Wednesday, January 04, 2006
What eD's doing
I'm devloping a mechanical 3D rig, simlar to Vik's. The top tray will be a bog standard carriage assembly:The trick to these things seems to be in the z-axis. Whereas Vik is using studding and a spider to move the z-axis, I'm exploring the possibility of using string. Here's the general concept:
I'm currently working on how feasible the idea by building an accuracy test rig. Will keep you posted...
Do the drawings represent where you are in the design process or have you been generating parts and testing your scheme?
Something I've wondered about is why Vik and you and seem so set on raising and lowering the work surface instead of just raising and lowering the extruder head. Can you tell me about the thinking that led you in that direction?
I fiddled with the one in the lab, and while it looks deceptively "floppy", it's actually solid as a rock.
Yeah, you could. The trick is to know exactly where the robot is. It's been something I've been toying with for 30-odd years now and one of the main reasons I'm participating in RepRap now. The team here is thinking about a lot of the problems that I contend with in making that scheme work. It's been a Godsend for me to be around some people who are actually confronting the same problems I'm interested in for a change.
Very straightforward, like most great ideas.
Sarrus' Mechanism suffers from having 6 precision bearings needed to support the platform, all of which experience loads from variable directions. Can we maintain the accuracy through this?
Cornell have built a very similar device, the SFF. One interesting aspect of it is their use of concrete to construct the supporting structure:
They've been printing zinc-air batteries and seem to have a source of flexible conductive plastic.
Drawings: They represent the concept level only. I've made critical pulley parts which are currently under test. Will put up a shot of the rig soon.
Configuration: I've always gone for a static xy table and mobile z tray because of the weight factor. The xy table is looking to be considerably heavy compared to the weight of the z tray (despite the average weight of a built plastic component on it). Moving the heavier weight increases the power consumption, motor capacity, necessary mechanical stability, unwanted vibration, wear & worsens confidence in a blind poisition control system (which mk1 may well be). However, I may be missing out on some crucial advantages which I haven't thought about?
Crawling concept: Having said all that, nothing would be sweeter than watching a legged contraption crawl over the static part it would be building... (memories of the matrix?)
2 X's vs 4 N's: Yes! And the non-slip advantage is very appealing. We can open up a side by simply throwing an extra ider roller into the design.
Tray binding on the runners due to misalignment: My biggest fear. Location manufacturing is one thing that RP cannot do (but it gets pretty close) so this rig will be a real test in adjustable assembly.
Now to check out Cornell...
Nice! A relatively simple mod and it potentially allows all four sides to be open. You'd probably need to keep one diagonal stretch to allow free movement of the turnbuckle (assuming there is one).