The purpose of this project is to augment the Nerf Mega Mastodon blaster with a Nordic nRF52840 dongle, RGB LED, and vibration motor so it becomes fly-by-wire and can optionally be controlled over Bluetooth. Without a Bluetooth connection the blaster's original operation is essentially unchanged. Schematics and photos are posted here.

About

The Mastodon is an interesting blaster because of its unique combination of fully-electric operation and deterministic dart handling. When fully loaded, up to 24 darts can be fired individually without further interaction from the user. The current replacements for the Mastodon either require the user to cock and/or press something to fire each dart (e.g. Ultra ONE) or shoot at an unpredictable rate (e.g. Prometheus MXVIII-20K). A common characteristic that is shared by all of these automatic blasters is a "flywheel" mechanism that throws the dart in a similar fashion to baseball pitching machines. The mechanism that sets the Mastodon apart is a motorized plunger that pushes each dart into the wheels, rotates the drum, and uses a switch to ensure that the plunger motor stays powered until the plunger is retracted (which would interfere with spinning the drum to reload it).

Without a Bluetooth connection the blaster's operation is changed slightly:

• After firing 24 darts the blaster automatically stops shooting until the triggers are released and pressed again
• No dart will be fired until the wheels have had a second to spin up
• An RGB LED on the top of the blaster signals that the wheels have spun up (green), a safety fault has occurred (blinking red), or a Bluetooth connection is active (blue)

Connecting to the blaster via Bluetooth adds the following functionality:

• The blaster's ammo count can be set and a notification can be sent after each dart is fired
• Three selective firing modes are available: single-shot, three-dart burst, and fully automatic
• Both triggers can be individually overridden
• Both triggers can be locked out
• Haptic feedback can be initiated for a specified amount of time

The blaster's safety mechanisms still function normally. Attemping to fire when either of these conditions is present will result in a safety fault:

• The jam door is open
• The drum is removed

If a safety fault occurs then the LED will blink red for 30 seconds before the blaster turns off. Rectifying the fault condition and pressing the triggers will reset it. The safety features can be disabled during development via CONFIG_NERF_SAFETY_FEATURES_ENABLED in the project file.

Although the blaster's wiring has been changed significantly, the original switches and triggers remain. The only modifications to the plastic housing are holes that were drilled to mount two PCBs (via standoffs), a vibration motor, and an LED. The bipod in the photo is off-the-shelf and attaches to the blaster's "tactical rail" using a picatinny rail adapter.

Building and flashing

This project is built from the v1.2.0 tag of nRF Connect SDK. The recommended project location is "nrf/samples/bluetooth/neRF".

Building and flashing on nRF52840 dongle

Enabling the log and USB console can prevent the application from starting if there is no USB host (i.e. if running from the blaster's batteries instead of a USB port).

If the log isn't required then make sure that CONIFIG_LOG is not set and build as usual:

$ west build -b nrf52840_pca10059

Otherwise, enable CONFIG_LOG and overlay the usb_console.conf:

$ west build -b nrf52840_pca10059 -- -DOVERLAY_CONFIG=usb_console.conf

Then generate a DFU package:

$ nrfutil pkg generate --hw-version 52 --sd-req=0x00 --application build/zephyr/zephyr.hex --application-version 1 nerf.zip

Press the reset switch while plugging in dongle to enter bootloader (the red LED will start pulsing).

Finally, perform the DFU:

$ nrfutil dfu usb-serial -pkg nerf.zip -p /dev/ttyACM0

Note that the nrfutil might need to be run with elevated privileges on some systems. Also, it's common for the process to fail but it always eventually succeeds on successive tries.