Here are some photos and details of a controller board that I just modified for Kevin K to support vectored-thrust on his ROV. As some of you know, he's building an open-frame ROV (similar to those made by Outland), and has had a running forum post about it for some time:
Though he's currently working with three thrusters, the design really begs to have a full complement of six thrusters for vectored-thrust operation. That is, two forward thrusters, two aft thrusters, and two vertical thrusters. The fore and aft thrusters are placed at an angle to allow sideways (strafing) motion. The two vertical thrusters enhance the lifting capability of the vehicle, and cancel out torques caused by using a single vertical thruster.
Kevin had the foresight to pot a bunch of extra wires into his endcaps to support future expansion, so......it was time to get to work on implementation.
This spring I experimented with an OpenROV modified into a 4-thruster "vertrans" configuration to allow it to move laterally. Here's a thread showing the modifications to the controller board:
For Kevin's ROV, I just expanded this concept to the fullest extent- mount an additional ESC over top of each existing one. Here's what it looks like:
And a closer view of the ESCs themselves:
Just as earlier, the power leads to the new ESCs are soldered into the spare pads that are on the board (they facilitate the use of 20A ESCs if there's a supply issue with the stock 12A ESCs). I drill out the spare ESC output pads to allow the output wires from the 3 new ESCs to go to the bottom of the board. 2 of the ESCs (6 wires total) are routed this way, and connect to the 6 spare leads on the DB-25 connector:
I avoided using the existing test pads TP20-TP25 since the traces attached to those pads are not designed for ESC currents.
As the DB-25 connector now has all its wires used, the third extra ESC, as well as any external lights or external servo channels, will need to use and additional connector.
Here is how I have the ESCs connected:
Existing servo connections:
D6 - rear port thruster
D7 - vertical thruster - with Y-cable to drive both vertical ESCs
D8 - rear starboard thruster
New servo connections:
D9- forward port thruster
D10 - forward starboard thruster
The D11 channel is still used for the camera tilt.
The ESC output pins are wired as follows:
DB-25 pins 20-22: port forward thruster
DB-25 pins 23-25: second vertical thruster
Free wires, to be added to an additional connector: starboard forward thruster
A couple of additional notes:
The AFRO12 ESCs can be purchased from HobbyKing, but note that they need to be reprogrammed to provide forward/reverse behavior (they come shipped working in forwards only). There is a script in the OpenROV software to do this (search the forums- the issue has come up before)- just plug the 3 new ESCs into D6,D7, and D8 temporarily, run the script, then plug all the ESCs back into their desired servo channels.
Note that this is not a long-term solution for big vectored-thrust vehicles. The total power-handling capability of the controller board has not changed, so in reality the power capability of each thruster has been cut in half. But what it will allow Kevin to do is to test the vectored-thrust software and mechanical layout, while working on a long-term solution for the power supply (probably using ESCs built-in to the Blue thrusters)
Hope this helps people with ideas for their own ROVs. Let us know if any of you do something similar!
-Walt
