Sunday, July 15, 2012

Mech: More detail on the feet and legs

The real goal here is to get the models to fully represent the mech. Now the act of modeling everything in detail will force me to consider the entire design before I start building and serve to make the simulations work just like the final product will.

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.

Sunday, July 1, 2012

Mech feet: It looks like they're too heavy

I just added the density settings to the mech feed that I designed and it looks like they're already super heavy. Just one foot is 852lbs.

I'm using 3"x3"x0.25" steel for the main spans, 2"x2"x0.25" for the long (1") cross bracing, and 1"x1"0.25" for the short cross bracing.

Mech feet

The goal at this point is making the mech match what I'll actually build. That way the simulations will be accurate enough to determine the exact walking sequence. Similarly, I'll be able to get the collision detection and weight measurements correct.

Got the basic supports done for the mech foot. I'm using a helix or spring-like pattern to prevent the truss that connects to the leg from bending in the face of the torque from the feet. I'm not yet sure how to measure the stresses on it.