Hula Hooper

"Hula Hooper" is a "follower inspired challenge" to create a mechanism that would mimic the operation of a hula hoop automaton from the "Cabaret Mechanical Theater". After watching the video for an hour or so, I designed the mechanism presented here. I'm not certain that it exactly matches the original hula hooper mechanism, but the motion seems to replicate that of the original, and of course, the grandkids love it!

As usual I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to comment as I do make plenty of mistakes. 

Designed using Autodesk Fusion 360, sliced using Ultimaker Cura 4.12.1, and 3D printed in PLA on Ultimaker S5s and an Ultimaker 3e.

1. Thick cyanoacrylate glue.
2. Thin double sided tape.
3. Soldering iron and solder.

I acquired the following parts:

1. One N20 6VDC 35RPM gear motor.
2. Ten 3mm diameter by 1mm thick neodymium magnets.
3. One twin AAA cell battery box with switch.
4. One sheet of thin stick on black felt.

I 3D printed the following parts at .15mm layer height, 20% infill, and no supports:

1. One "Arm, Left.stl".
2. One "Arm, Right.stl".
3. One "Axle, Drive.stl".
4. One "Base.stl".
5. Four "Bolt (M8 by 8).stl".
6. One "Cover.stl".
7. One "Cross Journal Mount Joiner.stl".
8. One "Cross Journal Mount Lower.stl".
9. One "Cross Journal Mount Mount.stl".
10. One "Cross Journal Mount Top Plate.stl".
11. Two "Cross Journal.stl".
12. One "Gear, Motor.stl".
13. One "Gear.stl".
14. One "Hand, Left.stl".
15. One "Hand, Right.stl".
16. One "Head.stl".
17. One "Hula Hoop.stl".
18. One "Leg, Left.stl".
19. One "Leg, Right, Lower.stl".
20. One "Leg, Right, Upper.stl".
21. One "Shoe, Left.stl".
22. One "Shoe, Right.stl".
23. One "Shoulder.stl".
24. One "Torso, Lower.stl".
25. One "Torso, Middle.stl".
26. One "Torso, Upper.stl".

This mechanism is a high precision print and assembly using at times very small precision 3D printed parts in confined spaces with highly precise alignment. I 3D printed all parts using the Ultimaker Cura 4.12.1 "Engineering Profile" on my Ultimaker S5s, which provides a highly accurate tolerance requiring minimal if any trimming, filing, drilling or sanding. However, prior to assembly, I still test fitted and trimmed, filed, drilled, sanded, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on your slicer, printer, printer settings and the colors you chose, more or less trimming, filing, drilling and/or sanding may be required to successfully recreate this model. I carefully filed all edges that contacted the build plate to make absolutely certain that all build plate "ooze" is removed and that all edges are smooth using small jewelers files and plenty of patience.

This mechanism also uses threaded assembly, so I used a tap and die set (M6 by 1 and M8 by 1.25) as required for thread cleaning.

To prepare the base, I performed the following steps:

1. Secured the battery box to "Cover.stl" using thin double sided tape then routed the battery box wires through the hole and into the cover.
2. Soldered the motor to the battery box wires such that the motor shaft rotated clockwise when viewed from the motor shaft end of the motor.
3. Pressed the motor into "Base.stl" such that the motor was 1mm below the top of the motor mount cavity.
4. Pressed "Gear, Motor.stl" onto the motor shaft.

To prepare the cover, I performed the following steps:

1. Snapped "Cross Journal.stl" into "Cross Journal Mount Lower.stl".
2. Slid "Leg, Left.stl" onto the hexagonal mount shaft.
3. Pressed "Shoe, Left.stl" onto the hexagonal mount shaft.
4. Glued the left leg assembly into the hexagonal hole in the cover assembly such that the hexagonal mount shaft was flush with the inside of the top of the cover assembly.
5. Slid "Axle, Drive.stl" down through the hexagonal mount shaft.
6. Secured the drive axle to the cover assembly using "Gear.stl" making certain the drive axle spun freely.
7. Slid the base assembly into the cover assembly engaging the motor gear with the drive axle gear.
8. Secured the base assembly to the cover assembly using four "Bolt (M8 by 8).stl".

To prepare the lower torso, I performed the following steps:

1. Pressed one neodymium magnet into the magnet hole in "Torso, Lower.stl".
2. Snapped the torso assembly onto the lower cross journal making certain the lower torso pivoted freely.

To prepare the middle torso, I performed the following steps:

1. Threaded "Cross Journal Mount Mount.stl" onto "Cross Journal Mount Joiner.stl".
2. Snapped the remaining cross journal into the mount assembly.
3. Glued "Cross Journal Mount Top Plate.stl" onto the top of the mount assembly.
4. Pressed one neodymium magnet into the top plate.
5. Glued "Hula Hoop.stl", flat side down, into the slot in "Torso, Middle.stl".
6. Slid the mount assembly into the torso middle assembly, then threaded the mount assembly into the lower mount assembly.

To prepare the upper torso, I performed the following steps:

1. Pressed two neodymium magnets into "Torso, Upper.stl".
2. Pressed the upper torso assembly onto the upper cross journal.
3. Pressed two neodymium magnets into "Shoulder.stl" making certain they matched the polarity of the upper torso magnets.
4. Magnetically attached the shoulder assembly to the upper torso assembly.
5. Glued "Hand, Left.stl" to "Arm, Left.stl" and "Hand, Right.stl" to "Arm, Right.stl".
6. Pressed the left and right arm assemblies into the upper torso assembly.
7. Carefully removed the stabilization material from "Head.stl".
8. Pressed one neodymium magnet into the head matching the polarity of the magnet in the journal mount top plate.
9. Magnetically attached the head to the upper torso assembly.

To prepare the right leg, I performed the following steps:

1. Pressed a neodymium magnet into the top of "Leg, Right, Upper.st" matching the polarity of the magnet in the lower torso.
2. Pressed neodymium magnets into the joint of the upper leg right and "Leg, Right, Lower.stl" such that the polarities matched.
3. Glued "Shoe, Right.stl" onto the lower end of the lower right leg.
4. Pressed a thin strip of thin stick on black felt onto the bottom of the right shoe to act as a hinge.
5. Magnetically attached the right leg upper assembly to the lower torso.
6. Magnetically attached the right leg lower assembly to the right leg upper assembly.
7. Aligned the right shoe than attached it the cover assembly using the thin stick on black felt.

And that is how I 3D printed and assembled "Hula Hooper".

I hope you enjoyed it!