Prior posts in the PiCasso Design Challenge:
PiCasso Design Challenge - Kinetic Art Mobile - Post 1
PiCasso Design Challenge - Kinetic Art Mobile - Post 2
In the lyrics of Billy Preston (Will it go round in circles), ... Will it go round in circles, will it fly high like a bird up in the sky? ... It was my goal to find out.
Today I assembled and tested one of the rotating arm/orbs for my Kinetic Art Mobile. There is never an end to the ways in which a simple exercise can end up taking your whole day, but today was proof again that it can and it does. I thought that I would embark on a simple experiment today. I had all of the steps in my mind and I thought for sure, this is going to be easy. Ha! Not quite so.
I have printed two separate halves of the my fan driven orb, each at a slightly different revision, but neither quite the final version. In each orb half I mounted a fan. I ran wires (individual 5 volt lines to each fan and a common ground) through all the support shafts and attach to the leads of the slip ring. After several attempts to attach the wires I finally found the correct sequence (pivot ball first and outside orb second proved to be the most successful order).
The image to the left is the original orb design. The fan was attached with bolts and nuts through the housing. This design broke up the sphere more and had some thin plastic edges that did not form well. On the second image, the fans are retained by self tapping screws from within the orb. The four slightly larger holes were additional air intake holes (that actually turned into exhaust holes - read more below).
I had assumed that I could achieve a balance with the orb 3 feet from the pivot and a counter weight attached 1 foot from the pivot. I could not attach enough weight on the short rod to get the system to balance (I used a first run of the pivot design as a container for BB's and attached a short extension rod with 8 bearings), so I added a 1 foot extension and tried again.
The end of the initial 1 foot section of counter balance tube is at the extreme right hand side of the image. The blue tap is sealing up the repurposed bearing/slip ring retainer housing that was filled with BB's. At the left hand end of the modified counter balance shaft is a section of 7/32" brass tubing with 8 of the same bearings that are used as pivots on the main shaft. This weight seems to have been enough to bring the assembly close to balance, but I was hoping to not need so much weight on the arms, as this will have a tendency to make the rotation of the obs sluggish with so dead weight in the rotating mass. I think I will have to further extend the counter balance arms (maybe even longer that 3 feet) to lessen the weight needed to balance everything out.
I then mounted a temporary support arm to suspend the test assembly. With the test arm attached to the support arm, I ran wires down to a lab power supply.
I the process of testing the movement of arm I noticed that while it would move in one direction, it would not move in the opposite direction. This is when I noticed that I have to different fan types installed in the orb. I had noticed different label colors (blue and green), but both labels had the same part number. Closer inspection showed that the fans had inverse vanes, i.e. with the same direction of rotation one fan would blow and the other would suck. I replaced one of the fans, so that each side of the orb now had the same fan type.
Here is a short video of the arm and orb moving in a clockwise (looking up) direction.
And here is a short video of the arm and orb moving in a counter-clockwise direction.
The arm is moving far more sluggishly than I had hoped. In closer inspection of the fans in the orb, it appears that I still might have the wrong fans in place. I had initially tested one of the fans (green label???) which appeared to be exhausting air on the labeled end of the fan. The orb currently has two blue labeled fans, which appear to be blowing air through the orb and exiting on the opposite side. This is not the preferred direction, as this is pressurizing the orb and likely losing propulsion in the process (leaking out the orb seam and fighting the resistance of opposite fan vanes).
But, the good news is yes, It will go round in circles!
Thank you for following along on my little journey, more to come!
Gene
Update - 3/27/2019
I reversed the two fans (now exhausting in the orb and retried the rotational tests. The thrust seems improved and the orb more quickly accelerates in it rotation. Reverse thrust braking and change of direction is also improved. I also noticed that my makeshift support was still not quite level and the orb was actually going 'uphill' a bit at times. Readjusting this also improved the startup speeds. 
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