amorti

Stud.io is hard, but kinda fun :D Thanks to @Philo for the buwizz custom part! Stud.io file here: https://bricksafe.com/files/A_morti/piterx-fast-rc-motorcycle/moto.io

10: DO something dumb 20: GOTO 10

My RC motor arrived today, and I've seen what you mean. Extending the swingarm by 2L with a few liftarms and a couple of gears is trivial, but the tyre is *just* too wide to fit in the centre of the swingarm. At that point there's no sensible way to get it working with these bigger wheels. Oh well I'll have another look at it once my vintage set 8422 arrives. Any luck that one can sit in the shelf with big wheels on it.

Humbly, considering the level of functionality, I think this awesome model lives in the technic forum, rather than the very quiet scale modelling forum

That looks brilliant! As shown in this thread, it is possible to get a Lego bike to stand up. Not sure if the high CoG would present an issue to that. I think the trick is to build in LOTS of trail, not necessarily by having cruiser-like rake angles, but by mounting the fork behind the steering axle.

I had fireblades and Daytonas in my youth, now I've a cb300r. Things change when you get a kid! It's really a shame about the wheels won't fit inside the motor. These bigger wheels are right for the scale already, IMHO. But, with the ≈2.5L lower tank, I hope the smaller wheels won't look quite as mini. I've never felt the creative spark to make a MOC from scratch. But give me one with great potential, and watch me optimise the heck out of it. Really there's no freeplay left except the "head bearings", and those have to be free to move. I might dig through my Chinese bricks and see what's suitable, ISTR CaDA friction pins have no slack but also minimal friction, might be good here. Please do give those mods a try on your model? I'd like to hear feedback if you try it.

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In a real bike there might be a few causes. As far as I know, the most common would be: lack of damping (and/or too low spring rate) in the rear shock, too much power lifting the front so it skims the tarmac, real wheel not in line with front wheel. There's two of those you can't really fix with Lego since Lego shocks don't have damping and this bike obviously has way too much power. Putting a stronger spring is easy enough. I'm using the one from 42036 (hard) and in a static test it feels balanced to the front, what do you have fitted? But, you can definitely do a few things to stiffen the frame and reduce slack across the whole model. I worked on it some more today. Got the geometry as you have it, relaxed the colour choices, used long panels in the belly pan, and stiffened up the frame which allowed mounting the fuel tank lower. I also note the buggy motor is attached across an axle; I think it'll be better mounted on non friction pins. Maybe pins with friction would act as damping, maybe they'd just make it too tight, will test it once the motor arrives. Here's some pics. Decided to order 8422. I'll get an hour of nostalgia building it, then use the tyres for this :)

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@piterx thank you! That's really helpful. I had placed the two 4*2 L-beams differently as I'd assumed it would be axle to axle. I'll try again how you have it I did wonder if the moments your video shows headshake could be due to flex or looseness in the frame. So I think some parts of mine could be improvements too, just between the frame's front downtubes. More pin to pinhole, less axle to pinhole connections. I can't wait to get my buggy motor and tyres and give it a go @piterx did you compare the grip of the tyres of 8838 and 8422? I like the look of street tyres better, but I'd get whatever grips more.

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I've had a go at building it. The colours are interesting, as it's built from mostly scraps of the Corvette and 42036. It's so bright underneath, it could almost be an official set Couple of questions. As you see I don't have a buggy motor yet, but I've brick built a placeholder and ordered a replica. Are these tyres going to fit or are they too big and I need to get the smaller old school motorcycle wheels? Funny as I had 8422 many many years ago and that would seem the ideal set. I couldn't figure out how the original headstock area was done from the available pictures, so I just did it on the basis of whatever lined up. It is surprisingly sturdy (form locking the forks helps) but has more rake angle than I'd really like. It has a decent tendency to run straight at "pushing it across the kitchen" speeds so I reckon it will work fine, but maybe it'll steer lazy at high speed. There again back-to-front yokes (all Lego bikes and RC bikes in general seem to have this) seem to suggest more trail is better? More pictures in my bricksafe album if anyone has any suggestions.

Where are they, please?

Looks brilliant, I'd like to make it. Could you make instructions? Or give us some more pictures so we can figure it out?

The sturdiest 4 speed gearbox out there is in brunojj1's red supercar. You can get the instructions free in the CaDA Facebook group. It's basically a pair of identical/mirrored gearboxes, one each for the two CaDA Pro L Motors, which are easily stronger than Lego XL Motors. Even so, that starts to get unhappy and make plastic dust when you put 4* CaDA Pro Motors in it, although it may have been the differential clicking.

Well, if your original is fine, I guess it can be that MouldKing used a slightly different type of plastic and it melts easier. There's not much other explanation since with two buwizz, yours would be packing more speed into that shaft. Or... MouldKing's version uses 3* identical 9.5L shocks. No idea how the spring rate is. Does yours use 6.5L shocks in the middle axle?

There are a lot of cases where the CV joint between the exhaust pipes is causing enough friction to waller out the hole in the large frame, and snap the CV joint. 25:40 6:45, and this guy confirms the problem is well known in the Chinese forum. It would be easy to put the failure on Chinese part quality, however I don't think it's the case. Let's look closely at this pic (deliberately high resolution), focussing on the area between the exhaust tips. The central suspension link is 9L long, the driveshaft is only 6L long. The suspension link and driveshaft pivoting points aren't even near the same location. These two things will mean the driveshaft needs to grow and shrink quite a bit with suspension movement, but the joints at each end don't slide. Also, I think I see the panhard rod pulling that centre axle "up" in the picture. This will also create friction exactly at the point where the CV joint has been failing. Any thoughts, @Zerobricks? Edit: I noticed the panhard links between the rear axles are from opposite side, and quite short. As the suspension travels, that's going to twist the axles in some interesting angles.

What have you oiled the cylinders with? I'd imagine anything from mineral oil would degrade the seals.

@Celeri - PM sent regarding Chinabricks sellers.

Not sure? I only have the powered up bits from 42099.

Looks cool! I'm guessing it has a CaDA Pro motor in there? You certainly wouldn't get that kind of speed with a Lego motor and 7.4v CaDA battery! This is the type of project where a Buwizz3 would really make sense. You could use a PU 45303 M-motor as a servo, saving yourself the pain of unreliable PF servos and allowing yourself to build it with <90 degrees of steering input to lock (PF servos tend to try and rip the model apart if you physically block them at <90 degrees), and then also get plenty of power for whatever brand L-motor you use for drive, whether PU (if it fits) or PF.

It seems worthwhile to try, as there's not really any good stepless steering solution with power functions. I just had another Lego servo (nowadays ~80€ worth!!) fail yesterday. Same thing as the last two, the metal tracks in the circuit board get continuity between neighbouring pads, and then you need to open it up. The first two times I sent to Lego for a new one before opening the broken one (how much more broken can it be than broken?) Now though, they don't have new ones. 2/3 I opened works again after that (one couldn't be saved or was my learning curve), but once opened its obvious and those are not worth 80€ anymore. They're working on it but MouldKing's PF servos still don't really do proportional steering properly, yet. So, considering everything I think it might be worthwhile to try mixing pf and p-up...

@Zerobricks how hard would it be to convert this to buwizz 3.0? Seems like the powered up M motor 45303 would fit fine for the gearbox, but I'm not sure what powered up motor could best be used for steering?

Very cool to see something other than the usual Lego suspension. Could you bring the wishbones back a little, to add caster angle? I guess it'll ideally need to replicate a FWD car with long suspension travel, or is it plausible to make it a 4wd?

+1 :)