Linear Actuators VS Pneumatics

[DeBriquesEtDeBlocs]

Linear actuators seems to have replaced the pneumatic system in 2007 when the Power Functions appeared.

I have never tried one or the other (I'm in the process of getting new sets) but I can already see several advantages for the actuators.

Lets compare the cost of both :

48mm pneumatic cylinder $7

Pneumatic Pump $3

Pneumatic Switch $4.5

Pneumatic T Piece $0.30

195L pneumatic hose $20 (why is this so expensive ??)

TOTAL $34.80

Linear actuator $12

Power Functions Battery Box $6.5

Power Functions M-Motor $14

Polarity Switch $10.5

TOTAL $43

The actuator system is more expensive (even though its polarity switch is not required).

But, the other pneumatic parts can only be used for pneumatics, while the other actuator parts (the PF) can be used for anything !

This I think is the main advantage.

The second advantage is that since it's electric, it can be automated and remote controlled.

With the pneumatic system you have to press the pump and turn the switches.

The third advantage I see is the precision and stability, that's why it's used in robotics.

Pneumatics (at least in real machines) make the whole assembly shake when they stop or start their movement.

Finally, there is the speed and the strength. Did anyone make comparative tests ?

[CP5670]

I posted about this issue in the 2009 sets thread a while ago:

I want to see a good mix of both the LAs and pneumatics in Technic sets, as they have different strengths and situations that they are best suited for. As you said, LAs provide much finer control over the position. On the other hand, the main advantage of pneumatics is that you can put them into otherwise hard to reach places and still get a lot of power out of them. The 8868 Airtech Claw Rig, for example, would have been impossible to make with LAs unless you mounted motors on the turntable, and even then the resulting geartrains would be complicated and would diminish the power that the pistons can provide.

Also, I don't know where you're getting those prices. Last I checked, you could buy two cylinders for $10 and five switches for $10 from Lego Education. The tubing is somewhat expensive (although not nearly as much as you say), but there is cheaper third party stuff out there that works equally well. I doubt TLG actually produces their own tubing anyway.

[DeBriquesEtDeBlocs]

I got the prices from bricklink.com

[gogoba]

Would be good to have an extra small motor that you could position on the end of arms, and power the LA from that.

[Front]

Would be good to have an extra small motor that you could position on the end of arms, and power the LA from that.

Exactly my thought after building the 2008 Excavator a couple of days ago. We have a M and XL motor, but if we had a very small motor that could attach directly to the Linear Actuator (or be used on its own with gears etc.), we would have the flexibility of the pheumatics, and the strenght and precision of electrics/mechanics. Motors could be placed at the end of multi-linked mechanisms, and only required a wire to be operational, opposed to now where you have to have a rotatiing axle transferring the power.

Something like that is seen in the real world too, where electric motors replaces (or will replace) hydraulic systems. Instead of having a central placed hydraulic pump and motors at each wheel of a vehicle, electric motors at each wheel could be powered more simply by wires.

[DeBriquesEtDeBlocs]

There is the micro motor 2986, is it compatible with PF ?

[Freddie]

Yes, it is. It's connected by the top end of the old 9V connectors, which effectively hinder using the PF-cables directly, but can be bypassed by using an old conductor plate or a short cable between the motor and the PF-connector. I see no reason why it shouldn't work.

Keep in mind its slow and weak, and has its own purpose-built slip-clutch to connect to technic axles. Keep in mind though that it only does 16rpm@9V (PF operates at roughly 7.2-7.4V), which combined with the linear actuators' 26 needed revolutions for full extension/compression, means you'll have to be patient when using it.

[gylman]

In the real world of construction and heavy equipment, pneumatics are still a very important way of delivering force/power through a full range of movement, so clearly pneumatics in relevant models would still be the best tools and I bet would provide more force.

Similarly, linear actuators have specific situations where they are the best tool in terms of control of the extent and speed of of movement that pneumatics do not provide as reliably.

So the best solution is to have both depending on the situation.

This being said, pneumatics are infinitely cooler. :-)

BTW I'd love to buy more pneumatic stuff from LEGO education, but in Canada it's actually quite difficult, and the prices are pretty bad in any case. So Bricklink prices quoted above are actually what most people end up paying.

[CP5670]

A new PF micromotor would be great, but that would become expensive very quickly if you had several LAs on a model and needed a separate motor for each one. The old 9V micromotor is probably not a good choice, due to its low speed and torque as well as the reliability problems.

I got the prices from bricklink.com

Well, the BL prices are high just because there haven't been any (mainstream) sets with pneumatics for a while now. The insane airtank prices are a good example. They don't really reflect what sets including pneumatics would cost, if TLG actually decided to produce new sets like that.

This being said, pneumatics are infinitely cooler. :-)

I agree that pneumatics have an additional coolness factor to them. There have been a number of very interesting robot MOCs built around pneumatic control circuits instead of an RCX or NXT, simply for the mechanical challenge of it, and they wouldn't be quite as impressive if they were just made with electronically controlled motors. This is one nice example.

[refro]

I wonder if the comparison is fair. With the pneumatic partlist you get a set where you must do manual action to move the cilinder. With the LA set you get it by the flip of a switch. So maybe throw the PF stuff out for the LA, or replace the handpump with a compressor for the pneumatic set.

In both cases I think the LA set will be cheaper. If my comparison is fair I don't know, but I only want to indicate it heavily depends on the context you place it in.

[Dryw Filtiarn]

48mm pneumatic cylinder $7

Pneumatic Pump $3

Pneumatic Switch $4.5

Pneumatic T Piece $0.30

195L pneumatic hose $20 (why is this so expensive ??)

TOTAL $34.80

Linear actuator $12

Power Functions Battery Box $6.5

Power Functions M-Motor $14

Polarity Switch $10.5

TOTAL $43

I suppose these are the prices you would pay when you would get the parts through BrickLink. By doing some smart shopping, i.e. use LegoDirect for ordering some of the parts (like the pneumatic switches, t-piece and (depending on what color of cylinders you want) the cylinders as well as the linear actuators) you can get them more price-efficient. I ordered a bunch of the LA's at LegoDirect and I believe I payed something around 4 euro each, which would be around 5.5 dollars. Obviously though, the power function parts won't come any cheaper then you mentioned.

My oppinion regarding which is best I tend to say that I like both. In some cases the pneumatic parts are better, in other cases the LA's are better. When I look at the things I've been working on lately I tend to use the LA's more then pneumatics though, but the main reason for this is that you have the advantage of good control on the rate at which it extends and the amount it extends. It's also easier to use LA's in combination with the IR elements to have remote control over a model, though obviously you can also achieve this with pneumatics. For me there's no real better one though, I like them both.

Edited April 7, 2009 by Dryw Filtiarn

[green dewback]

I don't like recharging or changing batteries for toy, it's such a chore.

The good thing about the pneumatic pump and hose is you can build a working submarine with umbilical cord.

Its disappointing to see the local Lego community doesn't really discuss or play with technics or pneumatic, I had been offering a 8455 at much lower price compared to bricklink and nobody wants it.

I'm inexperienced with overseas selling or mailing packages so thats not a option.

Edited April 9, 2009 by green dewback

[Blakbird]

Its disappointing to see the local Lego community doesn't really discuss or play with technics or pneumatic, I had been offering a 8455 at much lower price compared to bricklink and nobody wants it.

I want it!

[green dewback]

Nope sorry, vassals arent allowed to sell and I never mailed any package at the post office.

[Blakbird]

Nope sorry, vassals arent allowed to sell and I never mailed any package at the post office.

OK, vassals can't sell but I should at least be able to collect it in tariff.

[Brickthus]

My oppinion regarding which is best I tend to say that I like both. In some cases the pneumatic parts are better, in other cases the LA's are better. When I look at the things I've been working on lately I tend to use the LA's more then pneumatics though, but the main reason for this is that you have the advantage of good control on the rate at which it extends and the amount it extends. It's also easier to use LA's in combination with the IR elements to have remote control over a model, though obviously you can also achieve this with pneumatics. For me there's no real better one though, I like them both.

I agree. Pneumatics and LAs each have their best uses.

LAs are taking over much of the territory of pneumatics in sets. Before Power Functions, LAs would have been too expensive to produce. Their complementary effect on the PF medium motor (selling more motors, keeping motor volume cost down) has removed that cost barrier. The Excavator 8294 is a prime example of a set that needs a motor to go with its LAs, but the two work so well together. Previously, excavators were pneumatic (8455, 8851).

Pneumatics are best in applications that require full linear travel, such as rail points control. I have used pneumatic control for my points in places where there is room to hide the pneumatics underneath the track. I have used only the bottom nozzle of the cylinders because the top nozzle is prone to leakage (in up to 1/3 of the cylinders in my 10 8455s). This means I have set two cylinders end to end to push the point actuator. For the crossover track I have used four pairs of cylinders to achieve a good centre position (both tracks straight) as well as both diversionary positions. The other reason for using pneumatics is that it avoids electrical system obsolescence, considering that I need to support the mechanisms for more than 10 years!

It is possible to do automatic robots with pneumatic finite state machines. My Pick and Place Robot is an example of this. All electronic logic gates can be done with LEGO pneumatics.

It is also possible to get pneumatics to stop in the middle but it is not nearly as easy as it is with LAs.

It would be a real shame to lose pneumatics in favour of LAs. Power Functions can complement pneumatics. With the more powerful XL motor it is possible to get some serious power from a Pneumatic Pump, rather than using a car tyre air compressor (if you do that, get one with a pressure limiter, not just a gauge, and set the limiter to 20-25psi).

BTW it was the alternative model of crane truck 8868 that got me into automatic pneumatic models.

Mark

[DeBriquesEtDeBlocs]

I was wondering, why did Lego suddenly create a linear actuator when it has always been possible to make your own with existing parts ?

[CP5670]

Yes, it has always been possible to make one from existing pieces. The 8479 Barcode truck used such a mechanism, for example. However, the LA piece has a metal shank and is much more powerful and compact.

[Smithy]

I've not actually bought a set with anctuator yet but I can definatly see their advantage. The main issue with pneumatics is they realy only work fully out or in. My favourite sets have been the technic cranes - think most of them have had pneumatics. The problem has always been it's impossible to position the crane boom half way - it's either up or down. Leave it half way and try and pick up something - it always ends up lowering by it's self.

On the pneumatic diggers the actuators would also help. So many times when trying to scoop up small parts, the pneumatics suddenly move scattering the small parts with force.

The main advantage on the pneumatics is they're fast to act. They can also be operated remotely easier.

[5150 Lego]

I've not actually bought a set with anctuator yet but I can definatly see their advantage. The main issue with pneumatics is they realy only work fully out or in. My favourite sets have been the technic cranes - think most of them have had pneumatics. The problem has always been it's impossible to position the crane boom half way - it's either up or down. Leave it half way and try and pick up something - it always ends up lowering by it's self.

On the pneumatic diggers the actuators would also help. So many times when trying to scoop up small parts, the pneumatics suddenly move scattering the small parts with force.

The main advantage on the pneumatics is they're fast to act. They can also be operated remotely easier.

Great points Smithy and welcome.

The one thing that really bugs me about LA, are the time needed for them to get from fully retracted, to full extension. This can take a tole on your fingers, as well as playability. I could see myself as a kid getting tired real quick of constantly twisting a knob just to get a bucket of Lego bricks in the dump truck. And while a PF motor would for the most part solve this, that's an additional $30 to an already expensive set. I've bought two already for last years excavator as well as the Telehandler. I would have been hard pressed for my parents to spend this extra money just to have models more enjoyable.

[CP5670]

Great points Smithy and welcome.

The one thing that really bugs me about LA, are the time needed for them to get from fully retracted, to full extension. This can take a tole on your fingers, as well as playability. I could see myself as a kid getting tired real quick of constantly twisting a knob just to get a bucket of Lego bricks in the dump truck. And while a PF motor would for the most part solve this, that's an additional $30 to an already expensive set. I've bought two already for last years excavator as well as the Telehandler. I would have been hard pressed for my parents to spend this extra money just to have models more enjoyable.

This is mainly due to the stupid knob design TLG uses these days. I have replaced the knob gears on my recent sets with cranks of various sizes, like the 80s and 90s sets had. I have no idea why they moved away from that design, which worked very well.

As for motorization, if you already have a motor pack, it's probably better to just buy the M motor by itself and switch the battery box around when you want to play with the model. That would make the price more reasonable.

[shimon]

first of all i bought a "set" on ebay

which includes 2 clear cylinders (or 4 yellow at same price) 2 switches

4 t-pieces and more various connectors and 3 meters of hoses clear and black

for all i just payed 43$..

the linear is more effective because the pneumatics have maximum weight which at some state it loses the air

[Milan]

I think that mayor problem with pneumatic is that they come in only 2 sizes (3 with very old one), none which is usable in even slight bigger working model.

I have always wanted long and thin cylinder in my excavators or loaders...

LAs could be great great IF they produce micromotor which will connect directly to LA. Now it is still pain in the..to supply the torque to LA.

[5150 Lego]

This is mainly due to the stupid knob design TLG uses these days. I have replaced the knob gears on my recent sets with cranks of various sizes, like the 80s and 90s sets had. I have no idea why they moved away from that design, which worked very well.

As for motorization, if you already have a motor pack, it's probably better to just buy the M motor by itself and switch the battery box around when you want to play with the model. That would make the price more reasonable.

While cranks do work better than knobs, it still takes a while to crank LA's to full extension. It also makes it more difficult when there a load on them. (Such as lifting pallets with the telehandler)

As for switching the battery pack, that's true, you could switch them around, but depending on the model/set, that can be a real pain. But your right it would save money.

the linear is more effective because the pneumatics have maximum weight which at some state it loses the air

As do LA's. At some point the load will be to great, and the internals will just start clicking, as well as the gear train used to run the LA's. I found that pneumatics have a much higher lifting capacity than LS's do.

[M'Kyuun]

Well, aircraft hydraulics has been my field for 17 years, and I'm familiar with electrically and mechanically operated linear actuators, pneumatics, and hydraulics. The main benefits of hydraulics and, to a lesser degree because of its sponginess, pneumatics are that they can be situated amongst more dynamic parts of the mechanism due the use of hoses to move fluid or air. Thus a little more flexibility is inherent. Moreover, a great deal of force can be generated with a relatively small actuator. Also, very precise movement can be achieved with hydro or pneumatic actuators through the use of servo-operated valves, and at extremely great speeds. For example, the vanes on the nose of the B-1B Bomber are operated by hydraulic servo actuators capable of cycling so quickly that the vanes are merely a blur. I forget the exact cycles per second, but they were very quick, and dangerous to be near when the aircraft's accelerometers were active.

An electrically operated linear actuator offers strength and a degree of speed, and if the motor is housed within the actuator, a similar ability to locate the actuator nearly anywhere on the mechanism provided enough wire to allow for flexibility. They often operate similarly to solenoids, or use an internal screw drive. These are great for precision movement, and can be used in lieu of hydraulic actuators.

Mechanically operated actuators offer strength, speed, and precision, but suffer from their reliance on mechanical linkage from the power drive, limiting to some degree, their placement. However, in my experience, I've never seen a mechanical actuator move at the speeds achievable with a fluid driven system

As someone else said, pneumatics are just way cooler than a mechanical linear actuator. But the facts that seals wear out over time, manufacture is most likely more expensive, and that valves and hoses are required to make up a complete system, makes the mechanical actuator a more reasonable choice, I guess. I own several of the LEGO pneumatic sets, and have wowed friends and coworkers with the amazing functionality. I somehow doubt I'd get the same reaction from a mechanically driven system. There's just something awesome about all those hoses everywhere, flipping the little selector valves, and watching the model operate just like the real thing.