The project started in 2015 from an idea by Alexander Osika, at Chalmers University of Technology. The project was suggested for Smartgeometry 2016 at Chalmers.
Now a few years later (late Feb 2018) I saw cold weather coming on the forecast and started building a few days before it hit Denmark.
This (2018) version is made from a modified tripod with a fixed cogwheel and a bearing suspended platform holds all the electronics while it is turning around its own axis. A motor with cogwheel pull the platform around the larger fixed cogwheel and a motor with peristaltic pump propel the water, a battery powers the motors, heaters and sensors and a servo actuates the tilting nozzle. All settings and sensor data are transmitted wireless via Bluetooth. Electronics in total: Two stepper motors and stepper drivers, Bluetooth module HC-05, Arduino Nano, 5V voltage regulator, 2x TIP120 transistors, Servomotor 180′, 2xThermistors and kanthal thread as heating elements.
The peristaltic pump draws up water through a tube going down through a center hole in the ice cap. The water is then pushed through a tube to the end of the nozzle where it is sprayed on the ice. As the layers of ice are added, a wall of ice will build up, firstly in a circle, then as the nozzle tilts up the three dimensional shape will become spherical.
The speed of the peristaltic pump as well as speed of rotation, temperature settings and servo tilt is adjustable. In this first build the servo was not actively adjusted, just set to a height over Bluetooth like other variables like heat setpoints, flow and rotation. Two PID control algorithms run on the arduino to control the temperature for both the intake tube and in the long nozzle. To distribute temperature, and reduce power consumption the nozzle is constructed from a few layers: The water runs through a PVC tube of about IØ 5mm, on the outside of this is a thermistor placed. The tube and thermistor are drawn through the inside of a cobber tube of IØ8mm which is coated outside with polymide film (kapton tape). This film acts as electrical insulation between the kanthal thread being the heating element which is wrapped around the cobber tube. On the outside of the cobber tube and heater is another layer of polymide film and finally 8mm insulation layer of foam padding with reflecting aluminium tape on top to reflect infrared.
A final power consumption of 300mAh at 8v without heaters on, and 2100mAh with both heaters at maximum. The battery is a 2cell LiPo with 6000mAh capacity. The rig should be able to run for up to 10hours per charge.
Several attempts to print a dome failed due to various reasons. (1) Ice forming in the vertical central tube until rotation of intake PVC tube was jammed from rotating. This was solved by adding the second heating element and additional insulation between ice cap and aluminium tube, this meant a larger hole in the ice had to be drilled. (2) Leakage in peristaltic pump caused large ice formation in gears and bearings – solved by gluing PVC tubing firmly. (3) Ice forming in nozzle causing all tubes to freeze due to low setpoint temperature. -soon the system must run out of points of failure 🙂
(LEFT) To avoid dripping and back flow leading to overicing the first nozzle had its inner diameter reduced using shrink tubing, however, as it was outside thermal protection of the cobber, it soon froze up. (RIGHT) improved nozzle of metal. The PVC tube is squeezed by the cobber tube from the outside to hold this find stainless steel tube in place.
The wall was only a few cm after approx 2 hours of on-off printing (and failing to print further for various reasons)
The project is under development, and more testing is coming up -when the weather allows…