Battery Space Li-FePO4 with the spacers in the v2.6 OpenROV


#1

Dynamic functional testing was conducted by assembling the system, establishing contact with the ROV Cockpit and performing limited maneuvers while submerged in about 20 inches of water (bathtub). All functions and controls were tested numerous times and all functioned well with only a few exceptions as listed below:
a) Lost contact with the ROV three times during the test. At each “loss of contact” event we noticed that the ROV bumped in to either the side or the bottom of the bathtub just prior to loss of contact. First event was incidental, second and third events were intentional and confirmatory in purpose.
After determining that a bump or physical “shock” was leading to the loss of contact events we suspected a loose connection somewhere in the ROV unit.

Dynamic testing was terminated and the unit was removed to the work bench for some further testing and troubleshooting with the following results:
a) The system was tested, while energized, in order to attempt to reproduce the loss of contact issue and further isolate the cause. With the system energized, a bump (shock) was administered to the Electronics Tube assembly (several times) with no loss of signal resulting from the test. A similar bump was administered to the battery tubes (several times) and loss of contact occurred each time the bump was administered.
b) With the issue being localized to the battery tube assembly, careful inspection of the battery tubes and connections was conducted. No apparent issues detected in the springs, tubes, contacts and/or wires were detected. This inspection was conducted both visually and electronically (with multimeter).
c) After eliminating problems with all other connections, the only logical remaining connection is the connection between the batteries themselves. It is probable that at the moment of impact (shock), there is a momentary discontinuity through/between the batteries causing the controller or communications boards to shut down. The batteries being used are the Battery Space Li-FePO4 with the spacers.
d) Investigating possible remedies for this issue.

In conclusion, we found that here is an issue with the battery assembly that causes a loss of contact (shut down) with the ROV bumps in to anything. Current battery configuration uses the Battery Space Li-FePO4 with the spacers. This battery configuration allows for movement in the batteries (within the tubes).

Has anyone else experienced this issue? What have you done to remedy the issue? Suggestions please…


#2

Thanks for the great details on the problems and providing the troubleshooting that you have done so far. One thing about the batteries is how flat the ends are and this can cause the symptom that you are talking about. I would recommend removing the plastic wrapping on the bottoms of the batteries as shown to assist in good contact.

If this does not work I have a few other things I can suggest.


#3

Hi Brian. Yes, I have already trimmed the plastic from the battery ends. I did this way earlier, yet the problem persists. I am currently using the “spacers” as provided in the kit, but there is still not a lot of spring tension holding the batteries together. I fabricated a larger conductive spacer in order to increase the spring tension, and hopefully hold the battery stack together better. However, the increased spring tension is also exerted on to the battery tube “end cap” which pushes the end cap off of the battery tube. Additionally, the batteries are somewhat smaller diameter than the battery tube, so they move around, within the tube, quite a bit when bumped.


#4

One thing I am trying is to use electrical tape and tape the three batteries together in a stack. This must be done in such a way as to maintain end-to-end contact between the batteries at all times, yet so as not to add too much increase in diameter of the stack. Otherwise the battery stack will not fit in to the battery tube. Initial tests look good as the process appears to alleviate the momentary discontinuity issue. It is recognized that the batteries must be untaped and separated for the recharging process.

I used a short (approx 1 inch) tab of tape on opposite sides of the batteries being joined (provides tension to keep batteries together). Then I used a strip of tape around the circumference of the joint of the batteries to stabalize the joint. Important… Use only one layer of electrical tape as more layers create too much bulk and the battery stack will not fit properly in to the battery tube.

It should go without saying that the operator would need to keep a roll of tape with them as they are in the field operating.