OpenROV 2.7, Bad ESC?

propulsion

#1

Hi All,

I’m pretty sure I have a bad ESC (ESC1). After completing my build I realized that my unit pulls to the left (pushes to the left may be more accurate) and has a real tough time turning right. I’ve ohm’d out the motor windings and from winding-to-winding I get about .56 ohms. I checked for shorts between motors and those all measure open. I put a scope on the A, B, and C outputs of ESC 1 and I see a good pulse out of ESC A and C, but B is a terribly round hump, kind of erratic. I also notice when the ROV starts up ESC 2 and 3 beep right away, ESC 1 follows a few seconds after. Looks like this:

https://www.youtube.com/watch?v=g8eCVsT1ARA

I also notice when I use a gamepad and give some light throttle, the motor chatters until I push the throttle enough. Looks like this:

Here’s a shot of the scope on ESC1-A

Here’s a shot of the scope on ESC1-B

I’d like someone to confirm that I haven’t overlooked anything else before I order a replacement ESC. Any thoughts or suggestions would be great!

If not, I’ll order a replacement ESC. I see some threads when I searched that mention calibration. For the ESC’s used on the OpenROV 2.7, Afro 12’s…do they need calibration? I can’t find any reference to cal. Or I can just replace the bad one with a new one and it should work?

Thanks for your help,
Lenny


#2

Hi Lenny:

You can replace the ESC with a stock Afro12 ESC ordered from HobbyKing. It won’t need to be calibrated, but it will need to be reprogrammed- the stock ESC is meant for a quadcopter, meaning it only goes in one direction. It needs to be reprogrammed into car mode, where it goes in both forwards and reverse.

If you’ve checked the motor winding with a meter and there are no shorts, and all the windings have about the same resistance, and the motor turns by hand freely, then trying a new ESC seems to be an appropriate step.

The only other thing you might try is to make sure the Controller Board PCB isn’t defective in some way. I’m assuming that you measured the motor resistance through the wire harness DB-25 connector. You can also measure the resistance between the ESC mounting pads and the DB-25 connector on the controller board. Perhaps there is a defective trace on the PCB? This is a long shot but is easy to measure so its worth trying.

Brian has posted instructions before on how to program a replacement ESC using the existing OpenROV hardware (BeagleBone and Controller Board). A search of the forum might find that, or perhaps he can repost that info.

-W


#3

Hi Walt,

Thanks for the info. I did check the windings through the DB-25 connector. I just double checked the PCB only, to be sure. It looks OK. Also, thanks for the info on cal vs. programming the ESC’s. At this point I ordered a replacement ESC, I’ll pop it in once it gets here.

I did a search through the forums for programming the ESC’s. I found a reference to a wiki link but I get errors (connection refused). I have a 2.7 ROV so I then went to the 2.6 build guide but its clear the ESC’s are different for 2.7. Could you offer some assistance on where to find programming instructions?

Thanks,
Lenny


#4

Lenny:

I will ping Brian for you.

-W


#5

Yea, if you ssh on to the ROV, the following commands will re-apply the programming to the connected Afro ESCs. So simply soldier in your replacement ESC and run the following:

cd /opt/openrov/cockpit/linux

sudo bash ./install-afro-esc-firmware.sh

#6

Perfect, thanks for your help!

Lenny