How flexible are your cars?
Posted 03 January 2013 - 11:50 AM
My current studless car WIP model twists quite a bit. About 10-15 degrees under its own weight (when resting on its two opposite wheels) measured between the two ends of the chassis (body parts not taken into account). The model doesn't have PF elements, but it's quite heavy anyway. The wheelbase is 34 studs long.
The twisting doesn't seem to affect functions (gears won't slip), the model isn't for outdoor use and isn't for offroad-ish use. The model seems to bear repeated twisting (doesn't disintegrate), hatches stay well aligned etc.
So the question is: should I be concerned about this, is it a noobish mistake, if it's a mistake at all? How about your studless cars or official studless car sets (for example 8070)? The Unimog seems to twist quite a bit too, but it's not fully assembled at this time.
Thanks for any answers in advance!
Posted 03 January 2013 - 12:40 PM
Posted 03 January 2013 - 01:32 PM
I over-engineer my MOCs big time (not a good thing), but this does mean they don't twist/flex, whether studded or studless. My earlier creations used to, but the more big creations I've built the more solid they've become; now they're basically one solid beam.
Looking at your chassis (which looks great by the way), there are a few places where there's only 2 beams running longitudinally. This isn't enough to stop twist. Find a way to add another two and the flex will all but disappear.
Posted 03 January 2013 - 01:52 PM
To my experience, adding more longitudinal beams is much less effectively stiffens the chassis than adding stiff corners (one of the edges of the corner should be longitudinal). My chassis has quite a lot of longitudinal beams, the images may be misleading. Even the "cover" of the gearbox adds beams, because the half-stud offset is achieved by the placement of the gears. There is always at least 6-8 beams running parallel. At the gearbox, there is a second layer of frame 2 studs above the bottom. This second layer can1t be seen on the images.
The problem with corners is that corner parts doesn't fit in the chassis, but maybe I'll do something about it.
The question is that if twisting is not a big deal, then I don't have to sweat too much on reinforcing it when (if) I redesign the chassis.
Edited by Lipko, 03 January 2013 - 01:55 PM.
Posted 03 January 2013 - 02:22 PM
Posted 03 January 2013 - 02:34 PM
It's hard to believe, but your every day car has quite a lot of flexibility in its body. That is done for a few reasons, but most important it is for ride quality.
A lot of rally or racing cars are getting a lot rewelding done to them to increase its sturdiness. It makes for a lot better driving and handling characteristics, but ride quality suffers a lot. Though we don't know that racing machines are not for comfort ;).
I would allow some flexibility in lego technic sets. Obviously I would try to make as solid as possible, but when you work with plastic like this its hard to do fully solid construction. It's not like Otis needed.
Posted 03 January 2013 - 02:54 PM
Posted 03 January 2013 - 03:19 PM
I think the low twist is due to the diagonal beams in the lower chassis:
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Posted 03 January 2013 - 03:23 PM
If you build a RC car with gearbox you will need to build as solid as possible but with no RC cars I don´t think more important the flexibility.
Posted 03 January 2013 - 09:58 PM
Most modern cars don't even have a chassis. The body forms part of the structure of the shell, including the roof. This is why convertibles tend to be heavier because using only the lower for frame for stiffness is much harder. Trucks still have an old style frame and you will almost always find diagonal bracing.
Posted 04 January 2013 - 12:57 AM
The extra weight of convertibles is somewhat notorious in the car world. It's why you get so many "oversize sunroof" semi-convertible cars, and high step-over into the doors (alternatively: doors that are very sticky to open, and cars that fall apart if you open the door while driving). Just leaving a couple of beams at the top of the car helps a lot. If you want to see lack of torsional rigidity, look for photos of trucks rolling over. Often you can see one end of a flatbed semitrailer rotated 30° or more from the other. You more rarely see that with box trailers, even though the superstructure is typically quite flimsy because it's quite high/wide compared to the chassis.
Posted 04 January 2013 - 01:45 AM
Posted 04 January 2013 - 03:18 AM
Now on this truck there is no horizontal beam connection like the crawler has..
This is what things look like when you have all four tires on flat ground.
Now when you start to put the suspension to use. The vertical beam will begin to flex. You can use your mouse arrow to measure the distances on the two beams in the two pictures and see that the bottom one is definitely closer.
Edited by Boxerlego, 12 April 2013 - 05:53 PM.
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