tomacwhite

8043 Excavator - Lego update

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Well it shouldn't be doing that but I think it's a quite common problem with this set. It could be the design of the gear train to the track or it could be the motor that powers that track has become weakened by driving the LA's in the other mode.

One thing i'm wondering as it is not clear in this thread (or I have missed it) but the track that is not driving as it should, is it the track driven by the same motor that drives the pair of LA's that lifts the arm?

I just checked this out right now, and it seems the far left motor controls the left track, which is struggling as if it's under massive pressure; (the motor next to its right seems fine, which may explain why the right track moves so well without any strain) but when I switch to the LAs, they all struggle. At the beginning there was very little struggle in any of the LAs and motors, and I don't recall the far left M-motor functioning this badly. Idk, but I hope the issue with the LAs haven't damaged the motors.

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Wouldn't increasing the area increase the friction? Like increasing the width of a car tyre to get more grip.

Not in snow! ;) The opposite applies!

Frictional loss is proportional to force and area (like pressure) and frictional coefficient.

Taking the car analogy further, wider tires are more likely to aquaplane! this tells us that lubrication works best under lower pressures, and hence greater areas. If you think of lubrication as tiny balls it is sensible that more rolling balls (more area) equals more lubrication.

P.

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Not in snow! ;) The opposite applies!

Frictional loss is proportional to force and area (like pressure) and frictional coefficient.

Taking the car analogy further, wider tires are more likely to aquaplane! this tells us that lubrication works best under lower pressures, and hence greater areas. If you think of lubrication as tiny balls it is sensible that more rolling balls (more area) equals more lubrication.

P.

Well the larger tyres on supercars are there to give more grip. I know that in theory increasing the surface area reduces the pressure applied to each square unit of area meaning the amount of friction should stay the same but i'm not sure how well that theory transends into the real world. As far as I know the LA's are not lubricated. Aquaplaning only really is a problem on wet roads. So would increasing the surface area only work if lubrication is added?

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Ok. LA's with lubrications wich I use runs smoother and with less frictions. I first use it on 8265 Front Loader, which strugless the same, becouse of long gear trains and LA's friction.

Note that you can use only lubricants with Teflon (I use it for lubricating bicycle forks and shifters) which are not agressive to plastic. One other thing regarding LA's improvment - double treads may work cos they split force eqaly by two between screw and sleew, but main problem is contact between sleeve and LA's body. That contact surface needs to be solved. Solution: better tread surface quality (means slower production - by two or three passes by CNC production machine or by slower knife speed), and harder surface materials between plastic sleeve and body, maybe teflon plastic - hardened HSS metal plate.

Till new improved LA's come out, stick to teflon dry oil and fewer gear transmisions.

Edited by Petar

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Well, I've sent Lego an email too now, just to let 'em now about more people with the issues. I noticed the local store doesn't stock it anymore either.

I'll get some rubber bands in the meantime ;)

Oh, and the slewing of the superstructure goes without issues on my set, actually. Smooth as silk, only problem is the main boom.

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Not really. If the screw behaves ideally, then the friction is proportional to the normal force exerted by the screw. Increasing the number of contact points by a factor n will divide the normal force by n (assuming the load is distributed equally between the contact points), and summing them up will give (in theory) the same friction.

I by no means an engineer, but I work with a good number of them who are active in heavy steel industry and one of the things that have repeatedly come up is that no matter how long the thread of a screw, in the end it will always break at the thread closest to the head. the rest of them do not support the same forces and may even be completely 'idle' - in view of this I very much doubt that making the screw of the LA longer will increase performance due to sharing the contact surface, but maybe one of the real engineers here can set me straight...

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Hi.

I have the 8043 excavaor, bought from Lego Shop MK a few weeks ago, builded it slow so I don't miss any, it work great only that the main boom lifting a bit slow but fast on lowering boom, it work better with the rubber bands, the rest is ok. At the moment it's on a display shelf, I don't play with it, I like to look at it.

Should I sent it back? Should I wait for a service kit?

Dan.

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Hi.

I have the 8043 excavaor, bought from Lego Shop MK a few weeks ago, builded it slow so I don't miss any, it work great only that the main boom lifting a bit slow but fast on lowering boom, it work better with the rubber bands, the rest is ok. At the moment it's on a display shelf, I don't play with it, I like to look at it.

Should I sent it back? Should I wait for a service kit?

Dan.

Are you having the issue of the left track moving slower than the right track? I'm still not sure whether it's supposed to be like that. On full batteries it works better, but it still moves slower than the right track.

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I by no means an engineer, but I work with a good number of them who are active in heavy steel industry and one of the things that have repeatedly come up is that no matter how long the thread of a screw, in the end it will always break at the thread closest to the head. the rest of them do not support the same forces and may even be completely 'idle' - in view of this I very much doubt that making the screw of the LA longer will increase performance due to sharing the contact surface, but maybe one of the real engineers here can set me straight...

I think the screw breaks above the first thread not because the first thread is bearing all the force, but because the shaft between the head and the first thread is under more tension (all of it) than the parts of the shaft below the first thread. Below the first thread, the tension on the shaft may decrease proportionally to the number of threads above it, or it may not. It seems to me that all the threads should support an equal amount of force, so long as the threads are spaced properly (which could possibly be the problem with the LAs).

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I by no means an engineer, but I work with a good number of them who are active in heavy steel industry and one of the things that have repeatedly come up is that no matter how long the thread of a screw, in the end it will always break at the thread closest to the head. the rest of them do not support the same forces and may even be completely 'idle' - in view of this I very much doubt that making the screw of the LA longer will increase performance due to sharing the contact surface, but maybe one of the real engineers here can set me straight...

One of my daily duties is the structural analysis of threads. It is true that the root of the first thread has the highest stress because 100% of the tension stress is present at that location. However, that does not necessarily mean that the length of the threads does not matter. For a Class 3 thread (very high quality) like I use, a careful analysis will show that the first 5 threads carry all the load. The first thread transfers about 50% of the load and each subsequent thread carries less. Class 3 threads are very expensive so there's no way the LEGO LA's use them. A Class 2 thread has looser tolerances so a greater number of threads MAY carry some load.

Of greater importance than the load distribution amongst threads is the behavior due to side loading. The LA force is not purely axial, there is also a side component. A short thread is very inefficient at reacting any side load and results in a very large force couple which tends to jam the thread. Only a perfectly aligned actuator and load will prevent this. For actuators like I work on, we try to make the length of an actuator thread at least as long as the diameter.

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So how can the slewing problem be explained? As of now, the left-hand tracks (if u're looking at the excavator from behind) are barely moving- this is with fresh batteries. Is there something mechanical I'm missing here, like, aren't both tracks supposed to slew at the same time?

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One of my daily duties is the structural analysis of threads. It is true that the root of the first thread has the highest stress because 100% of the tension stress is present at that location. However, that does not necessarily mean that the length of the threads does not matter. For a Class 3 thread (very high quality) like I use, a careful analysis will show that the first 5 threads carry all the load. The first thread transfers about 50% of the load and each subsequent thread carries less. Class 3 threads are very expensive so there's no way the LEGO LA's use them. A Class 2 thread has looser tolerances so a greater number of threads MAY carry some load.

Of greater importance than the load distribution amongst threads is the behavior due to side loading. The LA force is not purely axial, there is also a side component. A short thread is very inefficient at reacting any side load and results in a very large force couple which tends to jam the thread. Only a perfectly aligned actuator and load will prevent this. For actuators like I work on, we try to make the length of an actuator thread at least as long as the diameter.

May I just say ... good answer :classic:

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My 8043 worked fine when I built it the first time following the instructions. But reading all the problems you have all mentioned, I decided gearing down some of the drive train was the prudent thing to do. May be one of these suggestions would solve some of your issues.

1. Replace the gears shown in step 53, replace 12T bevel gear to 20T idler to 12T second idler to two 20T bevel gear, with 8T to 32T idler to two 20T bevel gears. It takes 1.5 times the motor revolutions to do the same thing, but somehow, raising the main boom seems faster. Picture attached. I prefer this much more than rubber bands.

2. In step 36, replace axle 4 with stop, with 6 axle. It's the same thing Jurgens did in his MOD. This stabilized the top end of the axle and reduces friction.

3. Used a differential instead of the stacked driving ring and clutch gears to pass power thru turn table. This removed the slight delay in one of the tracks when switching from forward to backward.

I also added the modifications suggested by others. Swapped the two 16T gears for a 12T and 20T for the switching function. Placed both bevel gears on the same side at the LA's in the main boom. Been playing with it for about a half hour and everything is still running smoothly. I hope these steps will protect my LA's and motors.

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Just got a reply from LEGO, which essentially states that they are sorry for the problems, are aware of them and they are designing and producing a new part which will be sent my way when it is finished.

Could it be a new custom part to link to two LA's together at the base, with a built-in differential?

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Of greater importance than the load distribution amongst threads is the behavior due to side loading. The LA force is not purely axial, there is also a side component. A short thread is very inefficient at reacting any side load and results in a very large force couple which tends to jam the thread. Only a perfectly aligned actuator and load will prevent this. For actuators like I work on, we try to make the length of an actuator thread at least as long as the diameter.

There's an interesting point I hadnt thought about - basically what you are saying is that the 'extra' length of the thread helps to keep the actuator moving linearly instead of sideways? But doesn't the top of the actuator casing do much the same thing?

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Could it be a new custom part to link to two LA's together at the base, with a built-in differential?

I doubt it - the problems are more serious than just unbalanced actuators. Though I agree that a diff is a nice way to make parallel actuators self-balanced

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I doubt it - the problems are more serious than just unbalanced actuators. Though I agree that a diff is a nice way to make parallel actuators self-balanced

I agree. Although my "solution" would definitely improve LA alignment, wouldn't a differential and/or gearing also help with lifting the heavy boom?

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By the way the original 8043 is full of price-comprimises: only M-motors, a gearbox instead + 4 motors instead of 6 motors...

I doubt that the reason why the set contains only 4 motors instead of 6 motors is mainly the price. For me this set is more appealing with this solution than with 6 independent motors, I don't think I would spend money on this in the latter case. I don't mind if the model doesn't perform perfectly as long as the building is fun and I can see good tricks and ideas in the design. For me technic is more about building than playing with the final model. Otherwise I would purchase a ready radio controlled excavator toy. Also the b-model seems to be more powerful, so I could use that if I want a more playable toy.

I hope they will not ruin this set by making the motors independent or stop selling it. I really would like to get it.

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There's an interesting point I hadnt thought about - basically what you are saying is that the 'extra' length of the thread helps to keep the actuator moving linearly instead of sideways? But doesn't the top of the actuator casing do much the same thing?

To an extent but it depends on how far the LA is extended. There is a fair amount of axial play in the top. The actuators I use at work, particularly the smaller ones, are precision engineered all in various different steels, hardened and lubricated, there is no noticeable play at any level of extention, and they are very expensive to buy and to produce and there range of movement is not as big as the lego ones considering their length.

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For any interested... Amazon UK just shipped mine via Amazon Germany. It had been ordered just before I heard of the problems...

:hmpf_bad:

Never mind I will enjoy building it... and the repairs.

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To an extent but it depends on how far the LA is extended. There is a fair amount of axial play in the top. The actuators I use at work, particularly the smaller ones, are precision engineered all in various different steels, hardened and lubricated, there is no noticeable play at any level of extention, and they are very expensive to buy and to produce and there range of movement is not as big as the lego ones considering their length.

This is similar to the answer I was about to type. The further the actuator is extended, the shorter the couple between the end gland and the thread. In a real actuator, the end gland has hydraulic seals in it and you don't really want those seals supporting much side load or they will wear prematurely. You want the structural members to carry that load as much as practical. The LA doesn't have any seals, and I don't know how tight the gland fit is compared to the threads. In any case, side loading can't be helpful.

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Are you having the issue of the left track moving slower than the right track? I'm still not sure whether it's supposed to be like that. On full batteries it works better, but it still moves slower than the right track.

sometime I do see the left track a little slower than the right track, with a fresh batteries. I think it something to do with gearing in middle of turntable. I think the M motors may not be powerful enough for tracks and main boom. It would be like driving a small car pulling a 44 tonnes trailer.

I think it should have XL motors, the bulldozer has two, it is powerful, so why don't 8043 have one......

I think I shall keep it for now and wait till Lego's instruction.

Dan.

Edited by Daniel-Technic

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sometime I do see the left track a little slower than the right track, with a fresh batteries. I think it something to do with gearing in middle of turntable.

I think it should have XL motors, the bulldozer has two, it is powerful, so why don't 8043 have one......

I think I shall keep it for now and wait till Lego's instruction.

Dan.

I just finished building mine, I tested the gearing of the undercarriage when I was done with that part and one track was slightly more stiff than the other, however in my motor section the gearing for the same track is much stiffer. I did not manage to track down why.

Also I have to reverse the motor direction of a track on the remote so that the tracks sync up, is this normal?

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I just finished building mine, I tested the gearing of the undercarriage when I was done with that part and one track was slightly more stiff than the other, however in my motor section the gearing for the same track is much stiffer. I did not manage to track down why.

Also I have to reverse the motor direction of a track on the remote so that the tracks sync up, is this normal?

Hi S.I, welcome to the forum.

I'm not sure why it happen, I've taken it apart and rebuild again, checking that all gears are loose and free running, but still the same. Lego will know more and will explain soon.

As for the tracks, on the remote, there is a little switch next to jog stick, switch it to either forward or reverse to sync up tracks.

Dan.

Edited by Daniel-Technic

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Hi S.I, welcome to the forum.

I'm not sure why it happen, I've taken it apart and rebuild again, checking that all gears are loose and free running, but still the same. Lego will know more and will explain soon.

As for the tracks, on the remote, there is a little switch next to jog stick, switch it to either forward or reverse to sync up tracks.

Dan.

Thats what I meant, I just wanted to be sure that is normal because the instructions do not mention that.

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