Double Diabolo = Tetrabolo

Attach 2 diabolos together to have a tetrabolo

When you use it with only one pair of sticks, it is no symmetric there will be a whirling movement called precession in mathematics.

Material

2 Diabolos Vision from Henrys with bearings (with different colors)

2 Pairs of diabolo sticks (with strings of different colors)

M10x37x2.5mm Brad Hole Tee Nut Carbon Steel ( 2 pieces ) from Amazon

Thread Adapters Sleeve Reducing Nut for M10 10MM Male to M8 8MM Female ( 2 pieces ) from Amazon

M10 Threaded Rod

Glue Loctite 271 or Loctite 243 ( optional )

Adhesive tape (optional )

Tools

Tube wrench 10 mm

Saw ; file

Vise

Pliers

More simple but not reliable and not aesthetic

Is is more simple to use adhesive tape to paste 2 diabolos; but it will not last long, perhaps only a few minutes to 1 hour.

Cut it with a saw an don't forget to remove the burrs.

Cut it with a saw an don't forget to remove the burrs. (2 pieces)

Remove one nut on each diabolo

Check the direction of rotation the diabolos (clockwise and anti-clockwise)

Option 0: no glue

Option 1: glue the threads with Loctite 271 ( red ) but be careful because this glue is very strong and it is near impossible to unglue after, so try it before gluing. The Loctite 271 needs 4 to 24 hours for curing.

Option 2: use Loctite 243 (blue) that is less stonger.

You can use standard diabolos sticks or home made sticks.

The string must be of different color and the length must be adjusted ( here the green string is 4 cm longer than the red string so when you start the tetrabolo is horizontal with one turn of the green string around the green diabolo )

The sticks must be shorter than usual 25 cm

The most difficult part:

When the tetrabolo is used with one string , it has precession, so you have to rotate on yourself without being dizzy.

There are many dance and ice skating websites to explain whirling techniques but you will have to see the tetrabolo so you cannot use the spotting method, you must look in front of you.

It important to know that if you lost balance too often, you will be dizzy and ill. So you must rotate smooth without unwanted movements.

I will not explain all the mathematics of the gyroscope here, but there are a lot of publications. The precession concept is not intuitive because it is in 3 D. To understand the full theory a high level of math (university) is required.

Simple mathematics:

The precession is perpendicular to the rotation axis and to the torque applied to the gyroscope.

The product of precession speed * the rotation speed is constant ( equal to the torque / moment of inertia)

References:

Wikipedia Gyroscope: https://en.wikipedia.org/wiki/Gyroscope

Wikipedia Precession : https://en.wikipedia.org/wiki/Precession

de H Crabtree · 1909  An elementary treatment of the theory of. spinning tops and gyroscopic motion https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/34239/31151013251123.pdf

Use 2 pairs of diabolo sticks and rotate the tetrabolo as fast as possible.

Mathematics explanation ; the product of precession speed * the rotation speed is constant so if you want to move slowly, the rotation speed must be high.

When the rotation speed is fast then drop the red pair of sticks and rotate on yourself to follow the tetrabolo.

When you throw the tetrabolo and catch in on the other side, the precession change direction. So you must change your rotation too.