Cockpit crash

#1

Hi all,

I keep having cockpit crash when pushing a bit hard on the props while in the water. It looks like the batteries cannot deliver the required current.

Am I the only one facing this issue??

Do you have any idea on how I could isolate the problem?

Thanks for your help.

Ben

#2

Hi Benoit:

Yes, that is true, the current motors, if driven hard, can pull more current than the lithium cells can provide. If you are using lithium cells that have built-in protection circuitry, it shuts down the battery pack, and you have to recycle power on the ROV.

If you want to drive the ROV aggressively, I would definitely recommend that you upgrade to Graupner props (see this thread), like we'll be shipping in the OROV 2.5 kits. The Graupner props are far more efficient than the propellers that were shipped with the 2.3 (Kickstarter) and 2.4 kits, but even with the new props it is still possible to current-limit the batteries under very hard driving conditions.

-Walt

#3

Walt,

Thanks for your reply.

I have noticed that the crash happens when 2 or 3 motors are at full speed or when the rov is stuck.

I have already upgraded to the Graupner, but honestly I cannot see much difference.

When driving with the keyboard, I can use the speed until 3. If I use the 4th speed, it crashes when using one single thruster...

I suspect I have an issue somewhere...

I guess it would be easy to detect with the new board and all the amp sensors...

Any idea to troubleshoot in the meantime is welcome!

Kind regards,

Benoit

#4

I have been usually using the keyboard for control and I set the motor speed to 4 and am able to drive around with out crashing (sometimes at the end of a dive 5, I seem to get heavier the longer I am in the water). I have even had the vertical motor running to maintain depth and still can drive around. After maybe 30 or 40 min. in the water I have dropped out. I will see my voltage drop below 7.5 volts and I know I am going to have trouble. I am also sending 12 volts down my 200 ft. of 22 awg cable from a sealed battery on the surface. When I hook up the surface battery and the OpenROV 241 is at idle I will see a little over 10 volts on the screen.

I am running 8 1.2 volt batteries in series which on the screen show around 8 to 9 volts when running. I am using Panasonci NiMH - Nickel Metal Hydride Battery C 1.2V 3300MAH which at one point were recommended on this form. I did not come up with them.

I have been in the water for over an hour several times.

John

#5

Hi all,

I have now finished the upgrade to 2.5 board, and I have more details.

I still encounter the same issue:

When using the motors in water, I have sudden crashes.

Here are two logs before it dies:

Can anyone find where the issue could come from?

  • VOLTAGE: 11.0V
  • CURRENT: 0.500 A
  • hdgd 0.00
  • deap 0.00
  • pitc 0.00
  • roll 0.00
  • yaw 0.00
  • fthr 72.00
  • motors 1835,1500,1835
  • mtarg 2000,1500,2000
  • motorAttached 1
  • servo 1500
  • starg 1500
  • fmem 6372.00
  • vout 11.01
  • iout 0.5
  • atmp 0.00
  • ver255667012a08b8836d5475bb2d771b6b01a5aa0d -
  • cmpd Dec 13 2013, 03
  • cpuUsage 0.984375
  • time 339490.00
  • pres 0.00
  • temp 0.00
  • dlms0|219571|413742|97383|94244|4735|59116|10538
  • alps 4708
  • BRDT 0.00
  • SC1I 2.31
  • SC2I 0.74
  • SC3I 1.70
  • BRDI 0.41
  • BT1I 3.36
  • BT2I 3.30
  • BRDV 11.14
  • AVCC 4892
  • cmd go(2000,1500,2000)
  • CAPA 14
  • log No I2C devices found

Another crash:

  • VOLTAGE 10.5V
  • CURRENT 0.330A
  • hdgd 0.00
  • deap 0.00
  • pitc 0.00
  • roll 0.00
  • yaw 0.00
  • fthr 55.00
  • motors 1751,1500,1751
  • mtarg 1775,1500,1775
  • motorAttached 1
  • servo 1500
  • starg 1500
  • fmem 6372.00
  • vout 10.48
  • iout 0.33
  • atmp 0.00
  • ver255667012a08b8836d5475bb2d771b6b01a5aa0d -
  • cmpd Dec 13 2013, 03
  • cpuUsage 0.46341463414634143
  • time 338209.00
  • pres 0.00
  • temp 0.00
  • dlms0|215401|415922|93753|94184|653555|60146|10384
  • alps 4699
  • BRDT 0.00
  • SC1I 2.52
  • SC2I 0.00
  • SC3I 2.00
  • BRDI 0.43
  • BT1I 7.22
  • BT2I 0.00
  • BRDV 10.26
  • AVCC 4892
  • cmd go(1775,1500,1775)
  • CAPA 14
  • log No I2C devices found
#6

Be sure to follow the thread that talked about motors that potentially have shorts in them if you only see crashes in water. Given the first data set does not capture anything that looks out of the ordinary I would definitely do that check first. I am assuming you are using the trustfire 26650 3.7 Li-Ion batteries. As far as what is in the data sets:

The first data set, I don't see anything out of the ordinary. I can see that you were telling the system to go full bore and it was in the process of ramping up to speed via the motor target vs actual (mtarg = 2000,1500,2000 motor [actual] = 1835,1500,1835). Battery currents (BT2I,BT21) look normal. As does the battery voltage BRDV of 11.14.

For the second data set, you were pulling current from only 1 battery tube (BT2I = 0, BT1 = 7.22). You batteries were showing 10.26V at the time the last data set came in. Usually we can draw down to ~9.5V with the Lithium batteries we have been using before the protection circuits kick in. But the current and voltage are only coming in with a 1 second resolution so the voltage may have bottomed outside of the sample point.

#7

Brian,

Thanks a lot for your tip. That would explain why the upgrade didn't change anything...

Would you have the link to the discussion by any chance?

Kind regards,

Benoit

#8

http://openrov.com/profiles/blog/show?id=6365107%3ABlogPost%3A82907

#9

Brian,

Thanks! I did the test and the three thrusters are leaking!

I guess I am cursed... I will check the 2.6 build process!

Regards,

#10

I have seen this same sort of phenomenon with aerial UAVs. The guys at DIY DRONES came up with a way to prevent a "brown out" by using a separate circuit for voltage/current monitoring and directly powering the APM (Arduino Mega) from the input rail. Here's a link.

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

This seems to prevent excessive current draw and in my limited circuit experience, it appears to put the APM/Arduino board in a separate power loop via a DC-DC converter/step-down regulator. I am not sure if it would work here, but it might be worth a shot. My experience with the BBB is zero up to now, but I have played with APM/Arduino a lot in the last couple of years. I am sure there would be a way to adapt this sort of setup to the OpenROV. I will say that on the hexacopter I am currently building, I used this power distribution setup and my input voltage to the APM input rail (from the converter) was a rock solid 5.01VDC.

#11

We have a Similar Problem on full thrust (LiPo), the Board reboots. Even worser is it with external power supply. There is the Problem even on Speed stage 2 or 3 (because of the Voltage Drop through the wire.)

So we think of a Software solution.

If the Voltage drop to much, the software should reduce the Motor speed.