Linear Actuators

Hi,
I'm about to build a set (6) of linear actuators for my robot (AUV) and was wondering if I could run a few design issues by the group?
1) I'm thinking hat I can either use a rack and pinion or rotate a piece of threaded rod. Would I be right in thinking that if you were to push on the R&P method you would therefore be pushing on the motor and subsequently motor draw would increase proportional to force applied? I'm not thinking about using it as force feedback, but don't want to use up battery life if I have a constant force pushing on it. And therefore would the threaded rod therefore be the preferred method as the force is dissipated through the rod and teeth as opposed to the motor itself?
2) Sticking with the threaded rod method, I presume I could calculate the time to extend (I presume there's a better term) by multiplying under load RPM by thread pitch? I've always heard 'slow' and 'linear actuators' in the same sentence and using a 5000rpm turning a coarse metric thread (pitch 1.25mm) I get 3000(if we say this is load RPM)*1.25750mm/min which sounds pretty fast to me....
3) Has anyone here constructed a linear actuator and got any suggestions/comments/pictures etc that could help me design/make it?
4) And finally, in order to have level of position feedback, I was thinking about using a hall effect sensor on the rod/motor (depending which one I choose) and using that combined with knowledge of knowing which way the motor's turning fed into a 4029 to provide a value as to the current position that a uC could then read.
Am I heading in the right direction here?
Thanks in advance,
Cheers,
Michael
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
in message

was
I
rod
time
by
I
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Michael wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 .
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Michael wrote:

I've just built something similar for a FIRST robot.
notes:
1) Run the screwed rod in tension if possible.
2) You can run the screwed rod fast, but you may well see a lot of vibration etc - support at both ends if possible.
3) As a general principle I would always try to connect feedback sensors directly to the item in question - you don't need much accuracy here, so a simple pot would probably suffice.
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Michael wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 ..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 16 Feb 2007 18:37:04 GMT, "Michael"
wrote:

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. ;)
http://www.firgelliauto.com/default.php?cPath http://www.warnerlinear.com/lightdutyactuators.asp https://ws04.ipowerweb.com/smartweb/lado/product1.asp
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 16 Feb 2007 18:37:04 GMT, "Michael"

http://www.robotshop.ca/home/products/robot-parts/motors/actuators/firgelli-actuators/index.html
These should do the trick for what you are trying to do...
Later, Jon
-------------------------------------------------------------- Jon Hylands snipped-for-privacy@huv.com http://www.huv.com/jon
Project: Micro Raptor (Small Biped Velociraptor Robot) http://www.huv.com/blog
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

> or ... threaded rod.
.........but don't want to use up battery life if I Michael
__________________________________________
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 .
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.