Saturday, March 24, 2012

Middle School Robotics Project-Chapter Five

We have one session left, and I hope to use that mostly for test driving.  All components have been built, successfully tested, and in one or two instances broken.  This is all good, as we have just enough time to fix things, and it is our failures that teach us the most.

Main work today was on the arms.  One dispenses M & Ms, the other deploys a water squirter.  I thought long and hard about how best to do these mechanically, but in the end the engineering issues seem to have solved themselves.

Each arm is driven by a linear actuator.  This one came from a fancy quad wheelchair.  It is designed to run at 24 volts, so at the 12 volts we are using it is a little leisurely.  Here it is being secured with hose clamps.

Here is the linkage between arm and actuator.  It is simply a bit of nylon strap that is stapled onto the top of the arm.  This duplicates how tendons and muscles work mechanically in the human body, and it pulls the arm up into an extended stance without a hitch.  I was worried about how the arm would be lowered back down.  But I just had the kids file off a bit to make the arm fit loosely on the axle....
And here is the M & M dispensing arm in about the angle needed to dump candy on a cafeteria table.  When the actuator runs back out a combination of gravity and just a bit of natural stiffness from the black hose (which runs down from the candy dispenser) suffices for nice fluid movement downward.

The other arm contains a water squirter.  We have a faster actuator there, a smaller one from a satellite dish controller.  Here is some rather lousy film of it in action.  I have a bad habit of not holding the camera in the correct orientation for this...
video
So everything works.  The arms, the dispenser, the water gun, drive unit.  We have several remaining challenges for our last session.

The swivel device is less robust than we thought.  There were a couple of lag bolts not put in far enough, allowing some rocking.  This is not good, as a little more loosening could cause the whole top half to pitch forward.  A kludge solution should take about half an hour.

And we need to figure out to set the controls to most ergonomically control the golem.  It will take two students each with their own radio controller.  One will operate the bottom half, drive and swivel.  The other gets the top half with left and right arms, the squirt cannon and the M & M dispenser.  I wonder which assignment will be more in demand?

A view of the near finished product, only the M & M dispenser is out of view.  We have it up as high as possible to get more gravity feed.

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