ludov

The piece is maybe a weak point, but it holds up just fine in my model, which is manual. I agree that for RC models, specifically off road, it is probably not the most robust solution. The "egg piece" @I_Igor suggest can work better, or maybe just bracing the L-beams horizontally can help as well. Thanks for the feedback

I haven't been super active lately, due to moving house, changing job, etc., but I thought I'd share something I've been working on-and-off the last couple (*ahem* many) months: a solid driven axle for trucks. The reason it took so long is because I rebuilt it a gazillion times, probably because my requirements were difficult to meet (at least for me ). It had to be 19 studs wide, use only common parts only, and it had to be "chain-able", i.e. I wanted to be able to use the same axle for a 4x2 and a 8x6 or 10x6 truck. Finally I managed: I'd be happy to receive feedback on it, if anyway would bother to build it As shown, the frame should be 5 studs wide, but it's easily modified for 4. Also, leaving the yellow bushes off the axles allows you to put 64.2 wheel a bit closer to the frame (replace the 3L pin with bush for a regular pin) for a slightly-over 18 studs wide axle (replace the 9L axles with 8L obviously). A stud.io file can be found here. I found that stud.io has a pretty awesome instruction builder these days, so I made PDF instructions (here) as a learning experience.

Wonderful build! Like Model Team, but with more functionality, well done I'm having the same internal debate on suspension in Model Team-like builds. It's an interesting feature, but a hassle to squeeze in, while the added value can be argued about. Glad you managed though, it's a nice plus!

@Jim can the "community future direction"-part of this discussion be split into a separate topic? I agree with @howitzer that the scope of this topic is not suitable for this, indeed, very important discussion...

A question to those of you in favour of allowing CaDA models here:- Currently, CaDA seems to offer only pieces that are functional copies of LEGO models, but may have different colors. Hence, a CaDA model, like the model in this topic, can be recreated fully in LEGO, albeit maybe not in the exact same colors. What if CaDA starts introducing pieces that do not exist in the LEGO inventory, e.g. even-length beams, or 5x5 panels, etc.? Do you still feel such models belong here? (This is the slippery slope I'm afraid of, @Bartybum).

Then I would urge you to contact e.g. @Jim and, if he agrees, to start a discussion about it in the Technic subforum. In that way the community can voice their opinions on the matter.

If the forums are to be more accommodating, then have that reflected in the site policy. That is what that policy is for. It cannot be that a handful of users decide that it is acceptable to go against the site policy, just because they unilaterally decide that it is a "special case". If trying to defend the site policy makes me a "hard-line, black and white elitist", then so be it. If the policy is changed to allow clone brands across the forums, I will accept it (and leave). Until then, as far as I'm concerned, this is a LEGO fan site, and not a CaDA fan site.

Then I would maybe have been fooled and not noticed. But the point is moot: the community rules are clear, in my opinion. It's a LEGO fan community, not a generic construction toy community. Deliberately violating the community rules and hoping that nobody notices doesn't make sense to me. Just to be clear: it is a cool model. Not per se my style, but I can see the skill of the builder. But if we're starting to allow LEGO clone products on the subforums, I foresee it's a slippery slope downhill. Personally, I think allowing custom parts, custom lighting, etc. is already too much, but apparently there was a community need for that. If clone products are going to be allowed, I'm out - no longer the community I'm looking for.

I was (one of the) reporter(s). Thanks for your contempt for me and this community. Just as you should not push Samsung phone topics on an Apple fan forum, you should not push non-LEGO brands on a LEGO fan forum. It's rude. If you read the Site Guidelines, you would have read there: (Emphasis mine). So there is a place for discussing CaDA, MouldKing, etc. on Eurobricks, but it is not the LEGO Technic subforum. This Community section is the place for such topics, so it has been correctly moved. If you feel unhappy about that, you might want to consider a different community to join.

@lmdesigner42 Cool, thanks for trying! I forgot about this little experiment, glad to know theory agrees with reality I wonder if there's some use case where this singularity can be actually useful, maybe something where you'd put a ratchet normally...? The rotational direction (or better: direction reversals) definitely plays a role: I guess the weirdness of stiction forces has something to do with that, but I'm not a mechanical engineer. Maybe someone more qualified can enlighten us.

I really like that first one, the blue old-school tractor. Reminds me of wat Technic once was before all the studs disappeared

Very interesting and a useful application of the "magic" differential! In case you missed it before: the "magic" is in the torque multiplication in the loop of gears. This multiplies the internal friction, causing the gears to bind up. If you drive the 16z-side of the differential with a 16z gear (instead of the 24z-side with a 8z), the effect disappears, without fundamentally changing anything in the gear layout of the setup! I have posted some analysis here:

You're right of course. Not sure what I was thinking there. With two plates between bricks the holes are in system, so two plates plus the bit under a hole in a technic brick is 8 mm or 2.5 plate. Putting zero or one plates between two bricks thus gives you 0.5 and 1.5 plate distance between the holes, or 0.2 or 0.6 stud respectively (one plate is 0.4 stud).

I thought that was interesting. Would be nice to have it extended to 0.5 stud spacing, since that's rather easy to do with the various connectors we have nowadays. "Back in the days" you'd sometimes see offsets created by having two technic bricks with zero or one plate between them, creating 0.2 and 0.6 stud offsets respectively, so that would be interesting to see also. And don't forget the 14-teeth bevel gear; I believe it can be meshed with the 24 teeth, if I remember correctly.

I'd try two 2x1 jumper plates with only a 1x1 headlight on the outermost, or on both (so two headlights on each side). +-+-+ |.|o| +-+-+

This helps. I finally got some time to figure out how this works. The transfer ratio from the left to right is 1 - 2/N, where N is the ratio between the differential ring gear and the driving gear. Here N = 24/8 = 3 and we have a transfer ratio of 1/3. Conversely, the transfer ratio from right to left is the inverse, so 3. If you try carefully enough, you can verify that the mechanism is back-drivable with a transfer ratio of 3: ---> [ 1 - 2/N ] ---> 1 2 N = 3: w2 = 1/3 w1 T2 = 3 T1 If you try to impose a velocity on axle #2, you feel 3 times the torque that is present on axle #1, including the internal friction of the mechanism. The reason why it is so hard to back-drive is that the gears bind up internally, because they need to overcome 3x the internal friction of the mechanism. If you add more gears, it'll get even more difficult to back-drive. If you change the 8z for a 16z on the other end of the differential, you have N = 1 and the ratio is -1: direction is changed, but 1:1 speed and torque ratios. In this case the mechanism is back-drivable and feels the same independent of which axle you drive. I'm curious to see N = 2, which is a singularity. In theory you should be able to rotate axle #1 and nothing would happen on axle #2, while conversely axle #2 should be immovable. For N = 2 you'd need to have an 8z mesh with the 16z ring gear of the differential, or a 12z with the 24z ring gear, without introducing any change of direction with respect to the mechanism shown above. Should be doable with some u-joints or something.

Wow, that is absolutely beautifully done! Just love those old Defenders and this is an excellent representation. Well done!

I always appreciate a good Defender. I think you captured the looks really well, and it seems to have pretty good performance also. Well done, I like it

GXC maybe, for those who don’t have those balls?

Interesting video, but as you've found out, differentials don't work like that when you drive the outer gear. Without considering the external torques (e.g. you holding the output axle), the problem is ill-defined. Basically, the differential is a three-"port" system, where every "port" is a pair of rotational velocity and torque: ______| (w1, T1) | __ | (w2, T2) ---------|-| |-|--------- |______| | (w0, T0) (excuse me the poor ASCII drawing). Power = rotational velocity x torque, or P = wT, and since a differential is a passive component, the sum of all three products must be zero, i.e. all power that goes in must go out somehow: 0 = P0 + P1 + P2 = w0 x T0 + w1 x T1 + w2 x T2 If you choose to drive w1 and w2, then we know that w0 will be the average of the two. This is a consequence of the mechanics: the third internal gear is fixed to the housing and thus constraint. This means that w0 is an output variable and w1 and w2 are input variables: w0 = (w1 + w2)/2 In matrix form, you'd have [w1] w0 = [ 0.5 0.5 ][ ] [w2] If you have studied linear algebra, you know this relation cannot be inverted: there's infinitely many solutions for w1 and w2 that satisfy this equation. That's exactly what you found out when you drew the two lines in your graph and noted that there's not a unique value for x or y. The complement of the above equation is [T1] [0.5] [ ] = [ ] T0 [T2] [0.5] Which should be familiar also: both shafts of the differential get halve the torque in nominal conditions. To properly analyse your mechanism you need to consider the torques that act on the input and output as well, then the problem becomes well-defined and you can solve the equations uniquely. @ukbajadave showed how playing around with internal torques can give you some interesting results. (I'm still trying to find time to do the math on that)

I was referring to the tractor’s wheels, they’re Fishertechnik also?

Oh, I want to build that...! (...once I get my building desk back from the home office setup...). What wheels are that exactly? The same as in your other tractor?

I think that’s an improvement! Do you think you can close the gap at the bottom a bit? White is terrible in that respect: any gap is immediately obvious.

This is a nice explanation! The principle is simple, but a good, clear demonstration is always helpful.

Wow, I really like this! Works smoothly and you put in a lot of functions in such a (relatively) small structure. Well done