The one-hour shelters have done their job: all the Tinkerers slept in their creations without mishap. The excitement of the Juniors’ camp-out was not repeated (no earwig infestation and no sliding or rolling out of the tents).

Hanna helps Robyn with packing while she waits for Pearls’ welded gear cluster. She’s going to give the drill cart one more try. She has the patience of a saint.

Platinum has experienced a new form of failure, which no amount of welding will be able to repair. The drill chuck has completely separated from the drill. Time to remove all that dead weight for some gravity racing.

Some early morning welding has got the Slackers cart running again. The team takes turns roaming the parking lot (giving the other Tinkerers a go at it as well).

With their newly welded gear for the lower drill, and a hand-me-down gear (from Platinum) for the upper drill, Pearls just needs the chain installed. Hanna notes that today there is less hopelessness bubbling out (of the tire).

For a while there was some real doubt as to whether the Slackers could get powered, but it’s been done. The throttle seems to be controlling only one drill, but it’s enough.

At long last Hanna is rewarded with an actual ride across the parking lot on Pearls. Fully powered. Both drills, working perfectly, providing torque galore. Until….

Pearls throws the chain, for no apparent reason. With the derailleur-style tightener, the tension on the chain is substantial. Careful analysis shows that rather than jumping off the precision-aligned gears, the gear is stepping down through the chain rings. But why? It appears that the torque is so massive and the attachment of the drill is now so secure, that the plywood mount is flexing. Note that the lower (visible, since the cart is overturned) drill is mounted on a single small piece of plywood. Not even the 3/4″ ply – it had been determined to be unnecessary….

Twyen is not fazed by the irreparable failure of Pearls – he is test-driving all the other carts on the lot. While the power of Slackers is satisfying, it just can’t compare with the downhill speed of Platinum.

Now that Pearls has proven powerful (albeit flawed), Hanna does a downhill race against Isaac. But Pearls just wasn’t designed for speed, and torque and maneuverability aren’t needed for gravity racing.

In front of our favorite barn, we present the Tinkering School Class of 2009 (Seniors), along with the collaborators, experts, and documentarians.

A new timeline for pick-up results in everyone – including all the parents, siblings, and a few friends – getting a tour of the barn and projects at the same time. We’ll have to do this every year; it’s fun to show everything off at once.

Toby describes to his dad how the Slackers cart works.

Slackers (as the only reliable power system), is set up to demonstrate. And magically both drills get triggered by the throttle! The crowd roars.

Gever gathers everyone to say thanks, and Jiro points out that the week was a complete success – no fingers were lost! The parents are pleased, but Maxine thought she HAD lost a finger, and has to check to confirm that Jiro is correct.

Gever is happy to give a mini-tour of the animals, including a refresh of the mud pit and a little bonus bathing.

Chun isn’t so shy when he’s behind the wheel (or bars, but “behind bars” might give the wrong impression :-), and looks pretty happy. Theo is definitely happy, now that he’s shown Chun how the brake works and it hasn’t been held down during the entire push up the hill this time.

You don’t think that Theo intentionally sabotaged his helmet-cam so we’d ask him to redo his downhill run to get the first-person footage, do you? He certainly is happy to oblige, even with a camera duct-taped to his shirt and neck. After this he gets to help take everything apart and relocate Tinkering School back to Gever’s workshop. As do I. Thanks for following along!

Experience the fast-paced world of gravity cart racing, with Pearls.

Slackers chugs its way around, carrying all who want a ride.

At long last, Pearls muscles its way across the parking lot, under full power.

Theo rides one more time, for the cameras.

Maxine and Amy head out.