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Stupid questions:- Penumatic/hydraulic Servos


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WiperMotor



Joined: 04 Sep 2006
Posts: 301
Location: SA,Australia


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Stupid questions:- Penumatic/hydraulic Servos

Hello again

I'm after some advice here, I need an extremely big steering servo for a project, It needs to have alot of touque and come back to center when i let go of the stick.
I've been looking at industrial servo motors, but the are very expensive and need alot of parts to work (Input>controller>amplifier>feedback>motor) and alot arn't suited for a mobile application (well that just what I found), I also tired one of those Oatley electornics monster servo kits and poped it Sad with a wiper motor.

So I was wondering if its possibe to use air rams or hydraulic rams for servos? I found servo valves on ebay, will these make them work like servos? what are they controlled with?

Would it be possibe to use a standard servo to acctuate a manual valve, with a feedback device on the ram? I'd like to use a rotary table (penumatic, usualy made by festo,SMC or robomotion) maybe insted of a ram, the oatley electronics kit could be used to drive the standard RC servo directly on its motor terminals connected to the valve and the feedback pot on the rotary table. Do you think this could work?

I'm open to suggestions Laughing

Simon

Post Tue Jan 20, 2009 12:00 am 
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Spockie-Tech
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Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


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air is springy stuff.. do you need it to have positive position control of a high load ? will the load be constant ?

Air controlled steering would be bad, the wheels would wobble with bumps in the road. Hydraulic might be better, but heavy and complex.

You could get one of the ESC's that have a servo mode and use that. It all depends on whether you are talking steering a go kart at 10km/hr or a passenger vehicle at 100km.hr
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Post Tue Jan 20, 2009 12:43 am 
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Valen
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Joined: 07 Jul 2004
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Location: Sydney


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hydraulic rams would probably work ok, it'd need a fair bit of hacking on the electronics side to get things to work though.
basically you would just be making your own servo.

you might be able to cheat some with a normal servo pushing a 2 position hydraylic valve with the error correction on the actual steering bit.

you will loose all the proportional control with that and it might hunt.
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Post Tue Jan 20, 2009 2:57 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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Hydraulics and pneumatics need a lot of support gear; pumps tanks, regulators etc, which are bulky, heavy and can be expensive. What's your budget and application? You might look at the giant servos available at the Robot Market Place; I saw several episodes of Mythbusters where they use them to steer boats and cars. You could also make a giant servo using a controller from Roboteq and some appropriately slowed down motor.

Post Tue Jan 20, 2009 8:08 am 
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WiperMotor



Joined: 04 Sep 2006
Posts: 301
Location: SA,Australia


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Ok whats the catch with these Roboteq controllers?

They have an enourmous amount of functions and inputs and are well priced? Shocked

You can control eather 2 motors, 1 motor 1 servo or two servos!! Directly from an RC reciever!! Surprised

I better start saving my pennies! Twisted Evil 1:1 scale RC car here I come!!

Post Tue Jan 20, 2009 12:12 pm 
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Nick
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Ahhh, everyone wants to do that at some point Laughing. I suggest using an automatic with power steering - it means you save a heap on the controllers as you don't need as many channels or high current drive.

You can use linear actuators for the pedals and gear change and a highly geared down motor for steering. I'm guessing the steering motor output only needs to be around 10 rpm, so a fan motor and a worm driven gearbox might do the trick. You can likely use the cheaper AX1500 range for all that.

Post Tue Jan 20, 2009 12:40 pm 
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WiperMotor



Joined: 04 Sep 2006
Posts: 301
Location: SA,Australia


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Yeah thats the plan, a manual would be friggin hard to drive with a normal RC radio Shocked
I'd use a liner actuator for the gear change and possibly a 1/4 sale servo on the throttle under the bonnet
Then for the brake I'd use a penumatic ram with spring return with the pressure set right down so it would gradualy build up force on the pedal, once you let go it would return Razz

Only thing I'd be worries about is where to test it, might need a quarry for that Very Happy

Post Tue Jan 20, 2009 1:13 pm 
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Damien (not Damian)



Joined: 15 Sep 2005
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Location: The other side of The Wall...Melbourne


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Or you could slap some taxi stickers on it, tint the windows and pick up people at the airport (with no driver inside!) Laughing
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Post Tue Jan 20, 2009 1:41 pm 
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cerberus3112



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plenty of places to test ... like ahh shopping mall car parks at 4 am or back streets oo you could find a field XD
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Post Tue Jan 20, 2009 5:52 pm 
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WiperMotor



Joined: 04 Sep 2006
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Location: SA,Australia


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Just an update, AX2550 Headed my way! $400AU delivered from ebay Smile

Good investment for future projects I think, I'll put some andersons on it so I can move it between projects.

Post Thu Jan 21, 2010 8:08 pm 
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Philip
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Does anyone know the best place to find tiny solenoids to activate a mechanical pneumatic valve? I am after a 6 v solenoid with 5 mm travel. I can't find the required force on the spec sheet. It is for an ant so weight is important.
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Post Fri Apr 23, 2010 7:28 am 
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Knightrous
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Small 3-5gram micro servo is the only cheap/easy thing I can think of.
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Post Fri Apr 23, 2010 7:54 am 
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