The Case of the Wilted Broccoli (6 page)

Willow smiled. Elon had a touch of the artist in him when it came to building. Willow couldn't help but get involved.

"What do you want to do?" Willow asked.

"The electric motor is round, and it's got a hole in the side of it. The aluminum strut it attaches to has two holes in it."

"For the zip tie to pass through," Linden interrupted.

"If I had a round plastic mount of just the right size," Elon said, ignoring Linden, "with two screw holes on the side, we could use a twenty millimeter screw to hold both the mount and motor, and then stabilize it with a second screw."

"You want to make it on dad's 3D printer?"

"Yeah, can you call him and ask him to bring it home from work?"

Willow called their dad, who said he'd bring the printer home. She checked thingiverse, the website for 3D printed parts, to see if she could find what Elon wanted. She found eight hundred and seven motor mounts, including a few that were almost perfect. In the end, she downloaded a design, changed the position of the screw holes, and by the time their dad was home, had the print files ready to go.
 

They all gathered around the Makerbot as she printed the first mount. The fan spun up as the printhead heated to melt the plastic and soon the printer lurched into motion with a cacophony of noises as the printhead sped around the platform laying down plastic. Fifteen minutes later, the plastic part was done.

"Ow," Elon said, grabbing the still hot part off the platform. He trimmed the extra plastic off with a knife, and then fitted the motor mount in. The motor slid in easily. Too easily.

Willow's heart sank a little. The 3D printer was magical, but getting things exactly right was the hard part of the magic. She adjusted the inner diameter, and launched the second print. This time the motor mount was snug as it should be.

"Perfect!" Elon announced. "Make five more, please, so we can have spares."

Willow grumbled at Elon's bossiness, but set up the MakerBot for five more, which printed while they ate dinner.

CHAPTER TWELVE

"P
UT
IT
OVER
there," Elon said.

His father left the heavy tray of tools in the grass and retreated to the car to read a book. He'd offered to help, but Elon was sure they could do it themselves.

Elon and Linden carried the quadcopter over. The finished flying device looked like a giant X from the top, with a ten inch diameter silver propeller in each corner at the end of a long metal arm. Squat in the middle sat the electronics and battery pack, every wire carefully routed inside the aluminum metal frame. Each propeller sat on top of its own copper-colored motor, the motor being housed in the turquoise mounting brackets Willow had printed last night.

Four plastic legs extended down, and Elon and Linden carefully rested the copter in the grass on these legs.

Willow brought her laptop computer, the radio controller, and extra batteries in an old green milk crate.

Elon felt a little vibration in his legs and arms, a bit of nervousness and lot of excitement. For this first flight, they just wanted to see it take off. They'd control it with the radio, and if it flew okay, then they'd do a short test with the autopilot in hover mode.
 

"Everyone ready?" Elon asked. He got nods in return. "Radio?"
 

"On," said Willow.

"Battery?

"Fully charged," said Linden.

He looked over at Willow. He really wanted to be the one to fly it first. The whole project had been his idea.

Willow looked back at him, and handed over the transmitter.

"Thank you," he said in a small voice.

Willow just smiled in return.

Elon checked the throttle stick to make sure it was fully down. "Turn it on."

Linden leaned down, flipped the switch and backed away.

Elon pushed up on the throttle and nothing happened. He flipped the throttle up and down twice more, still with no effect. The power light on the transmitter was on. Strange.

"Is the copter on?" he asked. "Nothing is happening."

Linden looked closely. "Yup. I can see light on the receiver. It's got power."

Elon sighed. "Let's shut it down and check the connections."

Twenty minutes later they'd worked through the battery connections, receiver connections, the electronic speed control wires, receiver antenna, and motor cables.

At thirty minutes their dad came over, but they shooed him away.
 

At forty minutes, Elon was checking the radio transmitter. The radio station of the transmitter and receiver had to match. "What frequency is it set for?" he asked.

"They should find each other on C band," Linden said.

"Well, this is set for D band," Elon said. He flipped a switch.

"Bobby must have done it," Linden said. "Right, Bobby?"

Willow yelled, "Bobby IS NOT--"
 

But the blades on the drone began to spin, a high-pitched mini-roar that drowned out Willow's words, and the copter lifted off the grass!

"Yes!" Linden shouted, and then he and Willow high-fived.

Elon couldn't believe it -- the quadcopter was actually flying! And he was flying it.

They flew a dozen more times that day. Linden and Willow each wanted turns, just taking off, hovering, and landing again.

On Elon's next turn, he pushed forward, and the copter flew away. He gently pushed left, and the quadcopter began making a long, slow curve. He wanted to shout and jump up and down, but he couldn't let go of the controller, not for an instant.

Of course, then Linden and Willow wanted to fly it in circles, too.

Their dad came back from the car to watch.

All this was fun, but it was just testing the motors, frames, and receiver. What they really wanted was to test the autopilot.

They powered down one last time. Now Elon flipped the switch on the ArduPilot board. He looked to Willow, who had her laptop powered up.

"Got it," she said, when the laptop had connected with the brains of the autonomous drone, so she could trigger and monitor the autopilot.

Elon turned on the power to the rotors and backed away. Now it was Willow's turn to control the drone by telling the autopilot what to do.

"Turning on autostabilization and setting it for an altitude of three feet." It was a simple test, but it would let them know if the autopilot software on the drone was capable of controlling the little quadcopter by itself. She input the data, then clicked enter.

The drone came to life, propellers whirling into a blur, then lifted off the ground. It rose three feet into the air, and hovered motionless.

They all whooped, then gathered around it. Using the ground-facing ultra-sonic range finder, the drone could see exactly how far it was from the ground. At least when it was below fifteen feet. Above that, it needed to use the GPS, which wasn't nearly as accurate. But the ultra-sonic range finder was good for within a few inches. And they could see it doing that now: maintaining a nearly perfect thirty-six inches off the ground, only gently moving and then coming back when there was a breeze.

"We have to name it," Willow said. It felt like the right thing to do. Years ago they had named their dad's remote-control car Chitty Chitty Bang Bang, after the car from the movie.

"The Buzzing Hornet," Linden said. "It sounds like one."

"The Flying Wonder," Willow suggested.

"It's got silver propellers," Elon said, "and it roars as it flies. Let's call it the Silver Dragon."

CHAPTER THIRTEEN

T
HE
ALARM
WENT
off early Monday morning, too early. Willow's head swam as she shut off the buzzer. Why was it five a.m.? She sat on the edge of her bed, befuddled. Oh, right! It was Monday morning. They had to get to school early to watch the unloading of the supply truck.

It was still pitch-black out. Willow jumped out of bed, and fell with a thud onto the floor. Her feet were still tangled up in her blankets.

She distantly heard her parents calling to see if she was all right.

"I'm fine," she yelled back, then slowly and more gracefully got back to her feet. She went to her brothers room, and woke them up. At least, she tried to. They slept like logs. She had to shake Linden back and forth a dozen times before he even started to respond. Finally, she had to pull all the covers off them.

"Wake up!" she said in an urgent whisper. "We have to get to school early for the truck."

"It's too early," Linden said, and pulled his pillow over his head.

"Come on, if we don't solve this mystery, people will get sick. People could die. Atlanta could die."

Finally they sat upright, and walked like groaning zombies into the bathroom.

She dashed back into her own bedroom, threw on her clothes, and ran downstairs.

She poured cereal and milk for everyone. When Linden and Elon came down, they all ate in silence.

"Ten minutes till the bus. I'll go tell mom and dad we want to take the bus on our own."

Everyone dashed up from their seats, cleared their places, and grabbed their backpacks. Willow ran upstairs and came back down a minute later.

"Ready?" Willow asked as they assembled by the door.

"What did mom and dad say?" Elon asked.

"I think they seemed happy to sleep in. They said to be careful and take the right bus."

On the way to the bus stop, Linden turned to Willow. "You owe us chocolate chip cookies for getting up this early."

"I'll bake a double batch when we get home."

When they arrived at school, the Bannon Foods truck was just backing up to the loading area. They ran the last half block and made it to the back of the truck before the driver got out.

"What are we looking for again?" asked Linden.

"This is the Monday delivery," Willow said. "So it'll have the local foods on it. We're checking to see if the food is good or bad."

"Why?" asked Elon.

"If the food is good, then it means that the problem is in our cafeteria. Probably Miss Berry is in on it. If the food is bad, then it means Miss Berry is innocent, and the problem is at Bannon Foods or before."

"Then we have to hide somewhere," Elon said. "We can't hang around here and have the driver see us. What if he's in on it?"

"Good point," Willow said. She glanced around. "Elon, you stay by the bicycle rack, pretend you're locking up your bicycle, and watch him unload. Linden, you go to the front counter and distract Miss Berry. I'll sneak into the kitchen, hide in a closet and watch them unload."

"I'll have Bobby come with me!" Linden said.

"Bobby's not..." Willow trailed off as Linden had already turned the corner.
 

Linden ran around the school at top speed to the cafeteria entrance. It was so early he was the second kid in the school. He entered the kitchen from the front entrance, picked up a cinnamon breakfast bar, glanced at the ingredient list, and then called Miss Berry over.

"I'm allergic to allow-allow nuts, Miss Berry. Does this have any in it?"

Miss Berry grabbed the bar away. "Oh dear. I've never heard of an allow-allow nut. Let me check." She read through the list of ingredients. "No, it seems fine."

Linden saw Willow enter the kitchen from the maintenance door, hunting for a hiding spot. He needed to delay longer.

"Does it have pickleberries? That's a wild relative to the strawberry, and I'm not supposed to have that either."

"A pickleberry? I've never heard of it." Miss Berry peered closely at him. "You've never mentioned food allergies before."

"That's because I only eat brunch for lunch, and I know what's in the pancakes."

Miss Berry nodded as though that made sense, and read through the ingredients. "No pickleberries." She handed it back.

Willow was just crawling under a counter with a good view of the entrance, but the spot was so small it was taking a long time for her to squash herself in.

"And the wheat. Do you know if it's GMO? My mom says not to eat genetically modified foods."

Miss Berry grabbed the bar back from him, and gripped it a little tightly. Cream cheese oozed out of the ends. He hated cream cheese. She finished looking at the ingredients. "It doesn't say whether the wheat is GMO or not."

Willow was fully under the counter, and he could quit stalling. "Oh, that probably means it is. I'd better not get it. Thanks for your help, Miss Berry!"

On the other side of the kitchen, Willow wedged tightly under the counter. The space was so small she had to fold up into a square, like that time when a big package had been delivered to their house, and they all took turns folding up to fit into the cardboard box. But she had an excellent view of the floor, and unless someone looked directly under the counter, they wouldn't spot her.

The hand truck rolled into view, and Willow realized her first mistake. She couldn't see the driver's face, because the counter blocked her view.

"How are you, Ada?" the driver called.

"Just fine? And you?" Miss Berry replied.

Willow had no idea Miss Berry's first name was Ada. She tried to reach for something to write this down, but she couldn't move her arms she was so squished in.

The hand truck had three cardboard boxes covered in frost.
 

"Hamburgers, hamburgers, and more hamburgers," the driver said.
 

Willow saw Miss Berry's legs walk over to a giant stainless steel freezer and open the door. The driver carried two boxes and Miss Berry one. The driver disappeared for a few minutes, until he came back with three more boxes. "Breakfast bars, chicken patties. Stir-fry beef."

The boxes were put into a different refrigerator and the driver went away. He came back a few minutes later with black plastic crates, with greens sticking out. "Two crates local broccoli, one crate local Brussels sprouts."

Willow was ten feet away, but as the hand truck went by, she could smell a slight off odor.

"Oh, not again," Miss Berry called. "Come on, look at this broccoli. This isn't fresh!"

"Sorry, Ada. I just drive the truck."