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Rift
01-13-2009, 02:16 PM
I was curious if anyone knows of a solution to either making, or buy a completed product that will allow linear actuation through the control of an SSC-32 board.

I want to use linear actuators to allow 2 arms to move both left and right while simultaneously doing other things.

I have found one solution at servo city there linear actuators that can be plugged up to any hobby servo control board. The down side is that there a little expensive for me right now $300 a peace and I'm looking for a possible solution to come out a little cheaper. If there even is one.

Accuracy down to the mm is not totally necessary either.

Rift

jes1510
01-13-2009, 02:46 PM
A microcontroller, H-Bridge, and slid pot might could do what you want if there isn't already an off the shelf solution. I believe Ooops is using a servo driven linear actuator.

darkback2
01-13-2009, 02:49 PM
As with anything...make it yourself. I've scene pretty cool ones made from 80/20 aluminum, and threaded rod.

Twist the rod using a continuous rotation servo.

Chef Omega

Adrenalynn
01-13-2009, 02:54 PM
Have a look at the Firgelli L12 series. I'm running late to a meeting, so I can't go into too much right now, but they seem reasonably priced across the line from what I've seen. You want OPTION I:

Option I—Integrated controller with industrial and RC servo interfaces
Wiring:
1 (green) Current input signal (used for 4–20 mA interface mode)
2 (blue) Voltage input signal (used for the 0–5V interface mode and PWM interface modes)
3 (purple) Position Feedback signal(0–3.3 V, linearly proportional to actuator position)
4 (white) RC input signal (used for RC-servo compatible interface mode)
5 (red) Motor V+ (+6 Vdc for 6 V models, +12 Vdc for 12 V models)
6 (black) Ground

In fact, looks like Trossen did the leg-work already for us on that:

http://www.trossenrobotics.com/store/p/5311-l12-50mm-stroke-miniature-actuator.aspx

Rift
01-14-2009, 01:21 AM
Hrm Adrenalynn while those are indeed nice I'm looking for a bit more distance of travel then those can offer. Unless I'm missing something in the specs.


Rift

Adrenalynn
01-14-2009, 01:29 AM
And therein lies the rub. We can only scheme solutions to stated problems. ;)
How about something a little more detailed than "a bit more distance"?

Rift
01-14-2009, 01:44 AM
haha yeah that would probably help wouldn't it. Around 6-8 inches of travel would be the range.


Now I know these exist http://www.nookindustries.com/images/nookmodular.jpgand are far beyond what i need,but is there something in that style, which i can control through a servo board. Or is a separate controller going to be the only option?

The only reason I'm looking to control it though the SSC-32 is for simplicity reasons. I can this way control do all the work through SEQ as opposed to using another set of software for just the actuators.

Rift

Adrenalynn
01-14-2009, 02:00 AM
I don't see anything for less than $300.

You know you can control a motor controller from the SSC32, right? Motor controllers talk pwm, ie. they are like servos in the control signals they take.

robologist
01-14-2009, 04:46 AM
Servocity (http://www.servocity.com/html/linear_servos.html) has some interesting actuators. Not cheap though.

Rift
01-15-2009, 01:14 AM
Adrenalynn do you mean one of these? http://www.lynxmotion.com/Product.aspx?productID=562&CategoryID=10

How would you go about applying something like this to a linear actuator?

Would it be something like a rack and pinion setup or something else?


Rift

Adrenalynn
01-15-2009, 02:17 AM
I was thinking something a little smaller - like this:
http://www.trossenrobotics.com/store/p/4265-BaneBots-Motor-Controller-9A-peak-.aspx

mated to something like: http://www.trossenrobotics.com/store/p/4230-16-1-36mm-Planetary-Gearmotor-RS-385-Motor.aspx

A linear actuator is nothing but a motor driven screw with a nut and limit switches. It can be drive (slowly) with a continuous rotation servo, or with a motor with limit switches on it.

Did you see our team's Sci Oly 'bot for last year? It had a poor-man's screw on it. 8" of lift in <2sec, and we tested it to 30lbs and it was barely straining. Ours wasn't "pretty" but your could be. We had size constraints that were pretty brutal.

Let's see.. Ahh. This photo should show the concept:

1029


This was an early prototype that shows it better:
1030

metaform3d
01-16-2009, 01:14 AM
I built an ultra-cheap linear actuator about a year ago, before I had any idea what I was doing. It's just a threaded rod on a motor, an aluminum rider tapped for the rod, and a pot with a gear that meshes with the rod. I have an exploded view here:

http://forums.trossenrobotics.com/gallery/files/1/7/0/5/picture_002.jpg

Threads have a reputation for locking under torsion, although I have the rod well-lubricated and that has never happened. Of course part of that might be the aluminum rider which will give under pressure. Over the year it has gotten somewhat loose on the screw and might need to be replaced with a harder material.

Just emphasizing that a linear actuator can be a relatively simple device, although it does require that you implement your own control loop.

Adrenalynn
01-16-2009, 01:39 AM
If you use one of the "magic" thread types that are made for it, they don't bind up under almost any circumstance. Acme screw, ball screw, hitec screw, etc. They're also faster (fewer TPI and generally multiple starts) cycling and way more mechanically efficient.

The one I posted a photo of above was an acme-type thread, two start - you'd be stunned at how fast and torquie it is...

Rift
01-19-2009, 02:01 AM
Well this is all really awesome stuff! Thanks for all of the input I'm def going to give that motor controller a good look its so nice and small and I think would work perfectly for this.

So with that connected to the board I can basically control a motor like a servo?

Rift

elios
01-19-2009, 02:03 AM
adrenalynn - that is awesome, do you have a link to the competition?

cheers,

Adrenalynn
01-19-2009, 02:44 AM
YouTube - Science Olympiad Robo Cross 2008

The screw could have been driven much faster. We had enough torque to lift 20+lbs, we only needed to lift 4oz at a time.

Rift
01-20-2009, 09:54 AM
Any recommendation on where to buy a good threaded rod? I was looking at the Acme ones but every place I find seems to want you to buy in bulk.

Iv also noticed there are a bunch of different types. Any ideas on what would give the smoothest trouble free ride?


Rift

Rudolph
01-20-2009, 12:17 PM
McMaster-Carr (http://www.mcmaster.com/) could work. Grainger (http://www.grainger.com/) maybe. Where are you located? I know a place in Riverside, CA that has stuff like that too.

Edit = Hit McMaster link above. In "Find Products" search box type "acme", then wait a second (yay, ajax). Hit first returned page "About Precision Acme Threaded Rods" for some info about what precision means when it comes to Acme threads. I'd link straight to it, but they won't let me (yay, ajax).

If you need some odd size or something, any machine shop worth a darn can make you one, though that'd be an expensive way of doing it.

Adrenalynn
01-20-2009, 12:40 PM
Talk to Wanda at Precision Tech Machining. precisiontech [at]cfl.rr.com or 321-751-4212

They make 'em themselves and their prices are great. Remind her that she talked to "Jodie" about ACME screw math for robotics competition last year.

A 12" x 1/2" screw was about $20 with a Delrin nut...

They're really nice folks, family business, and really cared about some little one-off project.

Sigma X
03-30-2009, 06:27 PM
I've been looking for somthing
like this for a while now and I gotta ask where to get those
threaded screw bar like things? could someone post a link?

Adrenalynn
03-30-2009, 06:33 PM
Right above your post, I gave contact info for a screw.

robologist
03-30-2009, 11:11 PM
Here's another place that has some 1/2" cheap Acme 36" screw (http://www.surpluscenter.com/item.asp?item=1-2983-50-3) right now, surplus, and a nut for it.

Sigma X
03-31-2009, 12:39 PM
ok thanks for the info guys this can help alot!
@robologist; how long is this screw?

DresnerRobotics
03-31-2009, 12:46 PM
36" screw (http://www.surpluscenter.com/item.asp?item=1-2983-50-3)

Perhaps 36"? :)

Sigma X
03-31-2009, 01:06 PM
sorry when I checked the link it looked as it's 1/2"

lnxfergy
03-31-2009, 01:35 PM
sorry when I checked the link it looked as it's 1/2"

Thats the DIAMETER of the rod...

-Fergs

Adrenalynn
03-31-2009, 01:36 PM
it is a half-inch screw. And it is a 36" screw. Both. At the same time.

Stupid malfunctioning keyboard. ou beat me in there.

Sigma X
04-01-2009, 10:55 AM
thanks guys I get it now

what type of motor will I needed if I wanted my actuator to have power
and (or)speed

Adrenalynn
04-01-2009, 11:31 AM
Screws are crazy strong by nature. Ours would lift 30lb with just a little 7.2v motor.

The big question is speed. You want to run nearly as fast as the screw and the mechanics will allow.

Sigma X
04-01-2009, 11:39 AM
so speed is the main factor not torque
so I should look at RPM's?

Adrenalynn
04-01-2009, 11:45 AM
You should look at the screw and bearing-blocks specifications.

Sigma X
04-01-2009, 12:30 PM
ok I get it I think i know what to get

Adrenalynn
04-01-2009, 12:56 PM
What are the max RPM on the screw and blocks? And you're taking into account that there are two different numbers, one for horizontal and one for vertical, right?

robologist
04-02-2009, 12:56 AM
Lead screw equations, use consistent units :
F -> force (linear)
T -> torque (rotation)
L -> lead (distance per revolution)
P -> pitch (revolutions per distance)
V -> velocity (linear)
w -> speed (rotational)
e -> efficiency (estimate 0.9 for ball screws, 0.3 for Acme screws, prob 0.1 for threaded rod)

F = ((2pi x T) / L) x e = (2pi x T x P) x e

V = w x L = w / P

Above 36" long x 1/2" diameter Acme screw also lists 10 tpi (turns per inch) which is a Lead measure, inverted becomes 0.1 inches per turn as a pitch measurement.

Sigma X
04-02-2009, 10:01 AM
thanks for the lesson guys this will help alot

elios
04-03-2009, 12:29 AM
hmmmm, you want linear actuators aye.... try this (http://www.dynalloy.com/)but the stronger ones need 4 amps
(http://www.dynalloy.com/)

Adrenalynn
04-03-2009, 02:17 AM
As long as you only need a few mm of travel, muscle-wire can work well, yes. Not so much for driving arms, though.

Sigma X
04-03-2009, 08:03 PM
yes but wouldn't muscle wire need to cool down to return to it's original shape?

Adrenalynn
04-04-2009, 03:14 AM
Yes, but that happens almost instantly. It can be cycled very quickly under normal operating conditions - but again - with very short travel.

Sigma X
04-05-2009, 12:00 PM
so wire muscles have a strong strength pull?

Nelsontheunholy
04-11-2009, 08:03 PM
http://www.firgelli.com/products.php they have a new pq-12s linear actuator could prove fun as it has about and inch of actuation so an extend-o-fist punching action on a robot would be [email protected]!!!!