2GodBDGlory

Wow, very impressive! That's some clever mechanics going on in there

I'd appreciate that!

I would very much hope that we would still be able to post those in their respective theme forums. I regularly build Technic MOCs with maybe one unique clone battery, 95% original Lego parts, and 5% parts that are direct clones of Lego parts, but if we had a rule that would force those models into this forum, it would hardly feel worth posting them anymore. I really want my models to be a part of the Technic forum, as they always have been, and would be very frustrated if forum updates that were ostensibly meant to open up somewhat to clone brands resulted in me having to purge my collection of all clone parts to remain a part of the Technic forum!

Yeah, I definitely was challenging myself to make the wheelbase and track width as small as possible, though I'm not really sure why I felt like working so hard to do that! Maybe it was just challenge for the sake of challenge

And we're done! Since last time, I finished the bodywork, but then for some reason I was getting issues with the steering, in which some of the 16T gears spinning to drive the steering were interfering with the 16T clutch gear in the transmission. They were mounted in the same plane, at a 2x1 offset, which theoretically works fine, but forces on the gears were bending them in such a way that they were locking up on each other. In order to fix this, I rebuilt the gearbox with different ratios, allowing a 12T clutch gear to go in that slot, and solving the issue. The old ratios were 1:1, 3:5, and 1:3, while the new ones are 5:3, 1:1, and 3:5, meaning that this update also makes the truck faster, which is a perk, since it still has the torque to use top gear, and the gearbox to increase torque as needed. Aesthetics: I'm not sure how I feel about the looks. It seems a bit uninspired to me, with an interesting front end, but somewhat phoned-in bodywork elsewhere. On the other hand, I suppose it's more creative than if I had just modeled some boxy old pickup truck as I had initially been planning? I had been hoping to add some stickers with the Agents logo, but unfortunately my printer wasn't in the mood to work. (I've had it with that thing! It usually takes hours of troubleshooting every time I want to use it. It seems a shame that I can 3D print all day, but the 2D printer never works, and can't really be fixed!) Functions: 4WD with V8 piston engine, driven by PF XL motor 4WS with PF L motor Steering mode control with PF M motor 3-speed transmission with PF Servo motor Four-link live axle suspension front and rear Manual pneumatic axle brakes Drive: Drive was pretty routine, with the XL motor and piston engine. There was no central differential, naturally, and I just left open differential front and rear, to the great detriment of off-road performance, but to the benefit of steering. Steering used an L motor for torque, and honestly probably could have used some more torque, since steering struggled when not moving. Still, it worked reliably. I used small linear actuators on each axle to try to simulate the hydraulic rams that would be used on real monster trucks Steering modes were probably the most unique function in the model. An M-motor drove an 8T gear through a worm gear, which then drove a small linear actuator, which moved this weird linkage back and forth. The front and rear steering systems were not mechanically connected by default, and the rear wheels were only steered when a mechanical connection was established between the front and rear systems. This was done by moving this linkage to mesh 24T gears with the 16T gears in each half of the steering system. When the linkage was moved all the way to one side, a pair of 24T gears on the same axle were used to connect the two without affecting rotation, while moving it all the way to the other side connected them through two 24T gears that had their relative rotation flipped through the use of three 12T bevel gears. Because of the linear actuators used for the steering, the rear steering was unable to be backdriven when disconnected, forcing it to stay where it had been left. Changing steering modes took a long time, because of the worm reduction before the linear actuator, but allowed me to be precise enough to control it reliably, putting the proper amount of force into the gear mesh. This system allowed for RC switching between normal 4WS, front-wheel steering, and crab steering. The transmission was a 3-speed of the trivially easy kind enabled by modern clutch gear selection, using 12T, 16T, and 20T clutch gears. I ended up having to use an old 2L driving ring and old 16T clutch gear to reduce gearbox length by one stud after swapping the 2M long 12T clutch in late in the build process (I don't have any original Lego modern 2L driving rings, unfortunately). Shifting was done by a PF servo, with each position corresponding to one gear. I used a Bionicle ball joint on the controller to provide enough friction to leave the remote in any of its three positions. Overall the gearbox worked flawlessly, with super easy gear selection and reliability! The suspension was a fairly simple triangulated four-link setup with hard 9.5L shocks The brakes were trying to emulate the interesting axle-mounted disc brakes of real monster trucks, which are mounted before the the differential, and brake the drivetrain itself rather than the wheels. I had small pneumatic cylinders integrated into the axles, pulling linkages with small rubber track inserts on them against the brake discs. I had hoped to use a compressor for this function, but it proved to not generate enough pressure, forcing me to pivot to a manual pump and switch. I doubt it made a lot of braking force, but the differential and planetary hub gear reduction would multiply its effectiveness significantly. Apparently I didn't get any good pictures of this function, but you can see the discs and a glimpse of one of the cylinders here (though they're shown more clearly in the video) I think the finished model worked well, and looked interesting, but it didn't end up really meeting my hopes for the project, which started out far more ambitious mechanically, and which would have had it more recognizably Agents-themed with stickers. However, I'm happy to have completed a model for this contest, and the steering mode selection felt quite unique mechanically! Unfortunately, towards the end of the build process, my old 8878 rechargeable battery started to fail, so for parts of the video I had to run the model off my MouldKing 6.0 battery pack slapped on the back. More images at: https://bricksafe.com/pages/2GodBDGlory/tc31-monster-truck

Huh, neat! Wow, that's a fascinating build!

I just tested that physically, and it works fine! 33299 also works:

That is the only part I've ever come across with that combination of bushing-style axle hole followed by another parallel hole, yeah.

Oh yeah, for sure! And tolerances can be printer-specific, too. Just having an editable STEP file is great, though

Cool, thanks! I print parts from time to time, and it's possible some of your parts could be useful! Usually I export .obj files from Bricklink Studio Part Designer, but then tolerances are usually off, and I can't edit them. I had found a guy on Grabcad who had done a ton of nice Lego modeling, with parts available to download as .STEP files, but the last time I needed a part I couldn't convince that site to let me log in enough to download parts, so perhaps I'll refer to some of yours in the future!

You got me thinking, so here's a prototype for ya! @TomSkippy I had mentioned a rubber band previously, but I was able to get reliable motion with the simpler solution of just using friction pins on the two red gears. The only difference is that it doesn't retract in the same order that it extends; moving to a rubber band would make that happen in the same order, which may be necessary for your build--I just didn't find an easy way to implement that on this mock-up. Is this what you're looking for? I hope it helps!

Hmm, that's not a trivial question. With a single control, I think I'd be looking at having some kind of rubber band making the second stage deployment more difficult, and then some kind of differential-type mechanism that has the option of driving either stage, but will take the path of least resistance. That way, your rubber band on the second stage makes that the harder option for it, and it will only deploy when the first stage hits some stop. Implementing that still sounds tricky, though. Pneumatics could be a good solution, but might complicate your model more than you want. Otherwise I would look into mechanical differentials, but then getting drive up to the second stage might be tricky

Could you integrate some kind of pin to hold the pump in the compressed position for display? That might not be good for the pump long-term, but maybe worth thinking about?

I've never worried about having clone parts in the MOCs I post here

Ooh, looks very nice!

That's honestly pretty much the same problem I was having on my TC31 entry. I needed to get enough pressure to move two small cylinders, but the single small pump I had on my compressor couldn't get enough pressure to move it. Luckily I had the room and was able to pivot to a large manual pump, but it's odd we can't get higher pressure from those little pumps

Looks really nice! It's a shame those cylinders aren't strong enough, but they do look really good! That's the trouble with those thin long cylinders. Proportionally they look accurate, but they just don't exert much force. The other added functions are quite nice, though! I imagine you could add a removed spring from a short shock absorber in the area where that half bush is, but I can understand wanting avoid that technique, especially for something with instructions

Not sure you'll have any luck; according to the profile page, @syclone hasn't been here since 2022, but we can see!

Since last time, I did go ahead and attach the M motor to the linear actuator for steering modes, through a worm gear. It's very slow, but I like it that way so I can make precise adjustments. Beyond that, though, I've decided on a theme! I had been thinking I should make it in a fun color, and the dark blue parts I got from the Ford GT set came to mind. I've never used them anywhere else, and it seemed like it would be a nice idea to do here. Given dark blue, it struck me that I could make it in a Lego Agents theme, as if it were something being driven by the heroes from that old Lego theme: Set List. It's a theme that has some nostalgia for me, having had the Aerial Defense Unit helicopter set as a kid (though none of the others). To go along with that, I'll be using a dark blue, yellow, and LBG color scheme, and maybe adding some weapons? It's kind of a loose theme, but it gives some structure to the build, that was previously lacking it. I have very limited parts in dark blue, which has also been an interesting constraint to work under! I'm pretty happy with the shaping on the front, but the roof definitely needs some work, and it looks like I'll need to move the IR receivers. M-motor hooked up to steering mode actuator ^ Hopefully I can get this done fairly soon! I haven't been feeling super inspired to work on it, but it is taking shape.

That is looking great!

Nice work! The stickerless livery must have been challenging to build, but it worked out nicely!

Nice job, that's impressive! I see you're using a 64T gear. Did that new part contribute to the higher accuracy of this design?

I haven't been working too fast, but the chassis is now potentially done! (Unless I make some changes, but more on that later) Since last time, I've moved the V8 to the other end of the vehicle, essentially switching which were the forward and backward sides of the vehicle, after I realized that in the two-wheel steering mode, it was the back wheels that were turning. After swapping that over, it's now a proper FWS mode! I've also added this Servo motor to shift the 3-speed transmission through a chain: Changing steering modes is currently done manually, by extending and retracting this small linear actuator, to move the linkage and gears shown in previous posts. Finally, I installed a pneumatic autovalve using a PF M-motor, to run the brakes: However, that's where I'm running into issues. For some reason, I can't seem to get enough pressure out of one of these small pumps to actually move the cylinders for the brakes. It works perfectly fine with a large manual pump, but not off the compressor. The strange thing is that it's essentially a direct copy of the autovalve I just used in my AWDrola MOC, which moved three small cylinders without major issues. Maybe there's a way for me to coax it into working better, but I'm not sure. If I can't get it working better, I'm considering instead hooking up that M motor to the linear actuator for steering modes, and then installing a manual pump to make the brakes a manual function. The only issue with that is that the steering modes are kind of touchy, and it would be somewhat nice to have fine manual control. I think it could work fine either way, though!

Which I really don't think is a radical change, given that the Community forum has already included that

Sorry, just edited that post to try to make it more clear