DropArt - Precision Two Drop Photographic Collider

Hello one and all,

In this instructable I present my design for a computer controlled two liquid drop collider. Before we get started on the design details, I think it makes sense to explain exactly what is the purpose of the design.

A fun, interesting and beautiful branch of photography involves capturing images of liquid droplets as they hit a pool of similar liquid. This in itself can produce interesting images. To get some really cool images, we need to collide two liquid drops. So the first drop hits the pool of liquid and creates what I call an 'up-spout' which rises up from the pool directly above where the first drop impacted. Now a second drop, precision timed, hits the top of the 'up-spout' exploding the liquid outwards to generate some amazing and unique shapes.

The purpose of my DropArt design is to provide the following features :

• To release a liquid drop with a repeatable size
• To release a second liquid drop with repeatable size and precision timing with respect to the first drop
• To control a camera shutter to capture a drop collision
• To control a flash head to freeze the collision at a precision moment in time
• To provide a user friendly stand-alone controller providing the ability to control all parameters and multiple configurations
• To provide a user friendly Windows-based user interface or GUI connected via USB
• To provide a bootloader to facilitate firmware re-flashing via USB

There should also be adequate protection between the control board and attached camera and flash devices.

Before getting into design detail, let us first look at some results from the DropArt project. If you, as a reader, like the results, you might want to look further into the design and maybe have a crack at building one yourself for which I will provide support.

Important aspects to DropArt photography

It should be noted that for best results the camera is set to B (or bulb) mode. This means that as long as the shutter is depressed the shutter stays open. This is the mode I find works the best for DropArt photography. It is actually the flash that captures the moment and not the camera shutter. In order to achieve a short flash duration the flash output power should be kept to a minimum. I tend to use two small flash units set to manual low output power (see image in the conclusion). One flash unit is coupled to the DropArt controller and is fired via a cable. The second flash head is opically slaving from the first.

As we are in B mode excess ambient light will cause image blurring. Therefore, drop photography should be performed in subdued lighting - just enough light to see what you are doing. I generally shoot images at around f11 and so effects due to ambient light are minimised.

Basic technique and setup

It should be noted that every setup will vary slightly and you need to be patient and methodical Once you have a basic two drop collide you will find the results almost 100% repeatable. For the basic setup below I was using tap water with red food colouring. The drop dispenser was about 25cm above the liquid pool.

Make sure that the Mariotte siphon is purged of liquid using the purge feature (see video example) and also ensure the liquid level does not drop below the bottom of the Mariotte siphon.

• First start with a single drop size 35ms
• Set the shutter delay to 100ms
• Set the flash delay to 150ms
• Increase the flash delay in +10ms increaments until you see the drop appear at the top of the frame
• You can now increase the flash delay through the entire drop sequence
• Keep increasing the flash delay until you have a full single drop up spout
• Now add a second drop size 35ms and delay of around 150ms
• Adjust the drop two delay in +/-10ms increaments until it appears in the top of the frame above the first drop up spout
• Adjust the drop two delay until the second drop collides with the up spout from the first drop

Now you have a basic collide occuring you can play with settings to get the effect you want.

Different density liquids will require different settings but you can store these in the different configurations.

Here I present a video - this a series of separate consecutive drops taken as stills with 10ms or 5ms advancing flash intervals to freeze motion. I have then stitched together the resultant still images to produce a short animation of the life of a drop and subsequent collision with a second drop.

Arguably the most important part of the DropArt project is the mechanical drop dispenser. This part of the design is critical for ensuring consistent regular drop size.

The heart of the design is a mechanical valve which is opened and closed using a 12v spring loaded normally closed solonoid. This solonoid is precision controlled using the microprocessor based control board.

The liquid vessel is a 36mm OD, 30mm ID acrylic tube. To cap the tube off, I have 3D printed in HIPS an end cap which is designed to accept standard 1/4 inch pipe fittings (see images). The drops are dispensed from a barbed hose tail - also 1/4 inch thread.

The top of the acrylic tube is sealed with a size 29 rubber bung. The rubber bung is supplied with a centre hole into which I have fitted a plastic tube to create a Mariotte siphon (see specific section on the Mariotte siphon).

The solonoid is enclosed in a small plastic project box and connected to an exterior power socket.

In this section, I present a short video overviewing the DropArt prototype control board and its construction.

The image here shows the control control board schematic. We can see that by utilizing the powerful PIC microcontroller the schematic is relatively simple.

You can download the schematic here :

https://www.dropbox.com/sh/y4c6jrt41z2zpbp/AAC1ZKA...

NOTE: in the videos the voltage regulator used is the small 78L05 type. I suggest anyone building this design use the larger 7805 in the TO220 package

In this section, I present a video detailing how to actually use the DropArt control system. The video covers using the stand-alone hardware and also the Windows-based user interface or GUI.

In this step, I attempt to describe a two drop sequence and illustrate the timing accuracy of the DropArt project.

Horizontal oscilloscope divisions 50ms / mark.

Initially, consider the second of the two images. This is a very simple trace from my oscilloscope displaying the basic 1ms tick which forms the timebase for all the project timing. This tick is generated in the PIC microprocessor using an embedded hardware timer programmed to generate an interrupt at a precise point in time. Using this timebase, the drop size, inter-drop delay, shutter delay and flash delay can be contolled very accurately producing very repeatable results.

Now consider the first of the two images:

The middle blue trace shows a two drop release. Each drop has a size period of 50ms and a drop 2 delay of 150ms

The bottom pink trace is the flash fire with a delay of 300ms after drop 1 release and a hold time of 30ms

The top yellow trace shows the shutter release. This has a programmed delay of 200ms. However, it is assumed the camera has a shutter lag of 100ms so the shutter release is 100ms earlier than programmed. The shutter stays open for the duration of the sequence (camera B mode). The shutter is closed after the 30ms flash on period has expired.

A very important aspect of the design is how to control the liquid pressure at the input to the valve. As the liquid level in the reservoir drops, the pressure at the input to the valve drops therefore so does the liquid flow rate. The drop size for any given time the valve is open decreases as the reservoir level falls. This makes controlling the drop collisions dynamic and dependent on liquid level. The video in this step explains how this problem has been solved.

The second very short video shows how the DropArt purging feature can be used to prime the Mariotte siphon as well as purge or clean the mechanical valve.

This short video demonstrates and explains the operation of the PIC bootloader which can be used to re-flash the PIC via the USB, negating the need to use a dedicated PIC programmer.

Attached is a word document listng the parts I used for the instructable

This is a list of the parts required to build the DropArt project. All the parts bar one is available off the self. The exception to this is the end cap for the acrylic liquid vessel which I 3D printed. I have attached the acrylic tube OD 36mm end cap modeI (STL format) to this step.

Active components

• PIC18F2550 microcontroller. As supplied, this is a non-programmed part so needs to be flashed with the DropArt firmware. If you have a suitable programmer you can do this yourself, or I can send you a pre flashed part or you can send me a blank part for flashing.

• Blue serial IIC 20x4 character LCD module
• 78L05 voltage regulator
• AN25 opto-isolator or similar – 2 off
• MOC3020 opto-triac
• IRF9530 P-channel FET or similar
• TLS106 SCR Thyristor or similar
• LEDs 2 off

Passive components

• 1N4001 diode (reverse polarity protection)
• 100nf ceramic capacitors 3 off
• 22uf 16v electrolytic capacitor or similar 2 off
• 22pf ceramic capacitors 2 off
• 4MHz crystal HC49/4H leaded
• SIL 8 pin isolated resistor network 1.8K 2 off
• SIL 8 pin common resistor network 4.7k 1 off
• 470R 1/4W resistor 1 off
• 10K 1/4W resistor 2 off

Connectors

• 2.5mm board mount power socket
• 2.5mm chassis mount power plug/socket
• 2.5mm mono jack socket (solenoid)
• 3.5mm mono jack socket 2 off (shutter and flash)
• USB type B 90-degree DIP female socket
• Pin header 2.54mm 4 way
• DIL 28pin turned pin IC socket
• DIL 6pin turned pin IC socket 3 off

Other

• 12cm x 8cm FR-4 prototyping board through hole plated
• Push to make through hole miniature buttons
• Rotary encoder switch 2 bit Gray coded
• Control knob to fit rotary encoder

Mechanics

• Clear acrylic pipe 36mm OD 30mm ID and 18cm long
• End cap (3D print) to fit acrylic pipe OD 36mm
• Mariotte siphon type to fit bung centre by 16cm long
• Rubber bung size 29 with centre hole
• Barbed hose tail 1/4” thread x 4mm exist aperture
• BSPP female bulkhead fitting with fixing nut 1/4inch
• Barrel nipple 1/4inch
• 12V DC 4W electric solenoid valve air/gas/water/fuel normally closed 1/4inch two way

I have really enjoyed building and perfecting this project. My projects almost always begin from the same starting point. I become interested in something that may require specialist equipment. Having found and often bought equipment, I am so often disappointed with the quality and functionality and subsequently feel compelled to design and build my own gear to do the job required properly. This was indeed the case with the DropArt project.

The DropArt project now enables me to perform liquid drop collisions with near 100% repeatability so I can concentrate on the images rather than the frustration of taking hundreds of images hoping to get a few drop collisions.

I produce and post these Instructable articles for three reasons. Firstly, I really enjoy producing the Instructable as it provides a way to document the project and acts as closure. Secondly, I obviously hope that people are going to read and enjoy the article, maybe even learn something new. And thirdly, to provide help and support to anyone who wants to have a crack at building the project. I have spent my entire working life as a design engineer in electronics and software; from an early age, an exceptionally keen electronics hobbyist. I really enjoy helping out others who maybe want to build for themselves but just need a bit of guidance and support.

Attached images shows my DropArt setup in my workshop.

Please feel free to comment or private message if you require any further detail.

Many thanks,

Dave