Walkie Walkie

The team custom designed and iterated through many versions of the handle using Solidworks, ultimately landing on a pommel-style top to accommodate more ways to hold the stick. The main body of the handle was resin printed with grey resin mainly due to its complicated geometry. Resin was also chosen over PLA or other plastics for a smoother finish and higher strength.

The handle was then coated with black paint and a protective clear coating. The body and lid of the handle are held together with 4 M3 screws that screw into inserts that are installed into the body of the handle.

The cover for the flashlight was also resin printed to conform to the curved shape of the handle. This component was printed clear and polished for a smoother finish. To prevent individual LEDs from being seen, a light diffusing sheet was attached to the back of the light cover.

The rubber grip and button covers were also custom designed and molded by the team, which is discussed further below. Each component was carefully designed and tolerances to fit.

The carbon tubes of the stick were outsourced and cut to size. The team decided to make an adjustable hiking pole so it could be personalized to each user's desired length. The tubes are 2mm thick with varying diameters for the telescoping features. The latches, which prevent the tubes from falling out of each other, were also outsourced. The team invested in high quality and secure latches to prevent any slippage which is a safety hazard while hiking over dangerous terrain. The largest diameter carbon tube extends through the rubber grip, holding it in place, until it hits an extruded stopper at the buttom of the top part of the handle near the talk-to-speak button. This reinforces the structure of the stick and distributes the load path through the carbon tubes instead of the resin handle. This prevents the handle from experiencing excessive load when the user exerts their weight onto the stick.

The grips and buttons were all molded using Smooth-On VytaFlex 60 (Liquid Urethane Rubber). The team experimented with multiple rubbers, but ultimately ended up choosing urethane rubber because of its hardness and durability. Different colors were achieved by mixing dye into the rubber before pouring.

The molds were made by extruding negatives in CAD over the grip and buttons to create the desired shape. The grip mold had 4 alignment holes to make sure the center of the grip was in the right place. The button mold also had alignment holes to make sure their centers were also in the correct place. This was critical to making sure that the buttons fit in the right place during installation with the electronic physical buttons, and ensuring the grip aligned with the handle as well.

The other end of the hiking stick houses the tips. Walkie Walkie has multiple interchangeable tips to accommodate different terrain: dirt, gravel, pavement, and snow. The tip insert is permanently attached to the carbon fiber tubes with a magnet inside. The interchangeable tips also have a magnet that is attracted to the end of the pole.

Users can easily switch which tip they need by pulling it straight out of the pole. The mating shape between the female and male parts of the tip were chosen to be a rectangle to prevent any rotation. The main tip attachment for dirt and gravel was machined out of aluminum with a stainless steel rod at the top for strength.

Walkie Walkie uses an Arduino Nano to control an OLED display, program RGB LEDs on the front of the device, and handle user input via pushbuttons. The buttons allow the user to activate the front LEDs, change speaker volume, and select radio channel. The volume level and channel number are shown on the display for five seconds after device power-on and any button press, turning off to save power after this timeout.

The microcontroller also sends commands to a radio transceiver (NiceRF SA818s UHF) over UART. These commands include changing speaker volume, channel frequency, and in future versions the squelch level and transmission power level.

We designed two PCBs that fit within the device. The display / microcontroller PCB holds the OLED display and buttons on one side, with the Arduino mounted on the reverse. There are two connectors from this PCB, one to the front LEDs and the other to the second PCB.

The radio PCB has the radio transceiver, amplifier, and connectors for the microphone, speaker, and PTT button. Both PCBs have screw holes that allow them to connect to our 3D-printed electronics bay. The bay has a back panel that secures the microphone, speaker, and PTT button despite these components not being on a PCB.

The electrical system is powered by a rechargeable 3.7 V LiPo battery. The device uses USB-C, accessible from a port next to the power switch.

First, all of the components are initialized with the display using I2C, the LEDs using Adafruit’s NeoPixel library, and communication to the radio module established with serial over two digital pins.

After initialization, polling is used to check button states and perform necessary actions in response to any presses, including sending commands to the radio transceiver or switching LEDs on or off. See the linked GitHub repo for complete code.

One challenge was getting the components running properly, specifically within the Arduino’s timing constraints, which were further limited running on the LiPo battery. We originally used the SoftwareSerial library for UART over two digital pins. This worked well on its own, but after putting everything together the microcontroller couldn’t keep everything running.

It turns out the SoftwareSerial library uses expensive polling, but another library, NewSoftSerial, implements the same functionality with interrupts. There were several issues getting the NewSoftSerial library running on current Arduino IDE versions, so we made a few fixes to the library for anyone to use: