I thought I would commend globula_neagra's patience and fine manners.

I myself had some difficulty making heads or tails of how to convince my U30GT2 to decide to play nice and get into firmware update mode. Even though I'm not a stranger to Android, or even Rockchip devices, this particular model had me stumped for most of the day.

Here is my report and success story, as I have managed to install CWM, and test a couple of ROMs tonight on the U30GT2.

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I was having heaps of trouble figuring out how to flash my U30GT2, even with all the recommendations of which keys to hold, which sequence, when to attach the microUSB cable to the tablet, and making sure the Rockchip USB drivers were installed in Windows...

I'm not a complete newbie to Rockchip devices. I've got a Teclast player (T51 for audio) and boy was that a pain to load the drivers and navigate the Rockchip Batch Tool (when these types of devices were much less common).
 
Anyhow on to the point of my post.

For ME; this worked:

Task # 1:

I was trying to flash the CWM Recovery.

The key sequence I used was:
1. Volume + button (held in constantly)

then

2. Power button (held in)

then

(with the USB "A" end attached to the USB Port of my Windows 7 x64 PC, with the RKAndroidTool 1.37 application opened as Administrator...);

3. I then inserted the microUSB end into the receptacle on my U30GT2 tablet (WHILE STILL holding _both_ Volume +, AND Power buttons)

then

4. I released the Power button (WHILE continuing to hold the Volume + button)

then

5. The RKAndroidTool 1.37 looked for and verified the Rockchip drivers for the tablet

then

6. The RKAndroidTool 1.37 proceeded to go ahead and flash (successfully) my tablet, and then reboot my tablet to Android.

---ADDITIONALLY---

Task # 2: Testing some of the different available Stock Android ROM firmware from Cube, as well as the Custom ROM firmware from ARCTABLETS:

The sequence 1. thru 4. work with the Rockchip Batch Tool (1.6) to load the firmware from Cube, or from ARCTABLETS (custom rom) via the "Restore" button on the Rockchip Batch Tool.

Hopefully this helps someone who is having difficulty accomplishing these tasks.

Best