Linear Actuators Stewart Platform

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Linear Actuators Stewart Platform

Postby bdring » Sat Jul 09, 2011 1:55 am

Here are some basic linear actuators made with Makerslide parts. The first uses an inline motor. The second is offset with a belt. The belted one is a little more compact and allows gearing up or down.

ms_linear_belted.jpg

ms_linear_inline.jpg


A contact I made through Kickstarter noticed that the linear bearing would be good for a Stewart Platform. Stewart platforms work with three or six linear actuators do do some pretty amazing things. Some have been scaled up to full size production milling machines. I did a quick rendering of one with MakerSlide actuators. I used the end plates mostly for aligning the parts. I intended to swap them out with extrusion, but did not get around to it. This is not intended to go anywhere in this form. It is just here to inspire ideas.

EMC2 can be configured to use these and run normal straight g-code.

ms_stewart.jpg


Here are some cool links and videos

http://www.festo.com/cms/en_corp/9782_1 ... m#id_10395


Bart
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Re: Linear Actuators Stewart Platform

Postby theyangster » Mon Jul 11, 2011 9:40 am

Wow, I learn something new each day...this is pretty cool stuff! It looks like it opens up a whole new area for beveled cuts and accuracy, etc etc. (or is this easy to do already?)

What's the max length for linear 'screw'? And what's the approximate cost of everything in the picture? You know I'm going to ask about adapting this to a camera slider :D. Is the stepper motor usually have high power requirements making it unsuitable for portability?

Last Question (I swear!), it seems with your initial makerslide samples, you had 3 wheel configurations and here is 4 wheels, is this going to be standard on the plate for the makerslide? I think for a Camera slider, I along with others would probably prefer to have all 4 wheels (if the horizontal method of mounting was used) and are the wheels mounted with eccentric spacers on all sides, one side or are the holes just the right distance that adjustment is unnecessary (preferable).

I don't want to hijack this thread, so feel free to post a reply in my original thread.
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Re: Linear Actuators Stewart Platform

Postby bdring » Mon Jul 11, 2011 12:59 pm

The plates have 3 wheel locations per side so you could use 3-6 wheels per carriage. On my router design I used some of 3 and 4 wheels. I just stole the 4 wheel carriage from that design. The end plates where the only thing I actually designed for that rendering. The rest was just bolted together from existing models.

When increasing the length of a lead screw, the first negative issue is usually "whipping". Instead of spinning perfectly on axis, it starts to act like a jump rope and bow out. This is a function of speed and length. There are calculators of the web that can help you with this. If you keep it slow, you can go longer.

Price estimate for a 1 meter linear actuator....

Maker Slide $10
Motor $15
Lead Screw $9
Wheels, Carriages, Bearings, End Blocks, Couplers, etc $30-$40


Note: The camera slider would probably work better with belts.
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6DOF Option

Postby bdring » Tue Jul 12, 2011 8:26 pm

The guy I am collaborating with on this concept suggested an interesting idea. If I turned the actuators 90 degrees and mated them to a second actuator, I would have a full 6 degrees of freedom machine. You could start with the carriage pairs hard linked together for a 3 axis machine, then upgrade later to a 6 DOF machine.

This is only a concept rendering at this point and a lot of issues would need to be worked out. We are trying to have the minimum number of custom parts and use as much stock MakerSlide and Misumi parts as possible. Right now the only custom part is the motor/bearing plates at the ends. I am trying to figure out the best way to tie them into the horizontal extrusions.

6dof_01.jpg
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Re: Linear Actuators Stewart Platform

Postby r691175002 » Tue Jul 12, 2011 9:48 pm

It looks like it would be very hard to get enough rigidity for cutting out of that setup.
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Re: Linear Actuators Stewart Platform

Postby dirktheeng » Tue Jul 12, 2011 10:47 pm

It's an interesting concept. I can see that developing a CAM program for this would not be easy though. No standard cam packages will do this kind of setup and it would have to be a custom written code... probably harder and more time consuming than developing the machanics.
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Re: Linear Actuators Stewart Platform

Postby bdring » Tue Jul 12, 2011 11:17 pm

Stiffness I am not going to defend the stiffness of a "sketch" that does not even have the ends on yet, but Steward Platforms and Delta machines are some of the stiffest machines made. All of the actuators are in pure tension or compression at all times. On conventional 3 axis machines most of the load is a pure bending load which is often the weakest mode. While the actual linear actuators on this machine will see bending load, it is usually not at a vector normal to the beam so the force vector is diminished. Also, at least 5 of the actuators are taking some of the load at all times.

CAM programs. The complicated control nature is removed from the CAM program. Controllers like EMC2 run all the motion through a kinematics algorithm so the CAM program just sends G0 X10 to the controller and all motors move as required to move the head 10 units to the right. You need to code that algorithm once and then all CAM programs can handle it. You do need a CAM program capable of 3+ axis, but that would be true of any 3+ axis design.

If you want complicated..check this out...and this using RC servos.

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Re: Linear Actuators Stewart Platform

Postby steves » Wed Jul 13, 2011 12:32 am

Pretty amazing.

I did notice that the 21 minute mark the foot at the left side of the frame was sliding a little. Still seemed to work OK, though.
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Re: Linear Actuators Stewart Platform

Postby akonneker » Mon Jan 09, 2012 5:50 pm

Hello Bart (and others)

I was planning on building a Delta robot/Stewart platform in the style of the first youtube video you posted, but after hearing about MakerSlide
(after the Kickstarter campaign was over) and stumbling across this thread I decided that your sketch seemed like a much easier way to go. I'm looking for a way to build something like this that requires no machining. I'm currently a starving college student and despite my dreams, I have few tools and no easy access to a lathe, mill, band saw, etc.

So on that note, have you been working on this at all? I've been busy with school/waiting for MakerSlide to be released to the masses so I haven't sketched up much of my own take on a Delta robot, but I was planning on working on it over the next few weeks. Mostly I've just looked around for things like carbon fiber rods and Heim joints for the arms.
I was thinking of making something along the lines of a three motor variant of the 6-DOF sketch that you posted, and I am very interested in being a guinea pig for the development of the idea if you need/want someone to tinker around with it.

Adam K
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Re: Linear Actuators Stewart Platform

Postby gene » Tue Jan 10, 2012 3:06 pm

Wonder if there is a way to use makerslide (or the future thick makerslide) to make a simple 6DOF design for a flight sim/driver sim. That would be pretty sweet. I've spent a bit of time looking at these kind of projects on X-simulator.de
http://www.x-simulator.de/forum/
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