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Wheel_Nut

Build Thread: Wheel Nut's 2WD Truck using a Lunchbox gearbox

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HI!   I'm Wheel Nut.    Welcome to my slow and boring build thread.   

Long ago I used to scratch-build model car chassis from FR4 sheet and aluminium sections.  So after a long break I'm at it again.

This project will have the following:

  • Custom fabricated chassis.
  • Lunchbox / Hornet Gearbox with 4-link conversion.
  • Rigid front axle with 4-links and a Panhard rod.
  • Wheels and Tires from either CC-01 or WR-02CB.
  • A Chevy Silverado body intended for a stadium truck.
  • Wheelbase will be around 260mm 

I've had this design on paper for a long time, but now I have the opportunity to cut out all the parts and hopefully just bolt it together. :D 

I may not reveal all the design right now, so it could to take a while to see all the elements come together.

So far I have only started marking out the lower chassis plate.

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Ooh, I am intrigued.  Custom builds are good.  This might even inspire me to finish my 4-linked Grasshopper truck build.

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This build will be more like a park and street runner than a proper monster truck.   Depending how this goes, I may adapt other Tamiya parts and build something with "Big Tires", to make it more capable off-road. 

There are obviously limitations for these builds.   To me that's just part of the fun.       If I wanted to buy a great handling 2WD truck, I could buy an Associated RC10T6.1.

One limitation for the Lunchbox based rear is the suspension travel.   My design will have only have a bit more suspension travel than a stock Hornet or other vintage buggy.   CC-01 chassis has similar issues.

I hope people will start to build more custom Trucks with Tamiya parts.   The world is in dire need of better performing Lunchboxes, Pumpkins, and other Grasshopper based creations!

 

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Today's progress on the lower chassis plate.   Battery retainer plates will attach on each side, but also need to be fabricated.

Next week I will cut more 2mm FR4 boards to create the chassis sides that will connect to the main chassis rails.

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Wow, looking good already!  Can't wait to see more.

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Thanks for the positive comments and appreciation. :)

Today I cut some more components:

  • Chassis rails, made from Aluminium channel section. Dimensions 16mm x 12mm x 234mm.
  • Mounting bracket for the front shock tower.
  • Central crossmember made from 1.5mm FR4  to brace the chassis rails to each other.

On the side view drawing of the chassis,  the tires diameter shown is 88mm, same as CC-01 tires from the Pajero Rally kit.   However I'm thinking to change to to WR-02CB wheels and tires.   The WR-02CB wheels should be a direct fit, increase the width and ground clearance, and probably perform better as well.   GF-01CB "Comical Avante" tires might be a suitable option as well.

 

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I am intrigued.  Your drawings are awesome.

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Looking good,  nice work . I can also appreciate your draftsmanship skills 

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Chassis sides have been added.   Pic shows the rear guide rods (aka radius arm) made up using heavy duty M4 ball links from G-Made.   Ball ends were trimmed down to make a link that is 40mm from centre to centre.   The rear guide rods attach to the chassis with M3 screws and a 6mm spacer.

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Rear shock mounts have now been added.   All the anchor points for the 4-link connection to the rear axle are now in place.   The 4-link arrangement will become clearer in the coming days as the rear axle will be fitted.  The two links at the rear that are not fitted yet, will locate the gearbox both laterally and vertically.  They create a hinge point where the links cross (intersect) with the 40mm guide rods to allow the suspension to compress.   They perform a similar duty as the slotted hinge mounts in the stock Lunchbox kit, although I hope to get some performance advantage.

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Nice work.

You clearly have an engineering and drafting background.

I'm looking forward to seeing how this progresses. B)

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Awesome , I think you need to work 24/7 so that we can see the end result  , can't  wait  :). Seriously though , great stuff .

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Wow, this build has got way more complex than I expected - top work!

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The gearbox was built up several months ago from mostly new parts.  I added a piece of aluminium angle to the bottom of the gearbox to attach the 5mm balls for the control links.  I am not 100% sure if its strong enough.   I used 5mm tamiya ball links and turnbuckles to make up the control links that locate the axle laterally and vertically.   The two links are roughly perpendicular to each other in a V-shape.   A similar function could be achieved with a vertical link and a panhard rod.   I prefer this V-shape linkage because it is more compact, and also because it moves the rear "Roll Centre" to be lower for better cornering grip.   I'm trying to avoid the situation where the car lifts the inside rear wheel when it goes into a corner.

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If I was a real engineer I would probably be doing this with CAD software.  So far I've always been happy to work slowly sketching ideas on paper and making lots of drawings.  CAD may be a better approach if I will make any further developments.   The last time I built a model car chassis was in the early 2000's, so its probably time to change.   Here is the "well-worn" drawing of the chassis that I used to figure out the angles and dimensions for the rear suspension.

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8 hours ago, Wheel_Nut said:

If I was a real engineer I would probably be doing this with CAD software

I'm old school like you

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One can extract more information from a detailed hand drawn sketch than a poorly executed CAD drawing.

Are you using Bluebeam for your markups?

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When I change something I just use the eraser and pencil, so its a problem if I want to go back!  Revisions would be a reason to use CAD.  I've been looking at some impressive projects that people have done with CAD and getting parts printed or professionally cut from Carbon.   So there is the "envy factor" of the convenience and more accurate manufacture.

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I've been working with the front axle assembly.   However I found there wasn't enough clearance for the steering links when fitted to the chassis.  I may need changes in a few places to make it fit.

The front uprights and hubs are very nicely made GPM components intended for GF-01, steering bell-crank is from Tamiya M-05 B Parts, and the aluminum steering post is from MST.

The photo of the assembly is delayed until I make some progress with the design changes.   

 

 

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If you turn the hubs upside down would that raise the links , then raise the bell crank if needed ?

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First step is to swap the knuckles left and right, so they will be upside down like you wrote.  Secondly I'm going to shift the bellcrank by a few mm to one side.   Thirdly I'll use another way of connecting the two tie rods together.   If I can't solve it tomorrow, I'll post a photo of the problem area.

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You can get a bell crank with two link holes in front to take the tie rods . The old Mardave Mini and Marauder had something like it if I remember correctly and also had a built in saver

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