Creating Linear motion for your NXT projects - Part 2

Following on from yesterday's piece about linear motion in robots.....
Today we will continue with a third and elegant way to achieve linear motion: Using the linear actuators.

1. What is a LEGO Linear actuator?

Linear actuator (LA) is a brand new piece of hardware just released by LEGO, that is used to turn rotational motion of a motor into linear motion similar to a piston. It is just longer than an AA battery when it is not extended and it sort of looks like this:

2. How do I use it?
Using a LA with a NXT kit is pretty intuitive. Just plug in an axle of a NXT motor (or a Power Function (PF) motor using the NXT adapter cable) to a LA. Write a simple program in NXT-G to drive the motor. I will post an example program in NXTLog ASAP. Programming does not need to be very precise as to the number of rotations - I did it long enough to do about 28 rotations to extend the LA fully - and it works fine. If you put too many rotations, the internal clutch handle it pretty well as you can see in the video below.

Here is something I knocked up within minutes of opening the box with a LA using a PF motor and a couple of gears and a NXT. I also used the bracket that came with the LA to make the connection easier.

3. Examples of LA's in action.

To demonstrate how cool the new LA is, I created a model that uses both the LA and the old pneumatic pump (that shipped with last year's LEGO TECHNIC Mobile Crane) and created a fully working fire extinguisher.

Warning: The use of pneumatic pump with water is not recommended. Also be cautious when working with fire and water.

4. Where can I get my LA?

You can not currently buy this item on its own. It currently ships with two models that came out this month and it is now shipping - so you should be able to order it.

Here are the two models that has a LA: 8294 (telescopic Extender), 8295 (Excavator).

What is inside a Linear Actuator?

I could not bring myself to break a brand new LA apart. However, I did find an excellent post by Conchas in the TechnicBRICKs blog a few days ago that did just that. It is well written and definitely worth a read if you want to know more !!



Anonymous said…
Excelent - Just what I have been waiting for, BlueToothKiwi.

I got a NXT and just bought the excavator. Now I can try to integrate the two.

The way u used both the Hydraulic thing as well as the Linear Actuator inline wiith each other as a water piston is just incredible - I did not understand it until I watched the video with annotations.

I cant wait for the next topic in the series!
BlueToothKiwi said…
Hi Craneboy,

Thanks for the comments - especially your comments about YouTube video. For some reason the annotations are not showing up whenyou embed the video in the blog (but when you click through to it in the YoutTube site and watch it in High Resolution, it seems to work. Does anyone know how to embed the video (e.g. extra tags to use) so the annotations shows up eve in embedded player?
Brian Davis said…
Just to point out something to folks who might not be familiar with linear motion, there are several more ways to generate it that have not been mentioned. Beside pneumatics (somewhat uncommon, but still around), two of the most popular methods are using gear racks (linear gears; there are both studded as well as "studless" variations, that can be attached using pins) and string (you can make a string mechanism that pulls a carriage in either direction, a very rapid and low-mass solution to the problem). In fact for any long distances, these two methods can be very important.

And as a historical footnote, true linear motion using only linkages is actually a long and complex problem, with a lot of approximate solutions. A lot of these make fascinating LEGO studies as well.
BlueToothKiwi said…
Thanks Brian,
Yes - The rack gears are one of my favourite - but not many people have them.

I will do a final part with those methods as well as a couple of more uncommon methods for completeness in a couple of days. Thanks again.
Brian Davis said…
You're welcome, and it's a nice post.

Not even 12 hours after I made the above comment, I found reference to the fact that I am (happily) wrong about the pneumatics. Not only are they still around... but there are new elements, and in trans-blue!

The very hard-to-find airtank it seems is also being released, which brings me to the next point...

You're correct that pumping water through the LEGO pneumatic elements isn't a perfect solution - it tends to degrade or wash away the grease faster, leading to the cylinder failing sooner. But you can accomplish a pump system (and get your "firehose" effect) using a two-stage system. First, pressurize a volume (like the airtank if you have one, or a custom-made version) with the outlet controled by a switch, and leading into the *top* (air-filled) space of a water bottle with a "straw" as a second outlet from the bottle. Now throw the switch: compressed air enters the bottle, increasing the pressure and ejecting water from the "straw" much more forcefully. AND with no water in your pneumatic elements.
BlueToothKiwi said…
Thanks Brian for the link. That is an excellent addition.

And it comes with a Manometer as well!! I am glad they have pitched it at the education market.

And $55.00 is very affordable considering what you get with it.
Anonymous said…
I see you are using a PF motor to power the linear actuator. How do you power a PF motor from a NXT ?
BlueToothKiwi said…

Please check out my latest post that talks about how to do just that: Link
Anonymous said…
Wow. Interesting robots. I think kids would love that.
Anonymous said…
In the majority of linear actuator designs, the basic principle of operation is that of an inclined plane. The threads of a lead screw act as a continuous ramp that allows a small rotational force to be used over a long distance to accomplish movement of a large load over a short distance.

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