Inside the new LA

[fmmjqtft]

The service bag has now arrived, so I have dismantled and compared an old and a new LA.

The new LA is almost identical to the old one; it still takes the same number of rotations to extend; it still extends to the same length; there is still a clutch.

I have cut the white plastic sleeves into pieces to look at their teeth, and from what I can see, the sleeve is identical on both LAs.

There seems to be only one change; the 'tooth' of the screw in the new LA is significantly smaller.

Performance changes:

-lower friction

-the new LA rattles less when extending/retracting

-the new LA is much quieter

-the new LA extends/retracts more smoothly, especially at high speed

Unfortunately, because the new LA has a thinner 'tooth', the new LA bends more when fully extended. The end of the rod can move by an extra mm in each direction. It is not actually as bad as the photo suggests, but is still noticeable.

Edit: There is also much more grease in the new LA. Grease has been applied inside the sleeve, inside the clutch and between the orange part and the outer casing. The plastic was also much harder to cut away on the newer LAs (more glue), which is why the two dark grey pieces look different in the picture below.

Edited October 4, 2010 by fmmjqtft

[Silcantar]

Have you tested it under load? Since the load exerted by the weight of the excavator arm isn't parallel to the actuator, the additional bending could increase the friction.

[fmmjqtft]

Have you tested it under load? Since the load exerted by the weight of the excavator arm isn't parallel to the actuator, the additional bending could increase the friction.

The bending only happens when the LA is fully extended. When fully extended, the friction is not really a problem, because the LA does not need to extend any further.

Even when fully extended (and under load), I don't think the friction is any worse than the friction in the older LAs.

[Front]

Have you tested it under load? Since the load exerted by the weight of the excavator arm isn't parallel to the actuator, the additional bending could increase the friction.

Let's be clear: there has never been a Technic set where the Linear Actuator was under any bending forces other than what the weight of the actuator itself applied.

[DLuders]

Let's be clear: there has never been a Technic set where the Linear Actuator was under any bending forces other than what the weight of the actuator itself applied.

This is correct; there is no "bending moment" on any of the 8043's Linear Actuators because they are free to rotate around a Technic pin. We have "pin connections" with forces directed down the long axis of the LAs. The cross-axle holes are not used. However, it is possible that the "axial" loading will cause the slender metal rod to "buckle" out of plane. From CHOOPS Brickshelf image:

Edited October 2, 2010 by DLuders

[fmmjqtft]

I have done more tests on a fully extended LA, and the bending is no problem.

When pulling load, the LA is forced straight (expected)

When pushing load, the LA is also forced straight (which is a surprise)

When under no load, the LA bends under its own weight.

This shows that when pushing load, the LA is shorter when straight, but when pulling load, the LA is longer when straight.

[allanp]

For those of you that use them (not me!) I hope the smaller pitch of the thread does not shorten their life span. The sideways play would also suggest that the full depth of this already small pitch is not used.

I guess now we know that a smaller surface area DOES reduce friction

Once again I have to say kudos to TLG for doing this so fast and without fuss.

Edited October 3, 2010 by allanp

[fmmjqtft]

For those of you that use them (not me!) I hope the smaller pitch of the thread does not shorten their life span. The sideways play would also suggest that the full depth of this already small pitch is not used.

I guess now we know that a smaller surface area DOES reduce friction

Once again I have to say kudos to TLG for doing this so fast and without fuss.

The thread pitch is the same. The only difference is that the thread is much thinner (it does not stick out as far from the rod). As you said, the smaller surface area of the thinner thread reduces friction.

[allanp]

The thread pitch is the same. The only difference is that the thread is much thinner (it does not stick out as far from the rod). As you said, the smaller surface area of the thinner thread reduces friction.

Sorry, my mistake, yes the pitch is the same, I meant the thread height is less. I was getting my terms a bit mixed up as per usual

Edited October 3, 2010 by allanp

[Blakbird]

This is correct; there is no "bending moment" on any of the 8043's Linear Actuators because they are free to rotate around a Technic pin.

I don't entirely agree, and I only think differently because I analyze actuators for a living. While an idealized model of a linear actuator is a "two force member" in that the pinned ends only allow tensile or compressive forces, in reality there is no such thing as a pinned joint. As an actuator moves through its stroke, it typically also rotates. The excavator is no exception. This motion creates a frictional bending moment applied at the "pin" at either end. This friction is proportional to the load on the actuator. A LEGO linear actuator has no bearings, and therefore the friction at the end under load is not inconsiderable. Therefore, I do expect to notice the bending in these new looser actuators.

Another significant component of bending on actuators is initial eccentricity. If the actuator is not straight (and these are not straight when fully extended), then compressive forces cause an inherent moment simply due to the geometry. The bigger the load, the bigger the moment.

So it remains to be seen how well this new design will work. While I've no doubt it has less friction, I'm not yet convinced that a less stable actuator is a net improvement. I received my service pack today. I've not installed the new actuators yet, but I have trouble finding the massive freeplay in the rod when extended to be a comforting thing.

For those of you that use them (not me!) I hope the smaller pitch of the thread does not shorten their life span.

As already mentioned, the pitch has not changed, but I also wonder about the longevity. Conchas showed when he disassembled his actuator that heavy load produces plastic shavings inside the actuator. The new design has essentially just loosened the tolerances on the thread. This will make it easier for "chips" to pass between the threads without jamming or slowing down, but it will not actually reduce the rate of "chip" production at all. From this point of view, I think heavy load will still end up destroying the actuator over time; it will simply take longer to notice the problem.

[fmmjqtft]

Another significant component of bending on actuators is initial eccentricity. If the actuator is not straight (and these are not straight when fully extended), then compressive forces cause an inherent moment simply due to the geometry. The bigger the load, the bigger the moment.

If the linear actuator behaved like a pair of line segments joined together at one end, this would be true. However, after testing, it is clear that as load is applied, the linear actuator is forced straight, because the distance between the two ends of the LA is shortest then the LA is straight (unlike a pair of line segments, which gets longer as it straightens).

Although some friction is generated at the 'pins' at each end, which creates a moment which bends the LA, I have not yet seen a case where this is enough to overcome the straightening caused by the LA's geometry (which is not a pair of line segments).

[Blakbird]

If the linear actuator behaved like a pair of line segments joined together at one end, this would be true. However, after testing, it is clear that as load is applied, the linear actuator is forced straight, because the distance between the two ends of the LA is shortest then the LA is straight (unlike a pair of line segments, which gets longer as it straightens).

Typically, a compressive load destabilizes a beam-column. The statics of the free body demand it. I think the only reason that this unit straightens under compressive load is that the load causes the threads to come into face contact. When there is no load, you can push the rod to the side which separates the threads on one side. When you put load on it, the threads straighten out. Fluid filled actuators do not have this behavior.

[hoeij]

This may have already been discussed before, but I'm wondering, is it a good idea to try to get some lubricant into the LA?

[DLuders]

This may have already been discussed before, but I'm wondering, is it a good idea to try to get some lubricant into the LA?

Yes, for the OLD (non-36XO) version of the Lego Linear Actuators, soak them in Olive Oil and remove the excess. It won't affect the plastic at all. Folks can brush this off as a flippant idea, but if you want to save your investment, you can salvage the LAs with more LUBRICATION. TLG found what the problem was with the 8043 set -- it was basically TOO MUCH FRICTION in the LAs.

[hoeij]

There seems to be only one change; the 'tooth' of the screw in the new LA is significantly smaller.

...

Edit: There is also much more grease in the new LA.

...

Has anyone else compared the lifting capabilities of the old LA versus the new LA? I did a very rough comparison: In the 8043B model, I counted how many wooden blocks it could lift with the old LA's, versus how many with the new LA's. This lead to a rough estimate that the new LA's lift about twice as much weight (using the same M motor). My measurement is not very accurate though because I did not carefully compare the torque.

Has anyone done a more precise measurement? (comparing the lift, while making sure to use the same torque in both measurements?).

I'm also wondering about something else: Assuming for the moment that a more precise measurement would still show a difference in performance between the old and the new LA, then the question is: What causes this difference? Is the performance difference solely due to the grease, or does the new screw contribute as well?

To figure out this question, we'd have to compare "an old LA with some grease added" with "a new LA". Dluders, you've mentioned that you lubricated some LA's with olive oil, do those lubricated old LA's have the same performance as the new LA's? For instance, the front-loader with lubricated old LA's, using the same amount of torque, does it lift the same weight as it does when you put new LA's into it? (looking at the picture in the first post, it looks like there is no need to add lubrication to the new LA's)

[DarkShadow73]

Ok, then a couple of questions on lubrication of the older LA's. I did receive my service bag for the 8043 but Lego screwed up and only sent me 1 bag instead of 4 as I own 4 of the 8043 Excavator. I don't personally like the freeplay at the end of the new LA, it is too loose and appears to wiggle at full extension.

At any rate, my question is about the olive oil. I am wondering in regards to that whether since the 1 person here mentioned friction as the main cause of the problem with the old LA's raising the boom, whether simply soaking the old LA's in olive oil would solve the problem and eliminate the need for the new LA's? Would the olive oil evenutally dry out and then the LA need to be resoaked? I don't how this compares to say a silicone oil or lithium grease? As far as soaking them in the olive oil though, do you extend the LA completely and immerse in the oil? Does it seep into the LA body itself to reach the threads, or do you have to periodically as you soak wind the LA back into its cylinder? I am looking at this olive oil idea as maybe a fix so I can build the other 8043's I have using the originally packed LA's and also possibly to soak the LA's from older sets like the 8258 Crane Truck, 8295 Telehandler and 8294 Excavator. The 8258 and 8295 especially had a lot of load on them to raise, extend the respective boom assemblies and at least those 2 sets' LA's had a hard time (even the 8295 motorized with an XL-motor instead of the M-motor) and struggled to perform their functions without a lot of strain on the motors and jerkiness. I am wondering if lubing the old LA's would solve that issue with these sets as well? Thanks for feedback.

Yes, for the OLD (non-36XO) version of the Lego Linear Actuators, soak them in Olive Oil and remove the excess. It won't affect the plastic at all. Folks can brush this off as a flippant idea, but if you want to save your investment, you can salvage the LAs with more LUBRICATION. TLG found what the problem was with the 8043 set -- it was basically TOO MUCH FRICTION in the LAs.

[DLuders]

Here's the thread about using Olive Oil to lubricate Lego Technc pneumatics: http://www.eurobricks.com/forum/index.php?showtopic=26091 . Here's the discussion about how to keep Linear Actuators working: http://www.eurobricks.com/forum/index.php?showtopic=45068 . I would just soak the old LAs in Olive Oil as-is; it will seep in past the seals. Wipe off the excess. If you want to use silicone spray (like WD-40, be advised that Mineral Oil will dissolve the ABS plastic. If you're not sure, try the lubricant on a regular Lego brick that you could sacrifice.

Or, you could do nothing, burn up your PF Medium motors, and then pay for the new 36X0 Linear Actuators. Reduce friction now or pay the price later.

[Milan]

So WD-40 is not good for any lubrication, including gears, axles and LAs?

[Zerobricks]

So WD-40 is not good for any lubrication, including gears, axles and LAs?

WD-40 melts bricks...

[fmmjqtft]

What causes this difference? Is the performance difference solely due to the grease, or does the new screw contribute as well?

This could be tested by trying the old LA's screw inside the new LA's sleeve (which has grease). Unfortunately, this would require destroying yet another new LA for the sleeve.

[DarkShadow73]

Well, I opened an 8043 and filled a dish with olive oil and completely immersed 4 the old LA's extended to complete length but no so much that the oil couldn't seep into the sleeve and left overnight. Messy as crap picking them out and cleaning them off, but they are definitely oily now. When I put a 4L axle in and turned the rod back into close the LA and I could see the olive oil oozing a bit out of the 2 small gray squares on the side of the LA and also a bit around the orange axle hole where the axle hole meets the sleeve, so there is definitely oil inside the sleeve. My only worry is that repeated extension/retraction the LA will cause more ooze and an oily mess since these sleeves aren't completely sealed, which is a good thing cause the oil gets in there unlike pneumatic cylinders where you can only oil the exposed piston itself which I have done many times with my pneumatic 8455 Backhoe and 8464 Front Loader, but it could cause quite a mess if the oil leaks from the sleeves especially with repeated use. I will assemble the excavator this weekend and extensively put the boom raise function to the test and see if it starts slowing down as was the problem described. I am really curious if any of you have ever tried the olive oil trick and had success in solving the 'burn-out' or 'slow-down' issue with the 8043, and also did you have a lot of oil ooze from the sleeves?

Thanks, Eric

[icks]

Would graphite work? That is assuming it's possible to get it in.

[DarkShadow73]

I thought about something like Crisco (the solid stuff in the can) on the completely extended actuator, but from what I can tell from the images Conchas posted the screw is larger than the actual cylinder itself and so a solid type grease wouldn't penetrate onto the threads of the screw or where the screw turns inside the sleeve. The olive oil sounded like a good, albeit messy, deal because it coated the inside threads of the sleeve and screw. The Crisco or any kind of solid grease, or even the grease I and others noted on the new LA would coat the screw and threads better, but since there is no way to disassemble the sleeve without breaking or cutting it, liquids seemed the only option, and only liquid lubes that would not kill the plastic.

[BrickWild]

WD-40 melts bricks...

Silicone Grease, which can be obtained at Dick Smith & a few other hobby shops is good for any plastic parts, even Lego elements!

[DarkShadow73]

Sounds less messy than olive oil, but how in the heck can you get it inside the sealed LA?

Silicone Grease, which can be obtained at Dick Smith & a few other hobby shops is good for any plastic parts, even Lego elements!