[REVIEW] 8043 - Excavator

[DLuders]

Maybe some Olive Oil lubricant would help reduce the friction. "furious" used it for Lego Pneumatics, but he said this:

"The olive oil is non reactive with plastics and rubber. A mineral oil will destroy rubber parts.

"I know that people use graphite powder for turntables. That would get messy.

"How I applied the olive oil is spray some on a paper towel then rub it onto the piston. So there is no messy excess. I would do the same on a stuck turntable."

See this Eurobricks post for the full discussion.

[tomacwhite]

I am really annoyed with this model, it has many problems. I am seriously considering contacting Lego about it and asking for a full refund on the model.

Why? Because put simply it doesn't work. Tested with fresh AA Energizer batteries.

Everywhere you look online many people are complaining that the motors struggle to do anything, and pretty much the only functions they are efficient at is the motor that switches between the modes (Drive and Arm) and the bucket. For me my problems are:

Slewing

Incredibly slow and a loud draining sound from the motor as it struggles to rotate. Movement is slow

Left track

Works OK

Right track

Incredibly slow and laggy, with a draining sound from the motor

Main arm (dual actuators)

Raising: So slow it virtually doesn't move. You have to help it with your hand, then it works perfectly.

Lowering: Works OK

Central arm

Raising: Again, incredibly slow with a loud draining noise coming from the motor as it struggles to lift the arm

Lowering: OK

Bucket

Fine in both directions

Notes:

- If I remove the connecting axles from the linear actuators they spin very quickly with no problems whatsoever. No draining noises

- If I hold the Excavator from the ground or upside down and operate the tracks, they work perfectly with no lag or drain from the motors.

For me put simply, the model cannot cope with the weight of the arm and the superstructure to operate at an acceptable level. The M motors don't have enough torque to operate it properly. At £140 I expect it to work a lot better than this. Playing with my 8275 Bulldozer is infinitely more enjoyable because it works (and has 2x XL motors which cope much better).

[mortenm]

i get all sad when i read your post tomacwhite - i've just bought the model today, so i'll hope i wont get these problems, but it sounds that i probably will...

i'll make sure that everything spins and rotates like a charm while completing every single step and hope it will all work when finished...

[tomacwhite]

That's a good idea, but I too did that. Like I said, everything spins perfectly when there is no load on the motors.

:(

[jason-l]

Edit: I've now completed the B model and there's huge amounts of spare parts. Stuff like panels, 3L universal joints, the entire gearbox components and tons more. The model a lot less complex but all the functions are great. I think I prefer this one after building both.

I built the B model this weekend, and I have to agree. After the slight frustrations of the Excavator's motors struggling, the B-model is an absolute joy to build and 'drive'. Much more efficient operation, which is hardly surprising when you see the number of unused gears! Only criticism is the simpler gear trains mean more speed/torque reaches the LA bevel gears, which seems to cause them to jump teeth if you hit their travel limit.

[tomacwhite]

I think I am going to give the B-Model a go, it looks like it might actually work.

[CP5670]

It's too bad people are having trouble with this set. It could be that the model is very sensitive to any friction in the geartrains, and you have to build it exactly right to get everything working. We've seen a few cases of this in the past.

I'm still in two minds about the set due to its US pricing, which makes it a remarkably poor value by Technic standards even if you leave aside these functionality issues. It reminds me of 8485 back in the day. I was planning to get one at Brickfair at a discount, but they had run out of stock by the time I got to the store.

[JunkstyleGio]

First:

Blakbird: again thanks for the review; it made the wait worthwile!

Just finished the excator. It's a great model!

But even during the buildingproces i came up with the (well known) problem of the two connected LA's.

The picture shows imo the main problem!

Is this happening because of the internal gearing in the LA's?

Or should one lubricate the LA's?

Fact is: even with one LA it seems to work better...

Sollutions anybody?

Edited August 9, 2010 by JunkstyleGio

[Blakbird]

Just finished the excator. It's a great model!

But even during the buildingproces i came up with the (well known) problem of the two connected LA's.

Is this happening because of the internal gearing in the LA's?

Or should one lubricate the LA's?

Fact is: even with one LA it seems to work better...

Sollutions anybody?

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.

Edited August 9, 2010 by Blakbird

[Buffalo]

I never thought about that, but that makes perfect sense now. I think the best solution would be to swap one of the grey idler gears to the other side of the LA, so they're both facing the same direction instead of facing towards one another. That way the LAs would rotate the same direction as they move in relation to the gears and once aligned properly would have precise alignment throughout their range of movement.

[JunkstyleGio]

And so we loose another night on Lego..... (Love it....)

But we're getting somewhere now.

@Blakbird: Thanks for the tip and the explanation!

@Buffalo: Please keep us posted on your findings.

[Blakbird]

I think the best solution would be to swap one of the grey idler gears to the other side of the LA, so they're both facing the same direction instead of facing towards one another. That way the LAs would rotate the same direction as they move in relation to the gears and once aligned properly would have precise alignment throughout their range of movement.

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.

[JunkstyleGio]

Correct me if i'm wrong but i think that Buffalo is right.

[Blakbird]

Correct me if i'm wrong but i think that Buffalo is right.

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.

[DLuders]

@ JunkStyleGio: Are you willing to experiment with your own 8043 Motorized Excavator, to see if reversing that "gray idler gear" makes any difference? From your own Brickshelf folder http://www.brickshelf.com/gallery/JunkstyleGio/8043Excavator/Buildinginstruction/dsc03847.jpg , is this the key step to making the arm perform better?

[dhc6twinotter]

I was planning to get one at Brickfair at a discount, but they had run out of stock by the time I got to the store.

You were at Brickfair? I wonder if I met you? I had Technic tractor on display over in the Mindstorms section. Awesome event.

I too tried to buy the excavator at the store, but like you said, they were sold out. I was really bummed.

[Blakbird]

@ JunkStyleGio: Are you willing to experiment with your own 8043 Motorized Excavator, to see if reversing that "gray idler gear" makes any difference? From your own Brickshelf folder http://www.brickshel...on/dsc03847.jpg , is this the key step to making the arm perform better?

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.

[Fyredog]

My take - The 2 actuators are more for show, you cannot have a mechanical advantage unless you power each LA by a separate motor. In fact you lose mechanical advantage by the drag of the 2nd LA. Also you are lifting all of the weight of the boom using one motor and two actuators. Whereas the other 2 actuators are not lifting as much weight and powered by a single motor with no drag of a second LA. Now if you added an XL to the 2 LA's you would have a better mechanical advantage as the XL has more torque. My crane works great with the 2 LA's and an XL motor and lifts a lot of weight - way more than the Excavator Boom. Just my thoughts.

I concur with Blakbird, Great plastic model with no glue!

[CP5670]

I was thinking the same thing. It may be worth trying to modify it to use only one actuator, and see if that improves anything.

You were at Brickfair? I wonder if I met you? I had Technic tractor on display over in the Mindstorms section. Awesome event.

I too tried to buy the excavator at the store, but like you said, they were sold out. I was really bummed.

We did in fact meet briefly, although I didn't realize you were a poster here. You showed me and a few others standing around the tractor's functions on Sunday. That was an outstanding creation.

Edited August 10, 2010 by CP5670

[JunkstyleGio]

Thanks to all: it seem we're getting somewhere.

@DLuders: Blakbrid did the (unfortunatelly unsuccesfull )test-rebuilding. So there is no need for me there.

@Blakbird: Thanks for trying. Which trainrugulator do you meen? And how is it connected to the model? In other words: Pictures please!

@Fyredog and CP5670 hope to see your proposed MODs soon.

And for me: I went to bed at 05.00 GMT+1(+1DST) so i lost a lot of sleep.

[tomacwhite]

Mine definitely worked better after the first time I made adjustments. But then it seemed to go out of sync a little so I readjusted. After that, I can't get it working efficiently at all, fresh batteries (alkalines) or not. I guess there is a very thin line of where it works and where it doesn't.

Still, mine is having problems throughout other parts now which is really odd.

[rgbrown]

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.

Surely just moving one of the grey idlers across to the other side of the LA bracket would eliminate that particular problem.

(edit. Seems jetlag has affected my ability to read this forum. This idea has been well and truly covered off already! Sorry for being dumb. I have an 8043 in my suitcase, taunting me. Bought it in US (179.99), now in UK, not home (NZ) until September)

Edited August 10, 2010 by rgbrown

[Jetro]

I have a couple of ideas about aligning the LAs al of which are not easily explained to a child building the model :( but as my excavator hasn't arrived yet I'll wait and test them before commenting in what is developing into a very interesting thread.

[JunkstyleGio]

@Jetro: I don't know how long you need to wait for your set, so a few tips in advance would be nice! Pictures, drawings, pre-model build-ups and test-models anything will do.

[eMHa]

If you turn a axle of a LA to maximum length, I've noticed that at the end the whole inner structure of the LA will be turning. The cylinder around can be rotated freely.

What does this mean? Not only you have to be sure both LAs are extended the same, you also have to be sure that when connecting gears to the LAs, both LAs have to be in the same state. Otherweise they have not the same length! I discovered this while building 8265.

So I think the best would be to expand both LAs to maximum till the stop. Then align the boom-connector of the LAs to each other. And only after this attach the gears or connect the two LAs together.

I hope I can soon check this myself with 8043

(It's very complicated for me to explain this because english is not my native language. Hope someone understands it.)