Archive for category: Other Projects

ARXTERRA APPLICAIONT & ARDUINO IDE

By Railly Mateo (Systems Engineer)
Approved by Paul Oo (Project Manager)
Approved by Railly Mateo (Systems Engineer)

Configuration:

To establish communication between the robot and the phone, its important to know how the Arxterra application works and what kind of information it will send to the microcontroller (Arduino Micro). To interpret what the various telemetry commands were: the Bluetooth device (HC-06) was connected to the Arduino Micro. Next, the arxrobot-firmware was uploaded into the Arduino Micro to establish communication between itself and the Arxterra application (Android version).

Testing Connectivity:

To test connectivity, begin by opening he serial monitor on the Arduino. Play around by pressing on the Arxterra application. When the phone is not connected to the Bluetooth, the monitor will display “emergency exception 0x0100”. When the phone is connected, it will display “robber received command: 11”. When pressing on a direction (forward), five data inputs will be displayed on the monitor. According Hill’s command PDF file, the Arxterra application sends a 7 element matrix to the microcontroller.

Data Interpretation:

Data [0] A5 = Command Packet ID
Data [1] 05 = Packet Length N w/o parity byte
Data [2] 01 = Move ID
Data [3] 01 = Left Motor Forward
Data [4] 80 = Half Speed (128/255)
Data [5] 01 = Right Motor Forward
Data [6] 80 = Half Speed (128/255)
Data [7] A1 = Longitudinal Redundancy Check (LRC)

For our robot, the only elements of interest are data [2], data [3], and data [5]. This is due to our project only using servos, in comparison to using servos and motors. Thus the speed of the robot will only be controlled by using delays in the walking code.

Data [2]: if the command bit is 1, that tells the command decoder to issue a move command.
Data [3] and [5]: These elements are direction bits. If both are set to 1, it is interpreted as forward direction (2 would mean the reverse direction). However, our servos don’t go in reverse, therefore we won’t be setting these elements to 2.

Setting Up Walking Code:

Begin by pressing on the arrow control panel. Then write down all the telemetry responses that would be needed. By playing with remote functions, you will notice that setting data[3] and [5] to 1 and 1 will be move forward, 1 and 2 will be move to the right, and 2 and 1 will be move to the left.

Walking Command Examples:

If (data3 == 1 && data 5 == 1), the Arduino will read a series of servos angle that will make the walking forward motion.
If ((data3 == 1 && data5 = 2)), the Arduino will read a series of servos angle that will make the right turn.
If ((data3 = 2 && data5 == 1)), the Arduino will read a series of servos angle that will make the left turn.

You can see the implementation of the code in the Prototype blog post.

FINALIZED SYSTEM BLOCK DIAGRAM

By Railly Mateo (Systems Engineer)
Approved by Paul Oo (Project Manager)
Approved by Railly Mateo (Systems Engineer)

The block diagram above shows the updated block diagram for BiRex. The blocks are positioned based on their subsystem information. This post will give brief descriptions to explain each section of the block diagram.

The top left section comprises of two analog (orientation & distance) sensors. The ultrasonic sensor (HC-SR04) connects to the microcontroller (Arduino Micro) through the PWM & GPIO pins. The gyroscope (ITG-3200) connects the Arduino through its data line (SDA) and clock line (SCL).

The bottom left section comprises of 2 hardware devices (Bluetooth device & Android smartphone) for wireless communication between the Arxterra app and the microcontroller. The bluetooth device (HC-06) connects to the microcontroller through UART pins (RX & TX).

The top right section comprises of components (battery and voltage regulator) for energizing the system. The LiPo battery connects to the voltage regulator to ensure that we do not overload our subsystems. The voltage regulator (LM317) then uses our connections that bridge to the Vin and GND pins on the microcontroller.

Finally the bottom right section mechanical components (servos & servo driver). The servo driver (I2C interface) has two inputs and six outputs. It is energized from the battery and gets commands from the microcontroller through its data and clock lines. Then the signal is outputted to the six µservos (MG92B) allowing BiRex to walk.

FINALIZED MASS BUDGET

By Michael Balagtas (Manufacturing Engineer)
Approved by Paul Oo (Project Manager)
Approved by Railly Mateo (Systems Engineer)

Part	Quantity	Individual Mass (grams)	Total (grams)	Margins
Servos	6	13.8	82.8	20%
#4 Hex Nuts and Bolts	18	20.7	372.6	10%
Frame	1	857.29	857.29	100%
Ultrasonic Sensor	1	8.5	8.5	10%
PCB (HC-06 & Arduino)	1	30.76	30.76	100%
Dynamite LiPo	1	86	86	10%
Grand Total (Grams)			1437.95	68%

The table above shows the data for mass of this year’s µBiPed project. The mass values obtained from data sheets are given a 10% margin of error. The frame’s mass is assumed to be an Aluminum build. Therefor, the mass may change drastically if a different material (polylactic acid) is more viable. The PCB mass is unknown, and was given an arbitrary value based on the components on the actual board. To account for different mounting methods, servos are given a 20% margin of error. This may change if custom flanges are utilized.

BATTERY TRADE-OFF

By Michael Balagtas (Manufacturing Engineer)
Approved by Paul Oo (Project Manager)
Approved by Railly Mateo (Systems Engineer)

Picking a battery with our level one requirements (Toy, compact, cheap) brings many conflicts to our final decision, so a trade-off study will be done between a generic 9V battery, two 3.7 LiPo batteries, and a Powerex Imedion AA batteries.

Our overall mission is very simple: climb up a short incline and come back down in a figure eight. At worst, the mission will take no longer than 10 minutes, and that is assuming that the robot will shuffle due to lack of traction. However, we still need to compensate for our large current requirements. The eight servos to be used have a current draw of about 150mAh each and the Arduino Micro has about 100mAh, putting our overall current budget to about 1.4Ah. Considering the mission duration, we can take some liberties with this amount and set our goal to about 300-400mAh. The characteristic curves of the batteries will be ignored to simplify this process.

Manufacturer	Material	Voltage	Quantity	Current Rating	Dimensions	Volume	Price
Energizer	Alkaline	9V	2	230mAh	46.4mm x 24.5mm x 15.5mm	17620mm3	$12.00
Syma	Li-Po	3.7V	3	500mAh	42mm x 25mm x 9mm	9450mm3	$8.95
Imedion	Ni-MH	1.2V	4	2400mAh	N/A	N/A	$10.95

The table above compares 3 possible batteries to use for the µBiPed project. The table compares material, supplied voltage, quantity, current rating, dimension, volume, and price. After comparing the 3 batteries, we realized that the project needed to pushed further into manufacturing before we could decide which battery to choose.

Considering that the device is marketed as a toy, safety and choking hazards are a priority, therefore Lithium Ion is out of the picture, leaving us with the above options. At first glance, it looks as if the Imedion would be a landslide decision because of its current rating, but that’s too much for our mission parameters. To narrow down our decision, we will conduct a few studies: size, operational time, and price.

As a toy, cheap power sources is a requirement for easy access to power off the shelf. By and large, the Syma Li-Po wins over every other choice

We want the biped to be as small and as light as possible, so the smallest and lightest battery is the most desirable. However, the number of batteries is also taken into account. The Energizer only requires one battery to operate properly, whereas the Li-Po requires two and the Imedion requires four. The Syma Li-po would be comparable to that of a 9V battery once stacked together but they’re also light; the Imedion is tempting but there was no data for the batteries. As for right now, this study is a stalemate.

The last and most controversial of the above parameters is the current rating, because the current rating can change based on the current draw. Therefore, to streamline the process, it is assumed that these are ideal. The Imedion easily overpowers everyone else in this department because of its 2400mAh rating, but that is due to its unloaded nature. Nevertheless, we will assume that it takes the edge here

Conclusion: Either the Syam Li-Po or the Imedion will be utilized. The decision is heavily leaning towards the Syam because of the mass and given data.