Doug's blog 23rd October: breakers and string

Yesterday was scrutineering.

We failed.

We rocked up somewhat before our appointed time at the Darwin showgrounds, some of us coming straight from our accommodation; some of us detouring to Hidden Valley to pick up the solar car. We all register, our drivers weigh in, and we are given ballast bags.

Meanwhile, Hammerhead has been moving around the scrutineering station. We pass the first two stations with flying colours. Since the first two stations are stickering (where they put a World Solar Challenge sticker on the car) and measurement (where they weight the car), it's hard to fail these.

The third station is driver seat angle and ingress/egress. The seat angle is close to passing, but not quite. Which is odd, because the same seat passed last year, and the rule hasn't changed. They let us through anyway.

They check the eye height. The rules require that the driver's eyes be at least 700mm above the road, and the way they check this is they put a driver in the car wearing black goggles, and shine a laser in. If the laser is below the mark on the goggles, it's a pass.

The laser hits out car below the bottom of the windscreen. So that's all good.

The ingress/egress rules require each driver to get in to the car in 15 seconds, and to get out of the car in 15 seconds. Some other teams are having trouble with this; we do it in half the time available.

Next is NT Roads, who check the car mechanically. They ask us to wrap some brake lines to protect them from abrasion. No worries.

Then it's electrical. There's a new electrical rule this year which requires battery isolation to be built integral to the battery box. Said isolation is to be operable by both the driver and the emergency pull on the side of the vehicle. Our car has isolation in both of these places, but it's not integral to the battery, so it leaves a metre or two of wire live, which is a no-no.

(Rumour later is that about half the teams have failed on this same rule.)

So we must re-work our isolation. John Storey, the electrical scrutineer, explains a way to do it with a 12V supply and some additional batteries to drive that supply.

We return to the track. Steve Morgan, on hearing about the problem says, "Just use some string!".

John and I pick up the relay from our old battery management system, and head out. We go to MM, who send us to Delta, who send us to ISAS, who haven't got a relay that big. We go back to the showgrounds and show our relay to John Storey, who says it's unsuitable: it's a solid state relay. The rule specifies that the isolator must be a mechanical device, and ours isn't. He tells us about a device called a "contactor", which is basically like a relay only bigger and uglier.

So we go back to ISAS, who send us back to Delta. We have a lengthy chat to Dennis at Delta, and John realises that we don't need the complicated deal with the 12V supply and the auxiliary battery pack if we have two separate breakers: one for the driver, and one for the side of the car. Both must still be contained within the battery pack, so to get the pull to those two locations, we'll just use some string!

Dennis sends us to MC, who sell us two breakers and some DIN rail. Back to the pits, to find the box we already have is just too small, so off to Bunnings and Jaycar to buy a bigger box and some conduit to run the string through.

Back at the pits we do enough work to prove to ourselves that this solution will work, then end for the day. Dinner is whatever we want at Mindil Beach markets.

The following morning it's a 7:30 departure for the pits to finish our new battery breaker system and some attendant rearranging of wires.

Then we want to get some track testing. I fire up the telemetry system and today it (flip a coin...) doesn't work.

We go without telemetry, and the car gets as far as the first corner, where it conks out. The people in the follow car leap out and have a look, but can't see what's gone wrong. They leave the solar car where it is and return to the pits to check with Challenge personnel as to how to retrieve it. They instruct us to bring it back up the drag strip. Peter S, the Challenge safety officer, meets us out there and guides us through the tyre debris all over the strip as we tow Hammerhead back to the pit. We troubleshoot, and track down the fault to a connector that I had assembled with insufficient force. We replace the connector, and the car goes again.

We do several laps, returning to the pits after each lap or two to change drivers. The car performs fine, except for the telemetry. Most people return to the accomodation while John goes to Jaycar for a null modem cable to help me debug it. We use the cable to grab a boot log from the car, and return to accommodation. This evening, most of the students will go to an official do at Parliament.

-- Doug Burbidge http://dougburbidge.com/