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MRC based micro/mini FOFF build...

89redranger

RCC Addict
Joined
Jan 25, 2009
Messages
1,577
Location
Bend
I'm not going to post up any lofty goals, lengthy story, or boring details. Just going to start posting pics of the parts as I go through them, and maybe get a little details for you guys about what it takes to give a car this small a serious attempt. Attempt being key here because, until the sand flies, it's all just theory.

Simple goals-

MRC based- How much will remain? Who knows..?

Small size- under an 8" wheelbase, 7" width, and on tires no larger than those designed for the Losi Mini T. Honestly, think straight-axle'd RC18/ProPulse/Mini Recon sized. Should be awesome for tearing up local construction sites, neighbors' flower beds, and backyards.

Lightweight- Shooting for roughly 1 1/2 pounds RTR, may end up closer to 2 pounds.

Low cost- The small lightweight nature of a build like this means it will require less for power, break less with said power, and cost less to fix if broken. In theory anyway...

So, starting with axle parts, here are the knuckles, c-hubs, and wheels slated for this build. I'll post up more pics, info, and parts as I go through it all. Remember though, I'm basically designing a rig from the ground-up, and this will take some time.


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These c-hubs and knuckles are designed around stock Losi MRC Pro or 3Racing CVDs, have built in 39* steering stops (limited by Shapeways' minimum wall thickness) which can be shaved further for up to 45* of steering, and give 16* of caster (double stock) with an 8* pinion angle and a completely flat servo at ride height.

The rear axle will consist of DravTech lockouts for the MRC Pro, the DravTech rear upper link mount, and Losi stainless straight shafts. Up next in the CAD program is a front servo/upper link mount.

Both axles will be stuffed with DravTech stainless spools, Exceed Maxstone 16 gears, custom pinion shafts, and some good grease. For the time being I will be working with the stock housing. I do have a housing designed and saved, but it would be quite a bit heavier, and will only be called in to play if the stock housings become a problem. As small and light as this will be, they shouldn't be a problem.
 
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BTW, a HUUUUGE thanks goes to Dravpnir for lending me his Wraptor model to modify for my own needs!
 
Here are a few teaser pics of a few mini bodies tossed over an old chassis and axles with a pair of Losi Mini T paddles mounted on modded RPM wheels. They're small, but match the axles perfectly. Actually, the ring and pinion are almost the exact size of the RC18 family. I really wouldn't want to push a tire much more than about 3" tall with this kind of wheel speed and power.

MRC Pro clear lid?

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Maybe a Baja Bug?

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For anybody wandering why the c hub and knuckle have a small recess around the bearing journals, it is because Shapeways has a 1mm unsupported wall thickness minimum for their strong and flexible nylon. On a mini knuckle the little lip (an unsupported wall...) that separates the two bearings is between .4 and .6mm thick. The lip in the c-hub measure between .8 and 1mm thick depending on the brand, material, and who was running the tools the day your parts were produced. It's easier to just design them to accept flanged bearings to keep them from sliding into the knuckle or c-hub with side load. If it weren't for the fact that the stock knuckles are only 6.6mm deep I would have designed the knuckles to accept a flanged bearing outboard and a larger 4x10x4 bearing to pick up a little beef. As we all know though, 3+4=7mm. That doesn't work in a 6.6mm deep knuckle.
 
High steer? How about a set of slotted 5 spoke wheels to drop a few grams? You'd be surprised how much one spoke extra per wheel totals up to over a full set of wheels.

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Servo/upper link mount done. Designed around Hitec's 225MG mini servos. While not enough for most rigs, this servo will probably be overkill for a rig this light and small.

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Next up...a chassis and enclosed gearbox. When all the parts of the puzzle are complete, I start ordering test pieces. From there I will make any necessary design changes.
 
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Got around to making some pinion shafts for these Exceed gears. Very easy to see the quality differences between these and Losi gears. Especially once DravTech stainless spools are added to the equation. The pinion shafts were custom cut because of a few differences that didn't allow Losi or Exceed pinions shafts at a level I was comfortable with. The shafts were cut from the necked down section of a Wraith long rear shaft, and the tangs cut to a slight press fit. Final install will use Loctite 648 for security.

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Mesh checked with grease after a little shimming. Perfect mesh, bevel to bevel, not too deep on the pinion depth, no noise, and butter smooth. Ahhhh.....

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I'm hoping that if enough people say that he may have some more made. They are a little on the expensive side, but ought to be pretty well indestructible.
 
looks to be a great start,subd

Thank you kindly!

Keep your eyes peeled though, as this build is about to grow a little already. I'm having a tough time fitting the drivetrain in the car with driveshaft and link lengths and angles I am happy with at anything under an 8.5" WB. A WB much longer than about 7 3/4" will be a belly dragger on these small Losi tires.

To top it off, I distinctly remember not being all that impressed with the Losi paddles on my Mini T. They just don't float on the softer sand under throttle at low speeds. They're trenchers! I like a tire that has a little more "lift" than "dig" in the sand.

My next option is a custom 1.5" wheel and Sand Scorcher paddles with a little grooving. If I still don't get the results I expect I will move on to the RC3WD 1.9 Sand Thrashers with a little cut 'n shut to bring them down to the 1.5" rim mentioned above. While the car won't be quite as small or light as I had hoped, this should be a step in a better direction.

New direction-

8 1/2" WB

8" max width

Modded Losi Mini T trans (tallest ratio- 20/50 pinion/spur X 2.6:1 internal ratio=6.5:1)

2lb MAX

3.5" tire max


Anybody else wanna play small scale sand slinger with me?
 
I'm currently building a foff rig based off of a redcat everest 16. Its a mrc clone. I am using the redcat axles and trans with mrc mip cvds. Im running a hobbyking 2445 3200kv with 2 2s 800mah batts in series for 4s.
 
I'm currently building a foff rig based off of a redcat everest 16. Its a mrc clone. I am using the redcat axles and trans with mrc mip cvds. Im running a hobbyking 2445 3200kv with 2 2s 800mah batts in series for 4s.

Where's your build thread?
 
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Borrowed some Tamiya Hornet rear wheels and tires to get a few measurements before cranking away at the cad program. Beings the tires are the same size as the Scorcher paddles I intend to use I figured I could give y'all an idea of how well they match the scale of an MRC. Please, keep in mind, this is neither Scorcher paddles or my FOFF build, just a comparison pic for size. Lol.

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Iguess i should take some pics and do some sort of a build thread. What is the od on those sand scorcher paddles?
 
so what ever happened to this build? I recently got 3 MRCs and was thinking about making one into a FOFF truck.
 
so what ever happened to this build? I recently got 3 MRCs and was thinking about making one into a FOFF truck.

It'll be a long term kind of build. In all honesty, it'll probably be next Summer before this thing sees the light of day. Designing your own parts is great and all, but it's fairly expensive and time consuming to do so. Thanks for the interest though, and I will post some updates as soon as I make more progress. "thumbsup"
 
looking forward to updates!!
i have a lot of mini parts and about 6 sets of axles and was thinking of this....
wanted to do a chassis like the BWD FOFF, but for the mini
 
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