Appie

I made a stud.io file for the chassis, available here: https://www.dropbox.com/scl/fi/00ccqyyzdxi3hlswbzzjj/CompactCrawler.io?rlkey=rdpojjy2399r0bb1e6mgnzrb6&dl=0 It should be complete, but if you find any issues let me know. Also something of note perhaps if you build this: when you press the front suspension so both springs have to compress, the movement is a little bit limited by the 12T gear from the steering that bumps into the L-motor. I have no issues with this, because for crawling action it's usually one side being compressed and not both. For one side being compressed it has no issues.

@AutoBacon Thank you very much. I like how sturdy it is yet compact as well. I made it a little sturdier even since those pictures. Secured the connector at the bottom better near the knobgear on the driveshaft and used the battery box to prevent the base from tearing apart down there (mostly a security measure for when it tumbles, not something the drivetrain tears apart). I don't have a studio file yet, but I would like to make one. And yeah, I am looking forward to the next round, quite confident with what this chassis can do. At the end of May we go again. As for the steering, it was a little annoying, because the space between the axle of the motor and steering axle is 4 studs. I didn't want to use 24T gears to bridge that gap, since those would touch the liftarms to the sides of the motor. So I came up with this: Not in the picture, but on the right side of this I placed a liftarm with half pins that act as stops above and below the top 2L liftarm from the motor, so the steering motor can't turn too far. Also, it's 5L liftarm between the 2 axles on purpose there, 4L had the tendency to get stuck on the lower rim of the battery box, this solution prevents that from happening. I have yet to have it happen at the top of the battery box, but then a 6L liftarm is an option. It being locked in by the battery box is something I like though. Making sure the whole mechanism won't run off axles. (also the tan axle from the motor is an axle pin. I used it as placeholder until I was done testing stuff) Also, yesterday I made an attempt to lower the springs one stud: In the end I didn't use it and reverted back to the original design. Obvious flaw is the springs not being able to move sideways naturally, but the suspension in general didn't work as smoothly as the previous design. And the axle as a whole felt a little less sturdy. Geometry with the new spring location felt off a little too. The spot I lowered them to is pretty much my only option and couldn't go wider there either or I'd touch the tractor tyres.

Thanks. Interesting method for the spring. Thanks for the suggestion. Personally I consider even just the spring legal, since that is also a Lego part (and I have made a MOC with it in the past with the spring running on an axle), but I want a normal alternative for which you don't have to disassemble parts that are normally not disassembled (for that old MOC my alternative was a suspension with rubber bands). It's just a weird personal rule I have when I make MOCs

Finished the chassis for that new axle I posted earlier, inspired by AutoBacon's work I wanted to keep the heavy parts of the model as low as I could, so I placed the battery box right above the drive shaft. As you can see I didn't manage to lower the front springs 1-2 studs. I might change the LBG part of the springs to yellow or something so I can hide it in the hood . The rear axle is pretty much a copy of AutoBacon's, except for the springs and I used another grey link on top (for symmetry with the front axle as the front has 2 as well to make sure an old style cv-joint for the steering won't pop out). Wheelbase is 18 studs. 3 studs shorter than my previous truck and if I am not mistaken 1 stud shorter than AutoBacon's pick-up truck (I was aiming for the same, but I misscalculated ). Gear reduction is 2.8:1. It climbs better than my previous truck. That truck had 4:1 reduction, but I think with the slippery obstacles and that with these tractor tyres, having some speed to get a running start on an obstacles helps. The balance is also far better with the lower center of gravity. Now to figure out what kind of body I want on it (will be something pick-up or Jeep-ish probably).

For this competition it was not, had to be 100% Lego. And actually, even if it wasn't a rule, I'd make it a rule for my own model. I like to keep my building solutions within the Lego options.

Yup, another builder noticed that while we were making the models (sadly he couldn't join for the video). Mahj's little truck from the video uses the same new CV-joints with that part and uses a 2x2 round tile with a hole in it to fix this rim touching problem (the extra surface also helps against the wobble you mention). As you can see in my picture I am using a 1/2 technic bush. For now at least, I'll probably change it to Mahj's solution. Ideally you want something of a 1/4 bush as a spacer to not rub the rim, but a tile is the closest we are going to get to that I think. As for the Mustang rims, I personally didn't notice a difference between them and the normal standard rim in terms of touching the above pictured part. Another solution would be this rim: https://www.bricklink.com/v2/catalog/catalogitem.page?P=6595#T=C With this rim the part does not touch the rim, but it's not a current rim, it was used in sets until 2006, but there is a 56mm tyre that would fit this (the red fire truck in the video uses these rims+tyres). Thanks, I love working on these small scales, like you said, you need to pick your parts carefully. For example, originally I removed that thin 7L liftarm at the bottom of the steering rack from your great design, then I noticed it functioned as a steering stop and prevented a little bit of the wheels bending outwards. So I put it back in I love such effective part usage.

Great to have you back. Gorgeous MOC!

What a great little buggy. I can see why you like that chassis, looks very clean and solid

Glad to hear it. Keep on MOC'ing, you make awesome stuff. Thank you very much. Here's another pic of it: It's driven by PU, 1 L-motor for drive and one L-motor for steering. This is basically what's under the bodywork: This was an early version, tweaked a few things since this picture. Mostly the 3 points where the axles are linked to the chassis (made the LBG 5L suspension arm in this picture parrallel to the 6L links so the suspension worked better). The reason I mounted the motors like this was so I could get some good gear reduction under it to crawl up obstacles. Yes, it's ackermann, like the original axle from Keymaker. Here are some close up shots of the axle. Keymaker could use 2x 5L thin liftarms for his axle, but for 9L I was a bit stumped for options. While making this axle I found out there's actually a thin 9L liftarm now, with 3 holes which could work for this setup, it's in the new Orient Express set. Since I didn't want to pay €5 for a single liftarm, I came up with another solution. The little rubber thing on top turned into the connector is to stop the connector from seperating (without it, I'd tear it apart when just removing the wheel). It adds a little bit more flex to the axle (wheels pointing outwards) than it probably would have with a 9L thin liftarm or Keymaker's 11 wide solution, but I had no other ideas or parts that were half a stud high and had a pinhole at the end. To prevent CV-joints from popping and have a little less flex on the axle, I started to build an axle with the new CV-joints similar to the one from this topic: My version so far of his axle: In order to make the axle sturdy where the one from AutoBacon used a 3rd party part, I needed 1 more stud towards the rear (where the red axle pops out, also the red axle is a place holder for the new CV-joint of which I ran out atm ) I want to figure out a way to lower the springs 1-2 studs. Not that I mind the solution from the original designer by just using springs, but I personally like to also have a "normal" alternative when I use that.

You sort of were. A few of us (I think I did it the most) took alot of inspiration from your Kraz 255 for you axle setup (and skid plates ). For fun I made it 9 wide instead of 11 wide (no dual drivetrain though), which made the car 15 studs wide, 2 below the allowed maximum. In hindsight not the best choice, I nicknamed my little car "the tumbler" after seeing the video where it's upside down quite a few times (and in the ranking as well) Originally both axles have steering, but one of the cv-joints on the rear axle kept popping so I adjusted it to a fixed axle before the video of the truck trial. Thought I'd mention that in case somebody wonders why the rear axle isn't steering in the video.

Thanks guys! It does drive, just not very well when steering (and still not because it won't move, but because it isn't really moving in the direction you want it to move). None the less, I agree, even if it did work perfectly while steering, it's still 1-3km/h you can get out of such a model this size with Lego motors which is hardly worth the effort, but I had to try

Exactly this. The XL's could handle it fine, the wormgear could handle it fine, the 36T gear however, it bends, not just to the sides, but also (due to how that 36T is constructed) inwards. I have tried 2 gears, it still skips under the weight. Swapped to 40T gears, still skips. 28T look alot more solid, but due to them needing half a stud offset with the new wormgear, not ideal. Not to mention that 40T and 28T both mess with the desired gearratio. The current plan that might work is 2-3 (normal or large) LA's in each leg instead of a wormgear. Or perhaps some sort of pulley system. I don't think I can optimize the cabin transformation anymore besides making it slower at the motor (so the weight stays longer in the center of the model). Nor do I see much options for Optimus to lose some weight Actually, when he was a skeleton, he got up with L-motors instead of XL's in the legs, but the guy needs some bodywork and I tried to keep it light. @Dennis Bosman Oh yeah, the trailer. I was considering that (also to cheat with a sort of rope system hidden in the trailer )

So I haven't changed anything since my last post in october, but figured a video and some more photo's might be appreciated. As I pointed out earlier, the steering (combined with drive) only works so-so. This is due to the arms being able to bend (no idea how to fix this without completely diverting from the look of the game model), slack in the gears and the (small) difference in rpm between motors make it near impossible to get it "perfect". I am now considering to change the purpose of this model to more of a "demo" and remove drive and put it on a stand. Also when I would do that, I'd change to PU instead of PF since you can control the rpm and I could program the transformation instead of doing it manually like in this video. Not sure when I will get started on this, but here's some more pictures of the current model: Managed to squeeze in some computers (on both sides) for Batman to use: Detailed shot of the turret: Easy accessible battery boxes: Belly shot: In the belly shot, the little wheels at the front and rear of the chassis is what actually drives and steers the model, powered by an XL each and some gearreduction they manage. To see how these wheels are angled I have 2 visual indicators from above, at the front it's the steering wheel in the cockpit, at the rear however: It's this little DBG thing under the "shark bat fin". It's also victim to a little slack, so it's not perfect, but better than no visual indicator at all Thanks for reading. Another update might be some time down the road though.

I made this last year and didn't get around to make a topic about it until now. A video of it transforming: The model weighs 1.6kg and most of that is on the front axle. I haven't been able yet to make a mechanism that will allow Optimus to lift himself without a "hand of god" Some more photo's The rope you see between the front wheels in the photo above is what makes the flaps with the headlights at the front besides the grill fold back when Optimus is standing, but flex (thanks to rubberbands) when the hands need to be folded back into the body when he's transforming into a truck. The little grey wheels you see at the rear wheels make the black rear wheels barely touch the ground, this helps the leg spread mechanism. Speaking of which, the clicking in the video comes from these 2 mini-LA's in the legs: They make Optimus spread his legs a little when he's standing. I thought that looks better than him simply having his legs straight when standing, but the gearratio is off. If I manage to make a mechanism for the legs that works in lifting the model on its own then I might be able to tackle this gearratio too. In case somebody wonders where I put the battery box, it's external Thanks for taking the time to read my topic, hope you enjoyed it. If you have any questions, feel free to ask.

What an awesome little nimble truck and the looks are perfect. Great video too. In march I got a truck trial with the LUG with 56mm tyres, so this is great inspiration for that, thanks.