We describe here the basic equipment required to carry out
: rotating turntable
equipped with slip rings, video
storage tank and pump.
For more information on the equipment (turntable, cart, camera,
video display, motors, electronics, pumps, tanks) required to carry out any of the
experiments, contact John Marshall (firstname.lastname@example.org
Note: All the equipment described here - the turntable, mobile cart,
fluid tanks and auxiliary laboratory materials - is manufactured,
and can be supplied by, Dana Sigall (e-mail:
email@example.com ), a craftsman working
in Gloucester, Massachusetts.
The central piece of
equipment required to perform the experiments is a turntable. The turntable
we have designed is shown in the photographs below. The turning platform —
the dial — is 18 in. × 24 in and can be made to spin at rotation
periods in the range 2 seconds to 60 seconds: i.e.
at a rate of 30
rpm (revolutions per minute) down to 1 rpm, and is measured by a digital
readout. The turntable has a simple but effective design; drive is achieved
through a friction wheel on the underside of the dial driven by a variable
speed motor. The experiments are typically carried out in a square 16 in. ×
16 in. tank placed on the rotating dial.
You can look at more detailed views of the turntable by clicking on the images
The experiment is viewed from a video camera corotating with the dial, whose
signal is passed through a slip ring for display in the laboratory frame,
either on a monitor or a projection device. Power to the table is only 12V,
an added safety feature because of the close proximity of water, but
sufficient to power (via the slip ring) pumps and fans in the rotating
frame. The table itself is sturdy and lightweight, being constructed
of high-quality, cabinet-grade plywood and finished with a water-resistant
The drive of the turntable is achieved by a friction wheel on the underside of the
dial driven by a variable speed motor. You can view the drive mechanism here:
The novel friction drive mechanism has a number of advantages over a more conventional direct-drive via a timing belt: (i) it provides an automatic clutch allowing the dial to be readily stopped in a safe manner without damaging the apparatus or the user! Indeed one can grab hold of the turning dial bringing it abruptly to rest with no un-toward consequences (ii) its simple but effective design
allows one to slide the friction wheel radially inwards (increasing the rotation rate, Ω) or outwards (decreasing Ω).
Combined with the adjustable speed of the motor, a continuous and wide range of possible rotation rates
can be achieved between 1 and 30rpm.
The tachometer makes use of the cadence function of a cyclometer (see below)
and does not need to be calibrated. The rotation rate reads in the lower
right corner of the cyclometer. Click the cyclometer face to enter the
cadence readout mode indicated by a small “C”. In order to align the
device’s sensor to an appropriate dial rotation range, ten sensor magnets
are set in the underside of the dial. Add a decimal place to the readout for
the actual dial rotation rate, e.g., 102 =10.2 rpm (revolutions per minute).
Note: you will find that the turntable may be capable of rotation rates both
slower and faster than registered by the cyclometer but most useful rotation
speeds are covered. In particular, stable rotation rates of less that 1rpm
(which are achievable with the turntable and useful in, for example, Hadley
Regimes) are beyond the range of the cyclometer. In this case directly
measure the rotation rate with a stopwatch.
Video Camera and slip-rings
Experiments placed on the dial can be viewed in the rotating frame from a
video camera (through a zoom lens) mounted on an arm that rotates with the dial. The video signal is passed from the rotating frame through a slip-ring. A video cable can be conveniently plugged in to a socket on the turntable base and the camera view displayed in the non-rotating frame on a TV/computer monitor, beamed up on to a large screen for viewing by many,
or captured by a computer.
Fluid tanks, white base and
Experiments are carried out in clear acrylic tanks placed on
a white plastic base centered on the dial. A 16"x16"x8" tank
is found to be convenient. A circular insert readily converts the square
tank in to a cylindrical one. The circular insert, secured by stainless steel
clips, is shown in place below. A stainless-steel container placed in the middle
is weighted down so that is does not float when the tank is filled with water.
When ice is added to the container, a radial temperature gradient is created.
In most experiments the water tank is placed on the white plastic base
centered on the dial (this makes the view through the camera uniform and
bright). However, in some experiments a tilted base is required. In this
case the white plastic base serves as a 'false bottom': it is inserted
inside the square tank and tilted
to mimic spherical effects. The base is conveniently tilted through the use of
spacers (a plastic bolt or upturned hockey puck).
Auxiliary materials and equipment
Useful (indeed, rather essential) auxiliary equipment is shown in the
photographs below and comprises:
In the square plastic container (click on the image below):
- plastic bottles for dye (food coloring) and to hold potassium permanganate
- spatula (for potassium permanganate)
- pipettes (for food coloring)
- black (white) plastic containers for black (white) paper dots
- Vaseline (for the Fronts experiment)
- ice pucks (for the Taylor Column experiment and, when upended, to tilt the
- sharp knife
- three orange spring clamps (various uses)
- porous pot with associated tubing including flow rate regulator (various
- three plastic beakers (for balanced vortex experiment and general use)
In addition, further useful auxiliary equipment is (click on the image
- 10 gallon grey bucket and 10 quart blue spout pail (general use)
- white 3 1/2 gallon bucket with stoppered hole in
center (for balanced vortex experiment)
- a metal rod to remove the stopper from the white bucket (for balanced
- a hollow silver paint can (for the front experiment)
- stainless steel ice bucket (for the general circulation experiment)
- a black metal weight with flat rubber base (to weigh down the ice
- Lexan insert with stainless steel clips to place inside the
square acrylic tank, rendering it circular
- plastic funnel with connector (general use)
- immersible bilge pump for filling and emptying the
acrylic tank powered by a 9VDC transformer
- (alternatively) a thick (3/4" inside diameter), 6'
long tube for siphoning water from the acrylic tank.
The turntable can be installed on the mobile cart (click on image below) which can
be used to transport the equipment to where it is to be used and as a
platform to carry the experiment. The cart is equipped with a 10-gal water
storage tank (blue) and pump, a tray to store and carry assorted
materials—such as ice buckets, cans, beakers, dyes, among others—and a post
on which to place a liquid crystal display (LCD) television monitor for
convenient display of the experiment from the rotating camera.
Three 110 ac ground fault circuit interrupter (GFCT) power outlets are
supplied on the monitor support of the fluid cart to power the 12V system,
video monitor, and any other ancillary equipment.
LCD television Monitor
The output from the turntable video camera can be fed in to a LCD television
monitor which is installed on the cart or any other useful devise such as a
VCR recorder and/or projection device or computer for use with large