Linear Actuators

I'm a bit confused as to if you want your linear actuator to drive something or to feedback something.

A screw will hold its place once powered down. A rack/pinion will not. If you put an LVDT in conjunction with either, you will have very accurate feedback for a servo system like in an RC circuit.

What is it that you are trying to do?

Be specific.

Hi,

I'm planning on using a set of linear actuators to drive the control surfaces (sternplanes and rudders) on an automated submarine I'm building.

Michael

I've just built something similar for a FIRST robot.

notes:

2) You can run the screwed rod fast, but you may well see a lot of vibration etc - support at both ends if possible.

4) It is kind of obvious - this kind of actuator can produce very large forces - think about limit switches and end stops - experience suggests that hitting a solid end stop at high motor speed can be spectacular.

Dave

Thanks Dave,

I seem to remember somewhere reading that you can't use 'normal' microswitches as limit switches as they have a high fail rate....Is that right?

Michael

If you are spending serious $$$, you may want to look at commercial actuator suppliers like below. Some have feedback pots for position indication. If you want to go really cheap and DIY, you probably can hack a standard servo to do most of what you need using the threaded rod. I'm currently looking at a similar simple DIY setup, but I need a roller skate wheel bearing to use as a cheap thrust bearing for the threaded rod. WalMart no longer carries replacement skate wheels, so I'll have to expand my range of parts suppliers. ;)

.........but don't want to use up battery life if I Michael

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I used cable around a 1/2" diam' drum . If you do it right , it has same loss as expensive rack and pinion .

But the ultimate is linear motor and quick clutches/ locks . The ram has springs to recover the lost energy . Its very efficient , dont waste batteries .

Microswitches have an 'operating' travel and an 'overtravel'. My experience is that some fail fairly rapidly if you use up all the 'overtravel' every time. The very small ones seem particularly bad.

Another common mistake with limit switches is placing them so that they are the end stop ! Your first control glitch will demonstrate the folly of this arrangement. Mount the switch off to the side, operated by a cam or similar

Dave

Wow ! Thats REAL digital , using MicroSwitches !

I use lots of ARM 7 mcu's with 144 pins ,

ussually one can use 60 GPIO's , for stuff

like reading 1n4148 glass diodes , in a string .

But if you need more precise , the ADC can

read 8 channels and the Timer-Match can do

many more inputs , to transducers , your

robot has .

Ideally , a robot should have ARM7 mcu's

in many places of movement , legs , arms ,

and wheels .

Each arm,leg , can send

rate of its "position"

to another ARM7 , thats reading the

rate gyros and other "centralized" stuff .

So , if robot falls/crashes ,

the s/w can improve automatically .

Robots are exciting , but human replicas

are not optimal , wheels are much more

useful , beacuse wheels can climb and

go fast , you just gotta articulate the wheels

clever like .

I will make one , but now im perfecting

a free OpSys for ARM , that trashes all

the silly C++ , assemblers and Pythons

and other farm animals .

New bidirectional protocol for USB ,

Software is fun to simplify ..

Those are things that rotate. Why do you want to put a linear actuator into the system? If you just need more torque and can accept slower speed, add a reduction gear.

Read the catalogs of Berg and of Stock Drive Products to get some idea of what's available.

John Nagle

Later, Jon

-------------------------------------------------------------- Jon Hylands snipped-for-privacy@huv.com

SubMarine ! Water has too much force.

You must use a long lever inside the Sub then when you want to turn sudden , you lock the planes , and take another step with the lever . When you want to return to nuetral , you release the lock . Its like a jack . Normal , is very easy and the force of water cant cause problems against such a long lever , but when you need to make a sharp turn , you crank the lever several times and after each step ,the planes are prevented from returning so they 'jack" to extreme position . Then simply release the planes , and spring force returns them to nuetral . On an Airplane , one would use "servos" But not electric , but aerodynamic servos that help to move the much larger control surface . You can do this on a SUB , but sailors dont like complicated . You could use a 2 piece plane ....

Good luck .