Duck synopsis

note: I've just been informed this isn't entirely correct - will update when I get more info.

So, as most of you know, a wedding in the Bunya Mountains prevented me from actually attending the duck race - my good friend Sara was left at the helm. I've finally talked to everyone involved and have gotten the full story on the duck and a reasonably clear explanation as to what happened. So here goes.

On saturday morning the last of the new changes were tested. Some minor modification was done with tape to clear the area around the propshaft entry, but the duck was driving fast and handling wonderfully. The new propellers were working well and everything was peachy. That's about where the good luck ends.

From what I can gather from various sources, one competitor's entry was a bodyboard with two ducks trailing behind it with fishing wire and various other decorations. Our duck was in prime position prior to the starting line being raised, upon which time said competitor's trailing ducks have floated off and gotten tangled around approximately six other ducks - about 1/5th of the field. The fishing wire became tangled around our duck as well as some tinsel that got caught around the propellers. A man in a kayak was sent to retrieve the ducks, however instead of bringing them back to shore, he decided to pick them up and THROW them over the fence onto the riverbank, several metres vertically and horizontally. Rather than untangling the ducks or cutting the line, he has also thrown our duck, complete with others entangled, in the same manner. This has had a three-way effect of bending the entire frame around the duck, loosening the connections internally, and dragging it through the water non-vertically has caused the water-resistant (not waterproof) sealing to be under water for some time, causing the duck to take on water. The impact has loosened the connections internally and the battery which was formerly taped down inside the duck away from the bottom of the hull has come loose.

At this point the duck is still technically working, so it's put back in the water, and given the opportunity to run again. However, the damage to the frame has meant that the motors are no longer even close to aligned with the propshafts. The severely mismatched angles of propulsion caused the propshafts to come loose from the motors and remove themselves from play, first one, then the other. This appears to have been the final straw that broke the internal electronics' back, as the joint between the power switch and the Lithium Polymer battery pack has broken off and caused the battery to earth itself into the water floating loose in the bottom with the 9v battery for the camera. This is a Bad Thing. Long story short, the Li-Po battery exploded and the inside of the duck is now filled with highly toxic battery materials. With no power we were officially dead in the water and had to be rescued. Again.

By throwing.

Autopsy photos here.

So that’s it - our duck race was a bust, but I still had an absolute blast building it. I had planned to reassemble everything and make repairs for a test-drive, but unfortunately the Li-Po battery explosion killed everything inside the duck. By all accounts, the entire race was a bit of a non-event on the day, but I had my fun beforehand anyway. So thanks for reading, and keep an eye out for our entry next year.

Ready to race

The testing on the weekend revealed a few things. We were a lot slower than I'd anticipated - the tiny propellers weren't presenting enough resistance and the motors were reaching their full RPM. So they needed more load - bigger props got installed. Unfortunately more rotational inertia meant a whole host of other issues. More vibration through the driveshafts only exascerbated the balance problems we were having. The driveshafts had to be reinforced half-way, had their entry and exit points glued down, the silicon joints glued down, and due to an unexpected overheating problem in the entry/exit points, high speed bearing lubricant added.

Only electronics were left after that. The switch I'd bought was unreliable at best and the LED seemed to alter the voltage enough to cause the receiver not to work, so it was replaced with a smaller toggle switch. I wired up a lead-acid battery pack in place of the 12V AC adapter for the video receiver, resoldered all the weak joints on the right motor and encased everything in heat-shrink tube. After sealing it all up with tape and the appropriate plastic (read: freezer bags), it was painting time. All extraneous metal except for the mounting plate for the flag were painted yellow, as well as the keel, which needed additional glue reinforcement due to the battering it received in transit. The skis were painted orange to vaguely resemble feet. Cause, y'know. Ducks are yellow, with orange feet.

I also used the remaining balsa-wood that we'd bought for the skis to make a proper dry-dock to actually sit the thing in, since it no longer sat comfortably on a desk. It got painted too - can anyone guess what colour?

Matte black. Of course.

Open water testing

Cameras, and balance

After the keel glue was dry, it was time to get the engines relocated. This should make the thrust vector better (more forwards, less down). It won't fix the problem, but it should mean that it needs less stabilisation and I can get away with less rolling (floating?) resistance. I had a lot of opinions and ideas being thrown around all day, although less than yesterday. I've moved the duck off the main table at work and onto my desk so I can get some work done, as everyone just wants to stop and talk about it. Nevertheless, a lot of good ideas and useful comments. Everyone's been really getting into it and it's good to get people thinking about the possibilities. Great to see people analysing and weighing things up. I didn't know anything about hydrodynamics when I started this either but I sure do now!

Anyway, so the motors had to move. I built a new bracket around the front of the duck and adjusted the position of the old rear bracket. I couldn't get a deep enough propeller position, or get them equal, so I ended up abandoning the original (which had been a guessed hack anyway) on account of too much counterbending looking and holding like crap. A new rear bracket and the removal of the old front bracket and we were on our way. In addition to that I added a coathanger to bridge the gap between the skis, to avoid other ducks getting caught and pushed along (wouldn't that be a shitty way to lose?) and also to give the pilot a reference point for where we were going.

After that it was camera work. The first test of the camera worked okay at first but highlighted a few issues. After deciding to install a power switch for the camera to avoid the need to get elbow-deep in the duck to turn the transmitter on and off, I cut some holes, wired up the switch and mounted it in the port hole. It turned out the 9v power for the receiver was a bad idea - terrible in fact. The receiver's sensitivity was way down and we only had a few metres range. After going home for a 12v power supply and hooking up the switch, all worked fine.

Nothing left for it but to secure everything, seal all the water-sensitive bits, remount the flag with a new piece of bracket, reverse the polarity of the motor connections because I am a retard who mounted them backwards, then clean up and take a photo, pictured above.

Plan for tomorrow:

1. Take the duck to southbank and tune the performance of the skis.
2. Fit the passive stabilisers and test.
3. Fit a power switch to the drive system.
4. Profit.

That's it, we're on the home stretch. The new drive system is much more stable and less prone to vibration than the old one and I theorise that tomorrow I'll be able to reach full throttle. Then it's just a matter of fine-tuning exactly how fast we can go at said 100%. Stay tuned for test videos tomorrow night.

Further modification

After our successful water test the other day, it became obvious that we had issues with the duck tipping forward. The way forward from there was pretty clear - the force needed to be countered. So I cut some skis out of balsa wood and started sealing them. That was going to be difficult to dry, so I took some of Trina's bobby-pins and fashioned them into an impromptu point stand. While that was drying, I marked out a plastic lid that Sara provided for a keel. After leaving them to dry, I left it for the night.

The next day I picked up a USB video capture card and went back to work to install the camera properly. After confirming that it worked and that the receiver worked on 9v instead of the prescribed 12v, the NSW sales manager walked past for a chat. He suggested that with such rolly-polly handling characteristics, it should have passive stabilisers - wings that hung in the water and dampened any particular movement. That gave me some ideas.

That night I went home and with Heather's help, cut out the two halves of the keel and two wings for the stabilisers. The down side of using a Dremel for a grinder is that you get covered in bits of melty plastic. I'd had an idea that I could use the old original prop shafts for the proof-of-concept to build the stabilisers, and a little reworking later, it proved acceptable in theory.

We glued the two halves of the keel together and cut some styrofoam out for skis. The keel looked like it'd hold, so it was cutting time. First the passive stabiliser mounts, then the frame for the skis. Dremels are fun.

Stopping for a second to lol at the fact that my camera mistook the M-Man for a face, it was time to see where the whole thing sat now. Unfortunately the duck no longer fitted in the sink. So I set about making my own pond in a box. The box test revealed what I suspected - the duck was a lot better balanced than before and the water line was acceptable.

After that it was just time for some branding and we were done for the night. I came in the following night to finish the keel and glue it on.

Next step - relocate the engines further forward, and water test for a water line so we can adjust the skis, and then figure out where to fit the passive stabilisers. After confirming that all works and refitting the camera (along with a switch to turn it off), we should be done.

Beta testing - round 1

Last night I brought the duck in to work with the intention of testing at lunch in the fountain pond in Anzac Square. I was expecting some stability issues to do with the thrust vector and tipping forward under power, and that was exactly what I got. As you can see in the video, the times I got too throttle-happy, the whole thing lurched forward and threatened to tip over. Fortunately, this is a problem we have four possible solutions for.

- Front stabilisers, similar to a snowmobile, to keep the nose from dipping
- Angling the drive at the tail with a geared or flexible driveshaft
- Installing a lengthy winged keel which will hold onto the water
- Moving the drive portion forward to move the point of body rotation forward more, to resist the roll forward

I'm going to go home tonight and try the stabilisers, and I have some flexi-silicone tubing that can do for the drive, but how to straighten it after the bend? I'd need another section of driveshaft .. not impossible, and I could clamp down with the bearings from the heli shafts but whether or not they're water resistant enough to withstand living underwater for any length of time without locking up later remains to be seen. Other things to try include adding a winged keel, which I plan to do tonight, and

Current plans:

Wednesday lunch - testing with keel
Thursday lunch - testing with stabilisers
Friday lunch - testing relocation of motors

Wish me luck.

racing duck enters Beta testing

Sara and I spent the second half of the day working on the duck. We installed the propellers and prop-shafts that Rachel and I bought earlier in the day, and then set about cleaning up for a water test. The laundry sink seemed like the place. After getting it in the water, and performing a thrust test to make sure the motors worked, we found two things.

1. The duck was extremely unbalanced, biased to the rear.
2. The length of the extended prop-shafts meant that with said rear bias, it still touched the bottom.

Both bad things. So, it was off to the city for tools and equipment. A dremel, spare bracing, and floatation devices to build stabilisers with. We came back with balsa-wood, a massive dremel kit and more alu bracketing. After cutting off the excess metal in the bracket, great news - the duck floated normally. It was time to test that it could move.

And it could.

After that it was just a matter of cleaning up and optimising. The camera cabling was routed through a port hole in the duck’s head, the control box and the battery were internally mounted through a port hole in the back. After that we sealed everything up with freezer bags and it was done. No time for a live water test as it was dark by the time we were done, so will test during the week.

As usual, complete build photos here.

(The workspace was a bit chaotic afterwards)