Brick Technology Hydraulic Lego Excavator

[2GodBDGlory]

I just saw this video on YouTube, and thought the hydraulic system in it deserved some discussion on here!

Spoiler

I considered reviving this thread from 2013, but decided it would be pointless! 

 

Unlike previously proposed hydraulic systems, he's not using a standard one-way pump to draw fluid in from a reservoir, which allows him to make the model much smaller, and cuts down on mess a lot!

Instead, he's using a peristaltic pump, made using one modified Lego part and one 3D printed part, but he also demonstrates a purist Lego one in a different video, that was just a lot larger.

Using this pump, he is able to make an entirely closed-loop system, with one motor and pump per cylinder, and the video seems to show it working well! I may be trying this in the near future, because it looks very interesting!

Any thoughts on this setup? It looks a little annoying to set up, what with bleeding all the air from the system, and perhaps the water would corrode cylinders?

Spoiler

He's also using a custom slip ring to transfer electricity from the upper body down to the tracks for drive, which could be worth some discussion alone!

This channel is always very satisfying to watch with the stop-motion build stuff, the clicking sounds, and the creative builds!

 

[MangaNOID]

That’s genius!

Do you think the tubes would pop off if you kept ‘feeding’ them Or the cylinders would leak first?

Yes, I wonder what fluid would be best that’s not hazardous and not corrosive to metal rubber or plastic. 

[2GodBDGlory]

12 minutes ago, MangaNOID said:

That’s genius!

Do you think the tubes would pop off if you kept ‘feeding’ them Or the cylinders would leak first?

Well, it's a closed-loop system, so it's never actually going to get more water in the system, and the pressure should never build up

[MangaNOID]

Isn’t the pump is trying to push more liquid to one side of the tube though?

Also wonder if that little CADA motor could pump this 😁 

[2GodBDGlory]

53 minutes ago, MangaNOID said:

Isn’t the pump is trying to push more liquid to one side of the tube though?

Also wonder if that little CADA motor could pump this 😁 

Yes, but it pulls it all from the other side of the cylinder, so it's effectively sucking from one side and pushing on the other, and so it's not actually building pressure.

As for the micro motor... Not really, at least not without tons of gearing.

I just 3D modeled/printed the whole pump housing (to avoid drilling Lego) and tried it out, and it's really cool, but I can't even get a PF L-motor to run it! Mine might be tuned a little differently than his, though.

[Tazmancrash]

Thats badness. 8043 2.0

Would definitely buy this if it was a set.

As for fluids that are safe to use, looks like water would be the only safe way to go. Easly available & non toxic. 

Would probably have to change out the steel rods to plastic in the cylinders to stop them rusting. 

Not sure what the longevity would be with the current lego cylinders.  Thinking the factory grease could possibly wash out?

[gyenesvi]

That pump is ingenious indeed! Very smooth operation in a quite compact package, given it's RC with all 6 functions.

As for lubrication, I saw somewhere that water with some edible oil added was proposed as the best alternative for cost / ease of use / safety reasons. Thinking of things like what happens when a child happens to get some of it in his mouth, or when you spill some on the carpet accidentally..

The video shows that it works somewhat with air too, I wonder how well it could function with compressed air in a closed loop? Would it be possible to design such a system? Would it be enough to add a pump that connects to all the circles of the cylinders through a T splitter and one could manually compress the air in the circles after assembly? If that would work, then that would simplify the setup and solve all the issues with water.

[m2fel]

As liquid I would choose silicon oil as it should not affect the plastic (couplings and hoses) or the metal and is not toxic (still please avoid to eat it :)

If you want to pump air into the system you need to be able to separate all loops after.

This is an insane build and I love it!

Edited August 23, 2023 by m2fel

[TTFrA]

8 hours ago, MangaNOID said:

[...] I wonder what fluid would be best that’s not hazardous and not corrosive to metal rubber or plastic. 

I have been thinking about this as well and I think I would go with Ballistol, a medical-grade multi-purpose oil. From their documentation, reputation, and anecdotal evidence it is almost an "edible" cure-all and should address most, if not all the concerns. Mind you, I have never used it to this purpose and am not advertising it, but I have some at home and it appears to be more suitable than water. Agricultural and forestry machinery often use organic (or bio-degradable) oils to minimize environmental hazard, but at this scale (and set material configuration), this particular more expensive oil may be a good medium. Happy tinkering!

Edited August 23, 2023 by TTFrA

[Davidz90]

That's genius! Peristaltic pump is surprisingly effective.

[Saruzeufel]

The fact that there is no reservoir makes it a lot more maintenance though. different temperature means the volume of the fluid changes a bit. Also the cylinders are made for air so they will leak over time, meaning you have to keep topping up the fluid.

I wonder how well the hose in the pump holds up over time... constantly getting squeezed like that will surely weaken it sooner or later.

[Zerobricks]

Wow, really brilliant!

[2GodBDGlory]

3 hours ago, gyenesvi said:

That pump is ingenious indeed! Very smooth operation in a quite compact package, given it's RC with all 6 functions.

As for lubrication, I saw somewhere that water with some edible oil added was proposed as the best alternative for cost / ease of use / safety reasons. Thinking of things like what happens when a child happens to get some of it in his mouth, or when you spill some on the carpet accidentally..

The video shows that it works somewhat with air too, I wonder how well it could function with compressed air in a closed loop? Would it be possible to design such a system? Would it be enough to add a pump that connects to all the circles of the cylinders through a T splitter and one could manually compress the air in the circles after assembly? If that would work, then that would simplify the setup and solve all the issues with water.

In my experience, closed-loop pneumatic systems don't work very well. I was attempting to make a closed-loop pneumatic brake system on one of my previous MOCs, with a motorized compressor to automatically resupply air to the system, but the issue is that air will leak out over time, and an automatic compressor like I had isn't sensitive enough to work properly.

 

4 hours ago, Tazmancrash said:

Thats badness. 8043 2.0

Would definitely buy this if it was a set.

As for fluids that are safe to use, looks like water would be the only safe way to go. Easly available & non toxic. 

Would probably have to change out the steel rods to plastic in the cylinders to stop them rusting. 

Not sure what the longevity would be with the current lego cylinders.  Thinking the factory grease could possibly wash out?

 

2 hours ago, Saruzeufel said:

The fact that there is no reservoir makes it a lot more maintenance though. different temperature means the volume of the fluid changes a bit. Also the cylinders are made for air so they will leak over time, meaning you have to keep topping up the fluid.

I wonder how well the hose in the pump holds up over time... constantly getting squeezed like that will surely weaken it sooner or later.

I think you raise some good points about the longevity of the system. It really probably isn't good for the Lego cylinders, what with rust and grease loss (I'm using cheap MouldKing ones), and you're right, I am having some leaking in my test setup. Also, I'd have to agree that the hose may well wear out under this use!

I think this system could be a good fit for people like me who like to build a MOC, keep it for a few days, and then rip it apart right away, because then the issues with leaking probably wouldn't build up too much, the rust probably wouldn't come too quickly, and the hose might survive! However, if one wanted to use it in a model destined for long-term play or a shelf, it's probably not the best.

Here's my setup!

Using this 3D-printed part instead of the Lego rim, so I didn't have to drill anything:

[Lego Tom]

That is an amazing build! 2GodBDGlory knocked this one out of the park and the system could easily be adopted/adapted to other builds such as the new skidder. Vegetable oil or silicone oil may mitigate any deterioration issues as well as help against leaks due the thicker viscosity. 

[2GodBDGlory]

46 minutes ago, Lego Tom said:

That is an amazing build! 2GodBDGlory knocked this one out of the park and the system could easily be adopted/adapted to other builds such as the new skidder. Vegetable oil or silicone oil may mitigate any deterioration issues as well as help against leaks due the thicker viscosity. 

Oh, to be clear, that's not my build! I'm just sharing a YouTube video I saw, because I thought it was worth discussion!

It is a very cool system, though

[Mr Jos]

Actually this system is not good at all, unlike most reactions here. They say you just pump from 1 side to the other so no need for a reservoir, no pressure buildup. Wrong and wrong.

• One side of the cylinder has an axle in the center, so volume of air = (surface area diameter piston-surface area piston axle) * length. The other side is (surface area diameter piston) * length. When moving, the length change is the same in both, but the volume of oil/water is different! So pumping from the axle side to the backside would require more water, you can see this clearly in this video as the little bit of air in the cylinder gets bigger, as the pressure is dropping (even though it is extending!) because there is an insufficient amount of water to fill the whole cylinder.
• If there was enough water inside, no air at all, and you move it from the backside to the axle side, the extra volume of water would have nowhere to go, pressurizing the hoses (as the axle takes space where water used to be). So yes, there is pressure in this system, but not the way it should be.
• If you would keep pumping whilst at the end of a stroke, and there is no leaking possible in the hose, the pressure would build up (rapidly!). But the flexible hose in this case would just stop the pressurizing and water would leak by the pump and stay still inside the hose. With real hydraulics, without an overpressure valve you would certainly destroy the cylinder gaskets if you kept pumping at the end of stroke from side to side.
• So in real circumstances, you would always need a reservoir (and overpressure valves) because volumes are different. It would be more plausible if you had a cylinder with an axle extending at both ends, then the volume stays the same when moving in any way (but these cylinder are mostly used to have the same power/speed in both directions). Plausible, but not for real as liquids are compressable (around 0.5% every 70bar for hydraulic oil).

Don't take me wrong, it's a great build, just not realistic. [Sorry for my view at it like a mechanic]

Edited August 23, 2023 by Mr Jos

[2GodBDGlory]

11 minutes ago, Mr Jos said:

Actually this system is not good at all, unlike most reactions here. They say you just pump from 1 side to the other so no need for a reservoir, no pressure buildup. Wrong and wrong.

• One side of the cylinder has an axle in the center, so volume of air = (surface area diameter piston-surface area piston axle) * length. The other side is (surface area diameter piston) * length. When moving, the length change is the same in both, but the volume of oil/water is different! So pumping from the axle side to the backside would require more water, you can see this clearly in this video as the little bit of air in the cylinder gets bigger, as the pressure is dropping (even though it is extending!) because there is an insufficient amount of water to fill the whole cylinder.
• If there was enough water inside, no air at all, and you move it from the backside to the axle side, the extra volume of water would have nowhere to go, pressurizing the hoses (as the axle takes space where water used to be). So yes, there is pressure in this system, but not the way it should be.
• If you would keep pumping whilst at the end of a stroke, and there is no leaking possible in the hose, the pressure would build up (rapidly!). But the flexible hose in this case would just stop the pressurizing and water would leak by the pump and stay still inside the hose. With real hydraulics, without an overpressure valve you would certainly destroy the cylinder gaskets if you kept pumping at the end of stroke from side to side.
• So in real circumstances, you would always need a reservoir (and overpressure valves) because volumes are different. It would be more plausible if you had a cylinder with an axle extending at both ends, then the volume stays the same when moving in any way (but these cylinder are mostly used to have the same power/speed in both directions). Plausible, but not for real as liquids are compressable (around 0.5% every 70bar for hydraulic oil).

Don't take me wrong, it's a great build, just not realistic. [Sorry for my view at it like a mechanic]

That's true about the issue with the area difference from the two sides (I think I saw that in a YouTube comment as well, and it makes sense) In practice, it seems that eventually it leaks to the point where there is just enough air in the system to work in both states, which is definitely a downside, but I don't think it's a huge problem.

You're right that there is pressure in the system, but I guess the difference is that there's a limited amount of water in the system, and so there's a limit to the maximum pressure, and the pump will slip before anything too crazy.

I think it's probably the most practical Lego hydraulic system I've ever seen, but you're definitely right that it has some shortcomings, and isn't realistic compared to real hydraulics.

[allanp]

It looks great, but yeah there is that issue of how is the volume of the piston rod accounted for when it is fully retracted into the cylinder as opposed to when it is fully extended out of the cylinder. You would need an air bubble at least the same volume as the piston rod but likely bigger in reality. In terms of realism, is it really more realistic? The way it uses a liquid as a fluid is more realistic than using air as a fluid (both air/gasses and liquids are classed as fluids), but mechanically there are 3 "engines", one for each circuit, where as in reality there would only be one engine feeding all three, and a series of valves to direct the pressure*  flow to where it's needed, like you get with pneumatics.

*pressure is a resistance to flow, no resistance = no pressure.

Having said that, the pump itself appears to work really well. If you have the room for it, you could use this pump, perhaps have it be powered by a more powerful motor, but include a reservoir. Only tricky part is the valves, as current pneumatic valves don't have a ported return path, I wonder how difficult it would be to make a hydraulic spool valve though. For anyone with access to a lathe it would be fairy easy. 

[2GodBDGlory]

Yeah, I wouldn't say it's worth doing to be more realistic-I think you'd just have some performance advantages in lifting capacity and control, since pumping is very precise

[gyenesvi]

11 hours ago, m2fel said:

If you want to pump air into the system you need to be able to separate all loops after.

Hmm, that is true. It could be done with valves though, and one valve could be used for pressurizing two separate circles, son only half the amount of valves needed. Or a small pump for each circle could also do.

@2GodBDGlory, since you are already experimenting with it, could you try how a single circle works with pressurized air vs non-pressurized air?

[2GodBDGlory]

2 hours ago, gyenesvi said:

Hmm, that is true. It could be done with valves though, and one valve could be used for pressurizing two separate circles, son only half the amount of valves needed. Or a small pump for each circle could also do.

@2GodBDGlory, since you are already experimenting with it, could you try how a single circle works with pressurized air vs non-pressurized air?

Hmm, so the challenge is to hook up this peristaltic pump to a cylinder with only air in the system, and see how it works, and then try the same thing, but with a setup to pre-pressurize the whole system first?

I could probably try that soon!

[gyenesvi]

6 hours ago, 2GodBDGlory said:

Hmm, so the challenge is to hook up this peristaltic pump to a cylinder with only air in the system, and see how it works, and then try the same thing, but with a setup to pre-pressurize the whole system first?

I could probably try that soon!

Exactly, great, thanks!

[allanp]

Interesting, I wonder what pre-pressurization would do. instincts would say that the force is equal to the difference in pressure from one side to the other, and increasing the pressure both sides wouldn't change anything. However, if they were pre pressurized then maybe there would be more of a solid, liquid feel? Hmmmmmm.

[Nazgarot]

I love this idea! But I would swap the water for silicon oil. som thin oil like 60 - 100 wt would do well i would think, and it would also lubricate all the seals...

I have to get my printer running. I need to try this!

_ED_

[gyenesvi]

3 hours ago, allanp said:

However, if they were pre pressurized then maybe there would be more of a solid, liquid feel?

Exactly, as I understand, the reason why hydraulics works better than pneumatics is because liquids are much less compressible than air, so you can adjust things more precisely. However, pressurized air is also less compressible than normal air, so it could have the same effect to some degree. I also realized that there would be no need for switches for pressurization, a simple regular valve (that lets air flow only in one direction) would do, then it would be possible to pressurize multiple circles with a single pump at the same time.

If this would work, the whole peristaltic pump could be made as a single lego part, with two (plastic) air outlets where pneumatic hoses can be attached (like on the cylinders), and the inner part of the hose could be preinstalled and could be made from some more flexible / durable material to withstand constant pumping. The whole piece could also include the simple valve for pressurizing (a third air inlet). That would be an amazing extension part for the pneumatic system, no liquids required, and RC ready! Each model would only require one manual pump for pressurizing the system from time to time when it gets jerky (which could also be detached from the model after pressurization).

Edited August 24, 2023 by gyenesvi