It's been a busy few months! I started a new job at a local record store- SONIC BOOM- for whom I electrified the bear as seen in the previous post. It takes a lot of time, both working on the floor and making projects and doing repairs, but it's a nice work environment.
The month after the bear was completed Tim proposed building a motorized cosmic swamp monster based on the cover of the not so good modern metal band Mastadon. The band earned a stunning window display just because it would be fun to build! I haven't heard the record but that did not affect my role as the guy to make it light up and move.
Tim and I discussed various options for the location and orientation of various moving parts and I left to let him start construction (a mad genius, he does not like to work near others during the formative stages).
When I returned a few days later I found a chicken wire and two-by-four frame with a five foot, jointed arm and massive fist as well as another arm to be holding a crystal ball of some kind. There was strong cable running from the forearm through various holes and around corners to the back where I was to attach the motor. Pulling with pliers and leaning waay back I could get the arm to lift but it took a hell of a lot more force than I was comfortable with. The plan was to have this machine on in the front window of the store 14 hours a day for at least a month! I needed it to be designed in such a way that it wouldn't destroy itself! Tim on the other hand simply wanted it to look amazing!
We scratched our chins and looked askance at each other and modified the plans a bit to avoid some potential problems. I suggested that one massive arm waving was enough with some good lighting effects in the mix, but I would try everything first.
For a week or two everywhere I went I was picturing pulleys, cams and gears in various configurations. I even walked into a busy intersection one time, completely unaware, so focused on monster guts was I. I had to buy parts with enough room to leave me some profit and I knew high torque motors are expensive so I settled on a single 24DC motor with a large pulley and off-center connection to the cable pulling the arm. Once a revolution the pulley would yank the cable through about 10 inches of displacement, just enough to raise the arm fully. We tried connecting both arms to this mechanism so one would raise while the other lowered. This produced the effect of a giant robot monster fending off a bee as well as shearing the shaft of the motor within an hour. I sucked it up and purchased a replacement motor (total cost $110 for the two of them) and insisted that it be a one armed beast. This ended up looking really great since the rear arm held a plasma ball light while the front one waved and beckoned.
I wired up about a hundred super-bright white LEDs (Tim requested bright white as the front window is flooded with sunlight and he didn't want the LEDs washed out) to a few 555 circuits that would phase them on and off slowly and Tim scatted these through the arms and body. The real focus, however, was the eyes! I am proud of the eyes! 120 Led's soldered point-to-point in three concentric rings each ring tied to a step on a 4017 (via a transistor or mosfet) creating a strobing hypnotic effect. PLUS, clusters of bright red LEDs as pupils that faded on and off every 10 seconds or so. Good stuff! This was a bit of a hassle to solder up, but I ended encasing everything in plexiglass sandwiches with standoffs keeping everything safe and secure. These lighting effects have now been left on 24 hrs a day for two months with no problems!
Again I left for a few days and when I came back Tim had covered the whole frame in an assortment of fake plants and mosses and it looked amazing! The lights were embedded and the eyes were in the unfinished head. All that was left to do was the final motor connection, which was tricky due to the exterior finishing that had been done. Tim had left a flap and a gap in the back for access as this portion would be pointed away form the street.
I had wanted to use a pulse width modulated voltage source for the motor, giving me full torque at various speeds but didn't have time to debug my circuit (which worked at home on the scope but not under full load inside the monster belly) and was happy to find out that 12V DC was just fine for this motor and this application and left it at that. I was using a modified PC power supply for the job because I could get 5V for the logic circuits and LEDs as well as 12V 20A for the motor. This is what I used for the bear as well except that three of the bear's motors were driven by the 5V while only the jaw used 12V. The high current as well as circuit protection available in these supplies is good for avoiding problems with stall current etc in these public robot beasts. I like these PC supplies for these projects and built myself a little bench unit for testing at home for about $60 with bells and whistles.
In the end I had to add significant counter-weight to the shoulder, add a series of small pulleys, slather the thing in grease and add strong springs etc before it would work reliably and safely. Of course all of these things wore out one by one. The cable perpetually sawed it's way through everything in its path, pulleys, wood, even steel eyebolts!! I was climbing back into a tiny corner in a 35 degree celsius window a lot to tinker with these mechanisms. I can happily say that the electronics has worked without flaw this whole time! It was a physically demanding apparatus and I think that the mechanism did quite well in the end. It was 90% functional for almost two months and went many weeks at a time without breaking down. Ha ha! If I had been there during the framing I think I would have run the cable differently and maybe the problems would have been different! Who knows! It was great greasy fun!