AxeSlash

Eurobricks Vassals
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Everything posted by AxeSlash

  1. I've been lurking here for a while but have never been satisfied with any of my MOCs enough to post them here. The nearest I came was an MLRS that worked well but looked rubbish :P Anyway, I'm in the process of designing a Grave Digger monster truck replica (approx 1:15 ish scale). Features: - 4 wheel drive - 4 wheel steering - Steering modes: 2-wheel, 4-wheel, crab - 4-link, very long travel suspension - Suspension travel is also to scale. Almost. - All motors contained in the chassis (no servo-on-axle affairs) - SBrick control - Tyres from a Tamiya Lunchbox I'm designing this in Sketchup and rendering with the Twilight Render (free) plugin. Note that I've drawn all the pieces myself, and they're all drawn to have a low polygon count so that my machine doesn't croak to a halt. Some of the pieces aren't very accurate atm (e.g. the XL motors). So far, I think I've got the chassis designed: And here's a couple of closeups: Issues I can foresee so far: - Friction from so many knob wheels - Bump steer (but I don't want to sacrifice suspension travel by putting the servo on the axle) - Not sure whether having the steering upside down like that will have any negative effects. - Not sure if I can get all of the parts in green that I want Can anyone see any other potential issues with this design (before I start putting in BL orders)? Thanks
  2. AxeSlash

    [WIP] Grave Digger

    I'm not familiar with the clod steering system, and google just seems to turn up images of a servo on each axle. However, I think I understand what you mean - solid rods coming from the centre of the chassis instead of an axle; i.e. it's a linkage instead of a gearing system. I like the idea, but that's a pretty major redesign to fit it in. Plus it would necessitate more ball links than I currently own. Definitely something I will investigate in the future though :) I've redesigned the steering transmission now, and there is only one set of gears involved now. Tomorrow I will test how much backlash there is between two knob wheels and between two 12z gears to determine which will be best to use. I've basically split the drive transmission in two, and fed the steering transmission down the middle of it (i.e. the opposite of what I was doing previously). So the drive will have more gearing (and thus more friction) in it, but the steering should be much better. It does, however, mean that I'm only using one servo, so I'm hoping it will be strong enough to turn the wheels. If not I think I've got room to chain two servos together without any extra gearing.
  3. AxeSlash

    Future Ultimate Technic Sets

    Cizetta V16T...but it won't happen - too obscure, it would make more sense for them to do a Diablo instead Ariel Atom Lotus 7 (or Caterham 7) Lister Storm (but I guess that's already been done by the recent 24 hr car) A Range Rover or Land Rover. They're made close to where I live.
  4. AxeSlash

    [WIP] Grave Digger

    So I've had a go at redesigning the axles a bit. Kingpin incline isn't possible until I can afford another Brick Owl order, so for now this looks a bit better...although it's physically much bigger. Some ground clearance has been sacrificed. The pivot point is much further out now, which should mean less stress for the servos and hopefully a bit more steering lock, but I've still maintained the 1:3 gearing at the axles. It should be a bit stronger as well, I was always dubious about the strength of the 0.5L thick parts used near the shock mounts on the previous axle design. The problem I'm having now is the steering transmission. It seems to be almost impossible to do without having the servo stick out somewhere awkward and/or making the wheelbase much longer. At this rate I'll end up with a motor on an axle, which I was hoping to avoid.
  5. AxeSlash

    [WIP] Grave Digger

    Thanks for the encouragement guys. If the speed problem was down to a lack of torque, I'd be expecting it to accelerate much more slowly, but it's actually pretty quick to accelerate to top speed. I already tried it with a 12 -> 20 -> 12 tooth combination in place of the 12 -> 36 combination, and it was VERY slow - it had plenty of torque, but was basically a crawler, which isn't what I wanted for this model. I have a crawler design that I'm working on already that will be a torque beast, but for this model I wanted to aim a bit more for speed. I'm aware of the limitations of lego - I just want to achieve the best that I can. It's quick enough for my liking on a flat, smooth surface (a wooden floor), but outside on a slightly uneven surface (crazy paving), it really struggles. Maybe some slight reduction is needed...but I'm in the middle of redesigning the axle completely at the moment anyway (I'm completely removing the portals, and moving the reduction to the other side of the UJ...hopefully the UJs can handle the torque with snapping :S This should move the steering pivot outwards quite a lot). The steering transmission is the bit that really needs work though...but that's a big job :P As for stickers...I guess I'd have to have some printed. I tried to find a 1:15 Digger sticker set, but couldn't find anything. I don't own a colour printer, so that idea is out of the window. Does anyone know of any (cheap) sticker printers that do one-off stuff (based in the UK)? Thanks
  6. AxeSlash

    [WIP] Grave Digger

    Just tried driving this outdoors...it's rubbish. a) it's too slow, b) it has nowhere near enough torque to get over any decent sized obstacles (i.e. it needs more motor power if it's going to maintain a good speed and have enough torque to do anything sensible), c) the steering is absolutely atrocious. It's almost undrivable, and d) the body roll is a major problem. It definitely needs sway bars. I won't be posting a video until I've fixed at least the steering and roll issues. I haven't got any more XL motors to put in it so that issue isn't going away until my bank balance looks a bit better. I might try a LiPo in it instead of the 9V box that's in there at the moment.
  7. AxeSlash

    [WIP] Grave Digger

    It's not bump steer I'm concerned about. It's actual slack / backlash / play in the steering - with servo centred, you can still manually move the wheels up to somethign like 30 degrees EACH WAY. That's down to the backlash from the UJs and gearing in the centre; it's nothing to do with the pivot point. And yes, the wheels DO rub on the 4 suspension links at full lock, hence the belt wheels to space the wheels out further. I could potentially lose the belt wheels if I sacrifice (and limit) steering lock instead. I am aware that the pivot point is in a stupid place, but the portal hubs limit my options for the moment. As I said in a previous post, the axles will be in for a complete redesign anyway, so stay tuned for that - I will be dealing with this problem then. In the meantime, everything else is now complete; there were some slight changes to the bodywork due to me failing to order a few parts from Brick Owl, and the bonnet (hood) needed strengthening. The entire body is removable by removing 4 quick release pins (the grey bush pins at the bottom of each side of the main bodywork. The battery can be turned on and off by a pulling/pushing a beam via at the rear (forgot to take a pic). The battery box is removable by 2 quick release pins as well. Hopefully performance testing and a video will follow tomorrow. After that I will attack improvements to the steering and assess whether I can get away with more speed and less torque. I suspect that I will need an anti-roll system as well - it's fairly unstable now that the extra weight of the bodywork is on. Also there still isn't enough sag in the suspension for my liking, and the whole thing is riding too high right now. I might have to order 4 more soft shocks and replace the yellow ones with them. That's gonna make the body roll horrific... It's not the slack in the rack/pinion that's the problem - it's the transmission from the servo to the pinion that has the slack.
  8. AxeSlash

    [WIP] Grave Digger

    Just done some more work on this - the quest to reduce steering play continues! The result...a more primitive rack & pinion setup: Note the rack is now half a stud further away from the chassis. so that the red parts clear the diff (you can see how close it is to fouling). The play has been reduced by getting rid of those wobbly links between rack and portal. There is now only one frictionless pin on each side instead of two, There is still too much play, but at least now the wheels are both pointing in the same direction :P Ironically, for some reason I seem to get more lock out of this setup as well. So much so that I'm a little worried that the tyres might rub on the suspension links. And as for the return of the UJs...the CVs couldn't handle the torque of turning those big tyres. I'm going to have to look into reducing the backlash in the gearing in the centre of the chassis instead, which will be difficult. In other news, the motors are now geared up 3:1 in the chassis, then 1:3 at the portals. Accounting for the diffs as well, that gives a final ratio of 1:1.4. It's definitely not a 'fast' model, but it's not a crawler any more. It feels like there's some torque to spare. Depending on how it copes once the bodywork is on, I might see if I can get away with going up to 5:1 in the chassis ( a 40T driving an 8T instead of the 36T driving a 12T that it now has). That would give a final ratio of 1:1.2. The area where the suspension arms mount to the axle isn't strong enough either, needs some reinforcement.
  9. AxeSlash

    [WIP] Grave Digger

    For anyone that's interested, here's the drivetrain and steering, although the UJs on the steering shafts are now CV joints:
  10. AxeSlash

    [WIP] Grave Digger

    That probably comes from the lack of limitations that Sketchup imposes :P I suspect that something LDD might not let one achieve some of those not-quite-pythagorean triangles :P The green stuff is loosely based on the real thing, as far as lego dimensions allow.
  11. AxeSlash

    [WIP] Grave Digger

    More progress. Changed some bits at the very front of the axle to reduce rack twist. Strengthened the bottom shock mounts a bit (they were prone to coming apart) Swapped out some UJs for CVs in an attempt to reduce backlash in the steering. It's a lot better, but still not very good...it's as good as it will get without redesigning the entire centre chassis section and/or doing away with the option of crab steering. Whether the CVs can cope with the strain of moving those big tyres remains to be seen. Added a beam across the bottom of the portal pivots to strengthen. Haven't checked if it's helped yet - ran out of time to do the other side. Added some retro axle safety chains, 80's monster truck style :P Bought a PS4 controller so I can use the SBrickController app (never could get the Xbox One controller to work with my M8) The two tan 20T gears visible in the last shot are the main culprits in the steering backlash problem. The axle on the right is now in it's finished state. The axle on the left still needs some bits changing to match the other one. Next up: battery and SBrick supports, then bodywork (during which I will almost inevitably change something and as a result run out of black parts, then have to wait for a Brick Owl order to arrive...)
  12. AxeSlash

    [WIP] Grave Digger

    The truck in Fury Road is not a Bigfoot. In fact, there were two trucks used in the film, both of which were Australian...I'll try and find the source on that info. I toyed with doing that as well (Fury Road is pretty much my favourite film ever), but the curves would be difficult/impossible to make look good without going with a full stud body...which my bank balance can't cope with right now :P EDIT: Ah I see, it's called 'The Bigfoot' in the film, although in real life it is not a Bigfoot 4x4 Inc. truck (pretty sure Bob Chandler's lawyers are itching right now): http://monstertruck.wikia.com/wiki/Shattered_Silence
  13. AxeSlash

    [WIP] Grave Digger

    Built some more on this tonight: The steering is a joke - way too much play. Once I've added the bodywork, the steering at the axle will be in for a redesign (when I know what parts I have left to play with). Probably going to use the longer racks and cut out the two 3L beams completely. It's also a bit slow. There's plenty of torque available so I think it's time to gear the XLs up a bit. The suspension has no sag at the moment, but hopefully the weight of the bodywork will help with that. Other than that the suspension works quite well at the moment, although I had to flip the saddles at the top of the shock assembly around to make the shock assembly longer so that the chassis did not bottom out when fully compressed. Body roll might be a problem when the rest of the weight is added, but I'll cross that bridge when I come to it. Might need to add a sway bar system. The lunchbox tyres can hold the weight easily so far - no sign of deformation yet. We'll see how they hold up when the bodywork is on :P The axles might need some lateral strengthening - I get a slight (unintentional) kingpin incline at the moment ;) Slapping a 7L beam across the top of the diff will probably do the trick, although that may limit the suspension travel a bit.
  14. AxeSlash

    [WIP] Grave Digger

    Build progress: You can see the triangulated 4-link suspension arms there (and the horrific steering geometry). Lunchbox tyre + 44772 just to show that they fit together, in case anyone was dubious. You can actually fit two 44772's inside a Lunchbox tyre, but this happens: You get an unnatural looking bulge in the sidewall because the bead is being pushed outwards (the rims are slightly too wide). That's kinda the opposite of the effect most monster trucks have - they usually use thinner rims than recommended for their tyres so that they get a more 'balloonish' effect on the sidewalls. So I'm opting to just put one rim in there, and leave the other bead entirely unsupported. I reckon the tyres can handle it. If not I'll make some foam inserts for them. So far I haven't had to modify the original design at all (apart from having to use a grey worm gear - one of the black ones I own turned out to have too much friction inside), and everything feels fairly sturdy...the only minor problem so far is that at full suspension compression and extension, the worm gears on the driveshaft and steering shaft foul on each other. That said, I suspect that once the springs are installed that they will limit the travel before it gets to that point - if my calculations are right I should get around 6L of axle travel with the springs in place, which is less than the approx 8L of axle movement at the moment (with no springs)....we shall see. I may need to give the racks more guidance as well, there may too much play in them at the moment. I'll deal with that once the chassis is built and I can see whether it causes an issue or not.
  15. AxeSlash

    [WIP] Grave Digger

    Yeah the OD and width is correct, but I was talking about the RIM diameter - lunchbox rims are too big. There are some older monster trucks that had rims of a similar size, but most modern ones are much smaller.
  16. AxeSlash

    [WIP] Grave Digger

    Yeah thought that was what you meant, I just wasn't familiar with the term 'double shear' Lunchbox tyres aren't exactly correct scale dimensions, but they're the nearest I've found. I'd still prefer something that would fit on a smaller rim (with the same overall diameter), but it just doesn't seem to exist. The tread pattern isn't technically correct either, but again it's the best compromise that can be found at the moment without going up to something silly like Clodbuster tyres and custom parts to mount them on...which would result in an ENORMOUS MOC that would be fairly difficult/impossible to power without stripping gears etc. I also didn't want to go cantilever because the real thing doesn't have a cantilever system. If I was doing one of the older Bigfoots then yeah, that would be cool and probably work a little better. I guess it's always difficult to draw the line between realism and functionality...I'm trying to lean towards the former here.
  17. AxeSlash

    [WIP] Grave Digger

    Yeah I thought that might be the case. Drive is 2 x XL motor, steering is 2 x servo. There is an M motor for switching the steering mode, but I might be able to get rid of it if the SBrick profile designer will allow me to do it there instead. I've used the suspension setup before and the links are easily secure enough on the ball pins themselves; but yeah I see your point about the ball pins popping out of the beam. Can you explain what you mean by 'double shear'? Thanks
  18. AxeSlash

    [WIP] Grave Digger

    Also I did do a potential second bodywork design - Bigfoot 18's trophy truck-esque body: But a) those curved panels are too rare in blue at the moment, and b) some of the other stuff in blue is rare/difficult to find at the moment, and c) the wheelbase of the chassis is actually a bit too long for that body to be in scale. Potential improvements I may make at a later date: - Custom 3D printed rims, which would leave much more room for... - ...Custom 3D printed planetary hubs (real monster trucks have planetarys, and the portals mean that the axle ends up too high, making the suspension a pain to get correct. Not to mention the atrocious steering geometry) - Pneumatically dampened suspension, like the real thing - Gear box - going to leave this until I can assess how it performs without one, so I can see what kind of ratios I need.
  19. AxeSlash

    Efferman's Custom Parts

    I see your point. Yeah the outer hub is only connected to the beltwheel with the 3 pins...I thought that would probably be strong enough, but didn't consider the play. It might be better if the 3 pins were actually part of the outer hub, then you could just have a short pin at the end of each one that would fit the beltwheel better, and the whole thing would be stronger/less play? The ring gear housing probably needs a slightly different shape on the outside so that the beltwheel and outer hub touch it and thus cause less play. Obviously it would need some polishing before use.
  20. AxeSlash

    Efferman's Custom Parts

    I had an idea in the shower earlier (where the best ideas are often had and forgotten!) - having read about peoples' experiences trying to make pneumatic suspension work, the common problem is that it's either too slow or too hard unless you drill out the inlets. So, I thought "why not have two inlets next to each other to attach the hoses to - that gives you twice the airflow = less dampening"...Something like this: Is that possible with Shapeways, Efferman? Would the plastic be smooth enough for the seal to move down? We wouldn't want to wear out the seal due to abrasion, either. To clarify, I'm only talking about making the yellow part - the rest would be the standard parts from 21828c01 / 19476. Note that I've also shortened it by 1L by putting the pin hole on the side. That hole might even be better off as an axle hole for this application (like the existing 9L shocks). As a real life application, you would connect the two bottom inlets to a couple of spare small cylinders that are fixed (i.e. cannot move) that would act as miniature air tanks. As the suspension compresses, the air is forced through the inlets into these (fixed) cylinders at a faster rate than would be possible with the current stock Lego cylinders, but still slower than undampened suspension (i.e. like Lego's existing 'shock absorbers' that are actually just springs). What I'm trying to replicate (kind of) is a bypass shock (google it). Monster Trucks and Trophy Trucks use them. I have a scale Grave Digger MOC in the works at the moment that would benefit enormously from these new cylinders. For suspension usage, I can't see a need/use for the top two inlets, but I've included them in my drawing just in case someone finds them useful for 'normal' pneumatic usage.
  21. AxeSlash

    Efferman's Custom Parts

    I had a similar idea a while back, although I wondered if using bushes as bearings would help with the friction: Also had some ideas for cross blocks: Also we could really do with some proper long-travel shock absorbers. With pneumatic dampening. I'm in the process of building a monster truck (hence the planetary idea), and need something with 5-6L of travel in order to be in scale with the real thing. Or maybe shocks that can be connected in series without introducing friction. I might knock up a Sketchup idea to illustrate. Edit: Hah. just noticed you already some of the cross block ideas :)
  22. Further to this thread, if anyone is interested in monster truck tyres (as an alternative to the Power Puller tyres), I've discovered that you CAN fit the tyres from a Tamiya Lunchbox / Midnight Pumpkin onto a pair of 44772 rims. I've got some pics but can't figure out how to post them on here without having to upload them to a separate server. There are only a few problems with this combination of tyre & rim: 1. You have to use two rims due to width of the tyre; this in itself isn't a problem, but pinning the two rims together without ending up with a 0.5L gap between them is a bit of a pain. 2. The bead of the tyres is stretched to it's limit - DON'T do this if you intend to use them on your Lunchbox / Midnight Pumpkin again, as I suspect they will become a bit loose after some time on the 44772's 3. Two 44772s are actually a tiny bit too wide for the tyre, so the sidewall bulges out a little bit in a slightly weird profile. 4. The bead is actually too wide for the 44772s, BUT it still fits due to how tight they are. It takes a bit of messing about to get them to fit on properly. 5. The look isn't exactly as I was hoping for; the rim diameter is too big compared to the overall diameter, so it looks like a very oldschool monster truck wheel from the 80s, rather than the modern trucks where the rim diameter is tiny in comparison. All of that said, they still look good. Caveat: the tyres feel very soft and I haven't got as far as mounting them onto a MOC yet, so it may be that they need some foam inners to support the weight of a PF-based MOC. I'm in the process of building a 1/15 Grave Digger with PF motors, so once that's complete I'll report back. Also I don't know how well they will steer due to the huge width.
  23. Has anyone got some 6595 and 22253 rims on which they could do some accurate measurements (you'll probably need a set of calipers, but at a push a ruler might do it) for me? I'm trying to see if I can shoehorn some Tamiya Lunchbox (3rd party) tyres onto them; I'd need to use 2 hubs per tyre so that's a total of 8 hubs and 4 tyres that I don't want to pay for if they're not going to fit! I need the diameters of: The smaller outer rim The larger outer rim on the other side The inner rim The groove that the tyre sits in To the nearest 0.5mm would do. If it looks positive, I'll buy everything and if they fit I will report back; it would mean that we could all have realistic looking monster truck tyres without having to fork out for power puller tyres :) Thanks
  24. AxeSlash

    6595s and 22253 rims

    Thanks for this; it appears that the dimensions on Bricklink for those rims are way innacurate (it says 49.6mm). Need to find some other rim that will fit :P The problem I see is the bead size of the lunchbox tyres, it's 5.35mm, which seems way too wide for lego rims (which I think take somewhere between 1 and 2mm bead maximum). I could trim the internal diameter down a bit, but trimming the bid width down would be difficult I think. Unless anyone has any reccomendations for other 3rd party monster truck tyres that may fit a Lego rim? I'm after something that looks like the real deal (i.e. a really wide tire with a comparatively small rim size and chevron tread pattern). Before anyone mentions power puller tyres, they only satisfy the first of my criteria :P