Welcome to Robot Dialogs. This is a place where I will record my progress, mistakes, errors, failures, lessons learned and hopefully occasional success in my designs and implementations of robots and other technical endeavors. I will try to make it as educational, informative and entertaining as I can...

Sunday, December 6, 2009

Final Assembly

Well I managed to get all the parts purchased, designed and/or fabricated before the weekend of the event. As is often the case with project like this, my designs changed as I searched for parts. You will see below the final designs created in SketchUp (they really are final, based on the bot I took this weekend). I put a great deal of effort into getting exact dimensions in every place I could. In fact the only blatant differences between the drawings and the real robot are in the purchased parts(drill and batteries) which have too many curves to replicate.

SketchUp Model

I'm pretty certain no one will want to duplicate this exact design (anyone capable would probably find that boring) ; however, some of the components may be useful. The motors, motor drivers, wheels and hubs are all precisely measured, and could easily be copied into another drawing.
I've decided on a name: "Spin Cycle" (a suggestion from my older brother). The name stems directly from the previously withheld weapon design. The "weapon" is a shiny stainless steel 14 inch rod from an old ink-jet printer. It weighs (about) 1.5 lbs. It is attached to a Craftsman 14.4 V cordless drill which has had it's handle chopped off. To attach the rod to the motor, I went to the local hardware store and purchased a galvanized steel 3/8" threaded "T" joint and short 3/8" coupler. The "T had to be bored out to 1/2" and finally two small 6-32 set screws added to secure the rod. Inserting a screwdriver into coupler and letting the rod rotate freely turned out to be a very easy way to check if the rod was balanced before tightening the set screws.I designed the following controller circuit (mostly based on the designs in an earlier post) for this motor. The controller takes up only one output pin from the micro-controller because it is only capable of driving the motor in one direction. Four power MOSFETs were used in parallel to increase run-time (by dispersing current and therefore heat). I recycled the big switching diode from the drill's trigger circuit to take care of back-emf when the driver was turned off with the motor still spinning.I left the drill motor and transmission intact so that the internal clutch would slip when the rod starts to spin. This is also safer from the electrical side because it allows the clutch to slip when the rod hits something thereby reducing the likelihood of a motor stall (huge current draw). I estimate that with full battery charge the rod/drill spins at ~200 rpm. It's enough to scare any little plastic robot away.

I finished the build by filling the house with the sweet smell of spray paint... all the metal components of the chassis were painted with two coats of metal primer and several (I lost track) coats of glossy black paint. I don't know if I'll put any designs or text on it...unlikely.

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