Monthly Archives: February 2017

Building a Drone

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Author: Jonah Siekmann

For this project, we’ll need to construct a drone that will carry the RFID reader around a crop field. It’ll need to remember the locations of every new RFID ‘Dogbones’ moisture sensor it encounters, and store the GPS coordinates so that it can return to the sensor later. We’re not sure yet how much weight it’ll need to carry, which leaves a lot of the the specs of the drone up in the air. We’ve come up with a general parts list, however, which includes the following:

CC3D Flight Controller

750KV Motor (x4)

30A ESC (x4)

4000mah 3s battery

12×4.5″ propellors

650mm frame

Arduino Uno

GPS module

RC Transmitter/Receiver

Our idea for flying the drone autonomously involves hooking up the Arduino to the CC3D flight controller’s RC receiver pins, and simulating the 1000-2000us pulses that the flight controller would expect from a receiver with the Arduino. This way, the CC3D flight controller does all the low-level attitude hold and hovering work, while the Arduino is free to read the GPS sensor and control the position of the quad by pretending to be an RC receiver.

Printed Super Calibrator System

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The system has been printed. There are so minor flaws with will be addressed, but we have our first prototype. 


3D printed Validator and pole attachment 3D printed Validator and pole attachment 

3D printed Validator and pole attachment 

In the image above we can see both of pieces that are 3D printed. The pole attachment is locked to a piece of aluminum extrusion just for demonstration purposes; it also has a battery sitting on it to keep it from falling. Our validator has a 6mm hole diameter siphon and will drain all the container in about 50-55 seconds. An ADC will be amplifying the signal coming from the strain gauge and outputting data to an Arduino UNO. All the electronics will be located on top of the pole attachment.

The flaws that were previously mentioned were about the attachment. The holes for the u-bolt are a little bit too close so I had to drill them out to get the u-bolt to fit. Another thing that will be changed is the little tube on the side that guides the wires coming from the strain gauge. It has a 90-degree corner that makes it difficult to pass wires through it, so I will modify the design to make it smoother. Other than that, our desing is complete. 

We Broke It

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Author: Brett Stoddard

Today the RFID team fried the Cottonwood when we supplied it with 12V instead of 5V. 

A new, better system was purchased and should be getting to us soon.

Super Validator Model and Electronics

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After many tests to figure out what would work out the best, we have chosen our best design. We will be using a 6mm diameter hole for the siphon, this will be sufficient for what we need it to do. I have been able to put together a model of the whole system to be able to visualize the prototype. Here is a rendering of the Super Validator configuration: 


Super Validator systemSuper Validator system

Super Validator system

This model only has the parts that will be 3D printed, the electronics will be sitting on the part that is attached to the pole. The electronics consist of a strain gauge connected to an ADC that will be sending data to an arduino.


Electronics setupElectronics setup

Electronics setup

The electronics have been calibrated and tested. We are currently printing both the validator and the pole attachement, and will soon have the first working prototype. 

RSSI Moisture Test 1

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Author: Brett Stoddard

Hello all, today the RFID team figured out how to use the Cottonwood to communicate with the Dogbone tags. To celebrate, we measured the Dogbone tag’s RSSI value in wet and dry conditions. This was done to see if RSSI value could be used as an indicator of moist conditions.

RSSI value is a measurement of received signal strength. It’s an acronym for “received signal strength indicator”. It’s often used in WIFI signals. Here is a good article from MetaGeek that explains it further: http://www.metageek.com/training/resources/understanding-rssi.html

For this test, we read multiple RSSI values when the tag was dry first. We then wet a piece of paper behind the tag and recorded the RSSI values again. The picture below shows our setup. It should be noted that while wetting the tag we might have disturbed the system which would mean that our results will need to be backed up with further, more precise testing.

wet_dry_test_setup

 

To receive the RSSI data, we sent an “Inventory Command with RSSI” command from the Arduino to the Cottonwood. The command was sent as a character array { 0x44 , 0x03 , 0x01 } and was taken from the Cottonwood’s datasheet. We got back a message that contained the RSSI value in the third byte of the response. Below is a table with the RSSI values measured in wet and dry conditions.

This is the table of the data. As you can see the Q value average was higher than the Q value average in dry conditions. A higher RSSI in wet conditions could be attributed to the presence of water tuning the signal.

In conclusion, there might be a slight correlation with moisture, but further testing is needed. Also, the distance between the antenna and tag is a large factor in the RSSI value and should be taken into consideration before implementation.

Pumps and Pump Mounting

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Several design decisions were made based on our pump parameters needed. For example, we need at least one meter of pump head and we need to be able to move water through roughly 5 meters of 3/16” (.476 cm) tubing (most likely there will be less tubing involved, but this is a good number to start with).

Through observation, I found that the throughput of a single pump at 1m head and room temperature was 50mL/min, or .83 cm^3/s, and the maximum suction head is greater than 1.5 meters, which was the highest I could place the pump without creating a more complex setup. 

With a tubing cross sectional area of .71 cm^2, the velocity of the water in the tube being moved by the pump is about 1.2 cm / s. With such a small velocity, the head loss directly resulting from the 26 tee joints is about .76 cm, and the head loss from the friction of the tubing is even less than that. 

Because we don’t have to worry about head loss, and the max head one pump can provide exceeds our requirements, I decided that the design should combine two pumps in parallel to improve throughput rather than in series to improve head. 

Now I could design the dual pump mount! I went with a design that mounted on the inside of the C-Channel spine, with the colinear, top-to-top facing pumps sticking out perpendicular to the c channel. The first 3D Print should be finished tomorrow! Pictures below.


twopumpmount.jpgtwopumpmount.jpg


twopumpmount2twopumpmount2


twopumpmount3twopumpmount3

Super Validator 7mm

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After running the test we were able to conclude that the 8mm diameter hole is too big to create the siphon at the slowest rate on the OPEnS Calibrator. 6mm diameter hole works just fine but takes a little more time than what we want it to. We are going to try a 7mm diameter hole and see how it performs. If this does not work, we will move to other designs. Here are links to the other designs we will try:


We will replicate design B. Designs  A & C  are similar to what we have already. We will replicate design B. Designs  A & C  are similar to what we have already. 

We will replicate design B. Designs  A & C  are similar to what we have already. 

 

http://makezine.com/projects/make-35/ctesibius-and-the-tantalus-cup/