Slow Turntables

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Slow Turntables - Slow Kinetics 

Peter Rand


A very slowly rotating turntable for art objects provides cryptic movement that makes the changing perspective of a rotating object less obvious, more interesting and even surprising.  Rotation can also provide the impetus for kinetic art. Distracting and inconvenient power cords detract from the art. A rotating unit small enough to be incorporated into a piece of art can completely disguise any  rotating mechanism. I could find no turntables that could provide all these advantages  and so designed one which is described here.


The turntable consists of the top rotating plate of a conventional lazy susan which is driven in small steps by a battery operated motor attached to the bottom stationary plate.  The unconventional part is to provide and control the small amounts of current that drive the motor in small steps. That requires putting together a little bit of inexpensive standard electronic circuitry which can be done in an evening by anyone who can paint by numbers or solder by pictures.




Figure 1 shows the heart of the turntable, turned upside down on its stand - the lazy susan, attached motor, batteries, an on-off switch, and the electric controller or ‘engine’, which consists of assembled transisters, capacitor and variable resistor.  Except for the lazy susan which can be obtained at any hardware store, the rest of the electronic components can be obtained at most electronics shops, although the motors are special. All the components and instructions can conveniently be found in one place http://www.solarbotics.com/  which is where I discovered the possibility of making such a mechanism.  It is based on the analog robotic hobby industry. A close-up of the assembly is shown in figure 2





The Motor

Very small direct current motors run at extremely high speeds and have low torque.  Therefore a highly geared-down motor is required. I use the GM2 or GM3 motor from Solarbotics which is geared down by 224:1 resulting in a 45 RPM motor if run  continuously.  However the ‘engine’ to drive this motor is designed to give it a brief pulse of current to drive it a tiny fraction of a revolution at a time. By controlling the frequency of pulses the revolutions can be continuously controlled to to one revolution per several seconds, minutes, hours, even days.  These motors are plastic and work well.  However I have had the gears worn by over-enthusiastic observers hand-rotating the turntable!  An alternative all-metal geared-down motor is the GM14 from Solarbotics and well worth the cost (about $30). These metal motors may withstand wear better and increase the load the table can turn.


The electric ‘engine’

Assembly of the electric ‘engine’ to drive the motor is very simple. The ‘engine’  is based on the so-called “1381-based solar engine”. “1381” refers to the electronic voltage detector used in the circuit – “solar” refers to the use of a solar panel instead of a battery for a source of electricity.  A battery can substitute for the solar panel and usually suits better.  Depending on the rate of rotation I have had 2AA batteries last over a year of continuous operation. However if your piece of art can accommodate an exposed solar panel of a few square inches and you have lots of light on it, it will run forever.!

 

Complete details of the engine circuit, how it works and how to put it together can be found at http://www.solarbotics.net/library/circuits/se_t1_1381.html. This includes a parts list and three sources for obtaining them.  Another site that describes in simple “paint-by-number” step-by-step detail how to put this together without understanding anything at all can be found at http://www.beam-online.com/Robots/Tutorials/Freeform/1381_SE/1381SE.html.  The Solarbotics website provides a wealth of information.


What I have added to the circuit are two things you can see in figure 1.  A variable resistor (RT20k from Solarbotics) is inserted between the battery and the capacitor This acts to enable you to control the rate at which the capacitor is charged and therefore the time between steps of rotation. The other addition is an on-off switch for the battery. One can vary the size of the pulse given to the motor by varying the size of the capacitor. Solarbotics provides physically small capacitors of large electrical capacity which can be ganged together. 


There are many ways to arrange the components. Figure 2 shows the “motor engine” assembled in the compact freeform method described on the above sites, and glued onto the motor.  The battery holder, the motor, and the switch are all glued onto the bottom stationary plate of the lazy susan.


The rotating plate.

The rotating shaft of the motor has to be attached to the top rotating plate of the lazy susan.  Figure 1 shows that I have turned a wood insert to fill the hole of the lazy susan and glued it into the top plate. The shaft of the motor, with or without a shaft-mating hub (that comes with the GM2/3 motors) is then fixed to the center of that wood insert and so drives the top rotating plate.  It is important to get the shaft dead center otherwise the mechanism will jam if it rotates off center.  Dead center is easy to find since you turned the central wood insert and can mark it. In addition, the motor is actually free-floating on its shaft and simply captured between two anchors on the bottom plate (figure 1 and 2) to prevent jamming due to any eccentricity as it rotates the top plate.


The turntable.

The top rotating plate of the lazy susan can act as the platfrom itself or carry a platfrom onto which your piece of art will sit. Normally I turn on the lathe a piece of masonite to the size I want and glue it, perfectly centered, to the top plate of the lazy susan.  Masonite is rigid, has a hard finish on one side and is easy to turn and finish.


The bottom stationary plate of the lazy susan with accompanying motor and parts has to be supported on a stand.  It can be attached directly to a stationary stand.  For more flexibility, Figure 1 shows a masonite base attached to the bottom plate with a large hole through which the motor axis and attached components protrude.  Usually I attach this bottom masonite base first and then fit the motor and other components after, as this gives much more room for the components to be spread out. This unit can then be moved around to be used on several stands of different heights (see blow)


The stand

The turntable with dangling parts has to be supported on a stand. Plastic sewer or gasline pipes of various sizes and diameters provide a versatile source for making stands, and can usually be found as scrap at building, plumbing or municipal maintenance sites. They can be turned and fashioned to whatever length required.  The turntable can be accommodated onto a stand as little as 1” high and contain ‘the works’.  On the other hand the stand can be as high  as several feet and provide a free-standing display stand as well as a holder for the turntable.


To support the turntable I simply turn, on the lathe, a shoulder inside one end of the sewer pipe, just big enough to take in and support the smaller bottom masonite base, and just shallow enough so the upper rotating plate does not contact the pipe, see Figure 1. Sewer pipe and turntable base have to be quite well matched in dimension as the wall thickness of the pipe into which the shoulder will be turned is only about 1/4 inch, and often the pipe is not perfectly circular.


Hidden turntables




Figure 3 shows a number of other possible turntable configurations, shown  separated from the kinetic pieces of art they display. The “turntable” can often be hidden.  The top rotating plate of the lazy susan can protrude the top of the stand and be made small enough to be covered by the piece of art ( “love” - right). The turntable can be incorporated into the art (“thingsect” - left).  The turntable can be accomodated under the piece of art (“cocktail party” - center).

The Virtue of "slow"

These turntables are silent, slow, and move with subtlety.  They provide a barely perceptible changing perspective for any art object and can impart movement to mobile art. "slow" avoids the often noisy, frenetic, and repetitive character of many turntables.  In my experience, this more friendly 'animation' adds real presence to a piece that is missed when it stops.


(Reprinted from  "Woodturning Design" #13 Spring 2007 pp71-73)

Peter Rand,

1278 Line 2 RR#6

Niagara-on-the-Lake, Ontario,

Canada. L0S1J0

Tel : 905-468-2889

e-mail:   rrand@brocku.ca

www:    http://www.peterrand.ca

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