It is powered by six medium PF motors with six linear actuators and three IR receivers. It is controlled by a single NXT with the HiTechnic IRLink. My version doesn’t have any feedback, so the motors linear actuators are turned on and off based on time. It took a few hours of research to get the linkages and joints down, but once I did that, building and programming took only one night.
Movement is sloppy because of the PF motors. I want to try to build this using servo motors, but mounting the huge motors is a problem.
UPDATE:
Here is what a well built Stewart Platform should look like...
how can i order it?
ReplyDeleteThis isn't a set, it consists of parts from many sets. Sorry.
ReplyDeleteHey Shep,
ReplyDeletei'm going to start a thesis on some 6dof algorithms for one of these..
got some q's for ya.. if you'd be so kind.
u mentioned some research for the linkages and joints... you couldnt pass that info on could ya?
How much kinematics did u get into?
got any other recommended resources?
Thanks
J
Sure thing.
ReplyDeleteWell, basically the linear actuator (6 of 'em) have to have essentially a universal joint at each end that cannot twist axially. When you look at the video, there is a yellow link toward the top of the linear actuator. Just above that is an actual U-joint.
Due to the restrictions of using Lego, the bottom joint couldn't be a U-joint, but when it is built it is effectively one. When disconnected, the LA can move in the X and Y plane.
One thing I found interesting about this is that when only 5 of the LAs are attached, the whole linkage is very floppy and hard to manage. But once you attach the 6th, it becomes rigid. Intuitively, I would have thought that 5 points of contact would be plenty to maintain some control of the platform but it isn't so.
I have built the platform a couple of times since this video and another thing I noticed was that if the circle diameter of the joints on the top is close to the diameter of the joints on the bottom it is more stable. If the diameters differ the platform becomes unstable at the extreme positions, i.e. some fully extended and some fully retracted.
Here is a photo of another one that I built within the last 6 months. This one was much more stable because I matched the diameters better.
http://1.bp.blogspot.com/_CVq5bbnuCpc/TIVYzSZAM3I/AAAAAAAAAUo/Rrzd9mm5bPg/s1600/Stewart.JPG
The platform in the video would collapse if I put much weight on it because the diameters were different but the one in the photo didn't collapse in any position.
Another think I think is cool is that there is no positions where the whole platform locks up. Any combination of positions on all of the LAs results in just a different position of the platform.
If you have the ability to actually build one, I strongly recommend it. Lego is great because you can easily change linkage lengths and such to see what it will do. I could build this in about an hour, not many other building mediums could boast that.
Good luck and I hope this helps. If you have any other questions, don't hesitate to call on me.
Shep
By the way, I controlled this using a Mindstorms NXT. There was no feedback on the motors, so I just ran them up and down to various random positions. I didn't do any kinematics on them because as you know it's a subject worthy of a thesis!
ReplyDeleteI'm also looking into building a stewart platform, but I'm confused on how to code the motion control. Can you recommend resources or could you make a post detailing how you coded the motion? Ideally I would like to have PID feedback....
ReplyDeletehiii ...im presently working on a 6dof controlled using bluettoth on my lap top and im stuck .....the mistake what i made is i made the base fixed as the one end of the lego actuator comes with a fixed end ....how did u make the lower base of all the actuators move independly...could you please share the sources with me...
ReplyDeleteand did u use any gear at the base cozz u are controlling the lower base of the actuator both linearly and horizontally...can u please educate me with that aspect as well..
ReplyDeleteHey, Which Technic set did you use for this?
ReplyDeleteI'm searching for a Technic set which contains ball joints and universal joints
Thanks
Hi, have to build one oh this for a project in my university. Can you write a list of the main lego component that you use for you Use for your project? Is there a way that I can use to contact you?
ReplyDeleteThanks