Avoiding a Voltage drop Rebbot of the BB

#1

We want to address the problem, that if the motors need a lot of current

and the Voltage drops under 6V the BeagleBone reboots.

We had this Problem with the LiPo-battery on Speed level 5 (keyboard) and with external Power Supply (because of the Voltage Drop on the Cable) even on speed level 3 or 2.

So we have two different solutions in Mind.

1. a Simple Workaround for fairs.

We want to configure the ROV so that it starts on Speed level 1 after Startup (keyboard control) .

It is really annoying, you put the ROV in go forward and the ROVs reboot, because you have forgotten to reduce the speed level.

This is also use full on a fair, if the Pool for demonstration is not so big. ;)

So is it possible to configure the Startup Speed level somewhere and where?

2. a nice software side solution

We want to implement a watchdog that monitors the Voltage.

If the Voltage drops to much, the watchdog reduces the speed of the Motors.

What is the best way to implement such a watchdog and where to start?

we are currently working with a 2.4 Rov with the 2.4 Stable Software.

#2

Hey Eik,

We have changed the speed so that it starts at speed setting #2 in the code.

https://github.com/OpenROV/openrov-software/commit/a4a95c8b51d724ed89a591d691e278d3b7da6f62

https://github.com/OpenROV/openrov-software/commit/d313e5c607e08acec60be070c09d85760f8732c1

For the watchdog on the motor speed vs voltage level we have been thinking about the same sort of solution. The only challenge is that people can pull lots of types of batteries, so we almost need some type of battery profile concept so that users can simply select and pull in the right settings for their battery formula. This would update not just a concept of alerts which I will post about, but also change the voltage low voltage warning number.

For the alerts, what I am thinking is that in the event loop in the node.js process can do this logic. It can monitor the voltage and the thresholds and change the power levels and send warning messages down to the browser.

#3

Why not have a second battery just to power the beagle bone and the other electronics. This is commonly done in a application high current load. Trying to sense that the voltages dropped is probably too late by the time that’s happened. A small six volt battery like the type used in R/C vehicles would be more than enough power to run electronics.

#4

New guy here with a suggestion for preventing brownouts of BBB and/or Arduino.

I have been working with airborne UAVs for about 2 years now and have seen what happens when you get an inflight reboot or power loss to the flight controller. It can be disastrous and VERY expensive. Here is one such workaround that uses a cheap little voltage regulator to provide power to the controller(s) and the other components while minimizing the chances of a brownout. The components for this power scheme are relatively cheap and easy to locate.

http://diydrones.com/profiles/blogs/powering-your-apm-drone-or-how-...

I think I may have posted this in another thread a few months ago, but here it is again. I have personally used this power scheme on a multi-copter and it does work. It would obviously require some adaptation to the OpenROV design, but it would essentially eliminate the chances of a brownout while the ROV is operating. As I type this, I can see the advantages to using a similar power distribution board approach for powering the OROV thrusters.

Here are a few links to the individual components.

3D Robotics Hexacopter Power Distribution Board - This is the one I used for my hexacopter. They also offer a quadcopter version.

Attopilot Current and Voltage Breakout Board - This is the current/voltage sensing board. I used the 180-amp version because my current at 100% throttle totals up to about 120 amps.

Buck Boost Linear Regulator - Provides a steady and clean 5VDC (or any other voltage) to your controllers.

So, for just over $50 worth of parts and with a little soldering, you can provide a clean, steady 5VDC to your controller boards. If you needed to provide 3.3VDC, you could always attach a second voltage reg to the PDB and dial it to 3.3V, but you would need to tie it into a common ground if you needed to monitor the voltage/current on that component. Another idea here would be to coat the Attopilot (and even the reg board) with PlastiDip or brush-on electrical tape to help protect the electronics from saltwater intrusion.

I know this is rather long-winded, but it seemed appropriate for the discussion at hand. I hope it offers some insight into how to solve the problem as originally posted.

#5

Just re-read the original post and realized that BBB needs 6VDC to operate. The voltage regulator can be dialed in to provide this. In fact, you have nearly infinite adjustment of voltage output within a range of 5-30VDC.

#6

For anyone who's having issues with battery dropouts under hard motor running-

Make sure you've seen this recent blog post. We're not using the Trustfire batteries here at OROV HQ anymore. There were a number of reasons for this, including the inability to fully eliminate nuisance trips of the protections circuit. Since we've switched to unprotected cells, there have been no more issues with having the batteries cut out.

-W

#7

The Problem is more important when we use an external Power supply wit an additional wire, for fairs.

#8

Hi Eik:

In this case, you might want to patch your software so that yawing (turning) motions are not done at full power. This should allow you to use the ROV at low throttle settings (1 or 2) with a small external power supply, and not have dropouts. This has been talked about in a couple of forum posts, but the small code patch is here.

The patch has is currently in the master tree and should be part of the upcoming 2.5.1 software release.

Hope this helps.

-W