[Google Chromecast] bhiga:
I've used multiple sticks (Emprex 128 MB, Patriot 2GB, Sandisk Cruzer Micro 2GB), and every version of FlashCast since the beginning (1.0, 1.1, 1.1.1), along with all the PwnedCast releases and Eureka-ROM 1.0 and 1.1

So pretty much everything :)

For USB stick, I recommend the Cruzer Micro because it has three states of its LED - off (port not active), slow in/out pulse (connected, but idle), and blink (active). If not, at least get one that has an LED. Not knowing when the stick is being accessed makes it a LOT harder to troubleshoot.

If you can, set up a router without Internet access, or just unplug your Internet connection while you do this.

Set up Chromecast on your wireless network, then check the Build Number in the Chromecast app. If it's anything other than 12072 you're not rootable, for whatever reason, and you may as well give up now.

If the build is 12072, continue on (and don't reconnect your Internet until you succeed or give up).

Now try this:

Unplug power from OTG cable

Holding down the button on Chromecast, attach power to OTG cable, don't let the button go

The LED should go red and you should see these tiny dots on your TV.

If you don't see dots after 10 seconds, let go of the button and Chromecast should boot up normally. Something might be wrong with your reset button or OTG cable.

Remove power from OTG cable.

If you did see dots, continue on.

Plug OTG cable into Chromecast

Plug prepared FlashCast stick into OTG cable

Holding down the button on Chromecast, attach power to OTG cable, don't let the button go

Continue to hold button down until FlashCast screen appears

If FlashCast does not appear after 10 seconds or so, Chromecast is not booting FlashCast - go back and write the .bin with dd or win32diskimager again (remember, you're not copying the .bin file - you load the .bin into dd or win32diskimager), then go back to step 3.

Once FlashCast screen appears, release button

Wait until Chromecast reboots or LED goes solid red. It usually is fast, but can take a few minutes.

If you're using a Cruzer Micro, its LED will mostly be slow pulse (idle) and will blink occasionally.

If Chromecast rebooted, your FlashCast stick is now ready to accept a mod or ROM for flashing. You are not done yet!

Unplug FlashCast stick from OTG cable

Plug FlashCast stick into computer. It should mount with volume name FLASHCAST.

If it does not mount, something went wrong - go back and write the .bin with dd or win32diskimager again, then repeat the steps in the section above.

If you get to this point after repeated attempts, FlashCast couldn't repartition the USB stick. Try a different USB stick.

Copy a rooted ROM like Eureka-ROM to the stick.

Rename if necessary so the file is exactly named

eureka_image.zip

For Windows, if you haven't changed the default settings, it will hide file extensions for known file types, which will mean the file will look like eureka_image in Explorer. Right-click and Properties the file to ensure it's really named eureka_image.zip and not eureka_image.zip.zip or just eureka_image

You should really consider changing the View options so extensions are shown. Open Explorer, Alt-T to get to Tools, choose Folder options, click the View tab, then un-check the Hide extensions for known file types option, then click OK.

Safely eject/unmount the FlashCast USB stick

Remove power from OTG cable

Plug the FlashCast USB stick into OTG cable.

Holding down the button on Chromecast, attach power to OTG cable, don't let the button go

Continue to hold button down until FlashCast screen appears

Once FlashCast screen appears, release button

Wait until Chromecast reboots or LED goes solid red. Mods are usually fast, ROM/firmwares can take up to 10 minutes or so. Be patient.

If you're using a Cruzer Micro, its LED will mostly be slow pulse (idle) and will blink occasionally.

If you flashed Eureka-ROM, you'll see the logo appear when Chromecast reboots.

Congratulations, you have root and no longer have to worry about Google OTA updates un-rooting you.