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Building an ordbot first post

PostPosted: Tue Dec 30, 2014 2:35 pm
by Steved
Hi all, first postl I am building an ord bot Hadron 300mm3.Just wondering is the 300mm3 version tried and true? When I push the top with my finger the structure resonates quite readily at a frequency of about 5 cycles per second (just guessing) and not fully diminishing for about 3 or more seconds, could be I have not fully tightened everything. It seems, however to be an inherent structural beam resonance as the whole thing feels " springy" not "loose". Intuitively I would think the inertia of the gantry and z axis would cause printing accuracy concerns due to this. Cant get my head around how that would not be the case. have I missed something? It is not a "wobble" caused by an uneven surface, I have isolated that. Hope someone has some experience on this.

Cheers

Re: Building an ordbot first post

PostPosted: Thu Jan 01, 2015 3:22 am
by cvoinescu
300 mm³ (three hundred cubic millimeters) is a tiny volume -- about the size of a large pea. I assume you mean a build volume that's a 300 mm cube (that's 27,000,000 mm³). :)

Did Bart publish plans for this, did someone else, or is this your design? Can you link to the plans?

Very rigid structures will resonate, and tightening things often won't help. You could add or remove mass to tune the resonance out of the frequency band where it's harmful, or, better, you could dampen it. Some materials naturally absorb energy (for instance pitch, or a container of oil-filled foam with lead shot embedded in it), or you could make some of the joints intentionally weaker (e.g. insert rubber gaskets). I'm not an engineer, and I haven't experimented with this -- hopefully others will come up with more useful ideas.