String Fountain

The challenge, how does one present 50's synchronized swimming, or water works like the Bellagio fountain in Las Vegas, without water. Pushing string with a motor is not a new idea. Adding servo motors and a microcontroller to create automated and interactive installation is what I was looking to do during my residency at Autodesk's new facility on Pier 9.

This Instructable goes through the assembly of one of my 1/4 scale string fountains. The second image above is 6 string fountains arraigned in a circle moving string though the air.

Enjoy.

Here they are all laid out. Always be knolling, or so they say.

I've attached a .zip file with all the STL files. I printed all the parts except for the base on an Objet Conex 500. The base plate was laser cut out of 1/8" acrylic.

McMaster Carr parts.

16pcs - 94150A305 - M2 Stainless Steel Nuts

4pcs - 90116A009 - M2 X 5mm Philips Head Machine Screw

6pcs - 90116A010 - M2 X 6mm Philips Head Machine Screw

10pcs - 90116A015 - M2 X 8mm Philips Head Machine Screw

3pcs - 90116A113 - M2.5 X 10mm Philips Head Machine Screw

4pcs - 90116A114 - M2.5 X 12mm Philips Head Machine Screw

3pcs - 90116A1531 - M3 X 8mm Philips Head Machine Screw

1pc - 90263A1165 - Shoulder Screw, 3mm Diameter X 8mm Long Shoulder, M2 Thread

1pc - 1265K311 - Metric Miniature Type 316 Ss Drive Shaft, 3 Mm Od, 200 Mm Length

3pcs - 7804K1249 - 3M X 6M X 2.5M Stainless Steel Bearing

3pcs - 7804K1269 - 3M X 8M X 4M Stainless Steel Bearing

36pcs - 96415K693 - 316 Stainless Steel Precision Ball, 3/32" Diameter

Tower Hobbies

1pc - LXXJW4 - Great Planes Rimfire 250 Outrunner Brushless Motor

1pc - LXKSY2 - Great Planes Silver Series 8A Brushless ESC 5V/1A BEC

1pc - HMXE7625 - Heli-Max Pro Linkage Set MX400

2pc - LXLGJ5 - Hitec HS-65MG Mighty Metal Gear Feather Micro Servo

Gather the part for this step.

Slip the nut into the nut slot.

Thread the servo wire through the back of the servo bracket.

Tilt the servo so the wire exit is inside the servo bracket.

Gently tilt the top of the servo into the servo bracket.

Slip a nut into the nut pocket.

Secure the servo to the servo bracket using the screws.

Gather the parts for this step.

Push the nuts into the nut slots.

Rotate the servo to find the center of travel.

Secure the servo horn to the servo with the screw.

Gather the parts for this step.

Thread the servo wire though the back of the servo assembly.

Slip the servo into the servo pocket.

Press the nuts into the two nut pockets.

Secure the servo to the servo assembly with the screws.

Collect the parts required for this step. Note the servo ball and the black screw are part of the servo linkage kit.

Push the nut into the nut pocket on the servo horn.

Slip the screw into the servo ball and tighten onto the servo horn.

Adjust the servo so that you're attaching the servo horn in the middle of it's travel.

Secure the servo horn to the secondary servo as shown in the last image.

I decided to use a second bearing on the primary servo. It stiffened up the design quite a bit.

Gather the part for this step.

Push the nuts into the nut pockets.

Press the shaft into the rear support.

Press the bearing onto the shaft until it is flush with the shaft.

Now press this assembly into the back of the servo assembly as shown in the last image.

Gather the part for this step.

Mount the feet on the base. The base is symmetrical so you can mount the feet on either side.

Mount the servo assembly to the base.

This is the assembly that 'pushes' the string. I used an outrunner motor so I could hide it in this assembly as opposed to having it stick out the side of the String Fountain.

Gather the parts for this step.

Press the motor rotor into the back plate. Note the location of the holes in reference to the motor rotor. Do your best to line them up.

Press the front plate onto the motor rotor.

Secure the front and back plate together with the screws.

Gather the parts for this step.

Feed the motor stator wires through the slot shown in the second image.

Press the motor stator on the spud. Note the exit location of the wires and do your best to line them up.

Press the bearing into their pockets.

Press the nuts into their nut pockets.

Gather the parts for this step.

Slide the rotor assembly into the stator assembly.

Attach the shaft clip onto the shaft.

Gather the parts for this step.

Press the bearing into the idler wheel.

Press the lock nut into the nut pocket.

Slide the shoulder bolt into the bearing on the idler wheel and secure to the stator housing.

This part of the design proved to be the most difficult to design. I wanted to keep the cross section narrow. Adding additional bearing to the motor assembly meant they would be spinning at the speed of the motor and feeding back into the servo assembly. After a bit of experimenting I ended up with this design for the slew bearing. Here's the proof of concept, 3d Printed Bearing.

Gather the parts for this step.

Push the nut into the nut pocket.

Slide the screw through the servo linkage ball.

Secure the servo linkage ball to the bearing retainer.

Place the slew frame over the motor assembly.

Roll the bearings in. This is way more fun than you can imagine.

Place the bearing retainer over the bearing.

Secure the bearing retainer with the screws.

Gather the parts for this step.

Feed the wires for the motor controller through the servo assembly, as shown in image 2

Feed the wires through the slew frame, as shown in image 3.

Use the screws to secure the slew frame to the servo assembly but don't them tighten yet.

Adjust the wires so they are equal in length and lay flat between the slew frame and the servo assembly.

Connect the motor wires to the motor controller wires.

Adjust the motor controller wires until you have enough wire to allow the motor assembly to move up and down with out straining the wires.

Take up the slack and then tighten the screws.

Slip the remaining motor controller wires through the servo assembly where the servo wires exit.

Slip the motor controller into the notch provided above the secondary servo.

Gather the parts for this step.

Slip the string between the motor rotor and the idler wheel. Just like flossing your teeth.

Rest the string in the string entrance and the string exit.

Press the bearing into the motor cover.

Place the motor cover over the motor assembly.

Secure the motor cover with the screws.

Gather the parts for this step.

Place the string guide in the string guide notch.

Secure the string guide with the screws.

Gather the parts for this step.

Snap the servo linkage onto the servo balls.

Make sure all your fasteners are tight. After you're happy with the assembly go back through and use blue Locktite on all the fasteners. The String Fountain has been known to vibrate a screw loose from time to time.

I'm using Pololu's Maesto series of motion controllers to control my string fountain. You would only need their micro model to control one string fountain. You can also use an Arduino or any other microcontroller that can PWM RC servos.

Here's a video of a string fountain, enjoy.