Blakbird

As long as we are going to make it really complicated, let's add a few more variables. First is that the tangential force between a rubber tire and a surface is not pure friction (F=mu*N), it is also adhesion. Unlike friction, adhesion is not necessarily a function of normal force. Then let's not forget that as a tire spins dynamically against a surface, it heats up. Both friction coefficient and adhesion change as a function of temperature. From a physics standpoint, the static friction coefficient is always higher than the dynamic friction coefficient, so you always have better traction when NOT slipping your tires (considering only friction). Neglecting aerodynamic drag, the forces on your car are exactly the same no matter how fast you are going up the slope (or are stopped) as long as your speed is not changing. So speed shouldn't matter. But clearly rotation does matter. What then, is happening? My colleagues and I have spent considerable time discussing this. Our consensus is that it is an effect of the shape of the tires. These tires are somewhat "knobby". When rotating, the irregular shape of the tire has a greater probability of striking and gripping the surface than a stopped tire. The vehicle therefore gets better traction when the wheels are turning quickly. This effect would be even more noticeable on an irregular surface like a gravel hill.

I also wrote a review of this model here on Eurobricks, and I agree with most of what you said. In general, I also prefer pneumatics. The 8459 would be an example of a similar 4WD loader with V-6 that is done with pneumatics and you can, of course, control both functions at the same time. One thing I do like about the linear actuators, however, is the mechanical complexity that goes with them. With pneumatics, you would simply route some tubes to the actuators. With the actuators, you get a pile of gears, a switching transmission, and a bunch of u-joints to pass across the articulation axis. You can debate whether or not all of this is a good thing, but I always enjoy as many gears and rotating parts as I can get my hands on. The same is true of 8862 vs. 8455. 8455 is the best pneumatic set ever, but I just built 8862 yesterday and I had forgotten how much I love the 5 mechanical features.

Personally, I can't decide if it is good news or not. For years, we AFOLs have been asking (begging) for bigger and more complex sets. Over the past couple of years, LEGO have been delivering with sets like 8258 and 8043, both of which I think are dreams come true. On the other hand, we may be getting to the point where the sets are so complicated and must be built so carefully that they will not work for a significant percentage of the buyers. If this is the case, LEGO may just decide that sets of this complexity are not worth it to produce because they have to deal with so many complaints which effects their image. I hope I am wrong. I want to keep seeing sets like this in the future, and it's OK with me if they get even more complicated. Anyone who works with complicated technical hobbies knows that things don't go right a lot of the time and a lot of trial and error is involved in getting something that works. I'm sure LEGO did lots of testing and I'm sure they are disappointed that some of their customers are having problems. Here's hoping there are some simple remedies for the issues of 8043 or at least that most people are not having problems.

Crowkillers builds a lot of muscle cars which you can see here. There are no instructions for most of them, but there are now free instructions for the Lamborghini Gallardo. Not exactly a muscle car, but a recommended build.

Very clever! It is certainly a crane. Since it is a crane in multiple senses (and is even lifting a heavy load), you are sure to win the competition. Competition or not, this is a well done MOC. The shape is quite organic. Show us what the gears do! It looks like the head bend downward on a 4-bar linkage.

Yes, it has been known to happen. See the page on the old 851 tractor, for example.

This is a cool idea which I like very much. By taking some of the load off the actuators, we can solve most of the problem. As you can see in the previously posted picture from 8851 in Technicopedia, the black rubber bands deteriorate and crack if left extended over a long period of time. However the silicon bands in this picture do not have that problem. By the way, nice job picking colored bands that match. Another tact to take on this same potential fix is to use one (or two) of the long stroke (10.5L) shock absorbers instead of rubber bands. If a little mechanism was employed to have them help lift the boom while still staying within the limits of their stroke, I think that could be a big help. In this picture, you can see a black bushing in between the two linear actuators. A shock absorber could be put in here and attached to a different point on the boom to help push it up. It would not be a huge change in lift, but it may not take much to make a big difference.

I wouldn't call anything "defective" here. The motors and actuators are simply being used at the limits of their capability. Who said anything about a "shelf decoration"? That's an exaggeration. The boom raises and lowers slowly under some circumstances, but this does not ruin the model. It is still an excellent model and among the most playable Technic sets possible. It is certainly still functional, but perhaps not perfect. I've stated it many times before, but I guess I'll do it one more to make sure it is clear. I am NOT A LEGO TECHNIC DESIGNER! I just wrote some articles for their blog. I have no access to anyone at LEGO any different than any other AFOL in the world. I have no ability to make recommendations on behalf of the community. You need an ambassador for that. At any rate, I'm still happy with my 8043. If anyone comes up with any modifications to the design to help improve it, they would be great to see. But it is a pretty special design out of the box.

It all depends on the load on the gears. My MOCs which have run all day at a convention have had very low loading and yet have shown visible wear. The linear actuators for the boom in the excavator have very high loading so the wear would happen much more quickly. Again, it is just a theory. The only way to know for sure would be to tear one apart. And of course, some people have had problems with their 8043 even when it is brand new. You connect one of these train regulators (which outputs 9V at a good current) to one of these PF extension wires which lets you connect it to the old 9V system. Sadly, this requires you to tether the excavator to a wire. Alternatively, you could also use one of the old Control Center units to get more power.

Cross posted from Lugnet... This is not my idea, unfortunately, but it is very clever. It uses a differential and a PF motor to control a pneumatic cylinder and valve. By reversing the direction of the motor (which drives the compressor), you also actuate the switch and change the direction of the actuator. It is less compact than Sariel's autovalve, but I like the concept very much. Original post: I haven't posted in this forum since 2008 and haven't built much, but upon looking at the new 8043 Excavator set at Toy's R'Us, it became apparent that although the new linear actuators dramatically simplify the process, they are not the only solution. I call them linear actuators because they are typically motorized and they extend/retract. It is possible to do the same with pneumatics....if you add a differential into the system. By doing this simply forwarding or reversing the motor will extend/retract the pistons. This is not the ideal execution of the idea and there have undoubtedly been others who found a different way to do this same thing, but it shows the general idea. One could obviously incorporate a bigger motor, a different gear ratio, or even shrink the size of the assembly. Hopefully this idea will help those of you who still want to use pneumatics do so. Sorry the youtube video is fuzzy. -Nathan Bell Brickshelf

I am starting to develop a new theory. My excavator worked fine at first with "normal" balancing of the linear actuator length. Now, despite the fact that I have balanced the actuators much better than they were originally, it seems to work worse. By that, I mean that the motor is working harder to move the boom. It still works; the motor doesn't stall. It simply moves slower and with more effort. Oddly, it now seems to take more effort to LOWER the boom than to RAISE it. At first, this doesn't make any sense since obviously gravity should be helping on the way down. If you use your finger to take a tiny bit of weight off the boom, then suddenly everything speeds up and the gear and motor system sounds fine. What this suggests to me is NOT that the actuators are misaligned, but simply that they have a lot of internal friction when being forced to move under load. And this behavior seems to get worse over time. If any of you have brought motorized MOCs to a convention and let them run all day, you have observed the fine bed of ABS dust that is generated by the wear of the gears over time. Eventually, the gear teeth will wear off, but even before that the dust gets into tight places and causes binding in the mechanisms. I found, for instance, that I had to rebuild my V-8 after Brickcon to get it running smoothly again, despite the fact that nothing had been done to it other then letting it run. My guess is that the LA outer ring (tube) gear which drives the threads on the rod is wearing when being forced to run motorized under heavy load. Over time, this dust builds up in the LA and makes it less efficient. This is only a theory. If correct, it calls into question the lubrication solution. A linear actuator which is lubricated when NEW may have reduced wear and last longer. But a LA which is ALREADY WORN when lubricated may just cause all the wear dust to stick together and make things even worse. Who wants to find out?

OK, I tried it. The good news: Everything still spins in the correct direction if you reverse one of the gray gears. The two linear actuator remain (apparently) perfectly in sync as they rotate with respect to the chassis. The bad news: Not only did it not help at all, it made mine perform much worse for some reason. My copy actually worked fine before the mod. So I changed it back to the original configuration and it still works terrible. So basically I managed to screw up my excavator by trying to fix it.I'd still say that this is a recommended mod from a technical standpoint, because it DOES keep the LA's in sync throughout their stroke which is a good thing. However the whole excavator seems to tax the motors to their limit and therefore it draws a lot of current from the battery box. The key to the whole thing seems to be fresh batteries. I'd switch to rechargeables except then the voltage would be lower which would be even worse. If you plug a train regulator into the whole thing, it works great! The moral of the story seems to be that Chinese made linear actuators are not all created equal. The external tolerances make them seem the same, but internally there are slight differences in the start points of the threads that change the length of different actuators as they extend. On top of that, LEGO spur gears are un-lubricated and do not have perfect efficiency, so there are just only so many stages you can use before the loss is noticeable. Probably most importantly, LEGO axles have no bearings, so when there is significant load on a system (like a giant cantilevered arm for instance), the drag becomes significant. Add that all up with the most complex (official) Technic gear system ever, and I think we have reached the limit of what can be accomplished. Personally, I'm OK with a plastic excavator I built myself with no glue or fasteners working as well as this one does.

That's what I get for typing something at my desk when I don't have any parts in front of me to try it! It would seem then, that the proposed solution would indeed keep the actuators in sync at all positions.

You can't do that. Then the LAs would move in opposite directions (one would get longer and the other one would get shorter). the grey gears need to be where they are. In order to reverse them, you would also have to reverse the direction of the tan input bevel gears that drive them.

Considering that he used this turntable for his massive Moutaineer excavator, I think we can conclude that it is a viable design. I think the primary reason he came up with it is that he wanted a minifig elevator to pass through the center of the turntable which can't be done with a central axis or one of the standard smaller turntables.

Unlike pneumatic actuators, linear actuators do not have any seals so there should really not be much to wear out. I suppose it is possible for the rod to corrode over time, but the internal threads are plastic and protected from UV, so I would not expect them to degrade. What is the problem with your older LA's? I just checked mine and they seem to be OK.

Interesting! My guess is that this is happening because of the fact that the input gear on the LA is actually rotating when you move it from the up to the down position. Think about it this way. Assume that the two gray gears circled in the image are fixed (which is true if the motors are not turning). When you lift the actuators up, the tan bevel gears feeding the LA input have to rotate which effects the length of the actuators. Because one of the gray gears is on the left and one is on the right, one of the actuators will get longer and one will get shorter. It is only about 1/4 turn of the actuator input, but as JunkstyleGio showed, it is a noticeable length difference. My suggestion is this. Synchronize the actuators in the UP position. Moving toward the UP position is when the most stress is on the motors, so that's where you want there to be as little misalignment as possible. The motors can probably handle more misalignment going DOWN because gravity is helping. My guess is that this would solve a lot of the motor stall problems. It is worth mentioning that parallel pneumatic actuators are self balancing and never have this problem.

I just purchased all the new Technic sets for 2H2010. 8043 (x2) 8051 (x2) 8052 8053 That kept me busy for a while!

If you are looking for a list of technic parts, I also recommend Jim Hughes' Technica. He has an element registry that has photos of every type of Technic part up until about the year 2000. It is an invaluable resource. It has not been updated in a long time, but it is still very useful for older parts. Here are a few samples:

The inventories posted in the instructions are always for everything in the box, often even including the extra parts. So you can't tell from the inventory what you need for the B-model. I often make inventories from LDraw files, but of course you have to model the whole thing in LDraw first!

Ooooo, a Metachronal rhythm. Never seen one in LEGO before, so you've made a first! Very well done indeed. It looks like the one tooth offset is the key to the whole thing. I can image this same mechanism constructed in a much longer chain with a continuous offset on the gears so you could actually see the whole wave.

Note that I just bought one at my local LEGO Store on Sunday and it was only $179.99, apparently cheaper than from Shop @ Home.

It's so smooth and chrome-tastic.

Obviously, quite a few people including myself have built this model and have had no problem with the power of the M-motors. There are a number of videos showing it working. I'd guess that there is a problem with your construction. Elsewhere in this thread, it has been discussed that if the two lift actuators are not at the exact same length, some binding may occur. I'd recommend fiddling with and seeing if you can get it to work better. I don't think there's a fundamental flaw in the design. Saying it sucks is pretty harsh.