ready to cut some metal and get the ball rolling. No pix yet (nothing to show really), but I have the following configuration in mind:

    - 1/8 scale using driveline parts from 1/8 buggy (yeah, my on-going luv affair with those sweet Hyper 7 parts)
    - 4-stroke OS FS40 powered, for some grunt
    - Independant front and solid axle rear suspension (sorta like the 1:1 rigs)
    - Combination pan & ladder type chassis (due to the suspension system requirements)
    - Most likely 2.2 sized wheels.
    - 1/8 scale Landmax Superflow F-150 lid


    I've been hard at work getting the engine mount squared away. I still have a few more tweaks to do before its ready to "show", but trust me - its weird....:lol

    As for the chassis, well its gonna be chunky enough! I snagged me some 5mm (!!) 7075 T6 for the pan section of the chassis, and if that don't do the job I don't know what will..

    I have not trimmed it down all the way yet, I prefer to keep it "rough" until I am 100% sure as to the layout. Usually easier to trim off extra material than to add more if you cut too much :lol . I have also made a rough-cut of a front bulkhead of sorts. It will serve as upper & lower suspension arm support, as well as mount to some additional chassis braces (yet to be done).

    And as you tell from the pix I have prepared for the mounting of the tranny. Yeah, its gonna be a 2-speed - a Monster Pirate 2-speed to be precise. And as you can tell its gonna be pushed ALL the way up front on the chassis. 2 reasons for this; first I wanted free space in the rear for the 4-link suspension. Second I wanted a good weight distribution, and this will push the engine mount pretty much smack-dab centered between the front & rear axle.

    And in order to do this I had to have the mother of all driveshafts - a whopping 20mm's worth of it :lol . I tried to make my own, but after several attempts I gave up on getting it 100% true - I REALLY need a lathe. Not to worry though, the excellent Mr Bill from RC Alloys whipped me up the perfect shaft. This baby will HOLD!

    Anyways - a few shots. Keep in mind its all SUPER rough - no smoothing, sanding or tweaking done yet. The chassis will be bother narrower and shorter when done.

    And the mother of all driveshafts:


    Ok, here's a minor update. Not going to explain it in any detail yet seeing that I'm still kinda uncertain about the details myself right now .

    As I mentioned earlier, this is going to be sort of a pan/ladder hybrid chassis (of sorts). The pan will be the main platform for engine & such, while a "spine" will both help stiffen & support the chassis, and provide some mounting for the rear suspension & shocks (I *hope* - LOL)

    So using some 2mm thick rectangular aluminum channel I had, I milled out some openings for the tranny & engine mount. This will be the "spine", and will run from the front bulkhead all the way to the extreme rear of the truck, beyond the rear end of the pan chassis.

    As you can tell from the pix its still very "rough", and I have not yet done anything to the rear section of it. The plan is to taper it towards the rear.

    Anywho - here are a few pix to give you all an idea of the overall weirdness of this design...

    The spine:

    And how it will sorta mount on the pan:

    To be continued....


    Finally have a front end of sorts done now. Not DONE done, but sorta done of course :lol . Using a lot of stock Hyper 7 parts here, as planned. Arms, knuckles, driveshafts are all stock. While I had planned (and started) to make my own shock tower I suddenly found that the stocker had the geometry I wanted...typical! I'm planning on using the rear shocks from the Hyper 7 up front for increased travel, as it is now the driveshafts are the limiting factor (as I pretty much thought they would).

    One minor difference is the mounting of the suspension arms. The reason I made that "bulkhead" behind the diffhousing was to slightly lower the pivot point of the upper and lower arms, they are now about 20 mm lower than the stock H7 set-up. Just for a bit more travel.

    Anyways, fairly straight-forward so no need for lots of hot air from me, here are a few shots of it:

    To be continued...


    Just a minor update.

    Figuring that this puppy might end up just a *tad* overweight, I've started shaving off a few ounces here and there. The good thing about having 5mm worth of chassis to work with means that there is plenty to go around :lol .

    So I milled out some 3mm deep "pockets" in non-critical areas. Right now I'll ballpark that its about 30% lighter than before I started, so every little bit helps!

    More to come...


    Okeydokey - moving right along after a slight delay (this whole "job" thing is really getting in my way - LOL)

    Finally got going on the rear suspension. Since it is the "unique" feature of ths truck I had already done quite a bit of pondering as to how I wanted it, so when I finally started work on it it was pretty straight forward.

    I wanted good "up & down" travel, OK (but not extreme) articulation and most of all I wanted to make it STRONG. So the first order of business was to get some industral-strength ball ends. I settled on some nice & beefy 5 mm threaded ones for the "chassis side" of the links, and some equally beefy captured ballends for the lower "axle side"of the link.

    I had decided to go with a 3-link set-up early on, since it seemed to offer the geometry I wanted combined with a nice & simple layout.

    So, on to the links...Oh, and beware that all of these are super-rough - I have not spent any time making the parts look nice & shiney. Plenty of time for that later when I have ensured that it all work - LOL!

    For the lowers, I milled a pair of aluminum links that I treaded the M5 threads on the ballends. I then milled slots for the shocks (yes, for link mounted shocks). The captured ballend on the axle end is made to mount directly under the rear axle thru a 5mm hole drilled in the axle housing. Trimmed down it will still give enough room for the axle (would be a bummer if it didn't, wouldn't it - LOL) Oh, and I "flipped" the hub carriers so that I would get a nice & "low profile" mount for the captured ballend (didn't want it to stick too far out).

    For the upper link I milled a "yoke" that would straddle the diff housing on the axle end, and threaded for a 5mm link to the ballend in the chassis end of the link. I pondered a few ways to attach the rear yoke to the diff housing, and settled on a 3mm titanium hingepin.

    To mount the lowers to the chassis I milled 2 blocks of aluminum that mount to the plate with 3mm screws. The blocks are drilled with for 5mm bolts that mount the links to the chassis. I then milled out a couple of slots to ensure full suspension travel.

    The upper link on the chassis end is finally mounted thou a 5mm bolt to the chassis "spine". The spine is trimmed in order to ensure good suspension travel.

    Articulation & travel seem good, just the way I wanted it. Here are a few quick shots of travel. Not "maxxed out" here, just to get an idea:


    After much pondering and lots of useful input I decided to re-do the upper links. Thruth be told I was never quite happy with the "yoke" over the diff. But I did want to retain the 3-link set-up.

    So going with conventional wisdom for once, I flipped the upper link. In order to do this, and get the single point on top of the diff housing, I first milled 2 brackets which I shaped to fit flush on the sides of the diff housing. The brackets where drilled for a 5 mm screw which would attach the single ballend.

    One the other end of the link I needed a set-up which would move up and down, but not from side to side. For this a milled a chunk of aluminum into a "T" section, with a 5 mm whole running thru the top for mounting to the chassis, and threaded for a 5mm screw in the bottom end for the link itself. The ends of the upper t-section where bored slightly to seat a bushing on each side to support it against the chassis walls.The link I made from stainless steel tubing which I threaded for 5mm screws in each end.

    While working on the brackets on the diff housing I figured I could try to integrate it with an axle brace. The brace would "lock off" the steering knuckles, and could help stiffen up the whole axle. I milled a one piece brace from 5 mm 7075 T6, and drilled it to fit suitable attachments on each knuckle.

    Turning my attention to the lower arms, I modified these slightly by expanding on the slots I had milled for the lower shock mounts. I milled these a bit longer in order to fit (if required) 2 shocks pr arm, and I milled them all the way thru (they where just "pocketed" before). I finished them up by tapering them a bit towards the ends and drilled & tapped shock mount holes.

    Upper & lower arms:

    And this is what it all looks like mounted on the chassis:

    OK - that does it for now..


    Time to talk about power..

    Lets see if I can try to keep this somewhat short n' sweet.

    - Engine(s): 2 x OS FS 40S-CX (pullstart) a.k.a Double-Thump
    - Flywheel(s): 2 x Kyosho 4-stroke (heavyweight) flywheels
    - Clutch: 2 x Kyosho Burns neavy duty clutch
    - Tranny: Ofna MP 2-speed tranny

    So, how to make it fit? Welp first off, 2 of these thumpers make for a heavy package indeed. A "conventional" layout would have pushed the engines to the rear of the chassis, making it pretty tail-heavy. Even worse, I needed some free space to the rear for the rear solide axle suspension.

    So, after some pondering I decided to hook the tranny up to the front diff with a small coupling, or if you will, the worlds shortest driveshaft (well, at least its the shortest I have laying around). Mr Bill at RC Alloys hooked me up with a perfect coupling.

    Long story short, this allowed me to plop the engines almost smack dab in the center between front & rear axle.

    OK, so now I have a nice front wheel drive set-up..what about the rear axle? No way I could hook up a driveshaft long and flexible enough to run all the way from the tranny to the rear axle. Well, hows about 2 shafts then?

    I found that one standard length axle would reach from the tranny to just about the rear of the chassis. With one more (same length) axle I would have the perfect length to reach the rear axle. Neat-oh!

    On to the engines. Wanting to fit it all inside a Landmax lid, and maintain a somewhat low center of gravity I found that a straight up & down install would not do. So I figured, well I got 2 engines - lets make it a VEE.

    So after a massive amount of trial and error (see post a few pages back), I made me a 60 degree V-mount for the thumpers, which allowed for individual adjustement (gear mesh), and which would serve as a mount for the coupling of the 2 rear driveshafts.

    Looks something like this:

    And with engines it looks a li'll bit like THIS:

    This will give ya'll an idea about the rear driveline. If anybody is wondering about the "slop" on the rear output (aft of the engine mount) thats where I'll most likely fit the brakes.

    Here the engines are installed..

    And here it is with the center "spine" installed..

    Still TONS of pondering & work left, but this gives ya sort of an idea....


    And here are a couple of shots showing it with the body I'll be using; a Kyosho Landmax "Superflow" F-150. Seems to suit it well so far!



    (FYI for those who might care; 2 mm 2024 T3 aluminum)


    OK, I'm gonna try to refrain from to much yakking (yeah, riiiiight..). Here comes some more stuuuuf..

    Time to show ya'll just what a whacky looking thang this truck is becoming. But hey, I warned ya'll - mostly function, not a lotta form.. Besides, oddly enough it seems like my somewhat "functional" approach has led to some similarities to the 1:1 rigs. No, not talking "scale" here, but layout wise its sorta on the same page...well, same book...oh whatever..hehe

    Lets run down zee list:

    Zee Cage: An attempt at protecting those poor (expensive) 4-strokes from my inevitable tumbles. Made to fit around the engines and inside the lid, will certainly break the fall in one way, shape or form. Made from 2 mm 2024 T3, excellent for box-structures like this. Lightweight yet very springy - same stuff we use in our fuselage skins.

    Zee Spine-extension: My way of fitting fueltanks and electronics into a somewhat overcrowded chassis. Fairly "tall" in order to fit these items without impeding on suspension travel. 2 mm (silver) c/f. Fits tanks off the side, RX inside rear of spine and RX batteries either inside or under the extreme rear of spine. Whacky-looking, yet very light & stiff. Connects to existing alu spine and cage.

    Zee Fuel Tanks: A pair of Hyper 7 Pro 125 cc tanks. Simple, eh?

    Zee Shock mounts: Really hi-tech piece of engineering; a whopping long 5mm threaded rod that connects thru cage and spine for extra strength. Will be modified a bit later, but overall layout is gonna be pretty much as-is.

    Zee Picture WARNING! This is ruff-stuff, ie no spit & polish. Do not be alarmed by nasty looking bolts and whatnot poking out everywhere. It'll get a bit better....

    Rear articulation aint to bad either:

    And with the lid on:


    The whole issue of steering has been on my mind ever since I started work with this rig. With the forward-mounted tranny and dual engines there is simply no enough room for a more conventional bell crank set-up here, not to mention finding a space for the servo.

    So after much pondering I decided that I wanted the servo up front, in front of the forward axle. However, I did NOT want to run the links & knuckles "pointed forward". Besides looking sorta odd (nothing thatís stopped me before :lol) it would leave the steering linkage and knuckles VERY exposed to any rock or solid object in my way. So I wanted a set-up with the servo up front, but with links and knuckles in the "normal" position.

    I found a suitable place for bell cranks right in front of the engine pinions, but was unable to find a ready-made bell crank that would fit in there. So I made me a pair of odd-looking bell cranks with what I had. I milled the arms from 5 mm 7075 T6 and fitted them to 8 mm stainless steel tubing. With an inside diameter of 6 mm these tubes would run perfectly on stock Hyper 7 steering posts. In order to fit the arms to the tubes, I tapped some 3 mm holes on the arms and installed some grub-screws that tighten the arms to the tubes. Seems strong, but it may have to be re-worked.

    I made a similar upper "input" arm that would let me run the steering link from the servo over the shock tower. I then milled a steering link from 3 mm 7075 to link the 2 bell cranks together.


    Moving on to the servo, I made a mount that lines the servo arm up with the input link on the bell crank. Its a bit of an odd looking thang, and will most likely see some changes. But it does the job!

    Here it is linked up:

    ..and when I start adding stuff you see why its sorta cramped there..

    More to come!


    Here's another mini-update:

    Servo mount V2.0:


    With the steering servo up front & the links and arms running on top of the forward bulk, I figured I'd try to cover it all up a little. And since I wanted a brace for the steering bellcranks, well I figured I might as well make some sorts of hood :lol

    I cut it from 2 mm silver CF (same as tail), and it connects the bellcranks to the servomount and out to the cage (not connected yet though).

    Yes, in really enhances the wierdness of it all IMO -LOL!

    In addition I'm doing some work to the rear section of the spine/tail. I found that I could drop the outer/rear part a bit without hampering the suspension, so figured I'd try to mount stuff a bit lower there (RX battery & such). Not done yet, as you can see.

    Anyways, here it is:

    And here are a couple with the lid on. Body is still not quite adjusted yet.


    Time to start with some minor details know - like brakes

    But first - the diet!

    Now that I have a pretty good idea as to where stuff is gonna go on this rig, I can start losing some of the unwanted weight. So, just to get the ball rolling on it, I expanded on the "pocketed" areas of the chassis. As mentioned this is a hunk of 5mm 7075 T6, ie: CHUNKY.

    By making 3mm deep "pockets" in certain areas the chassis is really losing some flab, and hopefully without much reduction in strength. Now I'd ballpark that it weighs slightly less than half its original weight.

    On to the brakes.

    Digging further into my pile 'o leftover Hyper 7 parts I came up with a pair of discs and calipers that I figured I'd mount to the engine mount (nice 'n sturdy). By keeping it "inside" the mount I'd figured I'd keep it from getting all wet & stuff, and it kinda keeps it all out of the way.

    As for actuating the brakes I went with a "plunger" type dealy, where I use a 3mm screw to push on the discs. This plunger will be moved by a lever of sorts (I think...)

    The "plunger":

    With discs & caliper installed:

    ..from the rear

    And on chassis with "center shaft" installed


    OK, here's a bit of an upgrade to the rear suspension.

    Considering the bulk of there here thingy, its quite clear that its gonna need some heavy-duty springage to soften its ride. I quickly found that a pair of Savage would simply be too wimpy, and that running double Savage shocks on each arm would take up way too much room. But a pair of shorter shocks might just work..

    So I went digging thru my pile 'o parts and came up with some GPM reservoir shocks. Not the best ones around, but with some nice thick shafts and heavy-duty springs.

    I made a crude lower "double mount" in order to fit 2 of these to each arm, For the upper mounts I wanted to reduce the shock angles a bit, while positioning each shock so that it would have the same angle to the arm as its "twin".

    I did this by milling some mounts from 5mm 7075 T6, which would "stagger" the shocks in order to give them the correct position vis-a-vis each other.

    Seems to work so far, so I think I'll be going with this. I may use some better shocks (like robbing the EDC-2's off my Maxx - LOL).

    Here are some shots:


    Join Date
    Los Angeles, California
    Holy ****

    Join Date
    Holy crap! That thing is absolutely amazing. What mill are you using to make that?

    Join Date
    Newport, Rhode Island, U.S.A
    OMG!!! Friggin amazing, nice job!!!!!

    Join Date
    Bras d'Or, Nova Scotia, Canada
    OMG, that is quite a piece of work, i admire your creativity and commitment.

    I'm so far behind I think I'm in first!!

    Thanks for the kind words guys! I'm still tinkering with it, hoping to get it all up and running soon - gotta hate it when work gets in the way of your hobby - LOL!

    The mill is a vertical mill from Sherline.


    In order to break in the thumpers, I used the chassis to make me a sorts of uber-hi-tech testbench:

    And good LORD whatta sound they made! Hard to discribe, but I had every one of my neighbors trying to get a glimt at what was going on!

    I do have a fairly cruddy avi file, taken with my Canon (still) digi, does not do the sound justice, but it'll give ya'll an idea! And sorry about all the shaking, I was trying to run the engines while filming. Oh, and the file is like 9MB (sorry, dunno how to compress these things yet), so you want to right-click, "Save target as".

    Double-Thump Test


    Join Date
    Los Angeles, California
    He is a "Aeronautical Engineer" that explains the A++++ Work ....

    Join Date
    Seattle Wa.
    Sweet scratch built. You are familiar with current off-road desert racing design. We ALL want to see it up & running!! De-bug it(if needed) and sell your design and buy some waterfront property!!!
    Looks like a mini-Herbst racing truggy!!!

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