Dawn Robotics Forum

The Dawn Powerpack has two usb connections. One USB port is 2.1A (left) and other is 1A (right). Labeling shows this on the power pack. Here is a summary of my findings using different combinations.
Note - My RPI is a B+ Model + Edimax wifi adapter. (Other models may act differently)

1) Best - RPI plugged into 1A connection (right) USB and Dagu +/- power USB connector plugged into 2.1A Left USB port. This seems to be the most reliable.

2) RPI in 2.1A and Dagu in 1A. RPI does not stay on very long after driving activity. Not sure why this is the case since it has 2.1A available but I am thinking the Dagu supplying the motors needs more amperage and results in a voltage drop to the RPI and it reboots spontaneously after a while. (This is just my theory)

3) RPI plugged via UBEC and Dagu plugged into 2.1 A connector. Not very reliable.

4) Tried option 3 but plugged into 1A usb. Pi reboots without even activating any motors. Not usable

Post if you have similar or different results with the RPI B+

Regards

Hi Claude,

Thank you very much for these tests. I think that I agree with your conclusion, although in the blog post where we introduced the powerbank, I recommended option 2. This is because the Pi seemed to need a bit more power when using some power hungry WiFi dongles (not the Edimax).

Option 1 is better however if the motors will draw a lot of current. The 2WD chassis motors should have a combined stall current of about 0.7A so it sounds a bit odd if yours are drawing much more than that. Do they seem to run freely and at a decent speed? I did need to use option 1 when building the robot using the 4WD kit we sell. What seemed to be happening there with option 2 was, the current draw from the motors was above 1A, this causes the Tecknet battery pack to shut down, and this obviously has a bad effect on the Pi...

As for options 3 and 4. These are highly unlikely to work, because the UBEC (a voltage regulator) needs an input voltage in the range 5.5V to 26V to work. The USB battery pack already includes a voltage regulator and so when using it the UBEC is not needed. I included the UBEC in the kit because it doubled the battery life of the robot when running off AA batteries (you still get an extra 2 hours from the USB battery pack). However, I can see that I need to make the documentation clearer to avoid confusion (you are not the first to have tried options 3 and 4).

Regards

Alan

Motors run very free and robot accelerates and spins quickly due mostly due to my robot driving ability. I would like to build in some better robot control mechanism to allow for smoother more controlled operation (No uncontrolled spinning).
At any rate the Dagu plugged into 2.1A and RPI plugged into 1A usb port on battery pack works the best for me, and believe me I was getting frustrated before I approached the problem more systematically. The UBEC definitely was a thorn in my side with the battery pack until I tested all the other options and found a working combination. Glad to know USB Battery Pack and UBEC don't coexist.
I RTFM and agree it could be updated to help other users. Docs could be combined into a downloadable PDF since sometimes it is easier although can get out of date if revisions are made.
Claude ...

Good point about the docs. The aim at some point is to combine the blog posts which currently form the docs into a manual using readthedocs.org, that will give a webbased manual that can also be downloaded as a pdf.