[HELP] Abilities of Lego Linear Actuators

[lol1419]

Hello everyone,

I'm new here and this is my first post. Forgive me if I seem a bit primitive in my knowledge of LEGO's. I was planning to use some linear actuators but I got two questions about them.

1) How long do they come? Is there anyway I could mod it to allow a larger stroke? (e.g. 2"/3"/4")

2)At a given point in their travel (i.e at very top of stroke) can they "lock" in place or hold a relatively large amount of weight (e.g. 1lb) WITHOUT the motor running?

Thanks,

-lol1419

[Blakbird]

The mechanical linear actuators only come in a single length with a stroke of about 5 studs. The answer to "is there a way" questions is always "yes", but there is no good way without totally destroying the part and having access to a machine shop. These are screw actuators, so they hold any position without backdriving without power.

[allanp]

LAs come in two sizes. There is no way to mod each size. The large one can hold an enormous amount of static load with no motor connected. They are a screw thread so don't require anything to hold a load in place. The smaller one however, although being a screw can slip in the threads.

Edited November 25, 2015 by allanp

[Saberwing40k]

I'd agree with the above statement, but I have seen some modified linear actuators to be longer. However, such a modification would be very involved, and difficult. However, many builders have built longer linear actuators, by various methods. You can use gear rack parts, or gang linear actuators together end to end in order to get the results you want.

[lol1419]

Thanks for the replies!

  On 11/25/2015 at 12:00 AM, allanp said:

LAs come in two sizes.

Do you know the part# of the large LA's by any chance?

  On 11/25/2015 at 12:07 AM, Saberwing40k said:

...such a modification would be very involved, and difficult. However, many builders have built longer linear actuators, by various methods. You can use gear rack parts, or gang linear actuators together end to end in order to get the results you want.

What would you recommend as the simplest way, while leaving a small footprint? (i.e. using minimal parts/space)

Edited November 25, 2015 by lol1419

[allanp]

How long do they need it to be? Would these do?

http://evolutiontoys...ators-c-39.html

Edited November 25, 2015 by allanp

[lol1419]

  On 11/25/2015 at 12:26 AM, allanp said:

How long do they need it to be? Would these do?

I haven't determined the exact length, but I would imagine in would be in the neighborhood of 100mm (maybe even more). Thanks for the link! It's about close to what I'm looking for.

Edited November 25, 2015 by lol1419

[Karle]

The large LA's can be modified by parting off the ends, the top of one and the bottom of the other. I used a metal lathe to ensure accuracy. The screw was machined off of one of the rods and a hole drilled in the end. It is a little smaller than the pin on the other rod. The other rod had the connector removed. The 2 were then mated by forcing them together and then silver brazed. The inner bodies were machined and a piece of brass tubing 12mm long was used to secure them together. When assembling them and before the glue sets, rotate one of them until the inner threads line up so that the rod screw can pass from one to the other without binding. The outer barrels were turned so that one would fit into the other by about 3mm.

I used 2 double LA's on my ultimate 42009 and a triple set on the Grove 6400, that was unnecessary because a double set will lift the boom to the stops, but triples do look good.

I an unable to up load my pictures from backlink.

Edited November 25, 2015 by Karle

[Saberwing40k]

I'd love to see pictures of the modified ones, Karle, but going by your description it is quite hard. @lol1419 what are you using this for? Supplying context for a part or mechanism helps people make suggestions.

Like this: On Shapeways, our good friend Efferman has come up with a 3D printed actuator that is quite large, in terms of length.

These links will take you to the various parts needed to complete it.

http://www.shapeways.com/product/62649TWYN/actuator-stroke-18-outside?li=aeTabs

http://www.shapeways.com/product/ZSWVQ4FRF/actuator-stroke-18-inside?li=user-profile&optionId=42220430

Pictures:

100_1356 by Michael Wirth, on Flickr

[lol1419]

  On 11/25/2015 at 3:23 AM, Saberwing40k said:

@lol1419 what are you using this for? Supplying context for a part or mechanism helps people make suggestions.

Well, my intended application is to simulate two gas springs lifting a car bonnet. Much like in this picture:

Link:

http://images60.fotk...at500RR1-vi.jpg

Probably should have mentioned that earlier. I just want to have enough clearance or "stroke" to open and close the bonnet, which is obviously motorized. (Using the Lego Power Functions Motor Set (8293)).

Edited November 25, 2015 by lol1419

[Kelkschiz]

The partnumber for the large LA is: 61927c01.

You could also consider using 18940+18942 as a large LA.

[Saberwing40k]

Unless you want it to look like that, you could use the standard linear actuators, but move them closer to the pivot point of the hood. By doing that, you decrease the lever arm, but improve the travel. Most cranes do this.

[lol1419]

@Saberwing40k I hear you. And you make an excellent point. Car gas springs are normally, if not always, mounted near the pivot point of the hood. But for aesthetic purposes (and mounting space), I want to keep it close to the modeled picture.

Edited November 25, 2015 by lol1419

[Saberwing40k]

Due to cartoon physics, you would not actually be able to close the hood if you built it as shown. My recommendation is that you drive the hinge of the hood directly, with a worm gear, and then use sliding axles to represent the actuators.

[Jurss]

Maybe pneumatics?

http://brickset.com/parts/6099775

Edited November 25, 2015 by Jurss

[nerdsforprez]

Expensive... but extremely strong.

http://www.bricklink.com/store.asp?p=Eezo

[allanp]

Ah, well why not use the new 1x11 pneumatics with an auto pump to motorise them? It would be all Lego, they have a slightly longer stroke than the large LAs and they would look more like the right dimensions as they are thinner.

  On 11/25/2015 at 1:05 PM, nerdsforprez said:

Expensive... but extremely strong.

http://www.bricklink...tore.asp?p=Eezo

That would be good for a 1:1 scale car!

[lol1419]

  On 11/25/2015 at 5:20 AM, Saberwing40k said:

...drive the hinge of the hood directly, with a worm gear...

I think I might settle for this. Do you know a good tutorial I can follow on how to make a motorized hinge with a worm gear. (Cuz I got no idea :P)

Edited November 27, 2015 by lol1419

[SevenStuds]

  On 11/27/2015 at 4:47 AM, lol1419 said:

Do you know a good tutorial I can follow on how to make a motorized hinge with a worm gear. (Cuz I got no idea :P)

I suggest to look at other official sets that use a similar part or mechanism. The 42025 Cargo Plane uses several flaps for example. You can see the principle in

around the 5min mark.

I'm sure others may suggest other models you can look at too.

[allanp]

You can look at how the arm raises/lowers from 8480 space shuttle or from 8292 cherry picker.

[BachAddict]

  On 11/25/2015 at 4:01 AM, lol1419 said:

Well, my intended application is to simulate two gas springs lifting a car bonnet. Much like in this picture:

Link:

http://images60.fotk...at500RR1-vi.jpg

Probably should have mentioned that earlier. I just want to have enough clearance or "stroke" to open and close the bonnet, which is obviously motorized. (Using the Lego Power Functions Motor Set (8293)).

That model is unrealistic, as even when the springs are fully compressed the lid would be half open.