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#1 Saberwing40k


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Posted 15 April 2012 - 02:35 AM

so i find my self stuck against a wall once again. this time i'm trying to make an automatically reciprocating linear actuator. what i hope to accomplish is that the actuator will reach maximum extension, then stop, and come back to maximum retraction, without having to reverse the drive motor. i've tried everything my hopelessly busted brain can come up with, and i still haven't made it work. i've even tried making a copy of an auto reversing mechanism by nuno2500. it sadly, refuses to play nicely, and is quite unreliable. any ideas?

also, while i'm soliciting advice, does anybody have a reliable, compact, and studless pneaumatic auto valve? i've already tried building sofo's version, but it does not work. again, any ideas?

much appreciated, Saberwing40k
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#2 dhc6twinotter


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Posted 15 April 2012 - 02:45 AM

I don't have a definative answer for your LA question, but I'm sure it can be done.     If I have time in the next few days, I'll try to come up with something for you, unless somebody posts a good solution before then.  

As for the pneumatic auto valve, Seriel has a great design.   I can't remember his website off the top of my head, but you might be able to find a link to it somewhere in the forum.  

Here is a 3 valve design I used on my tractor:

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Sorry the picture isn't very clear, but it's fairly compact and uses clutch gears to keep the motor from stalling once the valves have hit their limit.

#3 DLuders


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Posted 15 April 2012 - 02:58 AM

Daniel's solution is great, but here is Sariel's Pneumatic Autovalve design:

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#4 Alasdair Ryan

Alasdair Ryan

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Posted 15 April 2012 - 12:40 PM

Mines quite good,It does not stall the motor but it does go buck to the center.More info can be found Here.

Edited by Alasdair Ryan, 15 April 2012 - 12:41 PM.

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Updated 10/03/15
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#5 88high


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Posted 15 April 2012 - 05:54 PM

Ok: here is my solution to the linear actuator problem:

You know how you can actuate a linear actuator by two ways: spinning the axle in the center and keeping the barrel straight, and vice versa. The only way i can think of getting a linear actuator back to center without the axle in the center moving, is to put a new-style technic turntable around the bottom mounting point of the barrel (be sure to mount on the half with the gear teeth) and then, you can have the bottom axle powered by a medium motor, and the turntable too. This us how it will work:

1.) the medium motor powering the LA axle starts spinning, and reaches the maximum extension point.
2.) the medium motor powering the axle stops, and the turntable motor starts rotating the turntable, which holds the linear actuator barrel.
3.) the medium motor powering the turntable goes down and stops.
4.) you are back where you started.

I don't know exactly how you can make this automatic, but you can make some type of NXT trigger or sensor which alerts another motor to turn a switch and that switch would power the other motor....

I hope that helps you for the returning actuator siduation. Good luck!

As for the pneumatic auto valve, there are many different solutions for this...I just use the hockey stick shooter piece (aka the return to center block) and I put that on the pneumatic switch and I use a m-motor to turn that...

Good luck!

#6 sqiddster


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Posted 15 April 2012 - 06:56 PM

The actuator problem is very interesting ;)

I gave it a bit of thought, this should work:

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Let me know if you don't understand ;)

#7 aeh5040


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Posted 15 April 2012 - 08:32 PM

Here is a mechanism that does what you ask.  I'm not sure how practical it would be for a real application, but it does work...

#8 Porty


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Posted 16 April 2012 - 01:07 AM

@dchtwinotter- WOW! That really looks impressive! Can you tell me where to find some info on that tractor of yours?  :sweet:

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#9 DLuders


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Posted 16 April 2012 - 01:25 AM

@ Porty: dhc6twinotter's Lego Technic Case Steiger 335 (a Power Functions articulating tractor with pneumatics and attachments) is described and pictured on this Eurobricks topic.   :thumbup:

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