[MOD] 42005 Monster Truck - Motorized RC (4WS-4WD )

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Hello everybody and let me present my version of a modified 42005 Monster Truck. It was my second set after my "dark age", that I've bought many years ago, after 42029 as supplementary set with a lot of useful pieces and planned to use for a live axle suspension and some other features for 42029 model. However, I liked the set as a simple and functional model and re-assembled it several times.

Here is the model and later I'll provide the all details:


A month ago, when I tired of infinite attempts to turn 41999 into a Muscle Car (the chassis isn't rigid enough, but I already did a great progress and hopefully will share it once) I returned to this model and set the task to motorize it adding 4WD, but keeping 4 wheels steering and current suspension (keep the original construction as possible as I can).

First, I've analyzed the all existing attempts that I could find over EB, Rebrickable and YouTube and it happens that there were several MODs by different authors:

  1. First of all, it's @Splat’s MOD with all steered and driven axles (see topic here).  I see no reason to duplicate its description, so let me just note that he saved the necessary features with adding Servo + L-Motor mounted under the hood and trunk. The chassis configuration is 4x4/4 or 4WD-4WS.
    It’s the best motorized model, I think, because of amazing simplicity and performance, but unfortunately it has a kind of “articulated” steering that isn't real, so was trying to made a "real" 4WD-4WS version, using this model as reference.
  2. Another one is Jan Dvorak’s (is he on EB?) MOD with all original features supplemented by on-axle L-Motor that drives the rear wheels and Servo for the 4WS. He added an additional 5X7 frame with differential that provided a necessary rigidness. The chassis configuration is 4x2/4 or RWD-4WS.
    Personally I don't like such a long axle sub-frame. However I've found a good idea of vertical gears inside the central shaft.
  3. The third one is @codefox421's MOD, inspired by Splat’s version, with the original front axle and non-steered custom rear axle with on-axle L-Motor. His custom rear axle, based on two portal hubs, is a quite compact and simple, but has no steering. The chassis configuration is 4x2/2 or RWD-FWS.
    It looks trial-ready with the portal hubs, but it's nearly impossible to add the steering here, so I got nothing from this model.
  4. An unusual @Tommy Styrvoky's MOD  with an interesting feature: he modified the front axle, not the rear one, by adding a solid drivetrain with worm gear and on-axle M-Motor, so result is a front-wheels driven Monster Truck with oversized fake engine. The chassis configuration is 4x2/4 or FWD-4WS.
    Very aggressive! WRRRRR :devil:
  5. Daniel Wirasantosa’s (is he on EB?) MOD that differs from the previous ones by using of chassis-mounted L-Motor that drives the rear axle (that has a bit low ground clearance due to the 5x7 frame) and, moreover, he used a custom steering shaft that comes directly to the steering rack. The chassis configuration is 4x2/2 or RWD-FWS.
    Starting this version, I got a more or less defined plan: 4WD with off-axle (chassis-mounted) L-Motor that drives the both axles through the existing “drivetrain” (former steering shaft) and the off-axle Servo that steers the both axles through the custom steering shaft above the driveshaft.

There were two more versions: Michael M’s stretched one and LEGOTechnic360’s solid-chassis version with no suspension, but they didn't help me with any new ideas. Nothing personal, guys, if you're reading it, I just had a full and consistent vision of my further MOD:

  • Hull - the original with no changes.
  • Axles geometry - original. I tried to save the all things like the wheels location, suspension mounting points, ground clearance, steering angles (that are even bigger a bit now)… And I still can't believe that made it, after a thousand tries!
  • Suspension - original, with no changes. However I put the hard shock absorbers in the rear end, as the default ones were too weak to keep the BuWizz battery.
  • Wheels - original. I decided to keep the original wheels and tires with no giant crawler ones or even Claas, that are too big even for a Monster Truck.
  • Frame - mostly original, but possibly modified since it will have an L-Motor and Servo mounted above the axles (right under the cargo platform and hood).
  • Drivetrain - it must be the ex-steering shaft that comes through the cardans inside the "big" ball joints to the both axles, connected to the L-Motor via the set of normal and clutch gears.
  • Steering - for the all wheels, like in the original model, but the steering shaft comes above the drive shaft, in parallel with it and can slide a bit while the suspension moves.

Enough the words...The most interesting part starts here.

Following my plan, the bigger challenge was to modify the original axles - I tried several options, even trial-like with solid axles, but 4WS provides an amazing maneuverability due to big steering angles, so axle diffs are likely vital for such model (solid axles were making a permanent clicking noise in the transmission even with motor stalling sometimes) and I decided to make a fast Monster truck, not a slow crawler with a high torque.

The drive train. There you can see how I did it: L-Motor rotates a set of 8T and 16T normal and clutch (required for the steering shaft) gears and then the main horizontal shaft, that were used for steering in the original model. After that the shaft rotates the 12T double bevel gears (ex-pinon gears from the original model), than 20T gears below, single-bevel 20T and the differentials.

As result, the gearing ratio is 1:1.667 X 1:1.4 = 1.2334, and provides about ~100 RPM with 15.12 N.cm torque.

The wheels connected by a wheel hubs, since I wasn't able to use the universal and CV joints with affordable steering angles, wheels position (I kept exactly the same position as in 42005) and rigidness.



The steering. Here you can see the servo (mounted upside down in order to provide more space for the battery block above, steering shaft that goes above the driveshaft, 12T gears (pinions) and 13L racks joined to the wheel hubs. In order to allow the suspension travel, the gears has 1/2L offset from the racks and slides together with the shafts along the mounting points when the suspension compresses. It's a fully legal, but still allowed in LDD and works like a charm!

The only mistake that the hubs must be from Claas, but they aren't presented in LDD unfortunately:23801.jpg



Just to explain why I used the clutch gears (but with no gearbox actually, ha-ha :grin:), the drive and steering systems intersects so hard, so followed TLG way and used the same solution that they did in the official models (42029, for example) - passed the one through the other. Green is a drive subsystem, blue - steering.


The Axles.

Here you can see how the steering shaft slides by 0.5L (notice the gap between the 12T black gear and LBG liftarm) - it provides about 1L suspension travel for the both axles.


Other images, the story of a modified hull (by Phil), LDD file and instruction in PDF are coming soon...

Edited by Void_S

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@Void_S - Nice work, and thanks for the detailed write-up :thumbup:

I like that you defined your goals up-front.  That is how I try to work too - set the parameters that I want to work within, and then keep building until I satisfy my initial goals.

You have a few interesting techniques, and although you have added some elements to the body, 42005 can still be recognized in there.

Have you built this with real bricks yet?  I'm interested to see how the sliding axle of the steering will work, and also what happens when the left wheel raises higher than the right (or vice versa).

Thanks for sharing.

Edited by Splat

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Wow... You did a lot of research on this one, and the renders are awesome! Good job! :thumbup:

There are stand ins made of several parts for the Claas wheel hubs. Check out the LDD of my Monster Truck because i don't remember how to make the custom hub at the moment.

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6 minutes ago, Splat said:

keep building until I satisfy my initial goals.

That's a literally satisfaction, to find the idea that finally meets the all goals and restrictions you've pre-defined. The body isn't fully original - I lent the "+2L" modification by Phil (he's not presented at EB, but I'll credit him appropriately in the second part of this story) just due to a great visual appearance. It didn't provide any possibility for the tricks that I wasn't able to apply to the original hull and chassis, but now it could be Ultimate 42005 in some meanings :sweet:

I did build it (but with some color vomits) and used as a test chassis first to debug the axles and transmission, and will share how the steering works once will have a bit free time: the mounting points aren't static (Part No: 15100  Name: Technic, Pin with Friction Ridges Lengthwise and Pin Hole) and rotates "when the left wheel raises higher than the right (or vice versa)". It was a surprise for me, but it really works! :tongue:

@Leonardo da Bricki, thank you, I'll check these hubs. Too bad that such a useful part isn't in LDD so far.

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