[MOC] Technic RC Pneumatic Dump Truck

[P McCatty]

Hi everyone. I’d like to introduce to you my latest MOC: Technic RC Pneumatic Dump Truck. It is on 1:17 scale, weighing in at 4.32kg with just over 5,000 parts. It is loosely inspired by the SinoTruk Howo 8 x 4 Tipper Twin Steer. I would love to get your thoughts & feedback!

More pictures on Flickr HERE

Instructions: BuWizz, 2.4GHz

Feature Summary

1. Powered by 2 x BuWizz 2.0 or 2.4GHz Box.
2. RC Drive 8 x 8. RC Twin Steering.
3. Springless Live Axle Suspension Front & Rear with maximum roll stability.
4. RC Compressor.
5. RC Pneumatic Functions. Tip Dump Bed & Driver Cab independently.
6. Dump Bed Automatic Gate Lock with optional Manual Override.
7. Opening Doors with Spring-Loaded Latch.
8. Foot Pedals (Brake & Accelerator), Signal Levers, Gear Shifter, Air Horn Chain, Ignition Key, opening Glove Compartment.
9. Working In-Line 6 Cylinder Engine (Connected to Drive Shaft)
10. Working Steering Wheel full-time, even when Cab is tipped.
11. Opening Hood, revealing Engine Fan.
12. Adjustable Sun Visors, Mirrors, Windshield Wipers.
13. Technic Figure Compatibility.
14. Locking Feature to secure Dump Bed & Driver Cab to Frame to add rigidity & facilitate ease of model transport.

 

Video

 

Comparison Pictures

 

Locomotion

All motorized functions are powered by dual BuWizz 2.0 or 2.4GHz Units integrated into the Cab. The model features RC Drive, with a full 8 x 8 train. Propulsion is delivered by 4 x PF XL Motors, geared down at 2 to 1 with the help of Planetary Hubs. There are no Center Differentials, which ensures that all 4 axles are driven full-time. The drive train is also connected to a (cosmetic) inline 6-cylinder Engine, complete with a fan. With an empty Bed, the weight distribution is closer to the front, which limits the traction on the rear wheels. In practice, the 8 x 8 drive configuration results in much better outdoor & overall performance (particularly over uneven terrain). Individual axle-mounted PF Servo Motors steer the Truck through a Rack & Pinion system, & this is independent of Suspension flex. Axle 1 (forward) has a tighter turning radius than Axle 2. There is a mechanical linkage connecting the system to the Steering Wheel in the Driver Cab with a +/- 167 deg range for a more realistic look. This function remains operational even when the Cab is tipped.

 

Suspension

All 4 Axles feature Live Suspension. Both the front & rear wheel sets are connected in tandem, similar to a Walking Beam configuration. By combining traverse & longitudinal pendular levers, articulation is achieved without the use of shock absorbers. This also offers maximum roll stability for high center-of-gravity applications. This idea was inspired by the All Terrain Crane by @Jennifer Clark.

 

Pneumatic System

The Pneumatic Circuit uses compressed air to control the pistons that operate the Bed & Driver Cab tipping functions. A Compressor generates pressurized air that is then redirected towards the pistons through corresponding switches. At the heart of the Pneumatic system is the Air Compressor. It is driven by a PF L Motor using 2 Pumps aligned out of phase for smooth flow. Compressed Air is fed to the Pneumatic Switches that control the tipping functions. The model features 2 Pneumatic functions: Tip Driver Cab & Tip Dump Bed. The air supply from the Compressor is redirected through Pneumatic Switches, which in turn control the Pneumatic Pistons that operate the functions. The Switches are activated by PF Servo Motors. With the Compressor turned on to supply airflow, the Servo angle (-90, 0, 90) corresponds to the Switch positions (-1, 0, 1), which then moves the Pneumatic Pistons as (retract, neutral, extend). Full credit to @functionalTechnic for the original RC Pneumatic Servo set-up. The Dump Bed tips at up to 45 deg & has a lifting capacity of 2.5 kg, with a total volume of 3,623 cubic cm.

 

Gate Lock

The Dump Bed contains a gravity-based Lever that automatically releases the Gate as soon as tipping begins. Conversely, it is timed to lock the Gate once the Bed is horizontal. An optional pin is included that secures the Lever in position so that it doesn’t release the Gate upon tipping.

 

Driver Cab Details

The Driver Cab features functional doors with a spring-loaded mechanical linkage to open & lock them. This mechanism fits in a single stud width & once locked, the door is fully constrained to the Cab. The driver side contains Foot Pedals (Brake & Accelerator), Air Horn, Signals, Ignition Key, Gear Shift Lever. The Windshield Wipers, Mirrors & Sun Visors are all independently adjustable.  The Hood on the front opens to reveal a working Engine Fan. Finally, Technic Figure compatibility has been maintained using vintage seats. Admittedly the Technician scale isn’t 100% accurate, but it is never a bad idea to include them.

 

Locking Elements

Both the Driver Cab & Dump Bed feature locking mechanisms that reinforce the tipping functions. This is ideal for model transport, where it can be easily lifted from above from any of the sections. Typically, it would be carried from beneath or by holding the front & back.

 

Aftermarket Tires

While the standard 62.4 x 20 tires work well, but the RC4WD 1.2” variants have always been preferrable. They are a bit larger & have a more rugged look overall. Due to the weight of the model, the supplied foam inserts were not sufficient for the tires to retain their shape. To overcome this, custom inserts were designed & 3D Printed for the Dirt Grabber option. They consist of symmetrical halves that are joined together on the rim & secured with Technic ½ Pins. The ID features inner shoulders that prevent lateral movement relative to the rim.

 

More Pictures

 

Edited October 16, 2024 by P McCatty
Formatting

[Milan]

Frontpaged.

[2GodBDGlory]

Very nicely done, and well presented! It feels like it has everything you could ask for in a dump truck, with lots of detail and functions. RC pneumatics are always cool, and I really like that servo valve control solution! Very compact and elegant. One question, though: Why did you use an old-style differential on the front axle? It looks like you had to go to a lot of effort to keep the same gearing despite using it?

[AJB2K3]

Oh wow, very nice.

[LEGO Train 12 Volts]

Wow I've never seen anything like it, it's incredible how everything is motorized.

Awesome video

Excellent solution for stiffening tires!

[Alex Ilea]

Absolutely insane build, and we love that over here! I really like your attention to detail with this build (those turn signal stocks are just perfect), and of course the functionality. Well deserved front page.

[onzenuub]

Great job 

[vliet]

Why has the front axle a different gear ratio with a different differential, or it just looks likes another ratio?

This is just a great build, like others said, motorized pneumatic reminder awesome, and.I love those tires.

Edited October 13, 2024 by vliet

[P McCatty]

On 10/12/2024 at 12:24 PM, Milan said:

Frontpaged.

Thank you. Much appreciated 

[P McCatty]

On 10/12/2024 at 1:23 PM, 2GodBDGlory said:

Very nicely done, and well presented! It feels like it has everything you could ask for in a dump truck, with lots of detail and functions. RC pneumatics are always cool, and I really like that servo valve control solution! Very compact and elegant. One question, though: Why did you use an old-style differential on the front axle? It looks like you had to go to a lot of effort to keep the same gearing despite using it?

Thank you!

Regarding the old-style differential on axle 1, it was chosen to provide clearance for the servo motor that sits directly on top. The curvature of the motor coupled with the 1/2 stud width of the gear was sufficient. There was no room to move it forward, & moving it up by 1 stud would interfere with the engine crankshaft during extreme suspension flex. The engine already sits a bit higher than I'd like.

Typically the approach would be to mirror the axles & so the burning question is, why doesn't axle 2 have the same gearing? During testing I found (with using the old-style differential on axle 2) that the input shaft torque was such that it would shred the new style cv-joint. This was overcome by gearing it up another 20-12 & using the new-style differential. With the 1-stud thickness of the differential gear, the original positioning of the servo motor (just like axle 1) wouldn't work due to interference. Fortunately, the steering arms on axle 2 are 1 stud longer than axle 1 to reduce the steering radius & this is typical on twin steer vehicles. With that, I was able to move the servo away from the differential by 1 stud & achieve the needed clearance. 

Finally, since the axles have dissimilar differentials, the gearing in between them was necessary. A close inspection of the render below may provide some clarity.

[bruh]

Ok. Wow, is this truck packed! I like the trick of usung 4 pneumatic cylinders back to back to get the desired bed tipping angle!

[Celeri]

Very impressive MOC, and excellent presentation: congratulations!

[Axadder]

I would like to hear all the hissing from this pneumatic working at full throttle!

Impressive model!

[P McCatty]

5 hours ago, Axadder said:

I would like to hear all the hissing from this pneumatic working at full throttle!

Impressive model!

Oddly enough, the pneumatics are pretty quiet. But it's the compressor that gives the model character. While it's working it sounds like a real heavy duty truck with the engine idling.

[allanp]

Excellent work! Looks very playable. 

[lmdesigner42]

Very impressive model! It's amazing how all of the features were fit in there, and it still looks like a real dump truck on the outside. And the clear renders and presentation are icing on the cake. Are my eyes deceiving me, or is that 6 back-to-back long pneumatic cylinders combined into one function? Very cool. The 3rd party tires look good, but it must have been expensive to obtain 12 of them.

[P McCatty]

6 hours ago, allanp said:

Excellent work! Looks very playable. 

Thank you!

3 hours ago, lmdesigner42 said:

Very impressive model! It's amazing how all of the features were fit in there, and it still looks like a real dump truck on the outside. And the clear renders and presentation are icing on the cake. Are my eyes deceiving me, or is that 6 back-to-back long pneumatic cylinders combined into one function? Very cool. The 3rd party tires look good, but it must have been expensive to obtain 12 of them.

Thank you! The pneumatic cylinders are really 3 in parallel, but I used 6 to get the range. They are coupled with a custom assembly that is a variation of THIS. If you notice, the pivot for the dump bed is not along its base, but rather quite low towards the bumper, such that it has an approximate overall "L" shape. This was specifically chosen to maximize the force delivered to tip the bed at the point where it is highest (horizontal). Regarding the tires - yes you are correct, RC4WD isn't cheap  but at the same time, they look much better than the standard LEGO tires in my opinion.

 

 

[nico71]

Nobody mentioned the clever solution to keep small the width at the back with this scale and dual-wheel ?

It uses the heavy CV joins connect to the diff, but without differential (so one stud save in width on each side, as on my Kodiak with 2L hinge cylinder instead of 3L join), but with a framing around the CV-joins to hold them, and leaded 12t gear on the crown of the diff to secure the position of the diff (because it is not maintain on its center). That is a pretty clever solution @P McCatty ! I did not see before in truck (see elsewhere but not for motorized drivetrain on big truck).

[M_longer]

9 minutes ago, nico71 said:

Nobody mentioned the clever solution to keep small the width at the back with this scale and dual-wheel ?

It uses the heavy CV joins connect to the diff, but without differential (so one stud save in width on each side, as on my Kodiak with 2L hinge cylinder instead of 3L join), but with a framing around the CV-joins to hold them, and leaded 12t gear on the crown of the diff to secure the position of the diff (because it is not maintain on its center). That is a pretty clever solution @P McCatty ! I did not see before in truck (see elsewhere but not for motorized drivetrain on big truck).

Nobody mentioned it, because nobody seen it ;)
I'm wondering if it will skip under heavy load though.

[nico71]

38 minutes ago, M_longer said:

Nobody mentioned it, because nobody seen it ;)
I'm wondering if it will skip under heavy load though.

^^ It seems to handle quite well the torque on the video, surely the 8x8 transmission help to reduce the resistive torque on each axle, but maybe it worth to try on a 6x4 config for instance. Interesting use anyway !

[M_longer]

7 minutes ago, nico71 said:

^^ It seems to handle quite well the torque on the video, surely the 8x8 transmission help to reduce the resistive torque on each axle, but maybe it worth to try on a 6x4 config for instance. Interesting use anyway !

This one had doubles too:
https://brickshelf.com/cgi-bin/gallery.cgi?f=571094
 

[P McCatty]

9 hours ago, nico71 said:

Nobody mentioned the clever solution to keep small the width at the back with this scale and dual-wheel ?

It uses the heavy CV joins connect to the diff, but without differential (so one stud save in width on each side, as on my Kodiak with 2L hinge cylinder instead of 3L join), but with a framing around the CV-joins to hold them, and leaded 12t gear on the crown of the diff to secure the position of the diff (because it is not maintain on its center). That is a pretty clever solution @P McCatty ! I did not see before in truck (see elsewhere but not for motorized drivetrain on big truck).

Very good observation! I tried a few different solutions, but none of them were robust enough. There was always be skipping under high torque. Examples below are from using the old 16T & new 8T gears.

With the aim of keeping the dual  wheels at ~ 19-wide, there was nowhere to mount supports around the differential. To get around this, I supported it by framing with 4 x 12T gears. I was actually surprised by how well it worked. The ground glearance suffers a bit, but the assembly is solid. This can also be done by framing with 8T gears, but it results in a bit more friction.

 

Edited October 16, 2024 by P McCatty
Formatting

[nico71]

22 hours ago, M_longer said:

This one had doubles too:
https://brickshelf.com/cgi-bin/gallery.cgi?f=571094
 

 

I do not see your point. This is not the same solution you shown on Pipasseyoyo's Truck. He uses classic portal hub, not geared one, so not very difficult to have double-tire at the rear in 19-stud wide with portal hub. Using geared hub requires to connect them with a CJ join which take place, and so keeping the width low which is the difficult trick (or you accept to be off scale with that tire or put bigger tire and use 21 studs wide).

 

14 hours ago, P McCatty said:

Very good observation! I tried a few different solutions, but none of them were robust enough. There was always be skipping under high torque. Examples below are from using the old 16T & new 8T gears.

With the aim of keeping the dual  wheels at ~ 19-wide, there was nowhere to mount supports around the differential. To get around this, I supported it by framing with 4 x 12T gears. I was actually surprised by how well it worked. The ground glearance suffers a bit, but the assembly is solid. This can also be done by framing with 8T gears, but it results in a bit more friction.

 

I have tried the same option with the 16t but it doens't work well. That is why I come up with my own solution on my Chevrolet Kodiak : 

 

The part : https://rebrickable.com/parts/57360/hinge-cylinder-1-x-2-locking-with-2-click-fingers-and-axle-hole-7-teeth/

The truck : https://rebrickable.com/mocs/MOC-155168/Nico71/chevrolet-kodiak-c70-control-version/#details

Which work pretty good, not suitable for front steerable axle because this is not a CJ join, but it handle well the torque on the fixed axle, with keeping the width low (2l instead of 3l). I have not tested on heavy truck (I will) but I think there will not be problem.

Nico

 

[Igor1]

On 10/13/2024 at 8:52 PM, P McCatty said:

Regarding the old-style differential on axle 1, it was chosen to provide clearance for the servo motor that sits directly on top. The curvature of the motor coupled with the 1/2 stud width of the gear was sufficient. There was no room to move it forward, & moving it up by 1 stud would interfere with the engine crankshaft during extreme suspension flex. The engine already sits a bit higher than I'd like.

To place a new differential under the PF servo motor, it is often enough to simply rotate the servo motor itself by 180 degrees, since it has an output to the axle in both directions.

The moc itself is awesome!

[nico71]

42 minutes ago, Igor1 said:

To place a new differential under the PF servo motor, it is often enough to simply rotate the servo motor itself by 180 degrees, since it has an output to the axle in both directions.

The moc itself is awesome!

Wise advice, are you sure it works with the 28t red gear of the differential ?