Installation and First Months of Project Curacao- Part 7

What is Project Curacao?

This is the seventh part of a series discussing the design and building of Project Curacao, a sensor filled project that hangs on a radio tower on the island nation of Curacao. Curacao is a desert island 12 degrees north of the equator in the Caribbean. Part 8 in the fall will show the upgraded sensor suite and replacement of the wind turbine. Project Curacao is designed to monitor the local environment unattended for six months. It operates on solar power cells and communicates with the designer via an iPad App called RasPiConnect. All aspects of this project are designed to be monitored and updated remotely (with the current exception of the Arduino Battery Watchdog).

System description

Project Curacao consists of four subsystems. A Raspberry Pi Model A is the brains and the overall controller.

Results of shipping

The box arrived in our luggage on March 3, 2014. Airport security (TSA) inspected the box twice, but aside from picking up the box with the outside temperature sensor (naturally the most expensive sensor in the box), pulling the wires off, it survived. One of the key things to remember about shipping a piece of equipment through airport security is to take out the batteries and put them in your carry on luggage. The other item is to make sure you provide a written explanation of what it is and what it does with the box in the luggage. We wrote a short letter about Project Curacao and included reprints of the MagPi series of articles. The temperature sensor was fixable. There were also a couple of loose grounds to be tightened. A group of sensors were giving odd readings so I knew to look for a loose ground. One bad sensor might be the sensor, where-as a bad group of sensors was likely a ground or power. Remember, you can always trust your mother, but you can never trust your ground. We put the box outside for the first time and the solar cells worked perfectly. The wind turbine needs to be up on the tower to really roar. The wind turbine only generated about 40ma on the ground but should do better up on the tower. RasPiConnect connected to the box and generated the first Caribbean picture:

Deployment

We spent ten days finishing off some software and preparing to put the box up the tower. Understand, however, this was in addition to going to the beach, dancing, coffee with the neighbors and some very nice parties. Eventually, we did put up the box. The box and wind turbine was deployed on the tower on March 13, 2014.

Geoff Howard, all round good guy and expert tower climber, was invaluable. This is dangerous work and safety belts and harnesses were used.

A picture of the resulting installation of the box and the wind turbine is next. The angle of the box is not what was designed however. The tower mounting platform that we carried down to Curacao did not fit. It was designed for a slightly smaller tower, so we had to strap the box flush to the tower and perpendicular to the ground.

This had a significant effect on the amount of solar power generated. Since the latitude is about 12 degrees, the solar cells should be pointing due south around 78 degrees in the current configuration. While the box is designed to adjust for the amount of power generated, the output was far less than designed. The problem with this was not with the Raspberry Pi, it was with the Arduino Battery Watchdog. We adjusted the run time of the Pi with the Arduino to fit the available power. However, the Arduino is meant to run 100% of the time and the behavior of the Arduino is ill-defined in very low battery conditions. It would glitch the real time clock which gave some very random behavior.

Note on the RasPiConnect screen below you can see the Arduino battery voltage going down and down and down until we turned it off for a few days and moved it to the roof. We were hoping the wind turbine would make up the difference but were disappointed on the two counts discussed below. Thanks to the license plate used for a mounting plate provided by our fine neighbor Marlies, we mounted a mirror at right angles below the solar cell hoping to improve the amount of power generated, but it wasn’t significantly increased.

After the wind turbine event described below, we moved the box down to the roof and increased the angle to increase the solar power.

Wind turbine results

Based on our measured 50W wind turbine measured curves (given on https://switchdoc.com), we did not expect too much from this turbine at wind speeds of 15 MPH. It would only contribute a trickle charge during the night to the project. Based on the limited data we received from the box, it would only add an hour of runtime every day. Following is an analysis of the wind data: Total Number of Data Points: 49 Number of Unloaded 50W Wind Turbine Data Points: 37 Average Windspeed: 7.1 MPH Low: 0.0 MPH High: 16 MPH Number of Current Samples (Loaded 50W wind turbine): 12 Average Current Delivered to Battery: 22ma Low Current Delivered to Battery: 0ma High Current Delivered to Battery: 138.6ma Max Power from Turbine to Battery: 0.5W This 50W wind turbine would need about 25 or 30 MPH winds to run this project.

First full week of operations – death of a wind turbine

We lost the wind turbine during the first week of operation to a wind storm, but the turbine was a last minute addition and so not very important to the overall success of the project. This occurred less han a week after we departed: we got an email saying that there had been a wind storm overnight with gusts about 35 MPH and that the wind turbine was destroyed.

The wind turbine worked as predicted by our models. We switched on the turbine at night to provide a trickle charge to the main computer. We got about 60 – 90ma of current at 15MPH. Nowhere close to the 200-300ma it takes to run the Pi. Note that the turbine popped out of the stand and thoroughly destroyed itself. We think that is was a sympathetic vibration with a particular wind speed (much like the “Galloping Gertie” Tacoma Narrows bridge [Ed: https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)]) since we observed that the stand was flexing in the wind. We will either prevent the next turbine from popping out or stiffen the stand to prevent the flexing or possibly both.

The first 8 Weeks of Operation

We recently hit eight weeks of Project Curacao running in the warm and windy climate. The project has been fairly robust to this point. We lost one sensor the other week. The light color sensor (BM017 / tsc3574) went dead and no longer responds to I2C requests although other sensors on the same bus do continue to respond. We have had no problems with the Arduino Battery Watchdog yet. Since we fixed the solar power problems, the Arduino is rock solid. Here’s an example email that came in from the Project Curacao box telling me the environmental monitoring system has turned the fan on because of high temperatures inside the box (degrees C):

From: ********@gmail.com
 Subject: ProjectCuracao Fan ON(TMP)
 Date: April17,2014at12:08PM
Fan turning ON: State: ot:36.50 it:38.10 oh:34.50 ih:49.40 sv:4.77

The box also emails bootup and shutdown messages as well as a picture from the Caribbean once a day at 15:20 Pacific time. September Upgrades We are planning a maintenance trip to Curacao. The planned upgrades are: 1) Replacement of wind turbine (possibly with a different type of turbine). 2) Stiffening the turbine mount to avoid another “Galloping Gertie”. 3) Addition of a vibration sensor on the turbine mount to monitor the flexing. 4) Adding a loose strap over the top of the turbine to allow turning of the turbine but not “popping out” of the mount. 5) Adding wind speed, wind direction and rainfall sensors. 6) Modification of the Arduino Battery Watchdog to record wind turbine current and voltage even when the Raspberry Pi is off. 7) Modification of the angle of the solar panels – maybe with a sun tracking system You can see the live hourly data and picture from Project Curacao at: https://milocreek.com/projectcuracaographs.

What’s Next?

In Autumn 2014, we will be upgrading Project Curacao. We will describe the upgrades and the required changes to the Project Curacao system. This has been a large project and we want to thank all of the people and companies that helped make this possible.