Ubiquity magni robot supply problems


I am working with the magni robot for my master’s degree thesis in the Politechnic Institute of Engineering in Porto, Portugal.
Lately I am having some problems regarding the power supply of the robot. First the batterys seem to not be working properly. Even though they are charged there is something that is making the robot lose connection with the computer periodically. Then we used a power cord extension to have the robot allways connected to the power supply. This solved the issues of the batterys but after a while the robot motors started having some problems. For example the connection is made with the computer but we cannot receive data from the /odom topic or publish data in the /cmd_vel topic. But this only happens sometimes. The remaining of the time it works. Other thing is a kind of “kick” that the motors do even without the robot having some program running that makes the robot lose connection the the computer.

I hope I am explaning the problem properly. I hope someone can tell me what tests to do to found the issue. Thank you very much.

Marcelo Cunha

Hey Marcelo

Just wondering, which Pi image and MCB firmware are you using there? The connection loss sounds a bit like the baud rate bug we fixed a while ago (the fix is to set init_uart_baud=38400 in /boot/config.txt). Newer firmware should also has that motor kick on estop disengage fixed, though I’m not sure in which version it was added exactly.

So my first suggestion would be to upgrade firmware to latest v43 and also test with the latest Pi image.

If that doesn’t work there may really be something loose in there that’s causing the Pi to lose power and reset when moved, but it would be hard to say what exactly.

Hello Marcelo,
1st of all please verify your MCB main board is rev 5.3. If that is the case, then check the writing on the far right edge of the MCB board so see if it has black sharpie pen that has ‘5.1’ in that text. Post a picture here if you cannot read it or tell me if you see no writing on the white band of silkscreen (paint) on the right edge of the MCB.


My MCB main board is version 5.2. In the white band there is no writing. thank you for helping me.

Only rev 5.3 boards sold in about the last 8 months had a modification that boosted the voltage that supplies the raspberry Pi 4 CPU boards to 5.1V so you would not see the black writing for the mod on a rev 5.2 board. We were caught by surprise in the change to raspberry P 4 board in that they are often (but not always) sensitive to dropouts in the WiFi and even some other issues when the raspberry Pi 4 does not get 5.1V. We recalled the stock from our warehouse of our remaining rev 5.3 boards and modified all the boards we had so they supply 5.1V to the raspberry Pi 4 boards that ship with the Magni (the rev 5.2 boards were long gone by this time). Thus I would not expect the mod on any rev 5.2 board. We on that same modification made another component change but that change was something that prevented the power supply on the board from running at all so that is clearly not your problem.

If you happen to have a Raspberry Pi 3B around for whatever reason for any hobby work may I suggest you try switching to use a Raspberry Pi 3B which never had this problem that the Raspberry Pi 4 sometimes shows.

I am telling you the most likely issue but I cannot know if it is actually your problem thus see if you can find a raspberry Pi 3B board to use with the Magni.

There is one other check that would be useful in debugging this problem you are having.
When the Magni gets into a state where it is not functioning properly look to be sure the 4 leds next to each other in the middle left of the pc board as you look at the magni have all 4 leds on. Be sure the right most 5th led does ‘blink outs’ every 4 sec or so. Also verify the 3.3V blue led in upper left below the large white jacks is on.

Visit: https://learn.ubiquityrobotics.com/ then click on ‘Verification’ about in middle on the left panel.
Then go down to section 1.1 that discusses these power checks.