PDA

View Full Version : Whoa, want some linear accuracy?



Matt
02-22-2008, 10:11 AM
Alex found this link and I'm stealing his glory by posting it :veryhappy:

Stepper motor driven linear actuator:

http://www.ultramotion.com/products/digit.php

http://www.ultramotion.com/images/digitcut.gif

Alex
02-22-2008, 10:58 AM
At thrusts up to 400lbs, repeatability to +/-.00004 inches, and if it's as fast as this linear actuator (the product page states 15 inches/sec), then let Skynet begin!!


http://www.youtube.com/watch?v=NWArsU45pQw

jdolecki
02-22-2008, 12:11 PM
These are way cool but I bet they are expensive. Just like the Squiggle motors I posted a while ago they are out of the price range for anybody but a serious robot builder.
and the PQ12 actuators thar are posted here on Trossen are 65.00, Higher than the price of a good high end hobby servo and they still need a driver.

So unless these manfactures can release a low cost verson geared for the hobby market not the comercial / industrial market. They will be out of reach to all but the serious hobbiest budget.

I Know they are all hoping for a comercial application that will sell 10 of thousands but in reality if they sell a 100 this year they will be luckey.

So Matt /Alex, How do we get the cool things at low cost?

Alex
02-22-2008, 12:19 PM
I just got off the phone with them.

$600 gets you the base model linear actuator...

To tell you the truth, given all of the incredible specs on these actuators, this price doesn't really surprise me.

Alex
02-22-2008, 12:21 PM
BTW, have you seen the new L-series actuators? We just got them in and they work GREAT with hobby servo controllers. They're controlled directly through PWM:

http://www.trossenrobotics.com/store/p/5311-L12-50mm-stroke-Miniature-Actuator.aspx
http://www.trossenrobotics.com/store/p/5310-L12-100mm-stroke-Miniature-Actuator.aspx

Matt
02-22-2008, 03:41 PM
So Matt /Alex, How do we get the cool things at low cost?

Crime man, there is always a life of crime to turn to.

DresnerRobotics
02-22-2008, 03:53 PM
Crime man, there is always a life of crime to turn to.

Bank robbing robots. If it's ever traced back to us we'll feign ignorance and blame Skynet.

jdolecki
02-22-2008, 06:26 PM
Bank robbing robots!

1 Build a small robot.

2 put it in a safety deposit box

3 when the bank is closed, the robot turns on

4 opens the safe from the inside.

5 turns off the alarm from the inside

6 opens the door

and you walk in and take what you want.

or it could take a little at a time and just go back into the box each nite.

LinuxGuy
03-29-2008, 04:17 PM
It's too bad there are not any linear actuators that could be used to build hobby scale robots. It would be really cool to have a biped or hexapod/octapod built using linear actuators instead of servos.

I wonder if a servo driven linear actuator could be made for a reasonable price. Would it be possible to even make such a thing?

8-Dale

cmmguy
03-29-2008, 08:14 PM
Bank robbing robots!

1 Build a small robot.

2 put it in a safety deposit box

3 when the bank is closed, the robot turns on

4 opens the safe from the inside.

5 turns off the alarm from the inside

6 opens the door

and you walk in and take what you want.

or it could take a little at a time and just go back into the box each nite.

LA LA LA LA LA LA LA LA LA LA ......
http://www.ecosherpa.com/images/notlistening.jpg

cmmguy
03-29-2008, 08:23 PM
It's too bad there are not any linear actuators that could be used to build hobby scale robots. It would be really cool to have a biped or hexapod/octapod built using linear actuators instead of servos.

I wonder if a servo driven linear actuator could be made for a reasonable price. Would it be possible to even make such a thing?

8-Dale

One of the manufacturers that make the drive actuators for some of machines that I program has a linear rail system that uses a servo motor to drive it.
http://www.kerkmotion.com/default.asp

LinuxGuy
03-29-2008, 09:21 PM
http://www.kerkmotion.com/default.asp
Interesting. They are probably pretty expensive though, even if they could be bought in single quantities. It would be cool to get something like this to experiment with, assuming they can be easily controlled by a microprocessor.

8-Dale

cmmguy
03-29-2008, 10:49 PM
There are several guys on eBay that buy discontinued automated factory production lines and then part it all out. I have found some cool expensive stuff for very little money.

I'll give Kerk a call on monday and see what those things cost.

LinuxGuy
03-30-2008, 03:52 AM
BTW, have you seen the new L-series actuators? We just got them in and they work GREAT with hobby servo controllers. They're controlled directly through PWM:
I looked at the spec sheets, but I have no idea what the force rating means, how it might relate to torque like in servos, or if there is a relation at all. We're used to seeing torque ratings. :D

I'd like to know how these would relate to a similarly priced standard size servo.

8-Dale

Dave
04-02-2008, 04:22 PM
I looked at the spec sheets, but I have no idea what the force rating means, how it might relate to torque like in servos, or if there is a relation at all. We're used to seeing torque ratings. :D

Well, first you have to think about the difference between measuring angular force and linear force. Angular force (like oz*in or kg*cm) contains a distance component, which represents the distance from the axis of rotation. The distance unit is important because the force decreases linearly as the distance increases.

With linear force, there is no additional distance component, because force is being exerted directly on a fixed point. On the Firgelli spec sheets, this is expressed in Newtons. One Newton is equal to ~3.6 oz.

So...

100mm (63:1 reduction): 14N = 50oz
50mm (210:1 reduction): 45N = 162oz

Does that help?

Adrenalynn
04-15-2008, 12:31 PM
My version certainly isn't as accurate, but it's nearly as fast, and costs less than $70.

A banebots motor turning a chaindrive to a surplus acme screw (feel free to substitute a ball screw if you need higher capacity, or a multi-start tec screw if you need more speed). A stepper instead of the banebots motor could provide tremendous accuracy.

My screw will actuate 8" in 2.5sec lifting a theoretical 41lbs, demonstrated ~27lbs, with a computer-controlled repeatability of 0.05". The original screw was 12" and needed to be cut down for my application.

All these specs can be creatively engineered to match reasonable hobby requirements. Linear actuation with a screw is awesomely controllable for very little money.

RobotGuy/anyone else

If you're interested, I have the formulas for computing all the parameters of screw actuation. You just plug in the numbers off the screw datasheets...

Alex
04-15-2008, 02:31 PM
Adrenalynn - this sounds like an awesome tutorial for members once we get our tutorials section up and running here in the TRC. I think the tutorials section is next on our plate after we finish the final touches on the downloads section:D

Adrenalynn
04-15-2008, 02:44 PM
That's sooo last-year's tech, so I'd be happy to write-up a tutorial, if you like. ;)

It's really easy and fun, and you can spend as much or as little as you want, outside of the screw and motor. We originally started with screen door slides and a rubber-band belt. It worked fine, but didn't have the accuracy/repeatability/speed that we wanted. The frame that it rides in is constructed from less than $3 in 1/2" pvc pipe pop-rivited together (easier to disassemble and maintain than gluing).

Everything except the PVC frame and the screw/nut combination come from Trossen. Banebots motor, motor controller, #25 roller chain, *gorgeously machined* sprockets, ... Trossen through-and-through. Screw and Nut come from an eBay seller that makes them, so availability and price are pretty consistant. Really nothing more to it. Sub the motor for stepper motor and controller if one desires, and/or sub-out the screw for more complexity with multi-starts, balls, techs, etc. I love the flexibility it provides...

I can even provide some advice on easily/cheaply shortening the chain which is a PITA without a $3 1/16" pin-punch from Home Depot or Lowes.

Anyway, I'll work-up some documentation whilst you're getting ready for that section. Great idea for an addition, btw!