Quote:
Originally Posted by AustinSchuh
What size and shape tube are you using/proposing to use? A 1x1 will be a lot weaker than a 2" round tube.
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We aren't using tubing for the arm.
Quote:
Originally Posted by EricH
What is your current projected robot weight? If you're looking at being under, you don't need to shed arm weight. If you're looking at being over, do the analysis. If you don't know how to do the analysis, say so--there are enough engineers on here that you'll get how to do the analysis and the analysis at the same time.
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It's not neccessarily an analysis that we need as far as weight goes, it's more a time analysis. We are trying to decide if changing the material and redesigning the arm will cost us more time that actually machining each piece by hand (we don't have a CNC machine, or any other fancyequipment). we wanted to know if any other team had a similar issue in the past and could possibly provide a little help. As of right now there isn't a weight problem.
Quote:
Originally Posted by Tristan Lall
Remember that comparing theoretical static stresses against material strengths won't be sufficient to guard against complicated load cases—like the ones you're likely to see in an arm that's in motion (i.e. has momentum) and may well be pushing or pulling on things (or being pushed or pulled itself).
The thicker material will be more resistant to deformation, because of the increased stiffness (the modulus of elasticity is roughly constant for all aluminum alloys), so you'll be less likely to suffer a dent that causes the member to buckle.
Also, depending on the details of the planned design, you may find it more convenient to lighten the arm by cutting strategically-placed holes, rather than making it from lighter stock.
We'll need lots more information to give you concrete suggestions about your particular design.
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From the very begining we designed the part to have triangular lightening holes to form a built-in truss like structure. The problem is 6061-T6 at 1/8th thick is not easy to machine by hand.
Quote:
Originally Posted by Mike Betts
I'm not sure of the particulars of what or how your arm works but a ratio of 2:1 is pretty fast. Perhaps it is too fast to control? Changing gear ratios may be easier than building a new arm making it slower and having more torque all at the same time...
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This is a point i brought up in our design sessions. I wanted to make it a 4:1 ratio for torque purposes and pointed out that ~40 rpm might be too fast for an arm that will be traveling ~180 degrees either way.
I'm sorry if the original post was not clear but we mainly want to know whether its worth it to go back and redesign at this point in time based on other teams past experience. Also consider that we don't have a CNC machine or a machine shop sponsor. I apologize for the unclear post and thank you all for your time.