Sunday, July 8, 2012

Mech: Material Science

I had some problems with the mech's feet and their colossal weight. I've made some reductions in the main spans to get the margin of error to about 8X it's standing strength. I also made the assumption I'd be using an alloy steel that's about 2x as strong (125k psi instead of 60k psi).

This has brought the mech feet down to 298lbs each, which is exactly under my target weight.

I'll need to do more calculations about the torsional forces on the foot that I've not yet figured out how to do. I also bought a book on material science to better understand what I'm doing now that I'm relying on more complex material properties for strength.

Also, while I was mulling over my changes to the mech I spent some time working on the table. I finished the H-bridge controlled that will drive the motors. It needed some debugging but then when it 'worked' it blew up, fracturing one of the transistors with the heat. It's clear there was a moment when both the high and low on one side were both conducting, allowing a high amperage of 120V through it.

Investigating some non-home-made H-bridge drivers I see that they often tout their abilities to prevent this. I bought some. I hope that their bragging about this feature does not imply that some of them still fail at it...

In other news, I left the soldering iron on when I got distracted by an attractive girl in my bed and need to buy a new tip for it.

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