Testing and testing....it´s not easy to syncronizate everything.I´ve got so many "crowns" but double colisions not yet!..... could you tell me more about times and delays of the potentiometers? ....the delay time of the CD starts counting from the moment the Arduino sends the second signal to the valve, isn't it?
Yes this is correct.
Experimenting with time delays can become very time consuming, but it's worth it.
I briefly talk about this in an earlier chapter -
LINK HERE
The main things that will affect the timings are the viscosity of the liquid, and the distance between the tip of the drop nozzle and the surface of the liquid in the 'drop catch tray'.
I use Xanthum Gum
(available from most health food shops or supermarkets) to thicken the water. A 1/4 of a teaspoon dissolved into 1 litre of water will yield a viscosity slightly thicker than milk, which is a good starting point.
I mix the xanthum gum with hot water
(not boiling) in a blender, then allow to cool.
The result is slightly cloudy, but slightly thicker water. It's a good idea to strain the mixture too - this filters out any bits of undissolved xanthum gum.
The bigger the size of the drop, the faster it gets to the water, is that so?
Not necessarily. Because the drops are so tiny, they would likely fall at the same rate.
The drop size will affect the type of collision however.
Some sources that I have read, suggest that the first drop size isn't as important as the second drop size.
The aim of the first drop is to create a 'Worthington Jet'. -
Here is Martyn Curreys page on capturing a worthington jet.
This is the rebounded column of water created when the drop hits the surface of the water.
The depth of the container you use for drops to fall into is quite important too - ideally the depth of the water should be at least 5 or 6 cm
There are ways to make the worthington jet taller....adding dish washing soap etc....but I have only just begun experimenting with this.
To achieve the 'crown' collision, it's probably best to start with a second drop that is smaller than the first one.
The height of the drop nozzle above the 'drop catch tray' is crucial for the timings.
This next image was taken with the following timings:
(all in milliseconds)
D1 - 30
D2 - 18
DD - 52
CD - 142
IMG_0587 by
Gareth Bellamy, on Flickr
I used a wine glass as a drop catch tray, and the height between nozzle and the drop tray
(wine glass) was ~ 40 cm
It's unlikely that you would be able to recreate the same exact same setup as me....liquid viscosity etc....so this is where the time is spent....in testing your personal system.
It can be tedious to cycle the drop controller, then take a photo, see nothing, cycle the controller again, take another photo etc.
I have pages and pages of notes I made whilst testing a huge number of time delays....most of them are worthless, but I did slowly begin to get a feel for what time settings worked and what didn't.
I do recommend making notes however, it can be very useful in the long run.
I would also recommend starting with just a single drop, and practising photographing the worthington jet.
Once you have a nice jet, you will have the basis of some good time delays.
And you need only concern yourself with adjusting one time delay value - namely the Camera Delay (CD) value.
Good luck Sérgio.
