Thursday, January 31, 2008

The Mechanical Muscle Mash


Picking up on the subject of pneumatics and the new 2008 TECHNIC sets, the question arose: will the new linear actuators, debuting in the upcoming 8294 and 8295 sets, completely replace the traditional Pneumatic system, whose current incarnation has been with us since 1989?
I’ve seen opinions claiming the new system is light-years ahead of the older, and others alleging the opposite; let’s compare them, shall we?

First, the "old champ", pneumatic cylinders (PC's).
Strengths:

  • Realistic;
  • Easy to transmit power from long distances and awkward/variable angles;
  • Motion is automatically distributed.

Weaknesses:

  • Imprecise;
  • Hard to power/control automatically;
  • Motion is automatically distributed.
Next, the "newcomer", linear actuators (LA's).
Strengths:
  • Precise;
  • Easy to power/control automatically;
  • Motion is always evenly distributed.

Weaknesses:

  • Unrealistic;
  • Difficult to transmit power from long distances and awkward/variable angles;
  • Motion is always evenly distributed.

I feel I need to explain what I mean with "motion distribution", because it can be both a bless and a curse. In spite of having more to do with MINDSTORMS than with TECHNIC (fans of one theme are almost always fans of the other, anyway), I'll use as example a walking robot.
Linked LA's have an even distribution of motion (unless you complicate the mechanism and insert a differential between them), whereas linked PC's have an even distribution of force.
If your robot has a head that rotates while it's walking, you may want to ensure it faces left when the right foot is advancing (to watch its step, obviously). The torques for moving a head and moving a leg are vastly different, yet you want to have the movements synchronised. This is an ideal application for LA's and terrible for PC's.
If the robot has multiple legs (six, for example) and it is standing on rough terrain, they can't touch the ground all in the same angle, or else the robot will tumble (think of a table with a leg longer than the others). The desired action is to have all legs contact the floor in a manner that the weight of your robot is equally distributed among them (no legs are "floating"). This is an ideal application for PC's and terrible for LA's.

So, after presenting each "fighter's" profile, which one would you bet on? If you want my opinion, I hope LEGO maintains both systems, because, like you saw above, their fields of application almost don't overlap, and therefore they complement each other nicely. Now it's your turn to give your opinion: that's what the poll (when Fernando closes the current one) and the comments section are for. ;-)

(note: naturally, the picture is just a lousy mock-up, for illustration purposes only)

7 comments:

Conchas said...

Old poll is now removed. Go ahead Alex!

Good topic, this one. I think I guess which will be the next poll. ;)

Anyway let me add a few 'Pros' and 'Cons' for both systems, as I was discussing precisely that, with Mauricio a few days ago. So bellow I will add combined inputs from both of us.

Pneumatic Cylinders
- Strong
- Fast but poor control
- Air powered, inexpensive operation plus environmental friendly
- 100% flexible working lengths thanks to availability of long pneumatic hose that can be easily cut to size
- Manual or motorized operation (pumping)
- Two cylinders can be easily setup back-to-back to extend actuation range
- Stop points are easily handled by design
- Deliver most compact and versatile designs in many cases

Linear Actuators
- To be tested if they are as strong or not...
- Slow but better control
- Battery powered, it costs money to operate and is not environmental friendly, because of wasted batteries
- Limited working length that depends on LEGO wire availability (specially for the new Power Functions) or Extension Wires required
- Only motorized operation. Manual is to less realistic
- Back-to-back setup can be difficult and I guess the design to transmit the rotation movement in the required place (the center), would be too complex and not practical for common applications
- Stop point seems to be difficult to handle!? Clutch gears should be added to a design to handle this, or LA screw will suffer and get damaged easily
- Mechanisms to deliver drive to the new LAs may be difficult and lead into complex designs

Parax said...

I think that I like the LA's I think they can offer far better control (reliability jerkiness etc), especially for remote or robotic applications, Lego never did release a simple electric compressor, which made PC's application difficult (and unknown, at what pressure?), I am looking forward to trying these and I hope they are engineered to a high standard (maybe metal!), if they are then Im sure they will be great.

AVCampos said...

Many of the pros and cons you suggested were already mentioned in the article... ;-) For example, I mentioned the PC's innaccuracy and the LA's difficulty in getting movement from far away motors.

But I don't think PC's are that fast: when I open a valve in the 8868 Air Tech, it takes a few seconds before the respective joint begins to move.

Regarding LA's in robotics: they aren't always better than PC's. For example, in a legged robot it is easier to route flexible pneumatic tubes through the hips to reach the knee joints, than to do it mechanically (universal joints, flexible axles or Flex cables would have to be used, neither of which can carry much torque).

So, therefore, I still hope LEGO maintains both systems. :-)

Conchas said...

Cylinders in the Air Tech (8868) are slow, because it uses a small and inefficient built-in compressor (and if batteries are weak... what else can you expect ;) )

Got into manual pump of Back-Hoe (8455), and you will see the difference. ;)

Conchas said...

Or every model operating with a full air-tank...

Conchas said...

Nice mock-up you made Alex, for the yet to be released 'Linear Actuator' part.
Very close to the original indeed!
Just needed to be a bit longer, but that's ask to much from MLCAD. ;)

AVCampos said...

Thanks, but I have no idea on proportions... I just used parts from the pneumatic cylinder and some other bits, to put it together with the PC, too make them appear to be "arm-wrestling".
I don't doubt a proper LDraw representation will appear soon after the first sets arrive, but, due to that licencing or whatever process that is happening at LDraw.org, a long time will sure pass before it becomes official... :-(

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