Friday, January 23, 2015

Robotic Desk Racers - Part 4.2

Racer C actually might teach the kids a few useful things.  It is a more complicated design, and one that has more potential failure points.  "That could have gone better" is probably the most instructive phrase in robotics.

Unlike the other two which use gear boxes from Barbie Jeeps, this one will (hopefully) be driven by four cordless drills.  It is an old trick from the combat robot days, back then these were mostly used for machines in the 30 to 60 pound weight class, and while the type of drill employed varied, most were 18 volt models.

A while back I picked up a lot of four vintage Black and Decker cordless drills.  Probably circa mid 90s, I was eventually able to ID them as 9.6 volt "Scrugun" cordless screwdrivers.  This seems auspicious, as screwdrivers are set for higher torque and lower RPMs than drills.  The mildewed spec sheet that came with these suggests they have a rating for 1500 RPM, and that promisingly, the clutch only engages when the screwdriver is pressed forward onto the screw.  Earlier "hacks" of screwdrivers I had undertaken were fussy this way, you had to disable the clutch otherwise the gears would disengage when the unit was put under sudden load.

Several challenges were present with this design, and they exceeded the skills and tools available for our class.  So it was down to my underground lair/shop to fab a few parts.  I am in matters mechanical capable enough to highlight my ignorance, but only because the latter is such a large object.

For axles it was necessary to have something that could be fitted into the drill "chuck" and tightened down securely, and also to have a means of attaching the wheel in a solid fashion. Many years ago, in the twilight of robotic combat, there was a lot of "stuff" for sale.  I purchased in disassembled form a robot named "Amish Rebellion".  I have been using the parts for various things ever since.

Among many other components there were some swell axles.  Some with pointed "Ben Hur" style tips, others without.  I needed to modify them for our purposes.  In order it was time to: Turn them down on the lathe, grind the fit point into a triangular shape that would mate well with the drill chuck, then cut them off to equal length.

The last step took a long time.  I guess these were some kind of hardened steel alloy.

The final set up also includes a bronze bushing to support the far end of the axle.  And a mounting system will be "McGivered" from a U-bolt and some metal plumber's tape.

Drill motors, wheels, axles and chuck key ready to go.

Base is cut.  The wooden blocks will have bronze bushings supporting the far end of the axles.  This machine is about 2 feet wide.  B is similar.  A with the big wheels is 3 feet wide.  The hallways we will race in are 11 feet wide.   That leaves 48 inches of clearance divided between the racers and the walls.  That will be interesting at the turns.

Steady progress, but as always we will be down to the deadline on completion.

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