Prior posts in the PiCasso Design Challenge:

PiCasso Design Challenge - Kinetic Art Mobile - Post 1


I have received my challenger's kit early this week (Thank you so much for the cool toys!).  The first step in the journey was a brief proof of concept on the rotary joints that will make up the backbone of my mobile design. I had ordered some tiny slip rings and then dug into sketching up some designs.  Here are the slip rings:


These turned out to be pretty tiny, but I think that they will work out fine.  I did a couple of quick tests, using blue painters tape to cobble things together, to see if the fans that I had laying around, could overcome the friction of the slip rings.  So far, even the tiniest fans that I have were quiet sufficient to spin the arms at a fast enough rate.  I went with one of the larger fans, so I should have plenty of airflow to play with.  (Note in the light balls photos, my fan has a 2000 date code, others in the bag have 1999 date codes). With the slip rings in hand, I turned my sketched concepts into Fusion360 drawings and started printing parts.  The first parts worked, but needed a few minor tweaks.  Here are some drawings and pictures of the resulting pivot joints:

Bearing pivot topBearing pivot bottomBearing pivot assembled

The brass tubing (to the left) is actually the main shaft that comes in from the top.  This tubing passes through a bearing affixed to the end of the brass top with a flared end and attaches to the rotor of the slip ring. The pivot will rotate about this upper shaft while the lower shaft with be fixed to the bearing retainer. The outer race of the bearing is captive to the bearing housing (tight fit - compressed by screws).  The six wires of the slip ring with be paralleled into two wires through the brass tubing, making up the power feed into the pivot (the same on the output/bottom side of the bearing retainer).  (Note the trapped green wire, this will not happen when the bottom tube is in place).  The output wires, will also connect to a pair of wires that will carry power to the outer ball, which contain the fans, RGB LEDs and the control electronics, through the aluminum tubing.  There are two aluminum tubes coming out the bearing retainer, a short one (12") for mounting a counter weight (balancing the pivot) and a longer one (~36") upon which will be the outer ball.  I still do not know if I will be staggering the outer balls as they come down from the top, or if they will all line up on the same length.


I have also created a first pass design of the end ball.  The first print (one half only) did show some problems (too little material between the fan output hole and the fan mounting screws), so I do have to do a little tweaking of the design.


Light Ball topLight Ball bottomLight Ball top 3DLight Ball bottom 3D

Each half of the light ball will have fans attached (blowing out in different directions) to allow for the balls to be blown in either direction.  I might allow find in necessary to turn both fans on (at varying speeds) to slow the ball down as it approaches its commanded position.  I have tried in the past to use PWM to control fan speeds, to varying degrees of success, but I have not these fans yet.  The ball is designed with center exhaust holes, surrounded by four intake holes for the opposite side fan.  These holes are intended to augment the intake airflow as the stationary fans blades will be a little restrictive.   The light balls are printed in clear plastic, but based on this half, I might want to thin out the shell a bit to increase the opacity of these pieces.


In the next design, I think that I will remove the through holes on the fan mounting and rework the mounting bosses for small, self tapping screws (blind, on the inside).  I also might want to rework the screw coupling to reduce the size of these holes (trying to make the balls a bit more spherical).  I also want to work on the mounting points for the PCBs (I envision two PCBs, with LEDs, above and below the top/bottom edges of the fan, plus several tiny PCB (strips) bridging between the top/bottom PCBs, to mount additional, side facing LEDs).  I am thinking that each ball will have between 24 and 40 RGB LEDs.  I will need to do some testing, as I want to find a good balance between current flow and achieving a highly saturated color effect on the balls.


I have an idea of trying to reuse the bearing retainer design to build the counter weights.  I can fill in the top/bottom holes and use the bearing/slip ring cavity to hold some BBs work weight.  I will have to think on this a little.


Anyway, that brings me up to date with the design and assembly work on my project.  Thanks for following along.