Damage Report

Thursday, July 30, 2009

We took a look at how our 3D-printed thruster coupling failed.

You can see in this picture that the coupling lost a big chunk on the side opposite from the direction of thrust. Basically, it cracked under the force of the thruster alone.

The amount of empty space in this printed part is clear now, and it's an open question whether the failure was related to salt or rust buildup inside these spaces.

There is mild corrosion on other parts of the thruster, about what you'd expect for 2 weeks underwater

Against All Odds!

Wednesday, July 29, 2009

Today was a great day!

Two divers helped us find the lost thruster, after 2 weeks of being lost.

We got special permission from the assistant Harbor Master to conduct our search in the middle of the shipping lane.

"Please tell me this thing's expensive," he said.

"About $15,000".

He nodded.

The divers searched by taking 2 compass readings and heading out to where the lines crossed. They worked by dropping an anchor with their dive flag, and making concentric circles around it, getting further and further out as they searched in the muck by hand. After a while, they found... nothing.

We turned back to the Harbor Master. Since we had a GPS fix of where the vehicle was when it started going in circles, we figured we should use that technology instead to compasses to find the start of the search pattern.

"Let us do just one more try, and if this doesn't work we'll give up for good".

He said OK.

As it turned out, the new center of the search pattern was pretty far from where the compass readings had put it.

So the diver started again. It seemed like they were down for much longer on the second search, and we realized that we had probably missed again.

But when they came back up, they had a thruster raised above their heads! SUCCESS! They had found it on the next-to-last circle that they planned to make, and it was buried under 6 inches of sediment. The diver had been pawing through the muck, and hit something solid: OUR THRUSTER!

Take a good look at these guys, they are heroes!

Finished the New Thruster Arm

Thursday, July 23, 2009

The 2 machined pieces.

Fitting and comparing to the existing arm... our version looks as good as the one that was machined professionally!

Seth prepares to weld it up


Roughly filed down, this part is complete! Now we just need to have it annodized.

Thruster Arm Progress

Wednesday, July 22, 2009

The thruster arm's end is nearly complete.

Plan B: A New Thruster

Tuesday, July 21, 2009

Since we have had no luck finding our lost thruster, we are moving ahead with "Plan B", machining a new thruster arm to hold our spare thruster. We will continue the search for the original, but at least now we can plan to be back in the water and testing by a specific date.

Since this is fairly simple fabrication, it is far faster and cheaper for us to do the machining ourselves at a local shop.

An Unsuccessful Search

Wednesday, July 15, 2009

Today we tried (unsuccessfully) to recover the thruster. We lost it in the middle of a shipping lane in very turbid water. Visibility is poor, and the panning underwater camera setup we are using has neither the field of view nor the accuracy to properly search for a lost object.

Our zodiac is probably not the ideal support boat for this operation either.

Disaster Strikes!

Tuesday, July 14, 2009

Our 3-D printed mechanical fuse for the RTU coupling cracked and broke, taking our thruster to the bottom of Gloucester harbor.

Justin: Mike, the vehicle is going in circles instead of forward. Can you check the connection to the thruster?
Mike: Sure.
Mike: What thruster?

It would have ordinarily been retained by the electrical cable but ... we had just set it up to unplug rather than put strain on the other cable. "Whoops" doesn't quite capture the disappointment.

Bypassing Sliprings

Friday, July 10, 2009

Of all the users of Parker DriveBloks, we seem to be the only ones that experience frequent capacitor failures. Of the failures we have, only the thrusters that go through the RTU (and its sliprings) seem to suffer.

Solution: bypass the sliprings by drilling a hole in the fairing for the cable. As a safety precaution against continuous rotation of the RTU (disabled in software, but... you never know), we aren't using the plastic shells to hold the cables together.

There's Your Problem...

Thursday, July 9, 2009

This image fails to accurately capture the cause of our non-functioning camera: the grey and purple wires being crushed in the threads of the housing.

Since this was largely the result of wires and plugs being crowded near the top of the bottle, I drilled a hole in the mounting plate for the PC boards and routed some of the wires to the back side.